GI secretions
Terms
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- functions of salivary secretion
-
lubrication,
solvation for taste
antibacterial (lysozyme, lactoferrin & IgA)
amylase - quantity of saliva produced daily
- 1/2 to 1 l/day
- function of amylase
-
hydrolyzes alpha 1-4 bonds of glucose (amylose=starch, resembles glycogen)
digest amylopectin, glycogen & amylose - concentration characteristics of saliva during slow flow
-
high K (so water reabsorbed)
secondary saliva-more processed - concentration characteristics of saliva during high flow
-
like plasma:
primary saliva- (not very processed)
Na (high)
Cl
HCO3
K (very little) - saliva secretion at acinar cells
- K, HCO3, H20, Na, Cl
- location of saliva transporters
- duct cells
- transporters and saliva processing
-
in duct cells
Increase K in lumen
resorb Na & Cl - components of gastric secretions
-
HCL
Pepsinogen
Mucus
Intrinsic Factor
(gastrin is endocrine) - parietal cell secretes
- HCL & Intrinsic Factor
- G cell secretes
- Gastrin (inhibited by somatostatin)
- D cell secretes
- Somatostatin (inhibited by gastrin)
- enteroendocrine cells in the stomach
-
G cell - gastrin
D cell- somatostatin - transporters in HCL secretion
-
K/H pump at lumen sends K into cell (drives CA to increase HCO3)
HCO3 out/Cl in
then electrochem gradient drives Cl into lumen - regulation of HCL secretion
-
gastrin increases
somatostatin decreases - stimulation of parietal cell
-
gastrin, ACh & Histimine
gastrin- G cell senses peptides, rls gastrin, acts on ECL AND parietal, (stronger signal than histimine)
Vagus stims ECL and Pariatel- get ACh stim and histimine
histimine & CCK from vagal stim
ACh - where does histamine stimulus in stomach come from
- ECL
- mechanism of stimulation of parietal cells
-
Gastrin & ACh stim Ca rls
Histimine stims Adenylyl Cyclase - product of D cell
- releases somatostatin- provides negative feedback to proton pump
- action of somatostatin
-
produced in D cell
when pH 2.5 or less
binds R on ECL to block hist rls
binds G cell to block gastrin rls - secretion of pepsinogen
-
secreted by Cheif cells
(stimulated by peptides)
activated by HCL and pepsin - mucus secretion
-
from goblet cells
80% carbohydrate
inhibits pepsin from approaching epithelials
mucus production inhibited by NSAIDs - Intrinsic Factor Secretion
-
made & secreted by parietals
necessary for B-12 absorption
(makes complex)
secreted with gastrin - Secretions of the pancreas
-
HCO3
enzymes - pancreatic enzymes
-
Amylase
Tripsin, Chymotrypsin, Carboxypeptidase, Elastase- zymogens
Lipase-colipase
PLA2
Cholesterol esterase-nonspecific lipase - stimulation of pancreatic secretion of HCO3
-
S cells sense H+ (pH> 4)
secrete secretin
increase HCO3 via cAMP on Ducts - secretory cells of pancreas
-
Acinars- secrete enzymes
Ducts- secrete HCO3 - stimulation of pancreatic secretion of enzymes
-
I cells
sense aa's, peptides & FA's
secrete CCK
increase enzyme rls via IP3 on acinars - anatomical features of colon
-
no villi
haustra
taeniae coli
cecum, ascending, transverse, descending, sigmoid, rectum - water absorption in small & large intestine
-
98% is reabsorbed
85% in SI
13% in LI - mechanism of water resorption
-
osmotic gradient- passive
Na/K ATPase at BL
draws Na in from lumen
drives CA rxn, HCO3 out/Cl in
Na & Cl increase in tissue
H2O follows - fluid input to GI
-
2 L food & drink
2 L gastric secretions
1.5 L (each) saliva, pancreas, intestines
.5 L bile - fluid absorption in gut
-
7.5 L SI
1.4 L LI
.1 L excreted in feces - mechanism of cholera toxin
-
constituatively activates CFTR--reverses osmotic potential
covalent modification of alpha subunit of GPCR
prevents GTP hydrolysis (to GDP) - effects of aging on digestive system
-
compromised nutrition
neural coordination
biochem (less enzyme/hormone, decreased sensitivity)
diminished vascular supply - inflammatory polyps associated with...
-
ulcerative colitis
IBD - adenoma colon polyps association with CA
-
>2cm, 50% are cancerous
<1 cm, 1% are cancerous
glandular in origin - polypoid carcinoma characteristics
-
malignant
originate from epis - colorectal cancer stages
-
I: submucosa
II: circ or long muscle
III: 1-4 lymph nodes
IV: metastasis - characteristics of diverticula
-
associated with age
herniation of colon wall
95% are in sigmoid
areas of vascular penetration cause weakness
bleeding from mechanical damage
bacteria collect