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Gastrointestinal System > Regulation of GI Function - Wondisford 2/17/16 > Flashcards

Regulation of GI Function - Wondisford 2/17/16 Flashcards

1
Q

functional layers of GI tract

A

**pay attn to locations of nerve plexuses**

  1. mucosa
  2. submucosa : contains Meissner’s/submucosal plexus (mostly glandular secretion)
  3. muscularis : circular muscle + longitudinal muscle : sandwich Auerbach’s/myenteric plexus (mostly muscle movement)
  4. serosa/adventitia : inflammation can cause gut to stick together

mucosa/submucosa separated by mucosa muscularis

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2
Q

innervation of GI tract

A

both intrinsic innervation (enteric nervous system) and extrinsic innervation (via ANS)

enteric nervous system

  • “little brain” bc of extensive interconnectedness of submucosal and myenteric plexuses
  • innervated by ANS
  • derived from migrating NC cells
  • contains PSNS ganglia and postgang neurons

autonomic nervous system

  • PSNS: craniosacral
    • cranial hits foregut/midgut [till around spenic flexure]
    • sacral hits hindgut (desc colon onwards)
  • SNS: thoracolumbar
    • celiac ganglion&sup mesenteric gang: foregut/midgut
    • inf mesenteric gang: hindgut
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3
Q

neurotransmitters of the ANS: basics

A

preganglionic: always cholinergic (Ach)

PSNS

  • pre: cholinergic/Ach
  • post: cholinergic/Ach [various organs]

SNS

  • pre: cholinergic/Ach
  • post: adrenergic & an exception
    • norepi/epi (adrenal medulla) [various organs]
    • Ach [sweat glands]
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4
Q

ANS neurotransmitters effects

Ach

norepi

A

Ach

  • promotes sm muscle contraction, relaxes internal sphincters
  • increases salivary, gastric, pancreatic secretion

norepi

  • relaxes sm muscle, contracts internal sphincters
  • decreases secretions
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5
Q

GI regulatory channels

A

endocrine: must travel in blood, act at a distance

  • gastrin
  • CCK
  • secretin
  • GIP
  • GLP-1

paracrine: no blood travel, act locally

  • somatostatin
  • histamine

neurocrine: specialized paracrine (released from a neuron of the GI tract) involving a neurotransmitter

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6
Q

neurotransmitters in ENS

A
  • Ach (PSNS-pregang): smooth muscle contraction, sphincter relax, increase secretion
  • norepi (SNS-mostly postgang): smooth muscle relax, sphincter contract, decrease secretion
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7
Q

vasoactive intestinal polypeptide (VIP)

A
  • relaxes smooth muscle
  • increases secretions

gets gut going

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8
Q

substance P

A
  • cosecreted with Ach
  • contracts smooth muscle
  • increases secretion

Ach helper

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9
Q

enkephalins (opiates)

A
  • contracts smooth muscle
  • contracts sphincters
  • decreases secretions

overall, opiates cause constipation - disrupts rhythmic propulsion

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10
Q

neuropeptide Y

A
  • relaxes smooth muscle
  • decreases secretions
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11
Q

gastrin releasin peptide (GRP)

aka

Bombesin

A
  • increases gastrin secretion
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12
Q

GI hormones

A
  1. gastrin
  2. cholecystikinin (CCK)
  3. secretin
  4. incretins (GIP, GLP-1)
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13
Q

gastrin: secretion and function

A
  • structurally related to CCK
  • 17 aa peptide (little form) secreted from…
    • antrum cells of stomach
    • G cells of duodenum
    • pancreatic islets
  • 34 aa peptide (big form) secreted at low levels between meals
  • fx
    • increase gastric H secretion
    • grow gastric mucosa
    • increase gastric motility
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14
Q

regulation of gastric acid secretion:

gastrin secretion

A
  • gastrin secretion stimulated by
    • peptide ingestion
    • vagal stimulation of G cells
  • vagal stimulation of G cells
    • ​PSNS: exception to Ach rule: gastrin releasing peptide (GRP) stimulates GRP-R on G cells
  • paracrine inhibition of G cells (by D cells)
    • ​luminal acid in antrum stimulates D cells to produce somatostatin
    • stomatostatin acts in paracrine fashion on G cells to block gastrin secretion
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15
Q

regulation of gastric acid secretion:

gastrin action/gastric acid secretion

[meds to reduce acid secretion]

