3 Digestion & Absorption

8/6/2019 3 Digestion & Absorption

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The GI tract is a flexible muscular tubefrom the mouth, through the esophagus,

stomach

, small intestine, large intestineand rectum to the anus.

The GI tract works with assisting organs -

salivary glands, liver, gallbladder andpancreas to turn food into smallmolecules that the body can absorb &used.


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Ingestions Receipt & softening of food

Transport of ingested food Secretion of digestive enzymes, acid,

mucus & bile

Absorption of end products of digestion

Movement of undigested minerals Elimination

The transport, storage and excretion of wasteproducts


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The process of digestionbegins in the mouth.

As you chew, your teethcrush large pieces of foodinto smaller ones, and fluidsblend these pieces to easeswallowing (tastemechanism as well)

When swallowing, the foodpasses through thepharynx.

To bypass the entrance toyour lungs, the epiglottiscloses off the air passages

After a mouthful of foodhas been swallowed, it iscalled bolus.


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The esophagus has a sphincter muscle at each end. During a swallow, the upper esphageal sphincter opens. The bolus the slides down the esophagus, which passes

through a hole in the diaphragm to the stomach The lower esophageal sphincter at the entrance of the

stomach closes behind the bolus so that it proceedsforward & dont slip back into the esophagus

The stomach retains the bolus for a while in its upperportion. Little by little, the stomach transfers the food to itslower portion, adds juices to it and grinds it to a semi liquidmass called chyme.

Then bit by bit, the stomach releases the chyme throughthe pyloric sphincter, which opens into the small intestine& then closes behind the chyme


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The chyme arrives at the ileocecal valve, the thebeginning of the colon in the lower right hand side ofthe abdomen.

As c

h

yme bypasses th

e appendix and travel alongthe large intestine up the right hand side of theabdomen, across the front to the left hand side,down to the lower left hand hand and below theother folds of the intestine to the back side of thebody, above the rectum.

During the chymes passage to the rectum, the colonwithdraws water from it, leaving semisolid waste. The strong muscles of the rectum and anal canal

hold back this waste until it is time to defecate.


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To breakdown food into small nutrients

that the body can absorb, 5 different

organs produce secretions: Salivary glands

Stomach

Pancreas

Liver (via the gallbladder)

Small intestine


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Organ orGland

TargetOrgan

Secretion Actions

Salivary

Glands

Mouth Saliva Fluid eases swallowing; salivary

enzymes break down carbsGastric

Glands

Stomach Gastric

Juice

Fluid mixed with bolus;

hydrochloric acid uncoilsprotein;enzymes break down protein;mucus protects stomach cells

Pancreas Smallintestine

PancreaticJuice

Bicarbonate neutralizes acidicgastric juices; pancreaticenzymes break down carbs,

fats& protein


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Organ orGland

TargetOrgan

Secretion Actions

Liver Gallbladder Bile Bile stored until needed

Gallbladder Small

intestine

Bile Bile emulsifies fat so enzymes

can attack

Intestinal

glands

Small

intestine

Intestinal

juice

Intestinal enzymes break down

carbs, fat & protein fragments,mucus protects the intestinalwall


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Most absorption takes place in the small intestine

Absorption of nutrients into intestinal cell typicallyoccurs by Simple diffusion

x H20 & small lipids are absorbed by simple diffusion.

x They cross into intestinal cells freely

Facilitated Diffusionx Water soluble vits are absorbed by FD. They need a specific

carrier to transport them from one side of the cell membrane tothe other

Active Transport

x Glucose & AA must be absorbed actively. These nutrients move

against a concentration gradient, which requires energy.


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Psychological influences Stress decreased gastric acid secretion, reduced BF

to the stomach, inhibits peristalsis

Chemical influence Plant protein less digestible than animal protein(Cooking protein increases digestibility)

Frying food in fat at very high temperatures, decreasesthe flow of digestive secretions

Cold food may cause intestinal spasms When food is consumed on an empty stomach,

absorption faster

Bacterial influence Low [hydrochloric acid], can cause gastric, stomach

lining inflammation.


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Constipation

Diarrhea

Diverticulosis Gastroesophageal Reflux (GERD)

Irritable Bowel Syndrome

Colon Cancer Gas

Ulcers

Functional Dyspepsia

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3 Digestion & Absorption