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WIRELESS NETWORKING

Posted by sarahkasumejaneares on February 12, 2013 at 9:40 AM Comments comments (0)

Wireless PAN

 

Wireless personal area networks (WPANs) interconnect devices within a relatively small area, that is generally within a person's reach.[3] For example, both Bluetooth radio and invisible infrared light provides a WPAN for interconnecting a headset to a laptop. ZigBee also supports WPAN applications.[4] Wi-Fi PANs are becoming commonplace (2010) as equipment designers start to integrate Wi-Fi into a variety of consumer electronic devices. Intel "My WiFi" and Windows 7 "virtual Wi-Fi" capabilities have made Wi-Fi PANs simpler and easier to set up and configure.[5]

 

[edit]Wireless LAN

 

Main article: Wireless LAN

 

A wireless local area network (WLAN) links two or more devices over a short distance using a wireless distribution method, usually providing a connection through an access point for Internet access. The use of spread-spectrum or OFDM technologies may allow users to move around within a local coverage area, and still remain connected to the network.

 

Products using the IEEE 802.11 WLAN standards are marketed under the Wi-Fi brand name. Fixed wireless technology implements point-to-point links between computers or networks at two distant locations, often using dedicated microwave or modulated laser light beams over line of sight paths. It is often used in cities to connect networks in two or more buildings without installing a wired link.

 

[edit]Wireless mesh network

 

Main article: wireless mesh network

 

A wireless mesh network is a wireless network made up of radio nodes organized in a mesh topology. Each node forwards messages on behalf of the other nodes. Mesh networks can "self heal", automatically re-routing around a node that has lost power.

 

[edit]Wireless MAN

 

Wireless metropolitan area networks are a type of wireless network that connects several wireless LANs.

 

§ WiMAX is a type of Wireless MAN and is described by the IEEE 802.16 standard.[6]

 

[edit]Wireless WAN

 

Wireless wide area networks are wireless networks that typically cover large areas, such as between neighboring towns and cities, or city and suburb. These networks can be used to connect branch offices of business or as a public internet access system. The wireless connections between access points are usually point to point microwave links usingparabolic dishes on the 2.4 GHz band, rather than omnidirectional antennas used with smaller networks. A typical system contains base station gateways, access points and wireless bridging relays. Other configurations are mesh systems where each access point acts as a relay also. When combined with renewable energy systems such as photo-voltaic solar panels or wind systems they can be stand alone systems.

 

[edit]Cellular network

 

Main article: cellular network

Top of a cellular radio tower

 

A cellular network or mobile network is a radio network distributed over land areas called cells, each served by at least one fixed-location transceiver, known as a cell site or base station. In a cellular network, each cell characteristically uses a different set of radio frequencies from all their immediate neighbouring cells to avoid any interference.

 

When joined together these cells provide radio coverage over a wide geographic area. This enables a large number of portable transceivers (e.g., mobile phones, pagers, etc.) to communicate with each other and with fixed transceivers and telephones anywhere in the network, via base stations, even if some of the transceivers are moving through more than one cell during transmission.

 

Although originally intended for cell phones, with the development of smartphones, cellular telephone networks routinely carry data in addition to telephone conversations:

 

§ Global System for Mobile Communications (GSM): The GSM network is divided into three major systems: the switching system, the base station system, and the operation and support system. The cell phone connects to the base system station which then connects to the operation and support station; it then connects to the switching station where the call is transferred to where it needs to go. GSM is the most common standard and is used for a majority of cell phones.[7]

 

§ Personal Communications Service (PCS): PCS is a radio band that can be used by mobile phones in North America and South Asia. Sprint happened to be the first service to set up a PCS.

 

§ D-AMPS: Digital Advanced Mobile Phone Service, an upgraded version of AMPS, is being phased out due to advancement in technology. The newer GSM networks are replacing the older system.

 

[edit]Uses

 

Some examples of usage include cellular phones which are part of everyday wireless networks, allowing easy personal communications. Another example, Inter-continental network systems, use radio satellites to communicate across the world. Emergency services such as the police utilize wireless networks to communicate effectively as well. Individuals and businesses use wireless networks to send and share data rapidly, whether it be in a small office building or across the world.

 

[edit]General

 

In a general sense, wireless networks offer a vast variety of uses by both business and home users.[8]

 

"Now, the industry accepts a handful of different wireless technologies. Each wireless technology is defined by a standard that describes unique functions at both the Physical and the Data Link layers of the OSI Model. These standards differ in their specified signaling methods, geographic ranges, and frequency usages, among other things. Such differences can make certain technologies better suited to home networks and others better suited to network larger organizations."[8]

 

[edit]Performance

 

Each standard varies in geographical range, thus making one standard more ideal than the next depending on what it is one is trying to accomplish with a wireless network.[8] The performance of wireless networks satisfies a variety of applications such as voice and video. The use of this technology also gives room for expansions, such as from 2G to 3G and, most recently, 4G technology, which stands for fourth generation of cell phone mobile communications standards. As wireless networking has become commonplace, sophistication increases through configuration of network hardware and software, and greater capacity to send and receive larger amounts of data, faster, is achieved.[9]

 

[edit]Space

 

Space is another characteristic of wireless networking. Wireless networks offer many advantages when it comes to difficult-to-wire areas trying to communicate such as across a street or river, a warehouse on the other side of the premise or buildings that are physically separated but operate as one.[9] Wireless networks allow for users to designate a certain space which the network will be able to communicate with other devices through that network. Space is also created in homes as a result of eliminating clutters of wiring.[10] This techonology allows for an alternative to installing physical network mediums such as TPs, coaxes, or fiber-optics, which can also be expensive.

 

[edit]Home

 

For homeowners, wireless technology is an effective option as compared to ethernet for sharing printers, scanners, and high speed internet connections. WLANs help save from the cost of installation of cable mediums, save time from physical installation, and also creates mobility for devices connected to the network.[10] Wireless networks are simple and require as few as one single wireless access point connected directly to the Internet via a router.[8]

 

environmentel concern

See also: Wireless electronic devices and health

 

Starting around 2009, there have been increased concerns about the safety of wireless communications, despite little evidence of health risks so far.[11] The president of Lakehead University refused to agree to installation of a wireless network citing a California Public Utilities Commission study which said that the possible risk of tumors and other diseases due to exposure to electromagnetic fields (EMFs) needs to be further investigated.[12]

 

Wireless access points are also often close to humans, but the drop off in power over distance is fast, following the inverse-square law.[13] The HPA's position is that “...radio frequency (RF) exposures from WiFi are likely to be lower than those from mobile phones.” It also saw “...no reason why schools and others should not use WiFi equipment.”[14] In October 2007, the HPA launched a new “systematic” study into the effects of WiFi networks on behalf of the UK government, in order to calm fears that had appeared in the media in a recent period up to that time".[15] Dr Michael Clark, of the HPA, says published research on mobile phones and masts does not add up to an indictment of WiFi.[16]

 

[edit]See also

 

§ Exposed terminal problem

 

§ Physical layer

 

§ Public Safety Network

 

§ Wireless community network

 

§ Wireless access point

 

§ Wireless LAN client comparison

 

§ RuBee

 

§ Wireless site survey

 

[edit]References

 

1. ^ "Overview of Wireless Communications". cambridge.org. Retrieved 2008-02-08.

 

2. ^ "Getting to Know Wireless Networks and Technology". informit.com. Retrieved 2008-02-08.

 

3. ^ "Wireless Networks: Bluetooth To Mobile Phones".

 

4. ^ "Wireless Network Industry Report". Retrieved 2008-07-08.

 

5. ^ "Wi-Fi Personal Area Networks get a boost with Windows 7 and Intel My WiFi". Retrieved 2010-04-27.

 

6. ^ "Facts About WiMAX And Why Is It "The Future of Wireless Broadband"".

 

7. ^ "GSM World statistics". GSM Association. 2010. Retrieved 16 march 2011.

 

8. ^ a b c d Dean Tamara (2010). Network+ Guide to Networks (5th ed.). Boston: Cengage Learning. ISBN 978-1-4239-0245-4.

 

9. ^ a b "Wireless LAN Technologies". Source Daddy web site. Retrieved August 29, 2011.

 

10. ^ a b "WLAN Benefits". Wireless Center commercial web site. Retrieved August 29, 2011.

 

11. ^ Lean, Geoffrey (2007-04-22). "Wi-Fi: Children at risk from 'electronic smog'". London: news.independent.co.uk. Retrieved 2008-02-08.

 

12. ^ "Canadian university says no to WiFi over health concerns". arstechnica.com. Retrieved 2008-02-08.

 

13. ^ Foster, Kenneth R (March 2007). "Radiofrequency exposure from wireless LANs utilizing Wi-Fi technology". Health Physics 92 (3): 280–289.doi:10.1097/01.HP.0000248117.74843.34. PMID 17293700.

 

14. ^ "WiFi". Health Protection Agency. 2009-10-26. Retrieved 2009-12-27.

 

15. ^ "Health Protection Agency announces further research into use of WiFi". Health Protection Agency. Retrieved 2008-08-28.

 

16. ^ Daniels, Nicki (2006-12-11). "Wi-fi: should we be worried?". The Times (London). Retrieved 2007-09-16. "All the expert reviews done here and abroad indicate that there is unlikely to be a health risk from wireless networks. … When we have conducted measurements in schools, typical exposures from WiFi are around 20 millionths of the international guideline levels of exposure to radiation. As a comparison, a child on a mobile phone receives up to 50 per cent of guideline levels. So a year sitting in a classroom near a wireless network is roughly equivalent to 20 minutes on a mobile. If WiFi should be taken out of schools, then the mobile phone network should be shut down, too—and FM radio and TV, as the strength of their signals is similar to that from WiFi in classrooms...."

 

[edit]Further reading

 

§ Wireless Networking in the Developing World: A practical guide to planning and building low-cost telecommunications infrastructure (2nd ed.). Hacker Friendly LLC. 2007. p. 425.

 

§ Pahlavan, Kaveh; Levesque, Allen H (1995). Wireless Information Networks. John Wiley & Sons. ISBN [[Special:BookSources/00471106070|00471106070]].

 

§ Geier, Jim (2001). Wireless LANs. Sams;. ISBN 0-672-32058-4.

 

§ Goldsmith, Andrea (2005). Wireless Communications. Cambridge University Press. ISBN 0-521-83716-2.

 

§ Molisch, Andreas (2005). Wireless Communications. Wiley-IEEE Press. ISBN 0-470-84888-X.

 

§ Pahlavan, Kaveh; Krishnamurthy, Prashant (2002). Principles of Wireless Networks - a Unified Approach. Prentice Hall. ISBN 0-13-093003-2.

 

§ Rappaport, Theodore (2002). Wireless Communications: Principles and Practice. Prentice Hall. ISBN 0-13-042232-0.

 

§ Rhoton, John (2001). The Wireless Internet Explained. Digital Press. ISBN 1-55558-257-5.

 

§ Tse, David; Viswanath, Pramod (2005). Fundamentals of Wireless Communication. Cambridge University Press. ISBN 0-521-84527-0.

 

§ Kostas Pentikousis (March 2005). "Wireless Data Networks". Internet Protocol Journal 8 (1). Retrieved August 29, 2011.

 

§ Pahlavan, Kaveh; Krishnamurthy, Prashant (2009). Networking Fundamentals - Wide, Local and Personal Area Communications. Wiley. ISBN 978-0-470-99290-6.

 

[edit]External links

 

§ Wireless at the Open Directory Project

 

http://en.wikipedia.org/wiki/Wireless_network

 

Titles, headers, paragraphs, input names, breaks, form method, submit form, input values, mail to...

Posted by sarahkasumejaneares on January 23, 2013 at 8:00 AM Comments comments (0)

Titles, headers, paragraphs, input names, breaks, form method, submit form, input values, mail to...