A

gastrin can stimulate parietal cells to release gastric acid both directly and indirectly

direct stimulation

  • binds to parietal cells via CCKB receptor

indirect stimulation : MORE POWERFUL

  • binds to ECL cells via CCKB receptor
  • ECL cells release histamine
  • histamine activates parietal cells via H2R

clinical connection! stomach acid reduction via H2 blockers (faster), proton pump inhibitors (stronger)

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16
Q

phases of gastric acid secretion

A

ALL INVOLVE GASTRIN

  1. cephalic: sight/smell/taste stimulates vagus; 30% gastric acid secreted
  2. gastric: distension triggers ENS and vagal systems and antrum gastrin release in response to peptides; 60% of gastric acid secreted
  3. intestinal: peptides in duodenum stimulates G cells to produce gastrin; 10% gastric acid secreted
17
Q

CCK (cholecystikinin)

A
  • 3 forms (58, 33, 8 aa long) but all with a 5 aa conserved sequence
    • same sequence is conserved in gastrin
  • binds to CCKA receptor (gastrin binds to CCKB)
  • secreted from I cells in duodenum and jejunum in response to fat and protein
  • fx
    • contracts gallbladder and relaxes Sphincter of Oddi: gets bile out to emulsify fat
    • stimulate enzyme secretion from exocrine pancreas: gets pacreatic enzymes out to digest proteins
    • inhibits gastric emptying: tells stomach to pause until ready for more
    • promotes growth of gallbladder and exo pancreas
18
Q

secretin

A
  • 27 aa
    • part of a larger family of proteins incl VIP, GIP, GLP-1, glucagon
  • secreted by S cells in duodenum and jejunum in response to H+ and fatty acids
  • fx
    • promotes secretion of HCO3 from pancreas and bile to neutralize stomach acid
    • neutralization imp for both luminal protection and fat abs (lipases denatured in low pH)
19
Q

incretins

A

GIP (glucose-dependent insulinotropic peptide) and GLP-1 (glucagon-like peptide 1) are the main players

  • released from intestine in response to glucose, protein, or fat load
    • only GI hormone that will respond to any nutrient load!!!
    • ​duodenum K cells: GIP
    • ileum and colon L cells: GLP-1
  • ​​​fx
    • ​augment insulin release from pancreatic beta cells only in presence of glucose
    • augmentation role and glucose requirement: failsafe to make sure you won’t become hypoglycemic
20
Q

GI reflexes: local

A

local reflexes entirely within ENS controlling…

  • secretion
  • peristalsis
  • mixing contractions
21
Q

GI tract reflexes: extrinsic

A
  1. gastrocolic: signals from stomach signal to cause evacuation of colon
  2. enterogastric: signals from small int inhibit stomach motility/secretion
  3. colonoileal: signals from colon inhibit ileal emptying (into colon)
22
Q

GI tract reflexes: cognitive awareness

A
  1. vomiting reflex
  2. pain reflex: general inhibition of whole GI tract
  3. defecation reflex: signal from colon to spinal cord, back to colon
23
Q

GI control of food intake

A

postive: hypothalamic input

  1. sight/smell/taste signals from cerebral cortex
  2. Ghrelin from empty stomach

negative: hypothalamic input

  1. fullness signals from stomach afferents
  2. GI hormones: insulin, PYY, CCK
  3. adipose tissue: leptin
24
Q

3 types of GI reflexes

A
  1. local: ENS
  2. extrinsic
  3. cognitive awareness

Gastrointestinal System (35 decks)

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