GI Secretion and Digestion

Question 1

what are the 3 functions of secreted gastric acid

Answer 1

1) Kills bacteria (disinfects food at pH 1.0)
2) Begins protein digestion - denatures proteins and activates pepsinogen (active form = pepsin)
3) Acid producing parietal cells also secrete intrinsic factor when secreting acid (vitamin B12 absorption)

Question 2

what are the mucosal defenses present in the stomach against toxicity from gastric acids

Answer 2

1) Mucus layer and alkaline (HCO3-) layer at the cell surface (surface mucus cells) protects the stomach lining – prostaglandins can increase mucus production
2) Tight junctions between cells prevent acid from infiltrating the layers of the wall
3) Rapid cell turnover maintains surface integrity

Question 3

IF/B12 complex binds to receptor in terminal _____ for absorption (the receptor is for IF)

Answer 3

ileum

Question 4

what is the Interdigestive (basal) phase of acid secretion.

Answer 4

occurs between meals following circadian rhythm (highest in the evening and lowest in the morning prior to waking)

Question 5

The smell, sight, taste and swallowing of food initiate the ________ of acid secretion, which is primarily mediated by the vagus nerve.

Answer 5

cephalic phase

Question 6

The cephalic phase accounts for of _____total acid secretion

Answer 6

30%

Question 7

Stimulation of the vagus nerve during the cephalic phase results in what 4 things?

Answer 7

(1) release of ACh;
(2) triggering of the histamine release from ECL cells; (3) release of gastrin-releasing peptide (GRP) from the vagal and enteric neurons (ENS);
(4) inhibition of somatostatin release from the delta cells (D cells) in the stomach.

Question 8

Acid secretion is stimulated by :

Answer 8

the parasympathetic neurotransmitter acetylcholine (ACh),
the hormone gastrin,
the paracrine substance histamine

Question 9

Entry of food into the stomach initiates the _______ phase of acid secretion. First, the food distends the gastric mucosa, which activates a vagovagal reflex as well as local ENS reflexes. Second, partially digested proteins stimulate antral gastrin (G) cells, which release gastrin.

Answer 9

gastric ,

Question 10

In the ______ phase, the presence of amino acid and partially digested peptides in the proximal portion of the small intestine stimulates acid secretion by stimulating _________ cells to secrete gastrin.

Answer 10

intestinal,
duodenal gastrin (G),

Question 11

what are the risk factors of peptic ulcer disease

Answer 11

NSAID use e.g. Asprin, Ibuprofen
Tumors (Zollinger Ellison Syndrome)
Helicobacter pylori

Question 12

Some digestion occurs in the mouth and stomach but most of the final digestion occurs in the intestinal lumen or at the surface of the _________

Answer 12

absorptive cells (enterocytes)

Question 13

Approximately _________ of total acid secretion occurs in the intestinal phase.

Answer 13

5% to 10%

Question 14

The gastric phase accounts for about _________of total acid secretion

Answer 14

50% to 60%