 

 

multiple-choice quiz form

 

 

 


 

 

 

Check the answer to each multiple-coice question, and click on the "Send Form" button to submit the information.

 

1. Ang akong ganahan nga website is:

Naay Logo og akong picture

Naay mga pictures

Naay links sa mga websites

Naa tanan

 

 

 

2. Ang akong ganahan nga design is:

Default design from the web

Custom HTML codes

Design nay nature

Design naay dagat

 

 

 

3. Ang akong ganahan nga school is:

School dunay computers

School dunay mga equipment

School dunay mga playground

School layo sa highway

 

 





 

What is your ideal output?

 

 

onSubmit="return checkAnswer(this,'B');"

>

 

A. Colorful

 

B. Black with discription

 

C. with picture and discription

 

 

 

 

 

 

Browse the display of the coded source codes....

PangutanaCheck the answer to each multiple-coice question, and click on the "Send Form" button to submit the information.

1. Ang akong ganahan nga website is:

Naay Logo og akong picture

Naay mga pictures

Naay links sa mga websites

Naa tanan

2. Ang akong ganahan nga design is:

Default design from the web

Custom HTML codes

Design nay nature

Design naay dagat

3. Ang akong ganahan nga school is:

School dunay computers

School dunay mga equipment

School dunay mga playground

School layo sa highway

 

 

 

 

What is your ideal output? A. Colorful

B. Black with discription

C. with picture and discription

View the source codes.... DOCTYPE in 4 lines

 

 

 

 

 

This is my first paragraph.

 

 

Smart person can travel around the globe.

 

 

He brings his Talk and Text mobile during Sunrise.

 

 

And he also brings his Red mobile Wifi built cellphone.

 

 

 

 

Browse the display of the coded source codes....

This is my first paragraph.

Smart person can travel around the globe.

He brings his Talk and Text mobile during Sunrise.

And he also brings his Red mobile Wifi built cellphone.

View the source codes... DOCTYPE with one paragraph

 

 

 

 

 

The smart person can travel around the globe. He brings his Talk and Text SIM and Sun cellphone at anytime. He also brings his Red mobile wifi booster....blablabla.....

 

 

 

Browse the display of the coded source codes....

The smart person can travel around the globe. He brings his Talk and Text SIM and Sun cellphone at anytime. He also brings his Red mobile wifi booster....blablabla.....

View the source codes of paragraph with line breaks and input elements such as

 

This is
a para
graph with line breaks

 

 

 

 

.

input elements

.

 

 

 

 

First name:

Last name:

 

 

 

Browse the display of the coded source codes....

This is

a para

graph with line breaks

. input elements .First name:

Last name:

View the source codes of subscript and superscript

 

This text contains subscript text.

 

 

 

This text contains superscript text.

 

 

Browse the display of the coded source codes....

This text contains subscript text.

This text contains superscript text.

View source codes of HTML links which are defined with the tag. The link address is specified in the href attribute:

This is a link

 

Browse the display of the coded source codes....

This is a link

View source codes...Tag DescriptionRenders as italic textRenders as bold textRenders as bigger textRenders as teletype textRenders as smaller text

Teletype text

Italic text

Bold text

Big text

Small text

 

Browse the the display of the coded source codes...

Teletype text Italic text Bold text Big text Small text

View the source codes....Tag DescriptionRenders as emphasized textRenders as strong (highlighted) textDefines a definition termDefines a piece of computer codeDefines sample output from a computer programDefines keyboard inputDefines a variable part of a textDefines a citation

Emphasized text

Strong text

Definition term

A piece of computer code

Sample output from a computer program

Keyboard input

Variable

Citation

Browse the display of the coded source codes...

Emphasized text Strong text Definition term A piece of computer code Sample output from a computer program Keyboard input Variable Citation

View source codes... in an abbreviation is marked up WHO

The WHO was founded in 1948.

Browse the display of the coded source codes

The WHO was founded in 1948.

View source codes.... in inline style

Browse the display of the coded source codes....

This is a paragraph.

View source codes... in HTML Style Example - Background Color. The background-color property defines the background color for an element:

 

Browse the display of the coded source codes....

 

Entrepreneurship

Posted by sarahkasumejaneares on January 23, 2013 at 8:00 AM Comments comments (0)

Entrepreneurship is the act of being entrepreneur or "one who undertakes innovations, finance and business acumen in an effort to transform innovations into economic goods". This may result in new organizations or may be part of revitalizing mature organizations in response to a perceived opportunity. The most obvious form of entrepreneurship is that of starting new businesses (referred as Startup Company); however, in recent years, the term has been extended to include social and political forms of entrepreneurial activity. When entrepreneurship is describing activities within a firm or large organization it is referred to as intra-preneurship and may include corporate venturing, when large entities spin-off organizations.[1]

 

According to Paul Reynolds, entrepreneurship scholar and creator of the Global Entrepreneurship Monitor, "by the time they reach their retirement years, half of all working men in the United States probably have a period of self-employment of one or more years; one in four may have engaged in self-employment for six or more years. Participating in a new business creation is a common activity among U.S. workers over the course of their careers." [2] And in recent years has been documented by scholars such as David Audretsch to be a major driver of economic growth in both the United States and Western Europe. "As well, entrepreneurship may be defined as the pursuit of opportunity without regard to resources currently controlled (Stevenson,1983)" [3]

 

Entrepreneurial activities are substantially different depending on the type of organization and creativity involved. Entrepreneurship ranges in scale from solo projects (even involving the entrepreneur only part-time) to major undertakings creating many job opportunities. Many "high value" entrepreneurial ventures seek venture capital or angel funding (seed money) in order to raise capital to build the business. Angel investors generally seek annualized returns of 20-30% and more, as well as extensive involvement in the business.[4]Many kinds of organizations now exist to support would-be entrepreneurs including specialized government agencies, business incubators, science parks, and some NGOs. In more recent times, the term entrepreneurship has been extended to include elements not related necessarily to business formation activity such as conceptualizations of entrepreneurship as a specific mindset (see also entrepreneurial mindset) resulting in entrepreneurial initiatives e.g. in the form of social entrepreneurship, political entrepreneurship, or knowledge entrepreneurship have emerged.

 

*Desktop publishing *

Posted by sarahkasumejaneares on January 23, 2013 at 7:50 AM Comments comments (0)


 *Desktop publishing *
 
 
From Wikipedia, the free encyclopedia
 
Digital media
 
page layoutpersonal computertypographyprintingmenus
 
word processing
 
History
 
[1]PCgraphics cardWYSIWYG[2]typesettingTeXLaTeXApple LaserWriterPageMakerAldus
 
Aldus CorporationPaul Brainerd[3]phototypesetting
 
[4]monochromeletter spacingkerningtypographic features
 
Adobe SystemsPostScriptROMPostScriptservice bureausoptical resolutionLinotronicMacintosh IImulti-monitorSCSI
 
GEMVentura PublisherMS-DOSstyle sheetsProfessional PageAmigaPublishing PartnerAtari STTimeworks PublisherCalamusAtari TT030Apple IICommodore 64The NewsroomgeoPublish
 
ransom note effectWeb
 
art directiongraphic designmultimedia developmentmarketing communicationsadministrative careersclarification neededadvertising agencyprepress productionprogrammingcommunication designgraphic image development
 
Terminology
 
electronic pagesphysical paper pagescomputer memorycomputer data storage
 
printedinternational standard physical paper sizespostersbillboardstrade show displaysWYSIWYGbleed printingdesktop printers
 
web pagecontentcontent to re-flow
 
Master pages are templates used to automatically copy or link elements and graphic design styles to some or all the pages of a multipage document. Linked elements can be modified without having to change each instance of an element on pages that use the same element. Master pages can also be used to apply graphic design styles to automatic page numbering.
 
Page layouttextimagesrenderedkeyeddatabase publishing
 
Typographystyle sheets
 
Comparisons
 
With word processing
 
word processing
 
graphical user interfacesWordPerfectWordStar
 
As computers and operating systems have become more powerful, vendors have sought to provide users with a single application platform that can meet all needs.
 
With other electronic layout software
 
TeXtroffUnix-liketypesettingWYSIWYGTeXLaTeXbatch modeWYSIWYG
 
HypermediaHTML editorsMicrosoft FrontPageAdobe Dreamweavercode bloat
 
DTP applications
 
List of desktop publishing software
 
Aldus Personal Press
Adobe FrameMaker
Adobe InDesign
Adobe PageMaker
Adobe HomePublisher
Corel Ventura
Fatpaint
iStudio Publisher
Microsoft Office Publisher
OpenOffice.orgLibreOffice
PageStream
PTC Arbortext
QuarkXPress
Ready,Set,Go
Scribus
Serif PagePlus
 
See also
 
Comparison of desktop publishing software
List of desktop publishing software
Document processor
Camera-ready
Desktop video
E-book
 
References
 
^
^
^"The Stafford papers"
^"MacIntosh Layout Package Remarkably Fast, Powerful"
 
Further reading
 
One of the early and comprehensive reference books on the art of desktop publishing is Desktop Publishing For Everyone by K.S.V. Menon. This publication deals with virtually every facet of publishing and nearly all tools available as at the time of the publishing of this book in the year 2000. It is currently out of print.
 
External links
 
 
Desktop Publishing Tips and Tutorials
 
Microsoft Publisher 2010
 
http://en.wikipedia.org/wiki/Desktop_publishing
 
Microsoft Office Publisher 2007
Mantalongon NHS ICT Department is using MS Office Publisher 2007 Application in Desktop Publishing... Students are required to make a design of a newsletter. Contents could be personal write ups or copied from other sites provided that names of writers must be coded underneath the title of the selection/writer's master piece; url must be linked in student's webpage or sub-page....
Step 1. Click Start, All Programs
Step 2. Click Microsoft Office.
Step 3. Click MS Office Publisher 2007.
Step 4. Click Newsletter.
Step 5. Click Photoscope or any of these designs.
Step 6. Click Create button at the bottom right
Step 7. Click page 1 icon at the bottom left.
Step 8. Click the pages 2 and 3 icon.
Step 9. Click the page 4 icon
Step 10. Click Newsletter Title to edit the title.
Step 11. Click the Lead Story Headline to change the headline.
Step 12. Click the Content Text Box to type the details of the headline.
Step 13. Click the Save icon or press Ctrl + S to save your newsletter in the drive.
Step 14. Press Ctrl + P to select a printer before printing your newsletter

DIGESTIVE SYSTEM(SCIENCE)

Posted by sarahkasumejaneares on November 6, 2012 at 7:50 AM Comments comments (0)

 Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones.

