GIT: (hormonal) regulation of GIT functions

Question 1

Enumerate all hormones affecting GIT

Answer 1

• Gastrin
• Cholecystokinin (CKK)
• Secretin
• Glucose dependent insulino-tropic peptid (GIP)
• Vasoactive intestine Peptide (VIP)
• Motilin
• Somatostatin

Question 2

Cells releasing Gastrin

Answer 2

G cells

Question 3

Site of Gastrin Release

Answer 3

• mainly in pyroic Antrum of stomach
• duodenum & pancreas

Question 4

Stimuli facilitating the release of gastrin

Answer 4

Mechanical:
* Distension caused by food

Chemical:
* basic pH
* Protein digestive products (phenyalanine, tryptophan, peptides)

Nervous:
* Post ganglionic vagal innervation (by release of GRP)

(pathologically)=Pernicious anemia

Question 5

Explain why Atropine doesn’t block gastrin secretion

Answer 5

post ganglionic Vagal innervation of gastrin secretion occurs by release of GRP (gastrin-releasing peptide) & not Acetylcholine

Question 6

Explain why pernicious anemia causes pathological secretion of gastrin hormone

Answer 6

1. It destroys Acid secreting cells
2. Less acid means no inhibition of gastrin secretion (negative feedback inhibition)

Question 7

Stimuli inhibiting the secretion of Gastrin

Answer 7

Acid (HCL) :
* Directly: by acting on G cells (releasing gastrin)
* Indirectly: by acting on D cells, causing it to release Somatostatin, which inhibits Gastrin secretion

• VIP (vasoactive Intestinal Peptide)

Question 8

Actions of Gastrin

Answer 8

1. Facilitates HCL secretion:
   * Directly: acting on parietal cells
   * Indirectly: stimulating Histamine secretion from ECL cells, histamine causes further acid secretion
2. Trophic Action on stomach: stomach increases in size
3. Stimulates insulin secretion

Question 9

Cells releasing CCK (cholecysetokinin)

Answer 9

I Cells

Question 10

Site of release of CCK

Answer 10

Mucous of Duodenum & jejunum (upper small intestine)

Question 11

Stimuli faciliting release of CCK

Answer 11

presence of digestive products of peptides, amino acids & fats

Question 12

Action of CCK on pancreas

Answer 12

1. Stimulate pancreatic Acinar cells to secrete enzymes
2. Trophic effect on pancreas (increase in size)
3. Enhances effect of Secretin hormone on pancreas

Question 13

Action of CCK on Stomach

Answer 13

1. prevents motility of stomach
2. (along with secretin) contraction of pyloric sphincter to prevent reflux from duodenum to stomach

Question 14

Action of CCK on gall bladder

Answer 14

1. relaxation of sphincter of oddi
2. Contraction of walls of gall bladder —> secretion of bile

Question 15

Describe positive feedback mechanism linked to gall bladder & CCK hormone

Answer 15

1. CCK faciltates secretion of bile from gall bladder
2. resulting in more digestion of proteins & fats
3. Therefore, there is more Digestive product
4. More CCK secreted
5. More Bile secreted

It stops when food moves on from duodenum

Question 16

Action of CCK on small intestine

Answer 16

it augemnts motility of small intestine

Question 17

Action of CCK on the brain

Answer 17

causes Satiety & decrease food intake

This is linked to anxiety & panic disorders

Question 18

Cells releasing Secretin

Answer 18

S cells

Question 19

Site of release of Secretin

Answer 19

glands of mucosa of upper part of small intestine (duodenum & jejunum)

Question 20

Stimuli facilitating release of Secretin

Answer 20

• Decrease in Duodenal pH (increase in Acidity)
• Protein digestive products

Question 21

Action of Secretin

Answer 21

1. Augments action of CCK
2. Decrease HCL secretion by parietal cells
3. Neutralize Acidic pH by Secretion of bicarb (from pancreatic duct) & water

Secretin job is to prevent acidity

Question 22

Cells Releasing GIP

Answer 22

K cells

Question 23

Site of release of GIP

Answer 23

(like CCK) mucosa of Deudenum & jejunum

Question 24

Stimuli facilitating secretion of GIP

Answer 24

presence of Glucose & Fat inside the duodenum

Question 25

Action of GIP

Answer 25

1. Stimulate **insulin secretion** by acting on **pancreatic B cells** 2. increase B cell **synthesis** 3. **prevent** B cell **apoptosis** 4. Along with **GLP**, play a major role in **Postprandial (after meal) insulin response** | its job is glucose utilisation

Question 26

Mention the link between GIP & obesity

Answer 26

GIP is present in high level in obese people, along with hyperplasia (increase in cell size) of K cells (cells secreting GIP)

Question 27

Site of release VIP

Answer 27

Myenteric & submucosal Nervous Plexuses (along with acetylcholine)

Question 28

Stimuli facilitating release of VIP

Answer 28

presence of (substances causing VD): * Acetylcholine * ATP * Serotonin * Substance P

Question 29

Action of VIP

Answer 29

1. VD of blood vessels of GIT 2. Inhibition of Gastrin, to decrease HCL secretion 3. Secretion of water, electrolytes & bicarbonate

Question 30

Cells releasing Motilin

Answer 30

* Mo cells * Enterochrouffin cells

Question 31

Site of release of motilin

Answer 31

(all except eosophagus): * Stomach * small intestine * Colon

Question 32

Stimuli facilitating secretion of Motilin

Answer 32

Binding to **G protein coupled receptors** (found mainly in **pyloric Antrum**)

Question 33

Stimuli inhibiting secretion of Motilin

Answer 33

* Ingestion of glucose & fat * Pregnency

Question 34

Action of Motilin

Answer 34

* Stimulate Contraction of GIT smooth muscles in between meals * Regulate Migrating motor complex (MMC)

Question 35

Explain why pregnent women have reoccuring constipation

Answer 35

Pregnency causes inhibition of Motilin hormone secretion, leading to decreased GIT movement in between meals

Question 36

Site of release & cells secreting somatostatin

Answer 36

D cells: * 65% from mucosa * 35% from pancreas

Question 37

Stimuli facilitiating secretion of Somatostatin

Answer 37

Food in Gut: * Glucose * Amino acids * HCL in duodenum & pyloric antrum

Question 38

Action of Somatostatin

Answer 38

provide **continuous supply of nutrients** in the GIT by **inhibiting all GIT (pausing it)**