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ACVIM General Boards > GI Physiology > Flashcards

GI Physiology Flashcards

1
Q

layering of the GIT (detailed)

A
  1. epithelial cells
  2. muscularis mucosa
  3. circular muscle
  4. longitudinal muscle
  5. submucosal plexus (Meissner plexus) and myenteric plexus
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2
Q

Meissner (submucosal) and myenteric plexus

A

= the enteric nervous system of the GIT; integrate and coordinate the motility, secretory, and endocrine functions of the GIT

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3
Q

autonomic nervous system (ANS) of the GIT

A

comprises both extrinsic and intrinsic nervous system

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4
Q

extrinsic innervation of the GIT

A
  1. parasympathetic nervous system

2. sympathetic nervous system

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5
Q

efferent fibers

A

carry sensory information from the brainstem and spinal cord to the GIT

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6
Q

afferent fibers

A

carry sensory information from chemoreceptors and mechanoreceptors in the GIT to the brainstem and spinal cord

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7
Q

function of the parasympathetic nervous system on the GIT

A

usually excitatory

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8
Q

parasympathetic nerves of the GIT

A
  1. vagus nerve

2. pelvic nerve

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9
Q

anatomy of the PNS of the GIT

A

preganglionic parasympathetic fibers synapse in the myenteric and submucosal plexuses; cell bodies in the ganglia of the plexuses then send information to the smooth muscle, secretory cells, and endocrine cells of the GIT

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10
Q

innervations of the vagus nerve

A
  1. esophagus
  2. stomach
  3. pancreas
  4. upper large intestine
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11
Q

vagovagal reflexes

A

= reflexes in which both afferent and efferent pathways are contained in the vagus nerve

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12
Q

innervations of the pelvic nerve

A
  1. lower large intestine
  2. rectum
  3. anus
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13
Q

function of the sympathetic nervous system on the GIT

A

usually inhibitory

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14
Q

sympathetic nerves of the GIT

A

fibers originating in the spinal cord btwn T8 and L2

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15
Q

anatomy of the SNS of the GIT

A

preganglionic sympathetic adrenergic fibers leave the vertebral ganglia and synapse in the myenteric and submucosal plexus–>

  1. direct postganglionic adrenergic innervation of blood vessels and some smooth muscle cells
  2. cell bodies in the ganglia of the plexus then send information to the smooth muscle, secretory cells, and endocrine cells of the GIT
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16
Q

intrinsic innervation (= enteric nervous system) functions

A

coordinates and relays information from the parasympathetic and sympathetic nervous system to the GIT; controls most functions of the GIT, especially motility and secretion, even in the absence of extrinsic innervation

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17
Q

MOA of the intrinsic nervous system

A

uses local reflexes to relay information within the GIT

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18
Q

plexuses of the intrinsic nervous system of the GIT and the functions they control

A
  1. myenteric plexus (Auerbach plexus)–>motility of GI smooth muscle
  2. submucosal plexus (Meissner plexus)–>secretion and blood flow; receives sensory information from chemo and mechanoreceptors in the GIT
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19
Q 
gastrin summary:
family
site of secretion
stimulus for secretion
inhibition
actions
A
  • family: gastrin-CCK
  • site of secretion: G cells of the stomach (antrum)
  • stimulus for secretion: = a meal
    1. small peptides and amino acids
    2. stomach distension
    3. vagus nerve via GRP (gastrin-releasing peptide)
  • inhibited by
    1. acid in the stomach
    2. somatostatin
  • actions of gastrin
    1. increase gastric acid secretion
    2. stimulate growth of gastric mucosa
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20
Q 
CCK summary:
family
site of secretion
stimulus for secretion
actions
A
  • family: gastrin-CCK
  • site of secretion: I cells of the duodenum and jejunum
  • stimulus for secretion
    1. small peptides and amino acids
    2. fatty acids and monoglycerides
  • actions of CCK
    1. contraction of the gallbladder and relaxation of the sphincter of Oddi–>secretion of bile
    2. increases pancreatic enzyme and bicarbonate secretion
    3. increases growth of the exocrine pancreas and gallbladder
    4. inhibits gastric emptying
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21
Q 
secretin summary:
family
site of secretion
stimulus for secretion
actions
A
  • family: secretin-glucagon
  • site of secretion: S cells of the duodenum
  • stimulus for secretion
    1. acid in the duodenum
    2. fatty acids in the du odenum
  • actions of secretin = coordinated to decrease the amt of acid in the SI lumen
    1. increase biliary bicarb secretion
    2. increase pancreatic bicarb secretion
    3. decrease gastric acid secretion
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22
Q 
GIP (glucose-dependent insulinotropic peptide) summary:
family
site of secretion
stimulus for secretion
actions
A
  • family: secretin-glucagon
  • site of secretion: duodenum and jejunum
  • stimulus for secretion
    1. fatty acids
    2. amino acids
    3. oral glucose
  • *NOTE: GIP is the ONLY GI hormone whose secretion is stimulated by carbohydrates (oral glucose)
  • actions of GIP
    1. decrease gastric acid secretion
    2. increase insulin secretion
23
Q