When food enters the mouth, its digestion starts by the action of mastication, a form of mechanical digestion, and the contact of saliva. Saliva, which is secreted by the salivary glands, contains salivary amylase, an enzyme which starts the digestion of starch in the food. After undergoing mastication and starch digestion, the food will be in the form of a small, round slurry mass called a bolus. It will then travel down the esophagus and into the stomach by the action of peristalsis. Gastric juice in the stomach starts protein digestion. Gastric juice mainly contains hydrochloric acid and pepsin. As these two chemicals may damage the stomach wall, mucus is secreted by the stomach, providing a slimy layer that acts as a shield against the damaging effects of the chemicals. At the same time protein digestion is occurring, mechanical mixing occurs by peristalsis, which are waves of muscular contractions that move along the stomach wall. This allows the mass of food to further mix with the digestive enzymes. After some time (typically an hour or two in humans, 4–6 hours in dogs, somewhat shorter duration in house cats), the resulting thick liquid is called chyme. When the pyloric sphincter valve opens, chyme enters the duodenum where it mixes with digestive enzymes from the pancreas, and then passes through the small intestine, in which digestion continues. When the chyme is fully digested, it is absorbed into the blood. 95% of absorption of nutrients occurs in the small intestine. Water and minerals are reabsorbed back into the blood in the colon (large intestine) where the pH is slightly acidic about 5.6 ~ 6.9. Some vitamins, such as biotin and vitamin K (K2MK7) produced by bacteria in the colon are also absorbed into the blood in the colon.[1] Waste material is eliminated from the rectum during defecation.[2]

 

 

 

 

Contents

[hide] 1 Digestive systems 1.1 Secretion systems 1.1.1 Channel transport system

1.1.2 Molecular syringe

1.1.3 Conjugation machinery

1.1.4 Release of outer membrane vesicles

1.2 Gastrovascular cavity

1.3 Phagosome

1.4 Specialised organs and behaviours 1.4.1 Beaks

1.4.2 Tongue

1.4.3 Teeth

1.4.4 Crop

1.4.5 Abomasum

1.4.6 Specialised behaviours

1.5 In earthworms

2 Overview of vertebrate digestion

3 Human digestion process 3.1 Phases of gastric secretion

3.2 Oral cavity

3.3 Pharynx

3.4 Esophagus

3.5 Stomach

3.6 Small intestine

3.7 Large intestine

4 Breakdown into nutrients 4.1 Protein digestion

4.2 Fat digestion

4.3 Carbohydrate digestion

4.4 DNA and RNA digestion

5 Digestive hormones

6 Significance of pH in digestion

7 Uses of animal gut by humans

8 See also

9 References

10 External links

 

[edit] Digestive systems

Digestive systems take many forms. There is a fundamental distinction between internal and external digestion. External digestion is more primitive, and most fungi still rely on it.[3] In this process, enzymes are secreted into the environment surrounding the organism, where they break down an organic material, and some of the products diffuse back to the organism. Later, animals form a tube in which internal digestion occurs, which is more efficient because more of the broken down products can be captured, and the internal chemical environment can be more efficiently controlled.[4]

Some organisms, including nearly all spiders, simply secrete biotoxins and digestive chemicals (e.g., enzymes) into the extracellular environment prior to ingestion of the consequent "soup". In others, once potential nutrients or food is inside the organism, digestion can be conducted to a vesicle or a sac-like structure, through a tube, or through several specialized organs aimed at making the absorption of nutrients more efficient.

 

 

 

 

Schematic drawing of bacterial conjugation. 1- Donor cell produces pilus. 2- Pilus attaches to recipient cell, bringing the two cells together. 3- The mobile plasmid is nicked and a single strand of DNA is transferred to the recipient cell. 4- Both cells recircularize their plasmids, synthesize second strands, and reproduce pili; both cells are now viable donors.

[edit] Secretion systems

Main article: Secretion

Bacteria use several systems to obtain nutrients from other organisms in the environments.

[edit] Channel transport system

In a channel transupport system, several proteins form a contiguous channel traversing the inner and outer membranes of the bacteria. It is a simple system, which consists of only three protein subunits: the ABC protein, membrane fusion protein (MFP), and outer membrane protein (OMP)[specify]. This secretion system transports various molecules, from ions, drugs, to proteins of various sizes (20 - 900 kDa). The molecules secreted vary in size from the small Escherichia coli peptide colicin V, (10 kDa) to the Pseudomonas fluorescens cell adhesion protein LapA of 900 kDa.[5]

[edit] Molecular syringe

One molecular syringe is used through which a bacterium (e.g. certain types of Salmonella, Shigella, Yersinia) can inject nutrients into protist cells. One such mechanism was first discovered in Y. pestis and showed that toxins could be injected directly from the bacterial cytoplasm into the cytoplasm of its host's cells rather than simply be secreted into the extracellular medium.[6]

[edit] Conjugation machinery

The conjugation machinery of some bacteria (and archaeal flagella) is capable of transporting both DNA and proteins. It was discovered in Agrobacterium tumefaciens, which uses this system to introduce the Ti plasmid and proteins into the host, which develops the crown gall (tumor).[7] The VirB complex of Agrobacterium tumefaciens is the prototypic system.[8]

The nitrogen fixing Rhizobia are an interesting case, wherein conjugative elements naturally engage in inter-kingdom conjugation. Such elements as the Agrobacterium Ti or Ri plasmids contain elements that can transfer to plant cells. Transferred genes enter the plant cell nucleus and effectively transform the plant cells into factories for the production of opines, which the bacteria use as carbon and energy sources. Infected plant cells form crown gall or root tumors. The Ti and Ri plasmids are thus endosymbionts of the bacteria, which are in turn endosymbionts (or parasites) of the infected plant.

The Ti and Ri plasmids are themselves conjugative. Ti and Ri transfer between bacteria uses an independent system (the tra, or transfer, operon) from that for inter-kingdom transfer (the vir, or virulence, operon). Such transfer creates virulent strains from previously avirulent Agrobacteria.

[edit] Release of outer membrane vesicles

In addition to the use of the multiprotein complexes listed above, Gram-negative bacteria possess another method for release of material: the formation of outer membrane vesicles.[9] Portions of the outer membrane pinch off, forming spherical structures made of a lipid bilayer enclosing periplasmic materials. Vesicles from a number of bacterial species have been found to contain virulence factors, some have immunomodulatory effects, and some can directly adhere to and intoxicate host cells. While release of vesicles has been demonstrated as a general response to stress conditions, the process of loading cargo proteins seems to be selective.[10]

 

 

 

 

Venus Flytrap (Dionaea muscipula) leaf

[edit] Gastrovascular cavity

The gastrovascular cavity functions as a stomach in both digestion and the distribution of nutrients to all parts of the body. Extracellular digestion takes place within this central cavity, which is lined with the gastrodermis, the internal layer of epithelium. This cavity has only one opening to the outside that functions as both a mouth and an anus: waste and undigested matter is excreted through the mouth/anus, which can be described as an incomplete gut.

In a plant such as the Venus Flytrap that can make its own food through photosynthesis, it does not eat and digest its prey for the traditional objectives of harvesting energy and carbon, but mines prey primarily for essential nutrients (nitrogen and phosphorus in particular) that are in short supply in its boggy, acidic habitat.[11]

 

 

 

 

Trophozoites of Entamoeba histolytica with ingested erythrocytes

[edit] Phagosome

A phagosome is a vacuole formed around a particle absorbed by phagocytosis. The vacuole is formed by the fusion of the cell membrane around the particle. A phagosome is a cellular compartment in which pathogenic microorganisms can be killed and digested. Phagosomes fuse with lysosomes in their maturation process, forming phagolysosomes. In humans, Entamoeba histolytica can phagocytose red blood cells.[12]

[edit] Specialised organs and behaviours

To aid in the digestion of their food animals evolved organs such as beaks, tongues, teeth, a crop, gizzard, and others.

 

 

 

 

 

A Catalina Macaw's seed-shearing beak

 

 

 

Squid beak with ruler for size comparison

[edit] Beaks

Birds have beaks that are specialised according to the bird's ecological niche. For example, macaws primarily eat seeds, nuts, and fruit, using their impressive beaks to open even the toughest seed. First they scratch a thin line with the sharp point of the beak, then they shear the seed open with the sides of the beak.

The mouth of the squid is equipped with a sharp horny beak mainly made of cross-linked proteins. It is used to kill and tear prey into manageable pieces. The beak is very robust, but does not contain any minerals, unlike the teeth and jaws of many other organisms, including marine species.[13] The beak is the only indigestible part of the squid.

[edit] Tongue

Main article: Tongue

The tongue is skeletal muscle on the floor of the mouth that manipulates food for chewing (mastication) and swallowing (deglutition). It is sensitive and kept moist by saliva. The underside of the tongue is covered with a smooth mucous membrane. The tongue also has a touch sense for locating and positioning food particles that require further chewing. The tongue is utilized to roll food particles into a bolus before being transported down the esophagus through peristalsis.

The sublingual region underneath the front of the tongue is a location where the oral mucosa is very thin, and underlain by a plexus of veins. This is an ideal location for introducing certain medications to the body. The sublingual route takes advantage of the highly vascular quality of the oral cavity, and allows for the speedy application of medication into the cardiovascular system, bypassing the gastrointestinal tract.

[edit] Teeth

Main article: Teeth

Teeth (singular tooth) are small whitish structures found in the jaws (or mouths) of many vertebrates that are used to tear, scrape, milk and chew food. Teeth are not made of bone, but rather of tissues of varying density and hardness. The shape of an animal's teeth is related to its diet. For example, plant matter is hard to digest, so herbivores have many molars for chewing.

The teeth of carnivores are shaped to kill and tear meat, using specially shaped canine teeth. Herbivores' teeth are made for grinding food materials, in this case, plant parts.

[edit] Crop

A crop, or croup, is a thin-walled expanded portion of the alimentary tract used for the storage of food prior to digestion. In some birds it is an expanded, muscular pouch near the gullet or throat. In adult doves and pigeons, the crop can produce crop milk to feed newly hatched birds.[14]

Certain insects may have a crop or enlarged esophagus.

 

 

 

 

Rough illustration of a ruminant digestive system

[edit] Abomasum

Main article: Abomasum

Herbivores have evolved cecums (or an abomasum in the case of ruminants). Ruminants have a fore-stomach with four chambers. These are the rumen, reticulum, omasum, and abomasum. In the first two chambers, the rumen and the reticulum, the food is mixed with saliva and separates into layers of solid and liquid material. Solids clump together to form the cud (or bolus). The cud is then regurgitated, chewed slowly to completely mix it with saliva and to break down the particle size.

Fibre, especially cellulose and hemi-cellulose, is primarily broken down into the volatile fatty acids, acetic acid, propionic acid and butyric acid in these chambers (the reticulo-rumen) by microbes: (bacteria, protozoa, and fungi). In the omasum water and many of the inorganic mineral elements are absorbed into the blood stream.

The abomasum is the fourth and final stomach compartment in ruminants. It is a close equivalent of a monogastric stomach (e.g., those in humans or pigs), and digesta is processed here in much the same way. It serves primarily as a site for acid hydrolysis of microbial and dietary protein, preparing these protein sources for further digestion and absorption in the small intestine. Digesta is finally moved into the small intestine, where the digestion and absorption of nutrients occurs. Microbes produced in the reticulo-rumen are also digested in the small intestine.

 

 

 

 

A flesh fly "blowing a bubble", possibly to concentrate its food by evaporating water

[edit] Specialised behaviours

Regurgitation has been mentioned above under abomasum and crop, referring to crop milk, a secretion from the lining of the crop of pigeons and doves with which the parents feed their young by regurgitation.[15]

Many sharks have the ability to turn their stomachs inside out and evert it out of their mouths in order to get rid of unwanted contents (perhaps developed as a way to reduce exposure to toxins).

Other animals, such as rabbits and rodents, practise coprophagia behaviours - eating specialised faeces in order to re-digest food, especially in the case of roughage. Capybara, rabbits, hamsters and other related species do not have a complex digestive system as do, for example, ruminants. Instead they extract more nutrition from grass by giving their food a second pass through the gut. Soft faecal pellets of partially digested food are excreted and generally consumed immediately. They also produce normal droppings, which are not eaten.

Young elephants, pandas, koalas, and hippos eat the faeces of their mother, probably to obtain the bacteria required to properly digest vegetation. When they are born, their intestines do not contain these bacteria (they are completely sterile). Without them, they would be unable to get any nutritional value from many plant components.

