Gih Week 1: Gi Hormones

Front 1

What antagonist blocks nicotonic receptors?

Back 1

Hexamethonium

Front 2

What compound blocks muscarinic recepters?

Back 2

Atropine

Front 3

Name a compound that blocks alpha-adrenergic receptors.

Back 3

Phentolamine

Front 4

Name a neurotransmitter that blocks beta-adrenergic receptors.

Back 4

Propanolol

Front 5

What is the general effect of sympathetic nerves on the GI tract?

Back 5

(Generally inhibitory)
1. Relax intestinal smooth muscle
2. Inhibit water/electrolyte secretion (promotes absorption of Na+, Cl-)

Front 6

What are the key inhibitory neurotransmitters of motility in the enteric nervous system?

Back 6

1. NO (nitric oxide)
2. VIP (vasoactive intestinal peptide)

(Result in relaxation in front of bolus/chyme)

Front 7

What are the key excitatory neurotransmitters of motility in the enteric nervous system?

Back 7

1. Substance P
2. Serotonin (5HT)

(Result in contraction behind bolus/chyme)

Front 8

Which neurotransmitters stimulate the submucosal plexus to promote secretion?

Back 8

1. ACh
2. VIP

(*VIP activates secretion in the submucosal plexus and inhibits motility in the myenteric plexus)

Front 9

Which 2 hormones influence secretion in the submucosal plexus?

Back 9

1. Serotonin (5HT)--from ECL cells
2. Histamine---from mast cells

Front 10

What is the effect of secretin on the pancreas?

How is secretin stimulated?

Back 10

Stimulates duct cells to secrete HCO3- and H20

Secretin is stimulated by the entry of acid into the duodenum

Front 11

What enzyme converts trypsinogen to trypsin?

Back 11

Enterokinase
(brushborder enzyme)

Front 12

What component of pancreatic juice prevents the activation of proenzymes prior to their entry into the intestinal lumen?

Back 12

Trypsin inhibitor

Front 13

What are the 2 most important hormones involved in pancreatic secretion?

Back 13

1. Secretin
2. CCK

Front 14

What is the effect of VIP on the pancreas?

Back 14

Stimulates duct cells to release HCO3- and H2O, but is less potent than secretin.

Front 15

Which hormones stimulate duct cells via cAMP second messenger system?

Back 15

1. Secretin
2. VIP (less potent)

Front 16

Which hormones stimulate acinar cells via a Ca2+ mediated mechanism?

Back 16

1. CCK
2. Gastrin (less potent)

Front 17

What initiates vago-vagal reflexes that act on acinar and duct cells?

Back 17

Entry of chyme into the intestine

(Vagal efferent fibers cause the release of both ACh and VIP from postganglionic fibers)

Front 18

What is the biggest effect of Vagus stimulation of pancreatic cells?

Back 18

Stimulation of the Vagus increases enzyme secretion from the acinar cells
(and to a lesser extent, it increases HCO3- and H2O secretion from the duct cells).

Front 19

What is the effect of sympathetic stimulation of the pancreas?

Back 19

Inhibits vagal and secretin-induced secretion

Front 20

ACh potentiates the pancreatic-stimulatory effects of which hormone?

Back 20

Secretin
(Does not potentiate effects of CCK b/c ACh and CCK both act on acinar cells via Ca2+-mediated mechanisms. Secretin, however, uses a cAMP 2nd messenger system, so ACh can potentiate its effects).

Front 21

What initiates the release of CCK from intestinal I-cells?

Back 21

Presence of fatty acids and peptides

Front 22

What does the enteropancreatic reflex involve?

Back 22

The vagal release of ACh in response to the presence of fatty acids or amino acids in the duodenum

Front 23

What hormones may be stimulated by the presence of fat in the lower intestine, and function to inhibit pancreatic secretion?

Back 23

1. Peptide YY
2. Pancreatone

Front 24

What hormone causes gallbladder contraction?

Back 24

CCK

Front 25

What hormone causes the sphincter of Oddi to relax?

