Flashcards in GI secretions/digestions  Deck (20):
What secretes Gastric acid?
What is GA and what does it do?
Is it passive or does it require E?
Secreted by parietal cells ( contains HCl and IF)
Begins protein digestion (denature prot + activates pepsinogen → pepsin)
E consumin processs (H+/K+ ATPase pumps across luminal surface against significant gradient)
- knows its getting E back via digestion
4 phases of gastric secretion
basal phase + 3 assoc w/ eating
1. interdigestive (basal) phase
2. cephalic phase
3. gastric phase
4. intestinal phase
interdigestive (basal) phase of gastric secretion
between meals, following circadian rhythm
- highest in the evening
- lowest in the morning prior to waking
Cephalic phase of gastric secretion
1. release of ACh
2. trigger Histamine release from ECL cells
3. release of GRP form vagal and ENS
4. inhibition of somatostatin release form Delta cells
- 30% of acid secretions
(note: somatostatin a hormone secreted in the pancreas and pituitary gland that inhibits gastric secretion - so you inhibit an inhibitor)
gastric phase of gastric secretion
initially neural, followed by endocrine (gastrin) and neural reg.
1. Food enters stomach
2. distends gastric mucosa
3. activates vasovagalreflex + local ENS reflexes
4. partially digested proteins stimulate ANTRAL gastrin (G) cells
5. release gastrin (50-60% of total acid secretion)
Intestinal phase of gastric secretion
mostly endocrine (largely inhibitory, telling us 2 stop prod acid)
1. presence of aa and partially digested peptides in proximal small intestine
2. stimulate acid secretion by stimulating DUODENAL gastrin (G) cells to secrete gastrin (5-10% of total acid secretion)
How do parietal cell secretagogues induce acid secretion
ACH → M3 receptor → ↑ intracellular Ca2+
Histamine → H2 receptor → ↑ intracellular Ca2+
gastrin → CCK3 receptor → ↑cAMP
These receptors in the basolateral membrane of parietal cells, potentiate gastric acid secretion (on lumenal side) when stimulated concurrently
- one of the most E costly of any electrolyte transport process in body.
- Together, Ca2+ and cAMP activates protein kinases to phosphorylate H/K+ ATPase
Direct/Indirect pathway of stimulating parietal cells to secrete gastric acid
direct pathway: ACh, His, Gastrin directly stim parietal cell
Indirect pathway: " " stimulate enterochromaffin like (ECL) cells to result in secretion of His → acts on parietal cells
Mech of gastric acid generation + secretion.
Role of: K+, Cl/HCO3, carbonic anhydrase, H+K+ ATPase
1. H+ is actively transported across APICAL memb (←)
in exchange for K+ by H/K ATPase (→)
- when H+ moves out of cells (←) [HCO3-] in cells goes ↑
2. HCO3- is transported across BASOLATERAL memb (→)
in exchange for Cl- (←)
3. Cl- that accumulates is transported across APICAL memb (←←) by facilitated diff
4. H2O follows Cl-
- pH of venous blood leaving stomach is high (HCO3- transport, known as ALKALINE TIDE)
(NOTE: all of this depends on Na/K ATPase, creating electronegative gradient (inside more neg than outside)
How does mucous serve as a protective barrier?
mucous secreted by goblet cells and mucous neck of the gland → form unstirred gel layer in which H2O is trapped + serves as neutralization zone for acid to be neutralized when diffused in
Peptic ulcer disease risk factors
1. NSAIDs (block cox I → ↓ PG → ↓ mucous)
2. Tumors (ZE synd)
3. H. Pylori
First step of carbohydrate digestion takes place in the ______ with the enzyme ______.
Final step in carbohydrate digestion occurs at _____ for all dietary carbs
Mouth - amylase
(note that amylase digests digest starch polysacc α-1,4 bonds to sugars that eventually → glucose)
Digestion of proteins starts _______ from the enzyme, ______ and is completed in the ______ with the enzyme ______.
stomach - pepsin
small intestine - gastric, pancreatic, enterocyte brush border and cytoplasmic peptidases
Only monomeric _____ can be absorbed
Fat digestion starts in the mouth with the enzyme ____.
It ends in the ______.
fat - lingual lipase
Brush border enzymes involved at enterocytes:
Maltase acts on _____ or _____ → _______
Isomaltase (SI) acts on ______ → _______
Lactase acts on ____ → _____+ _____
Sucrase acts on ____ → _____+ _____
Maltase: maltose or maltotriose → Glucose
Isomaltase (SI): alpha limit dextrin → Glucose
Lactase Lactose → Glucose + galactose
Sucrase: Sucrose → Glucose + fructose
Predict small int. and colonic consequences of a deficiency in brush border enzyme, lactase following dairy product consumption.
1. unabsorbed lactose will draw water into intestinal lumen → osmotic diarrhea
2. Gut bacterial flora metabolizes unabsorbed lactose → gas (H+, methane, CO2)
Apical, brush border, sugar monomer transporters of enterocytes
- regulates uptake of?
1. SGLT1: regulates uptake of glucose and galactose
2. GLUT5: regulates uptake of fructose
(moves from lumen INTO cell)
- both are Na+ dependent (goes in with Na+ - cotransport)
Basolateral, brush border, sugar monomer transporters of enterocytes
- regulates uptake of?
GLUT2: regulates glucose, galactose, and fructose
(moves OUT of cell into blood on basolateral side)
- not Na+ dependent