[edit] In earthworms

An earthworm's digestive system consists of a mouth, pharynx, esophagus, crop, gizzard, and intestine. The mouth is surrounded by strong lips, which act like a hand to grab pieces of dead grass, leaves, and weeds, with bits of soil to help chew. The lips break the food down into smaller pieces. In the pharynx, the food is lubricated by mucus secretions for easier passage. The esophagus adds calcium carbonate to neutralize the acids formed by food matter decay. Temporary storage occurs in the crop where food and calcium carbonate are mixed. The powerful muscles of the gizzard churn and mix the mass of food and dirt. When the churning is complete, the glands in the walls of the gizzard add enzymes to the thick paste, which helps chemically breakdown the organic matter. By peristalsis, the mixture is sent to the intestine where friendly bacteria continue chemical breakdown. This releases carbohydrates, protein, fat, and various vitamins and minerals for absorption into the body.

[edit] Overview of vertebrate digestion

In most vertebrates, digestion is a multi-stage process in the digestive system, starting from ingestion of raw materials, most often other organisms. Ingestion usually involves some type of mechanical and chemical processing. Digestion is separated into four steps:

1.Ingestion: placing food into the mouth (entry of food in the digestive system),

2.Mechanical and chemical breakdown: mastication and the mixing of the resulting bolus with water, acids, bile and enzymes in the stomach and intestine to break down complex molecules into simple structures,

3.Absorption: of nutrients from the digestive system to the circulatory and lymphatic capillaries through osmosis, active transport, and diffusion, and

4.Egestion (Excretion): Removal of undigested materials from the digestive tract through defecation.

Underlying the process is muscle movement throughout the system through swallowing and peristalsis. Each step in digestion requires energy, and thus imposes an "overhead charge" on the energy made available from absorbed substances. Differences in that overhead cost are important influences on lifestyle, behavior, and even physical structures. Examples may be seen in humans, who differ considerably from other hominids (lack of hair, smaller jaws and musculature, different dentition, length of intestines, cooking, etc.).

The major part of digestion takes place in the small intestine. The large intestine primarily serves as a site for fermentation of indigestible matter by gut bacteria and for resorption of water from digesta before excretion.

In mammals, preparation for digestion begins with the cephalic phase in which saliva is produced in the mouth and digestive enzymes are produced in the stomach. Mechanical and chemical digestion begin in the mouth where food is chewed, and mixed with saliva to begin enzymatic processing of starches. The stomach continues to break food down mechanically and chemically through churning and mixing with both acids and enzymes. Absorption occurs in the stomach and gastrointestinal tract, and the process finishes with defecation.[2]

[edit] Human digestion process

Main article: Human gastrointestinal tract

 

 

 

 

 

 

Upper and Lower human gastrointestinal tract

The whole digestive system is around 9 meters long. In a healthy human adult this process can take between 24 and 72 hours. Food digestion physiology varies between individuals and upon other factors such as the characteristics of the food and size of the meal.[16]

[edit] Phases of gastric secretion

Cephalic phase - This phase occurs before food enters the stomach and involves preparation of the body for eating and digestion. Sight and thought stimulate the cerebral cortex. Taste and smell stimulus is sent to the hypothalamus and medulla oblongata. After this it is routed through the vagus nerve and release of acetylcholine. Gastric secretion at this phase rises to 40% of maximum rate. Acidity in the stomach is not buffered by food at this point and thus acts to inhibit parietal (secretes acid) and G cell (secretes gastrin) activity via D cell secretion of somatostatin.

Gastric phase - This phase takes 3 to 4 hours. It is stimulated by distension of the stomach, presence of food in stomach and decrease in pH. Distention activates long and myenteric reflexes. This activates the release of acetylcholine, which stimulates the release of more gastric juices. As protein enters the stomach, it binds to hydrogen ions, which raises the pH of the stomach. Inhibition of gastrin and gastric acid secretion is lifted. This triggers G cells to release gastrin, which in turn stimulates parietal cells to secrete gastric acid. Gastric acid is about 0.5% hydrochloric acid (HCl), which lowers the pH to the desired pH of 1-3. Acid release is also triggered by acetylcholine and histamine.

Intestinal phase - This phase has 2 parts, the excitatory and the inhibitory. Partially digested food fills the duodenum. This triggers intestinal gastrin to be released. Enterogastric reflex inhibits vagal nuclei, activating sympathetic fibers causing the pyloric sphincter to tighten to prevent more food from entering, and inhibits local reflexes.

[edit] Oral cavity

Main article: Mouth (human)

In humans, digestion begins in the Mouth, otherwise known as the "Buccal Cavity", where food is chewed. Saliva is secreted in large amounts (1-1.5 litres/day) by three pairs of exocrine salivary glands (parotid, submandibular, and sublingual) in the oral cavity, and is mixed with the chewed food by the tongue. Saliva cleans the oral cavity, moistens the food, and contains digestive enzymes such as salivary amylase, which aids in the chemical breakdown of polysaccharides such as starch into disaccharides such as maltose. It also contains mucus, a glycoprotein that helps soften the food and form it into a bolus. An additional enzyme, lingual lipase, hydrolyzes long-chain triglycerides into partial glycerides and free fatty acids.

Swallowing transports the chewed food into the esophagus, passing through the oropharynx and hypopharynx. The mechanism for swallowing is coordinated by the swallowing center in the medulla oblongata and pons. The reflex is initiated by touch receptors in the pharynx as the bolus of food is pushed to the back of the mouth.

[edit] Pharynx

Main article: Human pharynx

The pharynx is the part of the neck and throat situated immediately behind the mouth and nasal cavity, and cranial, or superior, to the esophagus. It is part of the digestive system and respiratory system. Because both food and air pass through the pharynx, a flap of connective tissue, the epiglottis closes over the trachea when food is swallowed to prevent choking or asphyxiation.

The oropharynx is that part of the pharynx behind the oral cavity. It is lined with stratified squamous epithelium. The nasopharynx lies behind the nasal cavity and like the nasal passages is lined with ciliated columnar pseudostratified epithelium.

Like the oropharynx above it the hypopharynx (laryngopharynx) serves as a passageway for food and air and is lined with a stratified squamous epithelium. It lies inferior to the upright epiglottis and extends to the larynx, where the respiratory and digestive pathways diverge. At that point, the laryngopharynx is continuous with the esophagus. During swallowing, food has the "right of way", and air passage temporarily stops.

[edit] Esophagus

Main article: Esophagus

The esophagus is a narrow muscular tube about 20-30 centimeters long, which starts at the pharynx at the back of the mouth, passes through the thoracic diaphragm, and ends at the cardiac orifice of the stomach. The wall of the esophagus is made up of two layers of smooth muscles, which form a continuous layer from the esophagus to the colon and contract slowly, over long periods of time. The inner layer of muscles is arranged circularly in a series of descending rings, while the outer layer is arranged longitudinally. At the top of the esophagus, is a flap of tissue called the epiglottis that closes during swallowing to prevent food from entering the trachea (windpipe). The chewed food is pushed down the esophagus to the stomach through peristaltic contraction of these muscles. It takes only about seven seconds for food to pass through the esophagus and now digestion takes place.

 

 

 

[edit] Stomach

Main article: Stomach

The stomach is a small, 'J'-shaped pouch with walls made of thick, distensible muscles, which stores and helps break down food. Food reduced to very small particles is more likely to be fully digested in the small intestine, and stomach churning has the effect of assisting the physical disassembly begun in the mouth. Ruminants, who are able to digest fibrous material (primarily cellulose), use fore-stomachs and repeated chewing to further the disassembly. Rabbits and some other animals pass some material through their entire digestive systems twice. Most birds ingest small stones to assist in mechanical processing in gizzards.

Food enters the stomach through the cardiac orifice where it is further broken apart and thoroughly mixed with gastric acid, pepsin and other digestive enzymes to break down proteins. The enzymes in the stomach also have an optimum conditions, meaning that they work at a specific pH and temperature better than any others. The acid itself does not break down food molecules, rather it provides an optimum pH for the reaction of the enzyme pepsin and kills many microorganisms that are ingested with the food. It can also denature proteins. This is the process of reducing polypeptide bonds and disrupting salt bridges, which in turn causes a loss of secondary, tertiary, or quaternary protein structure. The parietal cells of the stomach also secrete a glycoprotein called intrinsic factor, which enables the absorption of vitamin B-12. Mucus neck cells are present in the gastric glands of the stomach. They secrete mucus, which along with gastric juice plays an important role in lubrication and protection of the mucosal epithelium from excoriation by the highly concentrated hydrochloric acid. Other small molecules such as alcohol are absorbed in the stomach, passing through the membrane of the stomach and entering the circulatory system directly. Food in the stomach is in semi-liquid form, which upon completion is known as chyme.

After consumption of food, digestive "tonic" and peristaltic contractions begin, which helps break down the food and move it onward.[16] When the chyme reaches the opening to the duodenum known as the pylorus, contractions "squirt" the food back into the stomach through a process called retropulsion, which exerts additional force and further grinds down food into smaller particles.[16] Gastric emptying is the release of food from the stomach into the duodenum; the process is tightly controlled with liquids being emptied much more quickly than solids.[16] Gastric emptying has attracted medical interest as rapid gastric emptying is related to obesity and delayed gastric emptying syndrome is associated with diabetes mellitus, aging, and gastroesophageal reflux.[16]

The transverse section of the alimentary canal reveals four (or five, see description under mucosa) distinct and well developed layers within the stomach:

Serous membrane, a thin layer of mesothelial cells that is the outermost wall of the stomach.

Muscular coat, a well-developed layer of muscles used to mix ingested food, composed of three sets running in three different alignments. The outermost layer runs parallel to the vertical axis of the stomach (from top to bottom), the middle is concentric to the axis (horizontally circling the stomach cavity) and the innermost oblique layer, which is responsible for mixing and breaking down ingested food, runs diagonal to the longitudinal axis. The inner layer is unique to the stomach, all other parts of the digestive tract have only the first two layers.

Submucosa, composed of connective tissue that links the inner muscular layer to the mucosa and contains the nerves, blood and lymph vessels.

Mucosa is the extensively folded innermost layer. It can be divided into the epithelium, lamina propria, and the muscularis mucosae, though some consider the outermost muscularis mucosae to be a distinct layer, as it develops from the mesoderm rather than the endoderm (thus making a total of five layers). The epithelium and lamina are filled with connective tissue and covered in gastric glands that may be simple or branched tubular, and secrete mucus, hydrochloric acid, pepsinogen and rennin. The mucus lubricates the food and also prevents hydrochloric acid from acting on the walls of the stomach.

[edit] Small intestine

Main article: Small intestine

It has three parts: the Duodenum, Jejunum, and Ileum.

After being processed in the stomach, food is passed to the small intestine via the pyloric sphincter. The majority of digestion and absorption occurs here after the milky chyme enters the duodenum. Here it is further mixed with three different liquids:

Bile, which emulsifies fats to allow absorption, neutralizes the chyme and is used to excrete waste products such as bilin and bile acids. Bile is produced by the liver and then stored in the gallbladder where it will be released to the small intestine via the bile duct. The bile in the gallbladder is much more concentrated.[clarification needed]

Pancreatic juice made by the pancreas, which secretes enzymes such as pancreatic amylase, pancreatic lipase, and trypsinogen (inactive form of protease).

Intestinal juice secreted by the intestinal glands in the small intestine. It contains enzymes such as enteropeptidase, erepsin, trypsin, chymotrypsin, maltase, lactase and sucrase (all three of which process only sugars).

The pH level increases in the small intestine as all three fluids are alkaline. A more basic environment causes more helpful enzymes to activate and begin to help in the breakdown of molecules such as fat globules. Small, finger-like structures called villi, and their epithelial cells is covered with numerous microvilli to improve the absorption of nutrients by increasing the surface area of the intestine and enhancing speed at which nutrients are absorbed. Blood containing the absorbed nutrients is carried away from the small intestine via the hepatic portal vein and goes to the liver for filtering, removal of toxins, and nutrient processing.

