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endocrine term 2 quiz 2 - julia's notes > chapter 8 - GI physiology > Flashcards

chapter 8 - GI physiology Flashcards

1
Q

extrinsic component of innervation of GI tract

A

sympathetic and parasympathetic innervation

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2
Q

intrinsic component of GI tract innervation

A

enteric nervous system

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3
Q

enteric nervous system

A

intrinsic component of innervation of GI tract
wholly contained within the submucosal and myenteric plexuses in the wall of the GI tract
communicates extensively with the parasympathetic and sympathetic nervous systems
can direct all function of the GI tract, even in the absence of extrinsic innervation

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4
Q

parasympathetic innervation of the GI tract

A

supplied by the vagus nerve and the pelvic nerve
vagus innervates upper GI tract, including striated muscle of upper third of esophagus, wall of stomach, small intestine, ascending colon
pelvic innervates lower GI tract, including striated muscle of external anal canal and the walls of the transverse, descending, and sigmoid colons
long preganglionic fibers that synapse in ganglia in or near target organs
in GI tract, ganglia in walls of organs within myenteric and submucosal plexuses
postganglionic neurons are cholinergic or peptidurgic (substance P and VIP)

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5
Q

vagus

A

mixed
75% afferent - sensory info from periphery to CNS
25% efferent - deliver motor info from CNS to target tissues in periphery (smooth muscle, secretory, and endocrine cells)

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6
Q

vagovagal reflexes

A

reflexes triggered by afferent info from mechanoreceptor adn chemoreceptors in GI mucosa via vagus nerve
afferent limb of reflexes is also in the vagus nerve

when both afferent and efferent limbs are contained in the vagus nerve

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7
Q

sympathetic innervation of the GI tract

A

preganglionic fibers short and synpase on ganglia outside GI tract
4 ganglia: celiac, superior mesenteric, inferior mesenteric, and hypogastric
postgangionic fibers are adrenergic - leave sympathetic ganglia and synapse on ganglia in myenteric and submucosal plexuses or directly innervate SM, endocrine, or secretory cells
about 50% are afferent and 50% efferent

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8
Q

NT in enteric NS (list)

A 
ACh
Norepi
VIP
GRP/bombesin
enkephalins (opiates)
neuropeptide Y
substance P
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9
Q

Acetylcholine (ACh)

A 
produced by cholinergic neurons in interic NS
actions:
1: contraction of SM in wall
2: relaxation of sphincters
3: increase salivary secretion
4: increase gastric secretion
5: increase pancreatic secretion

binds to muscarinic (M3) receptors on parietal cells
second messengers are IP3/Ca2+
activates phospholipase C => liberates diacylglycerol and IP3 => IP3 then releases Ca2+ from intracellular stores
Ca2+ and diacylglycerol activate protein kinases that produce final physiological action = H+ secretion by parietal cells

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10
Q

norepinephrine (NE)

A 
produced by adrenergic neurons in enteric NS
actions:
1: relaxation of SM in wall
2: contraction of sphincters
3: increase salivary secretion
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11
Q

vasoactive intestinal peptide (VIP)

A

released by neurons of mucosa and SM in enteric NS
actions:
1: relaxation of smooth muscle
2: increase intestinal secretion
3: increase pancreatic secretion
controls opening of lower esophageal sphincter during swallowing by producing relaxation of SM of the lower esophageal sphincter

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12
Q

gastrin-releasing peptide (GRP)/bombesin

A

released by neurons of gastric mucosa as part of enteric NS

increases gastrin secretion

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13
Q

enkephalins (opiates)

A

released by neurons of mucosa and smooth muscle as part of enteric NS
actions:
1: contraction of SM
2: decreases intestinal secretion

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14
Q

neuropeptide Y

A

released by neurons of mucosa and SM as part of enteric NS

actions:
1: relaxation of SM
2: decrease intestinal secretion

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15
Q

substance P

A

cosecreted with ACh by cholinergic neurons as part of enteric NS
actions:
1: contraction of SM
2: increase salivary secretion

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16
Q

GI peptides that are hormones (list)

A
  • gastrin
  • cholecystokinin (CCK)
  • secretin
  • glucose-dependent insulinotropic peptide/gastric inhibitory peptide (GIP)
17
Q

GI peptides that are paracrines

A

somatostatin

histamine (but not a peptide)

18
Q

GI peptides that are neurocrines

A 
ACh
norepi
VIP
GRP/bombesin
enkephalins
neuropeptide Y
substance P
19
Q

gastrin

- hormone family
- site of secretion
- stimuli for secretion
- actions
A 
of the gastrin CCK hormone family
secreted by G-cells of stomach
stimulated by:
1. small peptides and AA
2: digestion of the stomach
3: vagal stimulation (GRP/bombesin)
inhibited by:
1: low pH of gastric contents
2: somatostatin
actions:
1: increase gastric H+ secretion
2: stimulates growth of gastric mucosa (trophic effect)

reaches parietal cells by endocrine mechanism
binds to cholecystokinin B (CCKb) on parietal cells => stimulates H+ secretion through IP3/Ca2+ second messenger system

