Physiology 3120 Lecture Notes - Lecture 10: Peristalsis, Osmotic Concentration, Diarrhea

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Woods Lecture 10
a) Mechanical digestion: physically breaking up food into smaller pieces eg: chewing
b) Chemical digestion: enzymes break up bonds within macronutrients to make smaller units
that can be absorbed
2. Absorption: transport substances from GI tract into surrounding blood vasculature by going
through membranes that line GI tract
3. Motility: push food down entire length of tract eg: swallowing or moving food around to mix
it up eg: stomach mixing
4. Secretion: secretions from cells lining GI tract that go into tract eg: mucus, enzymes or
secretions going into blood vasculature that circulate body to act back on GI tract eg: hormones
-organs that are part of GI tract actually come in contact with food:
-pharynx: first part of esophagus
-stomach: little digestion, holds food until small intestine ready
-small intestine: most digestion, all absorption  most important
-appendix: very small outgrowth at junction b/w small and large intestine; stores good bacteria
that replenish large intestine bacteria when wiped out by bacteria
-rectum: last part of large intestine
-anus: end of tract
-accessory glands make products that go into GI tract to help process food:
-salivary glands: secrete saliva into mouth
-liver: makes bile that enters small intestine
-gall bladder: stores bile
-pancreas: looked at endocrine function before, now exocrine function which is to secrete
enzymes into small intestine to help chemical digestion
-most parts of GI tract made up of same tissue layers ie: stomach, small intestine, large
intestine  thus same for the most part
-little difference in tissue type of mouth, esophagus, rectum and anus
Mucosa - inner layer
-enterocytes: epithelial cells in single layer lining lumen to directly contact contents of lumen 
epithelial cells = polarized so one end acts differently from other for transport purposes
-can be absorptive enterocytes, mucus-secreting enterocytes, acid-secreting enterocytes or
endoenterocytes (hormone-secreting)
-lamina propria: thin layer of CT
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