The small intestine and remainder of the digestive tract undergoes peristalsis to transport food from the stomach to the rectum and allow food to be mixed with the digestive juices and absorbed. The circular muscles and longitudinal muscles are antagonistic muscles, with one contracting as the other relaxes. When the circular muscles contract, the lumen becomes narrower and longer and the food is squeezed and pushed forward. When the longitudinal muscles contract, the circular muscles relax and the gut dilates to become wider and shorter to allow food to enter.

[edit] Large intestine

Main article: Large intestine

After the food has been passed through the small intestine, the food enters the large intestine. Within it, digestion is retained long enough to allow fermentation due to the action of gut bacteria, which breaks down some of the substances that remain after processing in the small intestine; some of the breakdown products are absorbed. In humans, these include most complex saccharides (at most three disaccharides are digestible in humans). In addition, in many vertebrates, the large intestine reabsorbs fluid; in a few, with desert lifestyles, this reabsorbtion makes continued existence possible.

In general, the large intestine is less vigorous in absorptive activity. It produces sacculation, renews epithelial cells, and provides protective mucus and mucosal immunity. In humans, the large intestine is roughly 1.5 meters long, with three parts: the cecum at the junction with the small intestine, the colon, and the rectum. The colon itself has four parts: the ascending colon, the transverse colon, the descending colon, and the sigmoid colon. The large intestine absorbs water from the chyme and stores feces until it can be egested. Food products that cannot go through the villi, such as cellulose (dietary fiber), are mixed with other waste products from the body and become hard and concentrated feces. The feces is stored in the rectum for a certain period and then the stored feces is eliminated from the body due to the contraction and relaxation through the anus. The exit of this waste material is regulated by the anal sphincter.

[edit] Breakdown into nutrients

 

 

 

 

This section requires expansion with: digestion of other substances. (August 2011)

 

[edit] Protein digestion

Protein digestion occurs in the stomach and duodenum in which 3 main enzymes, pepsin secreted by the stomach and trypsin and chymotrypsin secreted by the pancreas, break down food proteins into polypeptides that are then broken down by various exopeptidases and dipeptidases into amino acids. The digestive enzymes however are mostly secreted as their inactive precursors, the zymogens. For example, trypsin is secreted by pancreas in the form of trypsinogen, which is activated in the duodenum by enterokinase to form trypsin. Trypsin then cleaves proteins to smaller polypeptides.

[edit] Fat digestion

Digestion of some fats can begin in the mouth where lingual lipase breaks down some short chain lipids into diglycerides. The presence of fat in the small intestine produces hormones that stimulate the release of pancreatic lipase from the pancreas and bile from the liver for breakdown of fats into fatty acids. Complete digestion of one molecule of fat (a triglyceride) results in 3 fatty acid molecules and one glycerol molecule.

[edit] Carbohydrate digestion

In humans, dietary starches are composed of glucose units arranged in long chains called amylose, a polysaccharide. During digestion, bonds between glucose molecules are broken by salivary and pancreatic amylase, resulting in progressively smaller chains of glucose. This results in simple sugars glucose and maltose (2 glucose molecules) that can be absorbed by the small intestine.

Lactase is an enzyme that breaks down the disaccharide lactose to its component parts, glucose and galactose. Glucose and galactose can be absorbed by the small intestine. Approximately half of the adult population produce only small amounts of lactase and are unable to eat milk-based foods. This is commonly known as lactose intolerance.

Sucrase is an enzyme that breaks down the disaccharide sucrose, commonly known as table sugar, cane sugar, or beet sugar. Sucrose digestion yields the sugars fructose and glucose which are readily absorbed by the small intestine.

[edit] DNA and RNA digestion

DNA and RNA are broken down into mononucleotides by the nucleases deoxyribonuclease and ribonuclease (DNase and RNase) from the pancreas.

[edit] Digestive hormones

 

 

 

 

Action of the major digestive hormones

There are at least five hormones that aid and regulate the digestive system in mammals. There are variations across the vertebrates, as for instance in birds. Arrangements are complex and additional details are regularly discovered. For instance, more connections to metabolic control (largely the glucose-insulin system) have been uncovered in recent years.

Gastrin - is in the stomach and stimulates the gastric glands to secrete pepsinogen (an inactive form of the enzyme pepsin) and hydrochloric acid. Secretion of gastrin is stimulated by food arriving in stomach. The secretion is inhibited by low pH .

Secretin - is in the duodenum and signals the secretion of sodium bicarbonate in the pancreas and it stimulates the bile secretion in the liver. This hormone responds to the acidity of the chyme.

Cholecystokinin (CCK) - is in the duodenum and stimulates the release of digestive enzymes in the pancreas and stimulates the emptying of bile in the gall bladder. This hormone is secreted in response to fat in chyme.

Gastric inhibitory peptide (GIP) - is in the duodenum and decreases the stomach churning in turn slowing the emptying in the stomach. Another function is to induce insulin secretion.

Motilin - is in the duodenum and increases the migrating myoelectric complex component of gastrointestinal motility and stimulates the production of pepsin.

 

DIGESTIVE SYSTEM(SCIENCE)

Posted by sarahkasumejaneares on November 6, 2012 at 7:50 AM Comments comments (0)

 Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones.

When food enters the mouth, its digestion starts by the action of mastication, a form of mechanical digestion, and the contact of saliva. Saliva, which is secreted by the salivary glands, contains salivary amylase, an enzyme which starts the digestion of starch in the food. After undergoing mastication and starch digestion, the food will be in the form of a small, round slurry mass called a bolus. It will then travel down the esophagus and into the stomach by the action of peristalsis. Gastric juice in the stomach starts protein digestion. Gastric juice mainly contains hydrochloric acid and pepsin. As these two chemicals may damage the stomach wall, mucus is secreted by the stomach, providing a slimy layer that acts as a shield against the damaging effects of the chemicals. At the same time protein digestion is occurring, mechanical mixing occurs by peristalsis, which are waves of muscular contractions that move along the stomach wall. This allows the mass of food to further mix with the digestive enzymes. After some time (typically an hour or two in humans, 4–6 hours in dogs, somewhat shorter duration in house cats), the resulting thick liquid is called chyme. When the pyloric sphincter valve opens, chyme enters the duodenum where it mixes with digestive enzymes from the pancreas, and then passes through the small intestine, in which digestion continues. When the chyme is fully digested, it is absorbed into the blood. 95% of absorption of nutrients occurs in the small intestine. Water and minerals are reabsorbed back into the blood in the colon (large intestine) where the pH is slightly acidic about 5.6 ~ 6.9. Some vitamins, such as biotin and vitamin K (K2MK7) produced by bacteria in the colon are also absorbed into the blood in the colon.[1] Waste material is eliminated from the rectum during defecation.[2]

 

 

 

 

Contents

[hide] 1 Digestive systems 1.1 Secretion systems 1.1.1 Channel transport system

1.1.2 Molecular syringe

1.1.3 Conjugation machinery

1.1.4 Release of outer membrane vesicles

1.2 Gastrovascular cavity

1.3 Phagosome

1.4 Specialised organs and behaviours 1.4.1 Beaks

1.4.2 Tongue

1.4.3 Teeth

1.4.4 Crop

1.4.5 Abomasum

1.4.6 Specialised behaviours

1.5 In earthworms

2 Overview of vertebrate digestion

3 Human digestion process 3.1 Phases of gastric secretion

3.2 Oral cavity

3.3 Pharynx

3.4 Esophagus

3.5 Stomach

3.6 Small intestine

3.7 Large intestine

4 Breakdown into nutrients 4.1 Protein digestion

4.2 Fat digestion

4.3 Carbohydrate digestion

4.4 DNA and RNA digestion

5 Digestive hormones

6 Significance of pH in digestion

7 Uses of animal gut by humans

8 See also

9 References

10 External links

 

[edit] Digestive systems

Digestive systems take many forms. There is a fundamental distinction between internal and external digestion. External digestion is more primitive, and most fungi still rely on it.[3] In this process, enzymes are secreted into the environment surrounding the organism, where they break down an organic material, and some of the products diffuse back to the organism. Later, animals form a tube in which internal digestion occurs, which is more efficient because more of the broken down products can be captured, and the internal chemical environment can be more efficiently controlled.[4]

Some organisms, including nearly all spiders, simply secrete biotoxins and digestive chemicals (e.g., enzymes) into the extracellular environment prior to ingestion of the consequent "soup". In others, once potential nutrients or food is inside the organism, digestion can be conducted to a vesicle or a sac-like structure, through a tube, or through several specialized organs aimed at making the absorption of nutrients more efficient.

 

 

 

 

Schematic drawing of bacterial conjugation. 1- Donor cell produces pilus. 2- Pilus attaches to recipient cell, bringing the two cells together. 3- The mobile plasmid is nicked and a single strand of DNA is transferred to the recipient cell. 4- Both cells recircularize their plasmids, synthesize second strands, and reproduce pili; both cells are now viable donors.

[edit] Secretion systems

Main article: Secretion

Bacteria use several systems to obtain nutrients from other organisms in the environments.

[edit] Channel transport system

In a channel transupport system, several proteins form a contiguous channel traversing the inner and outer membranes of the bacteria. It is a simple system, which consists of only three protein subunits: the ABC protein, membrane fusion protein (MFP), and outer membrane protein (OMP)[specify]. This secretion system transports various molecules, from ions, drugs, to proteins of various sizes (20 - 900 kDa). The molecules secreted vary in size from the small Escherichia coli peptide colicin V, (10 kDa) to the Pseudomonas fluorescens cell adhesion protein LapA of 900 kDa.[5]

[edit] Molecular syringe

One molecular syringe is used through which a bacterium (e.g. certain types of Salmonella, Shigella, Yersinia) can inject nutrients into protist cells. One such mechanism was first discovered in Y. pestis and showed that toxins could be injected directly from the bacterial cytoplasm into the cytoplasm of its host's cells rather than simply be secreted into the extracellular medium.[6]

[edit] Conjugation machinery

The conjugation machinery of some bacteria (and archaeal flagella) is capable of transporting both DNA and proteins. It was discovered in Agrobacterium tumefaciens, which uses this system to introduce the Ti plasmid and proteins into the host, which develops the crown gall (tumor).[7] The VirB complex of Agrobacterium tumefaciens is the prototypic system.[8]

The nitrogen fixing Rhizobia are an interesting case, wherein conjugative elements naturally engage in inter-kingdom conjugation. Such elements as the Agrobacterium Ti or Ri plasmids contain elements that can transfer to plant cells. Transferred genes enter the plant cell nucleus and effectively transform the plant cells into factories for the production of opines, which the bacteria use as carbon and energy sources. Infected plant cells form crown gall or root tumors. The Ti and Ri plasmids are thus endosymbionts of the bacteria, which are in turn endosymbionts (or parasites) of the infected plant.

The Ti and Ri plasmids are themselves conjugative. Ti and Ri transfer between bacteria uses an independent system (the tra, or transfer, operon) from that for inter-kingdom transfer (the vir, or virulence, operon). Such transfer creates virulent strains from previously avirulent Agrobacteria.

[edit] Release of outer membrane vesicles

In addition to the use of the multiprotein complexes listed above, Gram-negative bacteria possess another method for release of material: the formation of outer membrane vesicles.[9] Portions of the outer membrane pinch off, forming spherical structures made of a lipid bilayer enclosing periplasmic materials. Vesicles from a number of bacterial species have been found to contain virulence factors, some have immunomodulatory effects, and some can directly adhere to and intoxicate host cells. While release of vesicles has been demonstrated as a general response to stress conditions, the process of loading cargo proteins seems to be selective.[10]

 

 

 

 

Venus Flytrap (Dionaea muscipula) leaf

[edit] Gastrovascular cavity

The gastrovascular cavity functions as a stomach in both digestion and the distribution of nutrients to all parts of the body. Extracellular digestion takes place within this central cavity, which is lined with the gastrodermis, the internal layer of epithelium. This cavity has only one opening to the outside that functions as both a mouth and an anus: waste and undigested matter is excreted through the mouth/anus, which can be described as an incomplete gut.