20
Q

cholecystokinin (CCK)

- hormone family
- site of secretion
- stimuli for secretion
- actions
A

part of gastrin/CCK family
secreted by I cells of duodenum and jejunum
stimuli:
1: small peptides and AA
2: fatty acids
actions:
1: increase pancreatic enzyme secretion (lipases and amylase)
2: increase pancreatic HCO3 secretion, potentiates effects of secretin
3: stimulates contraction of gallbladder and relaxation of sphincter of Oddi - results in ejection of bile into small intestine
4: stimulates growth of the exocrine pancreas and gallbladder
5: inhibits gastric emptying, increases gastric emptying time - gives more time for fat digestion and absorption
slows delivery of chyme from stomach

21
Q

secretin

- hormone family
- site of secretion
- stimuli for secretion
- actions
A

part of secretin/glucagon hormone family
secreted by S cells of duodenum
stimuli:
1: H+ in the duodenum
2: fatty acids in the duodenum
actions:
1: increase pancreatic HCO3 secretion - neutralizes H+ in lumen
2: increase biliary HCO3 secretion - same as 1 - necessary because pancreatic lipases have pH optimums between 6 and 8
3: decrease gastric H+ secretion
4: inhibits trophic effect of gastrin on gastric mucosa (parietal cells)

22
Q

glucose-dependent insulinotropic peptide (GIP)

- hormone family
- site of secretion
- stimuli for secretion
- actions
A 
part of secretin-glucagon hormone family
secreted in duodenum and jejunum
stimuli:
1: fatty acids
2: amino acids
3: oral glucose - allows oral glucose to be more effective at stimulating insulin secretion than IV glucose
actions:
1: increase insulin secretion from pancreatic beta cells
2: decrease gastric H+ secetion
23
Q

C terminal tetrapeptide

A

minimum fragment necessary for biologic activity of gastrin, but only 1/6th as effective as entire molecule

24
Q

effects of gastrin-secreting tumors (zollinger-ellison syndrome)

A

H+ secretion increased
trophic effect of gastrin causes gastric mucosa to hypertrophy
tumor usually in non-beta-cell pancreas
duodenal ulcers
acidification of intestinal lumen => inactivation of pancreatic lipase => dietary fats not adequately digested or absorbed and fat excreted in stool (steatorrhea)
treat with H2 receptor blockers, administration of inhibitors of H+ pump, removal of tumor, gastric resection

25
Q

somatostatin

A

secreted by D cells of GI mucosa
in response to:
1: decreased luminal pH
actions:
1: inhibits secretion of other GI hormones
2: inhibits gastric H+ secretion
also secreted by hypothalamus and by delta cells of endocrine pancreas

26
Q

histamine

A

paracrine
secreted by endocrine-type cells of GI mucosa, particularly in H+ secreting region of stomach
stimulates H+ secretion by the gastric parietal cells

binds to H2 receptors
second messenger = cAMP via adenylyl cyclase and Gs protein
cAMP activates protein kinase A => secretion of H+ by parietal cells

27
Q

saliva

- characteristics 
- factors that increase secretion
- factors that decrease secretion
A 
high HCO3 and K+
hypotonic
alpha-amylase and lingual lipase
increase:
1: parasympathetic (prominent)
2: sympathetic
decrease:
1: sleep
2: dehydration
3: atropine
28
Q

gastric secretion (HCl)

- characteristics 
- factors that increase secretion
- factors that decrease secretion
A 
HCl
increase:
1: gastrin
2: acetylcholine
3: histamine
decrease:
1: H+ in stomach
2: chyme in duodenum
3: somatostatin
4: atropine
5: cimetidine
6: omeprazole
29
Q

gastric secretion (pepsinogen and intrinsic factor)

A

parasympathetics increase secretion

30
Q

pancreatic secretions

- characteristics 
- factors that increase secretion
- factors that decrease secretion
A 
A: high HCO3-, isotonic
increase:
1: secretin
2: CCK (potentiates secretin)
3: parasympathetic

B: pancreatic lipase, amylase, proteases
increase:
1: CCK
2: parasympathetic

31
Q

bile secretion

- characteristics 
- factors that increase secretion
- factors that decrease secretion
A

bile salts, bilirubin, phospholipids, cholesterol
increase:
1: CCK (contraction of gall bladder and relaxation of sphincter of oddi)
2: parasympathetic
decrease:
1: ileal resection

32
Q

intrinsic factor

A

required for absorption of vitamin B12 in ileum

33
Q

atropine

A

blocks muscarinic receptors on parietal cells and therefore blocks action of ACh

34
Q

cimetidine

A

blocks H2 receptors and blocks action of histamine on parietal cells

endocrine term 2 quiz 2 - julia's notes (16 decks)

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