PSL201Y1 Chapter Notes -Gastric Pits, Muscular Layer, Gastric Glands

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15 Apr 2012
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PSL201 March 20 GI 1 & 2
Generalized Structure of the Gastrointestinal Wall
4 distinct layers:
- mucosa: lines the lumen of the digestive tract
- submucosa: underlying layer of connective tissue
- muscularis externa: layer made up of primarily smooth muscle fibers
- serosa (adventitia): outter layer composed of mostly connective tissue
Mouth, Pharynx, and Esophagus
- mouth is the beginning of the GI tract
o chewing = mastication
- saliva: lubricates food and secretes an enzyme (salivary amylase) which
begins deigestion by breaking down starch and glycogen
- from there food is propelled by the tongue into the pharynx (throat)
- then to the esophagu s
o a muscular tube that conducts food from the pharynx to the stomach
o thin-walled and pliant to accommodate food (collapsed in absence of
food)
o circular muscles contract behind food and relax infront of it as it
passes down the esophagus
The Stomach
- j-shaped sac located beneath the diaphragm
- stores food after it is digested and stores until released into the small
intestine
- lining of glands in stomach (gastric glands) that secrete a watery gastric
juice into the lumen
- contractile action pulverizes food into smaller pieces and mixes it with juices,
producing chyme
- 3 anatomical regions:
o domed upper fundus (wall is thin and easily expands)
o middle body
o lower antrum contracts push chime into intestine
- chime passes through a narrow passage (pylorus) on the way to the SI
o regulated by the pyloric sphinter which opens and closes w/ each
cycle of stomach contractions
- gastric pits secrete products found in gastric juice
o neck cells: upper part of the pits
secrete mucus
o chief cells: secrete pepsinogen (precursor for pepsin)
o parietal cells: secrete HCl and intrinsic factor (necessary for B12
absorption)
o G cells: secrete gastrin
- Lining of the stomach is protected by the gastric mucosal barrier
The Small Intestine
3 Major Parts:
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