In a plant such as the Venus Flytrap that can make its own food through photosynthesis, it does not eat and digest its prey for the traditional objectives of harvesting energy and carbon, but mines prey primarily for essential nutrients (nitrogen and phosphorus in particular) that are in short supply in its boggy, acidic habitat.[11]

 

 

 

 

Trophozoites of Entamoeba histolytica with ingested erythrocytes

[edit] Phagosome

A phagosome is a vacuole formed around a particle absorbed by phagocytosis. The vacuole is formed by the fusion of the cell membrane around the particle. A phagosome is a cellular compartment in which pathogenic microorganisms can be killed and digested. Phagosomes fuse with lysosomes in their maturation process, forming phagolysosomes. In humans, Entamoeba histolytica can phagocytose red blood cells.[12]

[edit] Specialised organs and behaviours

To aid in the digestion of their food animals evolved organs such as beaks, tongues, teeth, a crop, gizzard, and others.

 

 

 

 

 

A Catalina Macaw's seed-shearing beak

 

 

 

Squid beak with ruler for size comparison

[edit] Beaks

Birds have beaks that are specialised according to the bird's ecological niche. For example, macaws primarily eat seeds, nuts, and fruit, using their impressive beaks to open even the toughest seed. First they scratch a thin line with the sharp point of the beak, then they shear the seed open with the sides of the beak.

The mouth of the squid is equipped with a sharp horny beak mainly made of cross-linked proteins. It is used to kill and tear prey into manageable pieces. The beak is very robust, but does not contain any minerals, unlike the teeth and jaws of many other organisms, including marine species.[13] The beak is the only indigestible part of the squid.

[edit] Tongue

Main article: Tongue

The tongue is skeletal muscle on the floor of the mouth that manipulates food for chewing (mastication) and swallowing (deglutition). It is sensitive and kept moist by saliva. The underside of the tongue is covered with a smooth mucous membrane. The tongue also has a touch sense for locating and positioning food particles that require further chewing. The tongue is utilized to roll food particles into a bolus before being transported down the esophagus through peristalsis.

The sublingual region underneath the front of the tongue is a location where the oral mucosa is very thin, and underlain by a plexus of veins. This is an ideal location for introducing certain medications to the body. The sublingual route takes advantage of the highly vascular quality of the oral cavity, and allows for the speedy application of medication into the cardiovascular system, bypassing the gastrointestinal tract.

[edit] Teeth

Main article: Teeth

Teeth (singular tooth) are small whitish structures found in the jaws (or mouths) of many vertebrates that are used to tear, scrape, milk and chew food. Teeth are not made of bone, but rather of tissues of varying density and hardness. The shape of an animal's teeth is related to its diet. For example, plant matter is hard to digest, so herbivores have many molars for chewing.

The teeth of carnivores are shaped to kill and tear meat, using specially shaped canine teeth. Herbivores' teeth are made for grinding food materials, in this case, plant parts.

[edit] Crop

A crop, or croup, is a thin-walled expanded portion of the alimentary tract used for the storage of food prior to digestion. In some birds it is an expanded, muscular pouch near the gullet or throat. In adult doves and pigeons, the crop can produce crop milk to feed newly hatched birds.[14]

Certain insects may have a crop or enlarged esophagus.

 

 

 

 

Rough illustration of a ruminant digestive system

[edit] Abomasum

Main article: Abomasum

Herbivores have evolved cecums (or an abomasum in the case of ruminants). Ruminants have a fore-stomach with four chambers. These are the rumen, reticulum, omasum, and abomasum. In the first two chambers, the rumen and the reticulum, the food is mixed with saliva and separates into layers of solid and liquid material. Solids clump together to form the cud (or bolus). The cud is then regurgitated, chewed slowly to completely mix it with saliva and to break down the particle size.

Fibre, especially cellulose and hemi-cellulose, is primarily broken down into the volatile fatty acids, acetic acid, propionic acid and butyric acid in these chambers (the reticulo-rumen) by microbes: (bacteria, protozoa, and fungi). In the omasum water and many of the inorganic mineral elements are absorbed into the blood stream.

The abomasum is the fourth and final stomach compartment in ruminants. It is a close equivalent of a monogastric stomach (e.g., those in humans or pigs), and digesta is processed here in much the same way. It serves primarily as a site for acid hydrolysis of microbial and dietary protein, preparing these protein sources for further digestion and absorption in the small intestine. Digesta is finally moved into the small intestine, where the digestion and absorption of nutrients occurs. Microbes produced in the reticulo-rumen are also digested in the small intestine.

 

 

 

 

A flesh fly "blowing a bubble", possibly to concentrate its food by evaporating water

[edit] Specialised behaviours

Regurgitation has been mentioned above under abomasum and crop, referring to crop milk, a secretion from the lining of the crop of pigeons and doves with which the parents feed their young by regurgitation.[15]

Many sharks have the ability to turn their stomachs inside out and evert it out of their mouths in order to get rid of unwanted contents (perhaps developed as a way to reduce exposure to toxins).

Other animals, such as rabbits and rodents, practise coprophagia behaviours - eating specialised faeces in order to re-digest food, especially in the case of roughage. Capybara, rabbits, hamsters and other related species do not have a complex digestive system as do, for example, ruminants. Instead they extract more nutrition from grass by giving their food a second pass through the gut. Soft faecal pellets of partially digested food are excreted and generally consumed immediately. They also produce normal droppings, which are not eaten.

Young elephants, pandas, koalas, and hippos eat the faeces of their mother, probably to obtain the bacteria required to properly digest vegetation. When they are born, their intestines do not contain these bacteria (they are completely sterile). Without them, they would be unable to get any nutritional value from many plant components.

[edit] In earthworms

An earthworm's digestive system consists of a mouth, pharynx, esophagus, crop, gizzard, and intestine. The mouth is surrounded by strong lips, which act like a hand to grab pieces of dead grass, leaves, and weeds, with bits of soil to help chew. The lips break the food down into smaller pieces. In the pharynx, the food is lubricated by mucus secretions for easier passage. The esophagus adds calcium carbonate to neutralize the acids formed by food matter decay. Temporary storage occurs in the crop where food and calcium carbonate are mixed. The powerful muscles of the gizzard churn and mix the mass of food and dirt. When the churning is complete, the glands in the walls of the gizzard add enzymes to the thick paste, which helps chemically breakdown the organic matter. By peristalsis, the mixture is sent to the intestine where friendly bacteria continue chemical breakdown. This releases carbohydrates, protein, fat, and various vitamins and minerals for absorption into the body.

[edit] Overview of vertebrate digestion

In most vertebrates, digestion is a multi-stage process in the digestive system, starting from ingestion of raw materials, most often other organisms. Ingestion usually involves some type of mechanical and chemical processing. Digestion is separated into four steps:

1.Ingestion: placing food into the mouth (entry of food in the digestive system),

2.Mechanical and chemical breakdown: mastication and the mixing of the resulting bolus with water, acids, bile and enzymes in the stomach and intestine to break down complex molecules into simple structures,

3.Absorption: of nutrients from the digestive system to the circulatory and lymphatic capillaries through osmosis, active transport, and diffusion, and

4.Egestion (Excretion): Removal of undigested materials from the digestive tract through defecation.

Underlying the process is muscle movement throughout the system through swallowing and peristalsis. Each step in digestion requires energy, and thus imposes an "overhead charge" on the energy made available from absorbed substances. Differences in that overhead cost are important influences on lifestyle, behavior, and even physical structures. Examples may be seen in humans, who differ considerably from other hominids (lack of hair, smaller jaws and musculature, different dentition, length of intestines, cooking, etc.).

The major part of digestion takes place in the small intestine. The large intestine primarily serves as a site for fermentation of indigestible matter by gut bacteria and for resorption of water from digesta before excretion.

In mammals, preparation for digestion begins with the cephalic phase in which saliva is produced in the mouth and digestive enzymes are produced in the stomach. Mechanical and chemical digestion begin in the mouth where food is chewed, and mixed with saliva to begin enzymatic processing of starches. The stomach continues to break food down mechanically and chemically through churning and mixing with both acids and enzymes. Absorption occurs in the stomach and gastrointestinal tract, and the process finishes with defecation.[2]

[edit] Human digestion process

Main article: Human gastrointestinal tract

 

 

 

 

 

 

Upper and Lower human gastrointestinal tract

The whole digestive system is around 9 meters long. In a healthy human adult this process can take between 24 and 72 hours. Food digestion physiology varies between individuals and upon other factors such as the characteristics of the food and size of the meal.[16]

[edit] Phases of gastric secretion

Cephalic phase - This phase occurs before food enters the stomach and involves preparation of the body for eating and digestion. Sight and thought stimulate the cerebral cortex. Taste and smell stimulus is sent to the hypothalamus and medulla oblongata. After this it is routed through the vagus nerve and release of acetylcholine. Gastric secretion at this phase rises to 40% of maximum rate. Acidity in the stomach is not buffered by food at this point and thus acts to inhibit parietal (secretes acid) and G cell (secretes gastrin) activity via D cell secretion of somatostatin.

Gastric phase - This phase takes 3 to 4 hours. It is stimulated by distension of the stomach, presence of food in stomach and decrease in pH. Distention activates long and myenteric reflexes. This activates the release of acetylcholine, which stimulates the release of more gastric juices. As protein enters the stomach, it binds to hydrogen ions, which raises the pH of the stomach. Inhibition of gastrin and gastric acid secretion is lifted. This triggers G cells to release gastrin, which in turn stimulates parietal cells to secrete gastric acid. Gastric acid is about 0.5% hydrochloric acid (HCl), which lowers the pH to the desired pH of 1-3. Acid release is also triggered by acetylcholine and histamine.

Intestinal phase - This phase has 2 parts, the excitatory and the inhibitory. Partially digested food fills the duodenum. This triggers intestinal gastrin to be released. Enterogastric reflex inhibits vagal nuclei, activating sympathetic fibers causing the pyloric sphincter to tighten to prevent more food from entering, and inhibits local reflexes.

[edit] Oral cavity

Main article: Mouth (human)

In humans, digestion begins in the Mouth, otherwise known as the "Buccal Cavity", where food is chewed. Saliva is secreted in large amounts (1-1.5 litres/day) by three pairs of exocrine salivary glands (parotid, submandibular, and sublingual) in the oral cavity, and is mixed with the chewed food by the tongue. Saliva cleans the oral cavity, moistens the food, and contains digestive enzymes such as salivary amylase, which aids in the chemical breakdown of polysaccharides such as starch into disaccharides such as maltose. It also contains mucus, a glycoprotein that helps soften the food and form it into a bolus. An additional enzyme, lingual lipase, hydrolyzes long-chain triglycerides into partial glycerides and free fatty acids.

Swallowing transports the chewed food into the esophagus, passing through the oropharynx and hypopharynx. The mechanism for swallowing is coordinated by the swallowing center in the medulla oblongata and pons. The reflex is initiated by touch receptors in the pharynx as the bolus of food is pushed to the back of the mouth.

[edit] Pharynx

Main article: Human pharynx

The pharynx is the part of the neck and throat situated immediately behind the mouth and nasal cavity, and cranial, or superior, to the esophagus. It is part of the digestive system and respiratory system. Because both food and air pass through the pharynx, a flap of connective tissue, the epiglottis closes over the trachea when food is swallowed to prevent choking or asphyxiation.

The oropharynx is that part of the pharynx behind the oral cavity. It is lined with stratified squamous epithelium. The nasopharynx lies behind the nasal cavity and like the nasal passages is lined with ciliated columnar pseudostratified epithelium.