Back 25

CCK

Front 26

List 3 pancreatic proteolytic endopeptidases.

Back 26

1. Trypsinogen
2. Chymotrypsinogen
3. Pro-elastase

Front 27

List 3 pancreatic proteolytic exopeptidases.

Back 27

1. Pro-carboxypeptidase A
2. Pro-carboxypeptidase B
3. Pro-aminopeptidase

Front 28

Which pancreatic enzyme digests carbohydrates?

Back 28

alpha-amylase

Front 29

List 2 nucleolytic pancreatic enzymes.

Back 29

1. Deoxyribonulease
2. Ribonuclease

Front 30

List 4 lypolytic pancreatic enzymes.

Back 30

1. Lipase
2. Pro-Phospholipase A2
3. Carboxylester hydrolase
4. Cholesterol esterase

Front 31

What are the 4 classes of enzymes secreted in pancreatic juice?

Back 31

1. Proteases
2. Lipases
3. Amylase
4. Nucleases

Front 32

List the 4 functions of CCK.

Back 32

1. Stomach--> reduces acid production/ emptying
2. Pancreas--> stimulates enzyme secretion from acinar cells
3. Sphincer of Oddi --> relaxes the muscle
4. Gallblader--> induces contraction

Front 33

What is the effect of parasympathetic innervation of the pancreas?

What neurotransmitters are released?

Back 33

Parasympathetic nerves release ACh and VIP which increases the rate of pancreatic secretion
(act on both acinar and duct cells)

Front 34

VIP released from vagal efferent fibers has what effect on pancreatic cells?

Back 34

Increases HCO3- and H2O secretion from duct cells

Front 35

ACh released from vagal efferent fibers mostly has an effect on which pancreatic cells?

Back 35

Acinar cells
(increases enzyme secretion)

Front 36

What stimulates the release of CCK?

Back 36

Presence of amino acids and fat in duodenum

Front 37

What stimulates the release of Gastrin?

Back 37

Presence of protein digestion products in the stomach

Front 38

What mediates pancreatic secretion during the cephalic phase?

Back 38

Vagus N

Front 39

What mediates pancreatic secretion during the gastric phase?

Back 39

Vagus N

Front 40

What mediates pancreatic secretion during the intestinal phase?

Back 40

Secretin from intestinal S-cells
(in response to acid in duodenum)

Front 41

What is the effect of Secretin on the bile ducts?

Back 41

Stimulates secretion of HCO3- and H2O

Front 42

What is the stimulus for bile secretion in the liver?

Back 42

Return of bile acids in enterohepatic circulation
(indicates meal in progress)

Front 43

The stomach receives sympathetic innervation from which ganglia?

Back 43

Stellate, celiac, and superior mesenteric ganglia

Front 44

Which portion of the stomach is "acid secreting"?

Back 44

Corpus

Front 45

Which portion of the stomach is "mucus secreting"?

Back 45

Antrum

Front 46

Which component of gastric secretions converts pepsinogen to pepsin, kills microbes, and denatures proteins?

Back 46

H+

Front 47

Which 3 major secretogogues stimulate acid secretion?

Which receptors do they bind to?

Back 47

1. **Histamine ---> H2 receptor
2. ACh ---> M3 receptor
3. Gastrin ---> CCK-B receptor

*Receptors located on basolateral side of parietal cell

Front 48

What portion of the stomach are G-cells located in?

Back 48

Antrum

Front 49

Which 2 hormones can act on the CCK-B receptor on parietal cells?

Back 49

1. Gastrin
2. CCK
(structural homology)

Front 50

Under experimental conditions, Gastrin and CCK can be blocked by the CCK-B receptor antagonist called...?

Back 50

Proglumide

Front 51

How is the intracellular pathway promoted by histamine different than the pathway promoted by Ach and Gastrin?

Back 51

Histamine promotes an increase in cAMP

ACh and Gastrin promote a Ca2+-mediated pathway

Front 52

Which 3 hormones inhibit gastric acid secretion?

