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Question 1

Gastrointestinal Hormones • They are ……….. secreted from the GIT ………… in response to certain specific stimuli & share in the regulation of GIT secretions and motility.

Answer 1

polypeptides

mucosa

Question 2

Gastrin
Site of release:
Structure:
Metabolism:
Actions:
Regulation of secretion:

Answer 2

Site of release 1) G-cells: in pyloric antrum (gastric gastrin).
2) T.G cells: in mucosa of stomach and small intestine (intestinal gastrin - secrete G34). 3) Pituitary & hypothalamus

Structure Polypeptide of 3 types according to number of amino acids: G14 & G17 (most important) & G34.

Metabolism Inactivated by the kidney & small intestine.

Actions
1. Stomach: ↑Gastric acid secretion, Gastric motility & Growth of the gastric mucosa. 2. Pancreas: ↑ Exocrine & Endocrine secretion (Insulin & glucagon secretion).
3. Sphincters: a) LES → contraction. b) Ileo-cecal sphincter→ relaxation. 4. Calcitonin secretion

Regulation of Stimulation of secretion:
-Distension of the stomach.
-products of proteins digestion (Polypeptides & amino acids). -Gastrin releasing peptide by Vagal Stimulation.

Inhibition of secretion:
 High Acidity (pH < 2) (-ve FB via somatostatin).
 Secretin & GIP & VIP
 Calcitonin & Glucagon

Question 3

Cholecystokinin pancreozymin CCK
Site of release:
Structure:
Actions:
Regulation of secretion:

Answer 3

Site : (CCK) is secreted by “I” cells in the mucosa of the upper release part of the small intestine (duodenum and jejunum) mainly in response to the presence of fat, AA, peptides and acid in the intestinal contents.

Structure There 2 forms which are equally active (one has 39 AA & the other 33 AA).

Actions
CCK strongly contracts the gallbladder and at the same time inhibits stomach contraction moderately and this gives adequate time for digestion of the fats in the upper intestinal tract.
1. Stimulation of gall bladder evacuation (cyclic GMP).
2. Secretion of pancreatic juice rich in enzymes.
3. Augments the action of secretin to produce alkaline pancreatic secretion.
4. Inhibition of gastric emptying & secretion.
5. It may enhance small intestine motility.
6. Stimulation of glucagon secretion.
7. CCK inhibits appetite to prevent overeating during meals

Regulation of secretion: + ve FB between CCK & AA.
CCK :digestion of protein,↑production of AA , re-stimulation of CCK.

Question 4

Secretin Site of release:
Actions:

Answer 4

Site of Secretin was the first gastrointestinal hormone discovered and is secreted by the “S” cells in the mucosa of the duodenum in response to acidic gastric juice emptying into the duodenum from the pylorus of the stomach.

Actions
1. It stimulates pancreatic secretion rich in HCO 3-
→ neutralize the acid in the small intestine.
2. It increases the secretion of HCO 3- in bile.
3. It decreases gastric acid secretion probably by competition with gastrin.
4. It inhibits gastric motility.
5. It augments the action of CCK on pancreas.
6. It may cause contraction of pyloric sphincter.
7. It increases insulin secretion.

Question 5

Gastric inhibitory peptide

Answer 5

Is secreted by the mucosa of the duodenum & Jejunum (K cells) due to the presence of mainly fatty acids & AA and to a lesser extent carbohydrates in the duodenum.

 Functions
1. Inhibits gastric secretion and motility (mild
effect).
2. Stimulates insulin secretion, for this reason is
also known as “ glucose dependent insulinotropic
peptide”.

Question 6

Vasoactive intestinal peptide (VIP)

Answer 6

Stimulates intestinal secretion of
electrolytes and hence of water.
• It causes inhibition of gastric acid
secretion.
• It causes dilatation of the blood vessels

Question 7

Enterogastrone

Answer 7

Is secreted by the mucosa of the upper
part of the small intestine in response
to the presence of fat & hypertonic
sugar.
• It inhibits gastric secretion & motility.

Question 8

Enterocrinin & Duocrinin

Answer 8

Released from the intestinal mucosa in
response to the ingestion of meal.
 Functions
1. Enterocrinin increases the volume &
concentration of intestinal juice. 2. Duocrinin stimulates the secretion of
Brunner’s glands in the duodenum.

Question 9

Villikinin

Answer 9

Is released by the duodenal mucosa in
response to acid & AA.
It increases the motility of the intestinal villi.

Question 10

Motilin

Answer 10

It has been extracted from the stomach, duodenal
and jejunal mucosa (M cells).
• It stimulates gastrointestinal motility
• Also, it stimulates gastric acid secretion.
• Motilin is released cyclically and stimulates waves
of gastrointestinal motility called interdigestive
myoelectric complexes that move through the
stomach and small intestine every 90 minutes in a
fasted person.
• Motilin secretion is inhibited after ingestion by
mechanisms that are not fully understood.

Question 11

Chymodenin

Answer 11

Is a polypeptide hormone extracted from the
duodenal mucosa.
• It stimulates pancreatic chymotrypsinogen secretion.

Question 12

Substance P

Answer 12

It is found in the neurons of the brain, local axons
and endocrine cells of the GIT. • It increases motility of the small intestine.

Question 13

Bombesin

Answer 13

Functions
1. Increases gastric secretion. 2. Increases the motility of the small intestine & GB.

Question 14

Somatostatin

Answer 14

Functions
1. Inhibits the secretion of gastrin, VIP, GIP, secretin and
motilin.
2. Inhibits gastric acid secretion & motility.
3. Inhibits pancreatic exocrine secretion.

Question 15

Prostaglandins

Answer 15

Normally present in the mucosa of the GIT. • Its secondary messenger is cyclic GMP.

Functions
1. Inhibits gastric, pancreatic & biliary secretion.
2. Relaxes lower esophageal sphincter.
3. Stimulates intestinal secretion and motility.
4. V.D. of GI blood vessels.

Question 16

Histamine

Answer 16

Normally present in the mucosa of the GIT especially in the gastric mucosa (high conc.)

Functions
1. Stimulation of gastric acid secretion by binding
to H2 receptors on parietal cells.
2. Increases the GI motility.
3. V.D. of GI blood vessels.