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Chapter 26: Gastrointestinal Structure and secretions - Coggle Diagram
Chapter 26: Gastrointestinal Structure and secretions
Structural consideration
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layers
epithelial interior
vili and crypts
CT layer
lamina propria
concentric SM layer x2
most rapidly dividing
brush border hydrolases
Salivary secretion
3 glands secrete
amylase, IgA, lysozyme, mucin
hypotonic and alkaline
1L -1.5L a day
PNS influence, but SNS modifies composition
xerostomia- more dental caries due to saliva being antibacterial
buffers gastric acid- helps heartburt
gastric secretion
Anatomical consideration
parietal cells (oxyntic)
hydrochloric acid and IF
IF- absorb vitB12
sterilize food and hydrolysis meal
chief cells - secrete pepsinogen
pepsinogen becomes pepsin
protein digestion
Origin & regulation of gastric secretions
trefoil peptides that stabilize the mucusbicarbonate
layer.
glandular secretion differ in places
fundus
body
3 stimuli for gastric secretion
gastrin from G-cells in antrum
fundic glands binds on parietal and ECL cells
releases histamine
vagal input
releases GRP and Ach
parietal cells specialized
alot of mitochondria
proton pumps to move H+ out
tubulovesicles
potassium exchange channels for HCL release
3 agonist of parietal cells:
gastrin
free Ca in cell
histamine
cAMP intracell
Ach
free Ca in cell
chronic reduced secretions- more infections susceptible
Pancreatic secretions
controlled by CCK and gastrointestinal hormones
alkaline and high in HCO-3
pH in jejenum is neutral
trypsin inh in pacreas,but phospholipase A2 activates trypsin
forms lyso-PC when active
regulation
secretin acts on ducts to secrete HCO-3 and bile, high volume low enzyme
CCK acts on the acinar cells to release enzymes w low volume
Ach
acinar cells - enzymes
Anatomical consideration:Pancreas
zymogen granules into a lumen into a duct
biliary secretions
metabolise lipids and dispose of cholesterol
p437
bile
bile acids
conjugated to glycine
or taurine, a derivative of cysteine.
synth from cholesterol
2 main types: cholic acid and chenodeoxycholic acid
bile pigments
glucuronides, bilirubin, biliverdin
substances resembling pancreatic juice
bile salts
reduce surface tension
emulsification of fat
amphipathic
also called micelles
hyrophilic out
hydrophobic face in
intestinal fluid and electrolyte transport
fluid is driven actively by chloride ions in lumen
small intestine- 2nd active transport of Na+ - help with glucose, amino acid and bile absorb
distal colon
ENAC channels
reabsorb fluid
K+ and Cl- secretion into lumen
more in diarrhoea
water moves in and out of lumen until plasma equillibrium met
Saline cathartics
MgSo4
increase intestinal volumume (laxative)