Like the oropharynx above it the hypopharynx (laryngopharynx) serves as a passageway for food and air and is lined with a stratified squamous epithelium. It lies inferior to the upright epiglottis and extends to the larynx, where the respiratory and digestive pathways diverge. At that point, the laryngopharynx is continuous with the esophagus. During swallowing, food has the "right of way", and air passage temporarily stops.

[edit] Esophagus

Main article: Esophagus

The esophagus is a narrow muscular tube about 20-30 centimeters long, which starts at the pharynx at the back of the mouth, passes through the thoracic diaphragm, and ends at the cardiac orifice of the stomach. The wall of the esophagus is made up of two layers of smooth muscles, which form a continuous layer from the esophagus to the colon and contract slowly, over long periods of time. The inner layer of muscles is arranged circularly in a series of descending rings, while the outer layer is arranged longitudinally. At the top of the esophagus, is a flap of tissue called the epiglottis that closes during swallowing to prevent food from entering the trachea (windpipe). The chewed food is pushed down the esophagus to the stomach through peristaltic contraction of these muscles. It takes only about seven seconds for food to pass through the esophagus and now digestion takes place.

 

 

 

[edit] Stomach

Main article: Stomach

The stomach is a small, 'J'-shaped pouch with walls made of thick, distensible muscles, which stores and helps break down food. Food reduced to very small particles is more likely to be fully digested in the small intestine, and stomach churning has the effect of assisting the physical disassembly begun in the mouth. Ruminants, who are able to digest fibrous material (primarily cellulose), use fore-stomachs and repeated chewing to further the disassembly. Rabbits and some other animals pass some material through their entire digestive systems twice. Most birds ingest small stones to assist in mechanical processing in gizzards.

Food enters the stomach through the cardiac orifice where it is further broken apart and thoroughly mixed with gastric acid, pepsin and other digestive enzymes to break down proteins. The enzymes in the stomach also have an optimum conditions, meaning that they work at a specific pH and temperature better than any others. The acid itself does not break down food molecules, rather it provides an optimum pH for the reaction of the enzyme pepsin and kills many microorganisms that are ingested with the food. It can also denature proteins. This is the process of reducing polypeptide bonds and disrupting salt bridges, which in turn causes a loss of secondary, tertiary, or quaternary protein structure. The parietal cells of the stomach also secrete a glycoprotein called intrinsic factor, which enables the absorption of vitamin B-12. Mucus neck cells are present in the gastric glands of the stomach. They secrete mucus, which along with gastric juice plays an important role in lubrication and protection of the mucosal epithelium from excoriation by the highly concentrated hydrochloric acid. Other small molecules such as alcohol are absorbed in the stomach, passing through the membrane of the stomach and entering the circulatory system directly. Food in the stomach is in semi-liquid form, which upon completion is known as chyme.

After consumption of food, digestive "tonic" and peristaltic contractions begin, which helps break down the food and move it onward.[16] When the chyme reaches the opening to the duodenum known as the pylorus, contractions "squirt" the food back into the stomach through a process called retropulsion, which exerts additional force and further grinds down food into smaller particles.[16] Gastric emptying is the release of food from the stomach into the duodenum; the process is tightly controlled with liquids being emptied much more quickly than solids.[16] Gastric emptying has attracted medical interest as rapid gastric emptying is related to obesity and delayed gastric emptying syndrome is associated with diabetes mellitus, aging, and gastroesophageal reflux.[16]

The transverse section of the alimentary canal reveals four (or five, see description under mucosa) distinct and well developed layers within the stomach:

Serous membrane, a thin layer of mesothelial cells that is the outermost wall of the stomach.

Muscular coat, a well-developed layer of muscles used to mix ingested food, composed of three sets running in three different alignments. The outermost layer runs parallel to the vertical axis of the stomach (from top to bottom), the middle is concentric to the axis (horizontally circling the stomach cavity) and the innermost oblique layer, which is responsible for mixing and breaking down ingested food, runs diagonal to the longitudinal axis. The inner layer is unique to the stomach, all other parts of the digestive tract have only the first two layers.

Submucosa, composed of connective tissue that links the inner muscular layer to the mucosa and contains the nerves, blood and lymph vessels.

Mucosa is the extensively folded innermost layer. It can be divided into the epithelium, lamina propria, and the muscularis mucosae, though some consider the outermost muscularis mucosae to be a distinct layer, as it develops from the mesoderm rather than the endoderm (thus making a total of five layers). The epithelium and lamina are filled with connective tissue and covered in gastric glands that may be simple or branched tubular, and secrete mucus, hydrochloric acid, pepsinogen and rennin. The mucus lubricates the food and also prevents hydrochloric acid from acting on the walls of the stomach.

[edit] Small intestine

Main article: Small intestine

It has three parts: the Duodenum, Jejunum, and Ileum.

After being processed in the stomach, food is passed to the small intestine via the pyloric sphincter. The majority of digestion and absorption occurs here after the milky chyme enters the duodenum. Here it is further mixed with three different liquids:

Bile, which emulsifies fats to allow absorption, neutralizes the chyme and is used to excrete waste products such as bilin and bile acids. Bile is produced by the liver and then stored in the gallbladder where it will be released to the small intestine via the bile duct. The bile in the gallbladder is much more concentrated.[clarification needed]

Pancreatic juice made by the pancreas, which secretes enzymes such as pancreatic amylase, pancreatic lipase, and trypsinogen (inactive form of protease).

Intestinal juice secreted by the intestinal glands in the small intestine. It contains enzymes such as enteropeptidase, erepsin, trypsin, chymotrypsin, maltase, lactase and sucrase (all three of which process only sugars).

The pH level increases in the small intestine as all three fluids are alkaline. A more basic environment causes more helpful enzymes to activate and begin to help in the breakdown of molecules such as fat globules. Small, finger-like structures called villi, and their epithelial cells is covered with numerous microvilli to improve the absorption of nutrients by increasing the surface area of the intestine and enhancing speed at which nutrients are absorbed. Blood containing the absorbed nutrients is carried away from the small intestine via the hepatic portal vein and goes to the liver for filtering, removal of toxins, and nutrient processing.

The small intestine and remainder of the digestive tract undergoes peristalsis to transport food from the stomach to the rectum and allow food to be mixed with the digestive juices and absorbed. The circular muscles and longitudinal muscles are antagonistic muscles, with one contracting as the other relaxes. When the circular muscles contract, the lumen becomes narrower and longer and the food is squeezed and pushed forward. When the longitudinal muscles contract, the circular muscles relax and the gut dilates to become wider and shorter to allow food to enter.

[edit] Large intestine

Main article: Large intestine

After the food has been passed through the small intestine, the food enters the large intestine. Within it, digestion is retained long enough to allow fermentation due to the action of gut bacteria, which breaks down some of the substances that remain after processing in the small intestine; some of the breakdown products are absorbed. In humans, these include most complex saccharides (at most three disaccharides are digestible in humans). In addition, in many vertebrates, the large intestine reabsorbs fluid; in a few, with desert lifestyles, this reabsorbtion makes continued existence possible.

In general, the large intestine is less vigorous in absorptive activity. It produces sacculation, renews epithelial cells, and provides protective mucus and mucosal immunity. In humans, the large intestine is roughly 1.5 meters long, with three parts: the cecum at the junction with the small intestine, the colon, and the rectum. The colon itself has four parts: the ascending colon, the transverse colon, the descending colon, and the sigmoid colon. The large intestine absorbs water from the chyme and stores feces until it can be egested. Food products that cannot go through the villi, such as cellulose (dietary fiber), are mixed with other waste products from the body and become hard and concentrated feces. The feces is stored in the rectum for a certain period and then the stored feces is eliminated from the body due to the contraction and relaxation through the anus. The exit of this waste material is regulated by the anal sphincter.

[edit] Breakdown into nutrients

 

 

 

 

This section requires expansion with: digestion of other substances. (August 2011)

 

[edit] Protein digestion

Protein digestion occurs in the stomach and duodenum in which 3 main enzymes, pepsin secreted by the stomach and trypsin and chymotrypsin secreted by the pancreas, break down food proteins into polypeptides that are then broken down by various exopeptidases and dipeptidases into amino acids. The digestive enzymes however are mostly secreted as their inactive precursors, the zymogens. For example, trypsin is secreted by pancreas in the form of trypsinogen, which is activated in the duodenum by enterokinase to form trypsin. Trypsin then cleaves proteins to smaller polypeptides.

[edit] Fat digestion

Digestion of some fats can begin in the mouth where lingual lipase breaks down some short chain lipids into diglycerides. The presence of fat in the small intestine produces hormones that stimulate the release of pancreatic lipase from the pancreas and bile from the liver for breakdown of fats into fatty acids. Complete digestion of one molecule of fat (a triglyceride) results in 3 fatty acid molecules and one glycerol molecule.

[edit] Carbohydrate digestion

In humans, dietary starches are composed of glucose units arranged in long chains called amylose, a polysaccharide. During digestion, bonds between glucose molecules are broken by salivary and pancreatic amylase, resulting in progressively smaller chains of glucose. This results in simple sugars glucose and maltose (2 glucose molecules) that can be absorbed by the small intestine.

Lactase is an enzyme that breaks down the disaccharide lactose to its component parts, glucose and galactose. Glucose and galactose can be absorbed by the small intestine. Approximately half of the adult population produce only small amounts of lactase and are unable to eat milk-based foods. This is commonly known as lactose intolerance.

Sucrase is an enzyme that breaks down the disaccharide sucrose, commonly known as table sugar, cane sugar, or beet sugar. Sucrose digestion yields the sugars fructose and glucose which are readily absorbed by the small intestine.

[edit] DNA and RNA digestion

DNA and RNA are broken down into mononucleotides by the nucleases deoxyribonuclease and ribonuclease (DNase and RNase) from the pancreas.

[edit] Digestive hormones

 

 

 

 

Action of the major digestive hormones

There are at least five hormones that aid and regulate the digestive system in mammals. There are variations across the vertebrates, as for instance in birds. Arrangements are complex and additional details are regularly discovered. For instance, more connections to metabolic control (largely the glucose-insulin system) have been uncovered in recent years.

Gastrin - is in the stomach and stimulates the gastric glands to secrete pepsinogen (an inactive form of the enzyme pepsin) and hydrochloric acid. Secretion of gastrin is stimulated by food arriving in stomach. The secretion is inhibited by low pH .

Secretin - is in the duodenum and signals the secretion of sodium bicarbonate in the pancreas and it stimulates the bile secretion in the liver. This hormone responds to the acidity of the chyme.

Cholecystokinin (CCK) - is in the duodenum and stimulates the release of digestive enzymes in the pancreas and stimulates the emptying of bile in the gall bladder. This hormone is secreted in response to fat in chyme.

Gastric inhibitory peptide (GIP) - is in the duodenum and decreases the stomach churning in turn slowing the emptying in the stomach. Another function is to induce insulin secretion.

Motilin - is in the duodenum and increases the migrating myoelectric complex component of gastrointestinal motility and stimulates the production of pepsin.

 

balagtasan(filipino)

Posted by sarahkasumejaneares on November 5, 2012 at 9:15 PM Comments comments (0)

MAHAL KITA vs MAHAL KA

Kung dalawa lang ang pagpipilian,

SINO ang handa mong pakasalan:

Taong MAHAL MO, ngunit di ka niya mahal?

O taong MAHAL KA, ngunit di mo siya mahal?

Mula sa panulat nina:

GONIE T. MEJIA — nagtanggol sa panig ng MAHAL MO, di ka niya mahal

— nagtanggol sa panig ng MAHAL KA, di mo siya mahal;

sumulat din ng iskrip ng LAKANDIWA

LAKANDIWA (Panimula)

Sa pagbukas nitong tabing na hudyat ng pasimula

Ng tagisan ng talinong paborito nating madla

Ako muna'y bumabati sa inyo at, harinawa,

Tanggapin ang malwalhating pagpapala ng Lumikha.