Back 52

1. Somatostatin
2. Prostaglandin
3. Secretin

Front 53

What is the effect of Prostaglandins on acid secretion?

Back 53

Inhibition of acid secretion
*Prostaglandins stimulate EP3 receptors on parietal cells which prevent histamine-induced increases in cAMP

Front 54

How do prostaglandins offer a degree of mucosal protection?

Which synthetic drug mimics this function?

Back 54

They stimulate surface mucous cells to secrete mucous and HCO3-

(So, Prostaglandins have 2 functions in the stomach:
1. Inhibit gastric acid secretion
2. Stimulate surface mucous cells to secrete HCO3- and mucus)

*Misoprostol (synthetic prostaglandin)

Front 55

Where are S cells located, what do they secrete, and what are they stimulated by?

Back 55

S cells:
1. Located in duodenal mucosa
2. Secrete secretin
3. Stimulated by acid

Front 56

What are the 3 functions of secretin?

Back 56

1. Inhibits gastrin on parietal cells
2. Blocks G-cells from secreting gastrin
3. Promotes HCO3- secretion from pancreatic duct cells

Front 57

What do D-cells secrete? What stimuli do they respond to?

Back 57

Somatostatin
Secreted in response to large amounts of acid in the gastric lumen

Front 58

What are the 2 functions of somatostatin?

Back 58

(Inhibition of gastric acid secretion)

1. Depress gastrin release from G cells
2. Oppose the effects of gastrin on parietal cells

Front 59

Which 2 cell types are stimulated by the Vagus N in the stomach?

Which neurotransmitters are released to stimulate these cells?

Back 59

1. G-cells stimulated by BOMBESIN to secrete Gastrin
2. Parietal cells stimulated by ACETYLCHOLINE to secrete HCl

Front 60

What stimuli causes G-cells to release gastrin?

Back 60

1. Presence of peptides/amino acids in the stomach lumen
2. Bombesin released by efferent vagal fibers

Front 61

Which two hormones secreted by cells in the duodenum stimulate gastric acid secretion?

Back 61

1. Gastrin (secreted by duodenal G-cells; only small amount present)
2. Entero-oxyntin

Front 62

During the intestinal phase of digestion, which is the predominant effect of duodenal hormone secretion?

Back 62

Inhibition predominates (Secretin, Neuropeptide Y and peptide YY depress release of gastric acid)

(This inhibitory effect overwhelms the excitatory effect of duodenal gastrin and entero-oxyntin)

Front 63

The presence of lipid in the duodenum stimulates the release of what substances?

Back 63

"Enterogastrones"
1. Neuropeptide Y
2. Peptide YY

*These depress the release of gastric acid

Front 64

The presence of acid in the duodenum stimulates the release of what hormone?

Back 64

Secretin

Front 65

Which portion of the stomach exhibits slow waves?

Back 65

Lower 2/3
(slow waves originate in pacemaker cells located in the mid stomach along the greater curvature)

Front 66

What are the mediators of gastric acid secretion during the basal (interdigestive) phase?

Back 66

1. Histamine
2. ACh
3. Gastrin

Front 67

What are the mediators of gastric acid secretion during the cephalic phase of digestion?

Back 67

1. Vagus N --> Ach
2. Gastrin

Front 68

What are the mediators of gastric acid secretion during the gastric phase of digestion?

Back 68

Mostly gastrin, which is released through several pathways

Front 69

What are the mediators of gastric acid secretion during the intestinal phase of digestion?

Back 69

1. Enterogastrones (Secretin, Neuropeptide Y)
2. Gastrin

(This phase is mostly inhibitory, despite small release of gastrin)

Front 70

What are the effects of secretin, GIP, and CCK on gastric acid secretion?

Back 70

INHIBITION

Front 71

What substance is released by the vagal-mediated reflex that causes a receptive relaxation of the stomach?

Back 71

Nitric oxide

(This reflex is induced by swallowing. Adaptive relaxation, which is induced by distension, is also mediated by the Vagus N and NO).