alimentary mechanisms

Question 1

what cells secrete gut hormones (paracrine of neurocrine factors)

Answer 1

enteroendocrine cells of alimentary canal

Question 2

specialisations of enteroendocrine cells for production and secretion of hormones

Answer 2

small apical membrane with lots of sensory apparatus (fingers of cytoplasm) and mitochondria (changes in gut contents or activation by neurotransmitters), broad basolateral surface which is close to blood vessels for rapid distribution of many secretory vesicles into blood by exocytosis

Question 3

where are most gut hormones secreted from

Answer 3

endocrine cells in mucosa or submucosa of stomach, small intestine and pancreas

Question 4

distance of effects of gut hormones

Answer 4

most regulate nearby organs as primary effect, but to get there must travel long way via liver, heart and lungs

Question 5

2 examples of paracrine cells in GIT

Answer 5

D-cells (in stomach), enterochromaffin-like cells (in gastric mucosa)

Question 6

what do D-cells secrete and what does it do

Answer 6

somatostatin, which inhibits secretion of acid from parietal cells in gastric pits

Question 7

what do enterchromaffin-like cells secrete and what does it do

Answer 7

histamine, which binds to H2 receptors on parietal cells and stimulates acid secretion

Question 8

hormones which affect gut hormone function

Answer 8

somatostatin, secretin, cholecystokinin, gastrin, glucose-dependent insulinotropic peptide

Question 9

what cells produce gastrin and where are they

Answer 9

G-cells in distal end of stomach (gastric antrum), proximal duodenum, pancreas

Question 10

lengths of gastrin produced (3)

Answer 10

34 amino-acid mostly, 17 and 14 also

Question 11

3 stimuli of gastrin secretion

Answer 11

presence of single amino acids and small peptides in stomach; mechanoreceptors in stomach wall detect presence of meal (stretch); parasympathetic nervous system (vagus nerve causing release of gastrin-releasing peptide from vagal efferents)

Question 12

3 effects of gastrin secretion

Answer 12

increased gastric acid secretion, gastric emptying, pepsinogen secretion

Question 13

negative feedback loop of gastrin secretion

Answer 13

if pH of chyme <3, secretion reduced to protect duodenal mucosa

Question 14

what cells produce secretin and where are they

Answer 14

S-cells in duodenum and jejunum

Question 15

stimuli of secretin secretion

Answer 15

drop in pH (<4.5) in duodenal kumen following acid chyme leaving stomach through pyloric sphincter

Question 16

3 effects of secretin secretion

Answer 16

stimulation of secretion of pancreatic HCO3- to neutralise acid; at high concentrations: reduced acid secretion by stomach, reduced gastric emptying to prevent further exacerbation of acidic environment in small intestine

Question 17

what cells secrete somatostatin and where are they

Answer 17

D-cells in stomach, gut mucosa, pancreas

Question 18

stimuli of somatostatin secretion

Answer 18

mixed meal and reduced pH

Question 19

inhibitory effects of somatostatin (hence universal inhibitor)

Answer 19

acid secretion, mobility, exocrine secretion, endocrine secretion, absorption

Question 20

how does somatostatin reduce acid secretion

Answer 20

via inhibiting G-cells from secreting gastrin and inhibiting enterochromaffin-like cells from secreting histamine

Question 21

what cells secrete cholecystokinin and where are they

Answer 21

I-cells in small intestine

Question 22

stimuli of CCK secretion

Answer 22

small peptides and fats after mixed meal

Question 23

effects of CCK secretion without input from ANS

Answer 23

increased secretion of pancreatic enzymes, reduced gastric emptying, increased gall bladder contraction, reduced appetite

Question 24

what cells secrete glucose-dependent insuliotropic peptide and where are they

Answer 24

K-cells in duodenum and jejunum

Question 25

stimuli of glucose-dependent insuliotropic peptide secretion

Answer 25

mixed meal nutrients (especially glucose)

Question 26

effects of glucose-dependent insuliotropic peptide secretion

Answer 26

increased insulin secretion; in high concentrations causes reduced acid secretion and reduced gastric emptying

Question 27

functions of GI endocrine system

Answer 27

regulate mechanical processes of digestion, chemical and enzymatic processes of digestion, control of post-absorptive processes, effect on growth and development

Question 28

somatostatin analogue use (e.g. octreotide)

Answer 28

treat neuroendocrine tumours

Question 29

why use somatostatin analogue not somatostatin (3)

Answer 29

somatostatin has short half life (be able to be turned off and broken down quickly), whereas analogue lasts longer in circulation; selectivity; peptide hormones must inject as otherwise broken down and not absorbed

Question 30

where is peptide YY (PYY) located

Answer 30

L cells throughout mucosa of terminal ileum, colon and rectum

Question 31

stimulus of peptide Y

Answer 31

post prandially (particularly protein)

Question 32

peptide YY functions

Answer 32

reduces intestinal motility, gallbladder contraction and pancreatic exocrine secretion; inhibitor of intestinal fluid and electrolyte secretion; inhibits food intake