Gastrointestinal tract
(ForPhysics term 'GUT', please referGrand unification theory)The gastrointestinal or digestive tract, also referredasGI tract oralimentary canal orgut, issystemorgans within multicellular animals which ingests, digests,egests food,inprocess, extracts energynutrients.
The GI tract differs substantially from animalanimal. For instance, some animals have multi-chambered stomachs.
Innormal human adult male,GI tractapproximately 25 feet longconsists offollowing components:
- Mouth (buccal cavity; includes salivary glands, mucosa, teethtongue)
- Pharynx
- Esophaguscardia
- Stomach, which includesantrumpylorus
- Bowel or Intestine:
- small intestine, which has three parts:
- large intestine, which has three parts:
The liver secretes bile intosmall intestine viagallbladderbiliary system. The pancreas secretes an isosmotic fluid containing bicarbonateseveral enzymes, including trypsin, chymotrypsin, lipase,pancreatic amylase, as well as nucleolytic enzymes, intosmall intestine.
Both these secretory organs aiddigestion.
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2 Your digestive systemhowworks 3 How IsDigestive Process Controlled? 4 Uses forgut 5 Specializationorgans 6 Reference 7 External links |
The processdigestionexcretion
Food, after being partially broken down inmouth, passes throughesophagus tostomach, whereprocessbreakdown continues. It then passes tosmall intestine where further breakdown occurs, anduseful particlesabsorbed intobloodstream. The remaining particles pass throughlarge intestine andultimately expelled as feces.
See also body, anatomy, Listhuman anatomical features, abdominal cavity
Your digestive systemhowworks
The digestive system isserieshollow organs joined inlong, twisting tube frommouth toanus (see figure). Inside this tube islining calledmucosa. Inmouth, stomach,small intestine,mucosa contains tiny glands that produce juiceshelp digest food.
Two solid organs,liver andpancreas, produce digestive juices that reachintestine through small tubes. In addition, partsother organ systems (for instance, nervesblood) playmajor role indigestive system.
Why Is Digestion Important?
When we eat such things as bread, meat,vegetables, theynot inform thatbody can use as nourishment. Our fooddrink must be changed into smaller moleculesnutrients beforecan be absorbed intobloodcarriedcells throughoutbody. Digestion isprocess by which fooddrinkbroken down into their smallest parts so thatbody can use thembuildnourish cells andprovide energy.
How Is Food Digested?
Digestion involvesmixingfood, its movement throughdigestive tract,chemical breakdown oflarge moleculesfood into smaller molecules. Digestion begins inmouth, when we chewswallow,is completed insmall intestine. The chemical process varies somewhatdifferent kindsfood.
The Digestive System
MovementFood ThroughSystem
The large, hollow organs ofdigestive system contain muscle that enables their wallsmove. The movementorgan walls can propel foodliquidalso can mixcontents within each organ. Typical movement ofesophagus, stomach,intestinecalled peristalsis. The actionperistalsis looks like an ocean wave moving throughmuscle. The muscle oforgan producesnarrowingthen propelsnarrowed portion slowly downlength oforgan. These wavesnarrowing pushfoodfluidfrontthem through each hollow organ.
The first major muscle movement occurs when food or liquidswallowed. Although weablestart swallowing by choice, onceswallow begins,becomes involuntaryproceeds undercontrol ofnerves.
The esophagus isorgan into whichswallowed foodpushed. It connectsthroat above withstomach below. Atjunction ofesophagusstomach, there isringlike valve closingpassage betweentwo organs. However, asfood approachesclosed ring,surrounding muscles relaxallowfoodpass.
The food then entersstomach, which has three mechanical tasksdo. First,stomach must storeswallowed foodliquid. This requiresmuscle ofupper part ofstomachrelaxaccept large volumesswallowed material. The second job ismix upfood, liquid,digestive juice produced bystomach. The lower part ofstomach mixes these materials by its muscle action. The third task ofstomach isempty its contents slowly intosmall intestine.
Several factors affect emptying ofstomach, includingnature offood (mainly its fatprotein content) anddegreemuscle action ofemptying stomach andnext organreceivecontents (the small intestine). Asfooddigested insmall intestinedissolved intojuices frompancreas, liver,intestine,contents ofintestinemixedpushed forwardallow further digestion.
Finally, all ofdigested nutrientsabsorbed throughintestinal walls. The waste productsthis process include undigested parts offood, known as fiber,older cells that have been shed frommucosa. These materialspropelled intocolon, whereremain, usually forday or two, untilfecesexpelled bybowel movement.
ProductionDigestive Juices
The glands that act firstinmouth--the salivary glands. Saliva produced by these glands contains an enzyme that beginsdigeststarch from food into smaller molecules.
The next setdigestive glandsinstomach lining. They produce stomach acidan enzyme that digests protein. One ofunsolved puzzles ofdigestive systemwhyacid juice ofstomach does not dissolvetissue ofstomach itself. In most people,stomach mucosaableresistjuice, although foodother tissues ofbody cannot.
Afterstomach emptiesfoodjuice mixture intosmall intestine,juicestwo other digestive organs mix withfoodcontinueprocessdigestion. Onethese organs ispancreas. It producesjuice that containswide arrayenzymesbreak downcarbohydrate, fat,proteinfood. Other enzymes thatactive inprocess come from glands inwall ofintestine or evenpartthat wall.
The liver produces yet another digestive juice--bile. The bilestored between meals ingallbladder. At mealtime, itsqueezed out ofgallbladder intobile ductsreachintestinemix withfatfood. The bile acids dissolvefat intowatery contents ofintestine, much like detergents that dissolve grease fromfrying pan. Afterfatdissolved, itdigested by enzymes frompancreas andlining ofintestine.
