Lecture 1- Control of the gut- hormones

Question 1

Hormones

Answer 1

oPeptidesreleasedfromendocrinecells o Intoportalcirculation
o Passthroughliver
o Entersystemiccirculation
o Endupprettyclosetowheretheywere

Question 2

paracrine hormones

Answer 2

o Relating to or denoting a hormone which has effect only in the vicinity of the gland secreting it.
o Peptides released by endocrine cells
o Act in local environment
o Diffuse short distances

Question 3

neurocrine hormones

Answer 3

o Peptides released by neurones in the GI tract

o Released after action potential

Question 4

how many categories of GI hormones

Answer 4

2

Question 5

name the 2 broad categories of GI hormones

Answer 5

Gastrin family

Secretin family

Question 6

Name the hormones of the gastrin family

Answer 6

gastrin

cholecytokinin (CCK)

Question 7

gastrin is released from

Answer 7

G cells

Question 8

where is gastrin released into

Answer 8

the antrum of the stomach

Question 9

effect of gastrin

Answer 9

• stimulates parietal cells to produce HCL
• Increasing gastric acid secretion
• increase motility

Question 10

Cholecystokinin (CCK) released from

Answer 10

I cells in the duodenum and jejunum

Question 11

effect of CCK

Answer 11

• increase pancreatic/ gallbladder secretion (enzymes, bile, HCO2)
• by increasing gall bladder contractions
• relaxes sphincter of Oddi

Question 12

CCK release stimulated by

Answer 12

fat and proteins

Question 13

Name the hormones of the secretin family

Answer 13

secretin

gastric inhibitory polypeptide (GIP)

Question 14

secretin is released by

Answer 14

S cells into the duodenum

Question 15

what stimulates S cells to release secretin

Answer 15

H+ and fatty acids

Question 16

effect of secretin

Answer 16

increase HCO3 from pancreas/gall bladder

decrease gastric acid secretion

Question 17

gastric inhibitory polypeptide (GIP) cells found

Answer 17

in the duodenum and jejunum

Question 18

gastric inhibitory polypeptide (GIP) release stimulated by

Answer 18

sugars, amino acids and fatty acids

Question 19

GIP effect

Answer 19

• increase insulin
• decrease gastric acid secretion
• decreases intestinal motility

Question 20

motilin released from

Answer 20

ECL cell

Question 21

motilin effect

Answer 21

• increase small bowel motility

- increase gastric emptying

Question 22

somatostatin released from D cells

Answer 22

decrease secretion and action of many hormones

Question 23

what do parietal cells release

Answer 23

HCL

Question 24

what triggers parietal cells to release HCL

Answer 24

Parietal cells bear receptors for three stimulators of acid secretion, reflecting a triumverate of neural, paracrine and endocrine control:

• Acetylcholine (muscarinic type receptor)
• Gastrin
• Histamine (H2 type receptor)

Question 25

histamine released from

Answer 25

ECL cells

Histamine stimulates the parietal cells to secrete HCl.
- gastrin-ECL cell pathway

Question 26

acetylcholine produced by which type of neurone

Answer 26

parasympathetic

Question 27

which hormones reduced HCL PRODUCTION

Answer 27

secretin, gastric inhibitory peptide, glucagon and somatostatin.

Question 28

change in morphology of parietal cells during HCL secretion

Answer 28

When acid secretion is stimulated there is a dramatic change in the morphology of the membranes of the parietal cell. Cytoplasmic tubulovesicular membranes which are abundant in the resting cell virtually disappear in concert with a large increase in the cannalicular membrane. It appears that the proton pump as well as potassium and chloride conductance channels initially reside on intracellular membranes and are transported to and fused into the cannalicular membrane just prior to acid secretion.

Question 29

mechanism of acid secretion

Answer 29

The key player in acid secretion is a H+/K+ ATPase or “proton pump” located in the cannalicular membrane. This ATPase is magnesium-dependent, and not inhibitable by ouabain. The current model for explaining acid secretion is as follows:

Hydrogen ions are generated within the parietal cell from dissociation of water. The hydroxyl ions formed in this process rapidly combine with carbon dioxide to form bicarbonate ion, a reaction cataylzed by carbonic anhydrase.
Bicarbonate is transported out of the basolateral membrane in exchange for chloride. The outflow of bicarbonate into blood results in a slight elevation of blood pH known as the “alkaline tide”. This process serves to maintain intracellular pH in the parietal cell.
Chloride and potassium ions are transported into the lumen of the cannaliculus by conductance channels, and such is necessary for secretion of acid.
Hydrogen ion is pumped out of the cell, into the lumen, in exchange for potassium through the action of the proton pump; potassium is thus effectively recycled.
Accumulation of osmotically-active hydrogen ion in the cannaliculus generates an osmotic gradient across the membrane that results in outward diffusion of water - the resulting gastric juice is 155 mM HCl and 15 mM KCl with a small amount of NaCl.