Paksa nating hihimayin sa sangkalan ng katwiran

Ay kung sino sa dalawa ang handa mong pakasalan:

Taong mahal mo nang labis ngunit di ka minamahal,

O labis na nagmamahal sa yo, di mo mahal naman?

Unang tindig at hahataw ay batikang manunula

Ang Hari ng Balagtasan na sa Tarlac pa nagmula

Gonie Mejia ang ngalan... Isa nga pong pampasigla

Palakpakan natin siya pagkat iyan ang syang tama!

GONIE MEJIA (Unang Tindig)

Kapag puso ang nag-utos at nasunod yaong nais,

Ang mabuhay ay marangal sa piling ng nilalangit

Subalit kung makakatwang, yaong hindi iniibig,

Tagumpay sa pagsasama, may kapisang hapdi't pait.

Pag-aasawa ang wika nga'y hindi kaning isusubo

Na dagling mailuluwa lalo't ikaw ay napaso;

Paano ba lalambingin ang hindi mo pinintuho

Kung ang damdamin ay tutol, umaayaw pati puso?

Malinaw po ang panig kong daan sa pag-aasawa

Sa dambana'y ihaharap ang labis kong sinisinta

Pagkat ayaw kong mabulid sa lagim ng pagdurusa

Kasamahin ang babaeng sa buhay ko'y di sinamba.

Dahil itong katalo ko ay salungat ang tahakin

Hindi ko na pagtatakhang balang araw sya'y mabaliw

Pagkat higit nyang pinili ang di tugon ng damdamin

Sa mali nyang kapasyahan, sarili ang sisisihin.

Sa piling ng aking mutya, habang ako'y maligaya,

Si Raffy ay nagmumukmok, luhaan ang mga mata;

Habang ako, sa liwanag ng buwan ay nagsasaya,

Si Raffy ay nakapikit, nagbibilang po ng tala!

LAKANDIWA

Si Gonie po'y nagsulit na ng katwiran sa publiko

Pakinggan po naman natin si Rafael A. Pulmano

Sa Laguna pa po galing; makunsyensya naman kayo,

Isalubong agad sana'y palakpakang masigabo!

RAFAEL PULMANO (Unang Tindig)

Sa amin pong munting bayan ay may isang hampaslupa

Palaboy at sadyang yagit, tampulan ng alipusta;

Ngumiti ang kapalaran, umasensong biglang-bigla

Nang pakasal sa babaeng ekta-ektarya ang lupa.

Doon din po sa 'ming bayan ay may pinag-isang dibdib

Mga mata ng babae'y mugtung-mugto sa pagtangis

Ang lalaking nahumaling sa kanya nang labis-labis,

Nakagawa ng di wasto masungkit lang yaong langit.

Ang pananaw ko'y praktikal — mas higit pang nanaisin

Na makasal sa babaeng sa 'kin, labis ang pagtingin

Umulan man o umaraw, bumagyo man at humangin,

Panatag ang aking loob, siya'y akin, aking-akin!

Samantalang si Gonie po, nasa piling na ang sinta,

Patuloy pang umaasa't nabubuhay sa pantasya;

Nagsasaing, nagluluto, naglalaba, namamlantsa,

Nag-iigib, nanunuyo... sa takot na layasan sya!

Ang babae'y parang prutas, kahit na katakam-takam,

Mapakla at walang tamis kung hinog nang sapilitan;

Si Gonie po, namimilit kahit mutya'y umaayaw,

Ako'y hindi! Mahirap nang matulad kay Echagaray!

LAKANDIWA

Mababagsik ang katagang kapwa nila binitiwan

Gayong nasa unang yugto pa lamang ng paglalaban

Si Gonie ang muli ngayong papagitna sa tanghalan

Kaya ang akin pong hiling: Palakpakan Natin, Bayan!

GONIE MEJIA (Ika-2 Tindig)

Ligaya kong tinatanaw ang sinta ay pagsilbihan

Ang gawin ang nararapat ay isa kong katungkulan

Ngunit di ko magagawang hangarin ang kayamanan

Ng babaeng hindi tibok ng puso kong iisa lang!

Napilitan man ang dilag sa akin ay magpakasal

Dahil ako ay lalaki, handa akong mapulaan;

Sa pagbigkas ng "Yes, I do" ni Rafael don sa altar,

Baka naman sa likod po nakaamba ang balaraw.

Ang pagpatol ng lalaki sa babaeng hindi gusto

Masakit man pong tanggapin, dalawa ang tinutungo

Isa dito ay ang yaman ng babaeng sumusuyo,

Ikalawa'y kasikatan, makilala sa publiko!

Dahil ako ay naglingkod sa maganda kong asawa,

Sa pagpanaw ko ay tiyak, sa langit ang aking punta;

Kung si Raffy hahanapin at doon ay di makita

Pagkat iba ang hinangad, t'yak nandoon sa kabila!

LAKANDIWA

Bawat tugong binitiwan ni Gonie ay tila sibat

Matulis at wari bagang pag tumama'y todas agad

Tingnan natin si Rafael kung mahusay sa pagsalag

Palakpakan natin upang mas ganahan sa pagbigkas!

RAFAEL PULMANO (Ika-2 Tindig)

Masaya raw si Gonie po na ang sinta'y paglingkuran

Ngunit ano'ng silbi nito kung sinta ay nasusuklam?

Ang hayop nga, pakanin mo't pag di gusto, umaangal,

Di lalo pa tayong taong ang puso ay di laruan!

Si Gonie po'y aminado, pinilit lang ang babae

Na pakasal kahit ito sa kanya ay diring-diri;

Palibhasa, ang hangad lang ay ligayang pansarili,

Wala siyang pakundangan kung may kapwang naaapi!

Kaya nga ang katalo ko'y hindi dapat kasiguro

Na pagpanaw sa daigdig, sa langit ang kanyang tungo;

Ako itong matulungin, mapagbigay, pasensyoso

Kung asawa'y liligaya, maligaya na rin ako.

Nagpakasal man kay Gonie ang babaeng sinasamba

May halaga naman kaya ang sumpaan nilang dalwa?

Ang babae, pag nagtaksil, pagkat mahal niya'y iba,

Sino'ng dapat na sisihin? Kayo, Bayan, ang humusga!

LAKANDIWA

Lumalaon, umiigting pang lalo ang patutsada

Ng dalawang walang balak padaig sa isa't isa.

Sa ikatlong paghaharap, hahayaan ko na sila

Hahayaan ko rin kayong pumalakpak — kung pwede pa.

GONIE MEJIA (Ika-3 Tindig)

Sa pinilit na babae, alay ko ay karangyaan

At matapat na pag-ibig, abot hanggang kalangitan

Si Rafael na pinikot, tinakot at tinutukan

Anong uring pag-ibig ang idudulog kay Bakekang?

Ang giliw ko'y hinding-hindi sa akin ay magtataksil

Pagkat sa aming tahanan, reyna ko syang ituturing

Di gaya ng katalo ko, sa bahay ay kukulungin

Ng asawang maskulado, mataray at mukhang boxer!

Maganda at seksing-seksi, mayumi at matalino

Ang babae kong pinili sabihin mang ginapang ko

Di katulad ng kay Raffy na ang mukha'y kunsimido

Ang katawa'y korteng lumpya, sa gabi ay parang multo!

RAFAEL PULMANO (Ika-3 Tindig)

Dalisay ba ang pag-ibig kung may halong pag-iimbot?

Yuyurakan ba ang puri para lamang mapasagot?

Paano nya masasabing langit anya'y ihahandog

Gayong langit na nga itong ninakaw nya at dinurog!

Lubha yatang nagigipit ang katalong lumihis na

Sa paksa po ng usapang napapunta sa itsura

Sa tutoo, si Gonie po ang pangit at walang iba

Kasi, kung sya'y pogi sana, bakit kaylangang mangreyp pa?

Kung ako man ay napikot, hindi dapat magparunggit

Ang mabunying kabalagtas na saksakan nga ng pangit

Palibhasa'y konti lamang kaming mga makikisig

Hindi natin masisisi kung chicks na ang namimingwit!

GONIE MEJIA

Malinaw ang aming paksa, si Raffy ang pipiliin

Ang sa kanya'y nagmamahal kahit ito'y mukhang tikling

Dahil ako ay may layang tibok ng puso ay sundin

Sa magandang iibigin, ang pansin ko'y ibabaling.

Makisig man ang binata, kung may isip na makitid

Tiyak din pong magagapi ng mautak kahit pangit

Balagtasa'y paligsahan, pingkian po ng matuwid

Sa malinaw na salita, ako'y di pa lumilihis!

RAFAEL PULMANO

Si Gonie raw ay may layang tibok ng puso ay sundin

Babae ba'y walang laya't karapatang pumili rin?

Kung sa mula't mula pa lang, winalanghya na ang giliw,

Paano nya tuturuan ng paggalang yaong supling?

Panlabas na kapangitan ay hindi ko kinukutya

Kapag ugali ay pangit, yan ang dapat ikahiya

Ang pag-ibig ng dalaga'y hinihingi nang may tyaga

Pag kinuhang sapilitan, may lason ang kanyang dagta!

GONIE MEJIA

Kasi, pangit ang panlabas na anyo ng kanyang giliw,

Kaya biglaang binawi ng pinikot na balimbing;

Sa dalawa bang lalaking nakaharap sa pagkain,

Ang sumandok ba ng panis ang pinalad sa pagtikim?

RAFAEL PULMANO

Maliwanag ang motibo ng katalong walang budhi

Sarili ang iniibig at di mutyang inaglahi

Ang masarap na pagkain, kahit di nya pag-aari,

Nanakawing pilit dahil ugali nya'y makahari!

GONIE MEJIA

Taas-noo ako kapag kaakbay ang aking sinta

Ang pinikot, nahihiya, nanlulumo at tulala!

RAFAEL PULMANO

Pangdispley at hindi kabyak ang kaylangan lamang pala,

Bakit hindi na lang siya bumayad at umarkila?

GONIE MEJIA

Sa pumili ay ligaya, ang pinikot ay magdusa!

RAFAEL PULMANO

Importante'y mahalaga: Mahal ako ng asawa!

GONIE MEJIA

Sadya nga bang mahal mo sya?

RAFAEL PULMANO

Ba't nga ba sya sukang-suka?

LAKANDIWA (Pangwakas)

Dito natin puputulin ang singhalan ng dalawa

At sa madla ibabaling ang tanong na "Sino nga ba

Ang marapat pakasalan: Yung mahal mo, o mahal ka?"

cells(science)

Posted by sarahkasumejaneares on November 5, 2012 at 9:05 PM Comments comments (0)

 

*The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing (except virus, which consists only from DNA/RNA covered by protein and lipids), and is often called the building block of life.[1] Organisms can be classified as unicellular (consisting of a single cell; including most bacteria) or multicellular (includingplants and animals). Humans contain about 10 trillion (1013) cells. Most plant and animal cells are between 1 and 100 µm and therefore are visible only under the microscope.[2]

The cell was discovered by Robert Hooke in 1665. The cell theory, first developed in 1839 by Matthias Jakob Schleiden andTheodor Schwann, states that all organisms are composed of one or more cells, that all cells come from preexisting cells, that vital functions of an organism occur within cells, and that all cells contain the hereditary information necessary for regulating cell functions and for transmitting information to the next generation of cells.[3]

The word cell comes from the Latin cella, meaning "small room". The descriptive term for the smallest living biological structure was coined by Robert Hooke in a book he published in 1665 when he compared the cork cells he saw through his microscope to the small rooms monks lived in.


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