AbsorptionTransportNutrients
Digested moleculesfood, as well as waterminerals fromdiet,absorbed fromcavity ofupper small intestine. Most absorbed materials crossmucosa intoblood andcarried off inbloodstreamother parts ofbodystorage or further chemical change. As already noted, this part ofprocess variesdifferent typesnutrients.
Carbohydrates: Based on2,000-calorie diet, itrecommended that 5560 percenttotal daily calories be from carbohydrates. Someour most common foods contain mostly carbohydrates. Examplesbread, potatoes, legumes, rice, spaghetti, fruits,vegetables. Manythese foods contain both starchfiber.
The digestible carbohydratesbroken into simpler molecules by enzymes insaliva,juice produced bypancreas,inlining ofsmall intestine. Starchdigestedtwo steps: First, an enzyme insalivapancreatic juice breaksstarch into molecules called maltose; then an enzyme inlining ofsmall intestine (maltase) splitsmaltose into glucose molecules that can be absorbed intoblood. Glucosecarried throughbloodstream toliver, where itstored or usedprovide energy forwork ofbody.
Table sugaranother carbohydrate that must be digestedbe useful. An enzyme inlining ofsmall intestine digests table sugar into glucosefructose, eachwhich can be absorbed fromintestinal cavity intoblood. Milk contains yet another typesugar, lactose, whichchanged into absorbable molecules by an enzyme called lactase, also found inintestinal lining.
Protein: Foods such as meat, eggs,beans consistgiant moleculesprotein that must be digested by enzymes beforecan be usedbuildrepair body tissues. An enzyme injuice ofstomach startsdigestionswallowed protein. Further digestion ofproteincompleted insmall intestine. Here, several enzymes frompancreatic juice andlining ofintestine carry outbreakdownhuge protein molecules into small molecules called amino acids. These small molecules can be absorbed fromhollow ofsmall intestine intobloodthen be carriedall parts ofbodybuildwallsother partscells.
Fats: Fat molecules arerich sourceenergy forbody. The first stepdigestion offat such as butter isdissolveintowatery content ofintestinal cavity. The bile acids produced byliver act as natural detergentsdissolve fatwaterallowenzymesbreaklarge fat molecules into smaller molecules, somewhichfatty acidscholesterol. The bile acids combine withfatty acidscholesterolhelp these moleculesmove intocells ofmucosa. In these cellssmall moleculesformed back into large molecules, mostwhich pass into vessels (called lymphatics) nearintestine. These small vessels carryreformed fat toveins ofchest, andblood carriesfatstorage depotsdifferent parts ofbody.
Vitamins: Another vital partour food thatabsorbed fromsmall intestine isclasschemicals called vitamins. The two different typesvitaminsclassified byfluidwhichcan be dissolved: water-soluble vitamins (allB vitaminsvitamin C)fat-soluble vitamins (vitamins A, D,K).
Watersalt: Most ofmaterial absorbed fromcavity ofsmall intestinewaterwhich saltdissolved. The saltwater come fromfoodliquid we swallow andjuices secreted bymany digestive glands.
How IsDigestive Process Controlled?
Hormone Regulators
A fascinating feature ofdigestive systemthatcontains its own regulators. The major hormones that controlfunctions ofdigestive systemproducedreleased by cells inmucosa ofstomachsmall intestine. These hormonesreleased intoblood ofdigestive tract, travel back toheartthrougharteries,return todigestive system, wherestimulate digestive juicescause organ movement. The hormones that control digestiongastrin, secretin,cholecystokinin (CCK):
- Gastrin causesstomachproduce an aciddissolvingdigesting some foods. Italso necessary fornormal growth oflining ofstomach, small intestine,colon.
- Secretin causespancreassend outdigestive juice thatrichbicarbonate. It stimulatesstomachproduce pepsin, an enzyme that digests protein,it also stimulatesliverproduce bile.
- CCK causespancreasgrow andproduceenzymespancreatic juice,it causesgallbladderempty.
Two typesnerves helpcontrolaction ofdigestive system. Extrinsic (outside) nerves come todigestive organs fromunconscious part ofbrain or fromspinal cord. They releasechemical called acetylcholineanother called adrenaline. Acetylcholine causesmuscle ofdigestive organssqueezemore forceincrease"push"foodjuice throughdigestive tract. Acetylcholine also causesstomachpancreasproduce more digestive juice. Adrenaline relaxesmuscle ofstomachintestinedecreasesflowbloodthese organs.
Even more important, though, areintrinsic (inside) nerves, which make upvery dense network embedded inwalls ofesophagus, stomach, small intestine,colon. The intrinsic nervestriggeredact whenwalls ofhollow organsstretched by food. They release many different substances that speed up or delaymovementfood andproductionjuices bydigestive organs.
Uses forgut
Musicians useduse strings madeanimal gut, nowuse strings madenylon, silk or steel.
Specializationorgans
Four organssubjectspecialization inkingdom Animalia.
-The first organ istongue whichonly present inphylum Chordata.
-The second organ isesophagus. Itinstead calledcrop. Itan enlargement ofesophagus usedstore foodexistspigeons, beesworms.
-The third organ isstomach. Itcalled gizzardbirds. It ismuscular stomach usedmechanically digest food insteadstoring it.
-The fourth organ islarge intestine. Itcalledcecumis presentnon-ruminant herbivores such as rabbits. It aidsplant digestioncellulose.
Reference
- National InstituteDiabetesDigestiveKidney Diseases, National InstitutesHealth.