four “official” GI hormones

A
  1. gastrin
  2. CCK
  3. secretin
  4. GIP
24
Q

most potent stimuli for gastrin secretion

A
  1. phenylalanine

2. tryptophan

25
Q

location of gastrin’s biologic activity

A

the four C-terminal amino acids

26
Q

anatomic feature of gastrin-secreting tumors

A

hypertrophy and hyperplasia of the gastric mucosa

27
Q

Zollinger-Ellison syndrome

A

= gastrinoma; occurs when gastrin is secreted by non-beta cell tumors of the pancreas

28
Q

structure of CCK

A

contains 33 amino acids

homologous to gastrin (the 5 C-terminal amino acids are the same inCCK and gastrin)

29
Q

location of CCK biologic activity

A

C-terminal heptapeptide (which contains the sequence for the same 4 C-terminal amino acids of gastrin)

30
Q

do triglycerides stimulate release of CCK?

A

NO! because triglycerides cannot cross intestinal cell membranes; only fatty acids and monoglycerides stimulate CCK release

31
Q

secretin structure

A

27 amino acids; homologous to glucagon (14 of the 27 amino acids in secretin are the same as glucagon)

32
Q

location of secretin’s biologic activity

A

all of the amino acids

33
Q

GIP structure

A

42 amino acids; homologous to secretin and glucagon

34
Q

HINT about GIP actions

A

THINK: it’s homologous to glucagon and glucagon causes insulin release (check)

35
Q

five candidate GI hormones

A
  1. motilin
  2. pancreatic polypeptide
  3. glucagon-like peptide-1 (GLP-1)
  4. leptin
  5. ghrelin
36
Q

cells that secrete the 5 candidate hormones

A

cells of the GIT

37
Q

motilin function

A
  1. increase GI motility

2. involved in interdigestive myoelectrical complexes

38
Q

pancreatic polypeptide function

A

inhibit pancreatic secretions

39
Q

GLP-1 functions

A

stimulate insulin secretion by the pancreatic beta-cells

40
Q

target cell of GLP-1

A

pancreatic beta cells

41
Q

leptin function

A

decrease appetite

42
Q

ghrelin function

A

increase appetite

43
Q

paracrines

A

= substances released from endocrine cells of the GI mucosa that diffuse over short distances to act on target cells

44
Q

GI paracrines

A
  1. somatostatin

2. histamine

45
Q 
somatostatin summary:
location of secretion
stimulus for secretion
inhibition
actions
A
  • location of secretion = throughout the GIT
  • stimulus for release = acid in the lumen of the SI
  • inhibition = vagal stimulation (because the vagus wants to increase acid for digestion)
  • actions of somatostatin
    1. inhibits release of all GI hormones
    2. inhibits gastric acid secretion
46
Q

histamine summary:
location of secretion
actions

A
  • location of secretion: mast cells of the GI mucosa
  • actions of histamine
    1. increase gastric acid secretion directly and by potentiating the effects of gastrin and vagal stimulation
47
Q

neurocrines

A

= substances synthesized in neurons of the GIT moved by axonal transport down the axons and released by action potentials in the nerves; then diffuse across the synaptic cleft to the target cell

48
Q

GI neurocrines

A
  1. vasoactive intestinal peptide (VIP)
  2. neuropeptide Y
  3. nitric oxide (NO)
  4. GRP (bombesin)
  5. enkephalins
49
Q

vasoactive intestinal peptide (VIP) structure

A

28 amino acids; homologous to secretin (whose function it is to DECREASE acid in the duodenal lumen)

50
Q

VIP summary:
location of release
actions

A
  • location of release = neurons in the mucosa and smooth muscle of the GIT
  • actions of VIP
    1. relaxation of GI smooth muscle (including the lower esophageal sphincter)
    2. stimulates pancreatic bicarb secretion (similar to secretin)
    3. inhibits gastric acid secretion (similar to secretin)
51
Q

secretion of pancreatic islet cell tumors

A

VIP; presumed to mediate pancreatic cholera

52
Q

GRP (bombesin) summary:
location of release
action

A
  • location of release = vagus nerves that innervate the G cells
  • action of GRP
    1. stimulates the release of gastrin from G cells (–>increase gastric acid secretion and stimulate growth of GI mucosa)
53
Q

two enkephalins

A
  1. met-enkephalin

2. leu-enkephalin

54
Q

enkephalin summary:
location of release
actions

A
  • location of release. = nerves in the mucosa and smooth muscle of the GIT
  • actions of enkephalins
    1. stimulate contraction of GI smooth muscle, particularly the lower esophageal, pyloric, and ileocolic sphincters
    2. inhibit intestinal secretion of fluids and electrolytes

ACVIM General Boards (3 decks)

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