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Physiology Part 1 > Lec 18 Control of GI function > Flashcards

Lec 18 Control of GI function Flashcards

1
Q

What are the layers of GI tract in order?

A
  • epithelium
  • lamina propria
  • muscularis mucosa
  • submucosa
  • submucosal plexus
  • circular muscle
  • myenteric plexus
  • longitudinal muscle
  • serosa
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2
Q

Where is auerbach’s plexus?

A

aka myenteric plexus

- between circular and longitudinal muscle

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3
Q

Where is meissner’s plexus?

A

aka muscosal plexus

- between submucosa and circular muscle

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4
Q

pathway of GI hormone action?

A
  • endocrine cell of GI tract secretes hormone

- -> enters portal circulation –> liver –> systemic circulation –> target cell

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5
Q

pathway of GI paracrine action?

A
  • endocrine cell of GI tract secretes –> diffuses to target cells
  • release hem transmitters into interstitial space surrounding nearby cells
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6
Q

pathway of GI neurocrine action?

A
  • neuron of GI tract secretes at action potential to target cell
  • reach target receptor on adjacent tissue
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7
Q

pathway of GI autocrine action?

A
  • type of paracrine communication, provides feedback inhibition to reduce further secretion
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8
Q

How does parasympathetic act on GI function? Where does it primarily act?

A
  • stimulates digestion via vagus
  • especially acts at esophagus and stomach
  • diminishes distally
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9
Q

What 2 parts of GI under voluntary response?

A
  • control of swallowing

- contraction of external anal sphincter

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10
Q

3 actions of parasympathetic on GI?

A
  • stimulates flow of saliva
  • stimulates peristalsis and secretion
  • stimulates release of bile
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11
Q

4 actions of sympathetic on GI?

A
  • inhibits flow of saliva
  • inhibits peristalsis and secretion
  • converts glycogen to glucose
  • secretion adrenaline/noradrenaline
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12
Q

What kind of transmitters in parasympathetic innervation of GI [pre and post ganglionic?]

A

preganglionic: ACh

postganglionic ACh or neuropeptide [peptidergic transmitters]

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13
Q

What kind of transmitters in sympathetic innervation of GI [pre and post ganglionic?]

A

preganglionic: ACh
postganglionic: NE

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14
Q

Via what nerves does parasympathetic reach GI?

A
  • vagas

- pelvic cholinergic nerves

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15
Q

Where is parasympathetic stimulation of GI mostly directed [2 places]?

A
  • esophagus + stomach

- decreased effect in distal GI tract

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16
Q

Via what nerves does sympathetic reach GI?

A
  • through splanchnic nerve

- paravertebral, celiac, superior mesenteric, and inferior mesenteric ganglia

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17
Q

Does enteric nervous system have more or fewer neurons than spinal cord?

A

more!

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18
Q

What does myenteric plexus do [2 things]? where is it located?

A
  • in between longitudinal and circular muscle layers
  • provides motor innervation to both layers
  • provides secretomotor innervation to mucosa
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19
Q

Where are cell bodies of the enteric nervous system located?

A

submucosal plexus [meissners]

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20
Q

True or false: most neurons in ENS have only 1 transmitter

A

FALSE – most neurons in ENS release more than 1 transmitter

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21
Q

What is function of NO in ENS?

A
  • primarily inhibitor neurotransmitter
  • responsible for sphincter relaxation
  • formerly called “non-adrenergic, non-cholinergic [NANC]”
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22
Q

Where are GI hormone secreting cells located?

A
  • islets of pancreas

- interspersed between mucosal cells throughout epithelium [columnar cells]

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23
Q

What are GI homrone secreting cells in the mucosa called?

A

enterochromaffin cells

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24
Q

What is the biggest endocrine organ in the body?

A

GI

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25
Q

What are most abundant type of chemical transmitters in GI tract? What is another name for them?

A
  • regulatory peptides

- brain gut peptides

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26
Q

What are 8 things normally secreted in GI as hormones?

A
  • gastrin
  • secretin
  • GIP
  • glucagon, GLP1, GLP2
  • motilin
  • pancreatic polypeptide
  • peptide YY
  • Ghrelin
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27
Q

What are 4 things normally secreted in GI as neuropeptides?

A
  • Gastrin releasing peptide [GRP]
  • VIP
  • substance P; tachykinin
  • neuropeptide Y
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28
Q

What are 2 things secreted in GI as hormones or neuropeptides or paracrine?

A
  • CCK

- somatostatin

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29
Q

Where is gastrin released from? What stimulates/inhibits its release? What type of release/action?

A
  • released from G cells in antrum [mostly] and duodenum
  • stimulated by high pH and AA
  • inhibited by gastric acid [via somatostatin + secretin]
  • mainly as hormone
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30
Q

What are 2 actions of gastrin?

A
  1. promotes gastric acid secretion from parietal cells
  2. acts as growth factor for ECL [enterochromaffin like cells]
    - -> tells ECL to make histamine = indirect parietal stimulation
    - -> in excess can lead to tumors
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31
Q

What does gastrin bind to?

A

CCK receptor

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32
Q

What 3 things act on parietal cell to induce acid secretion? And where do they bind?

A

Gastrin –> CCK receptor
Histamine –> H2 receptor
ACh –> M3 receptor

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33
Q

What are direct and indirect pathways that gastrin activates parietal cell acid secretion?

A

direct: gastrin activates parietal cells to secrete acid
indirect: gastrin tells ECL cells to grow and secrete histamine –> histamine activates parietal to secrete acid

34
Q

What stimulates CCK release?

A
  • amino acids and fatty acids
35
Q

Where is cholecytokinin released from? what type of release

A
  • I cells in proximal small intestine

- mainly acts as hormone

36
Q

What family of proteins is gastrin in?

A

gastrin/CCK family

37
Q

what family of proteins is CCK in?

A

gastrin/CCK family

38
Q

What are 2 main actions of CCK?

A
  • gallbladder contraction
  • stimulates pancreatic enzyme secretion [and HCO3]

also less important: slows gastric emptying, induces satiety

39
Q

What is secretin secreted from? where is it released from?

A
  • S cells in proximal small intestine
40
Q

What stimulates secretion of secretin?

A
  • gastric acid [pH < 4.5]

- other acid [fatty acid, bile acid, spicy food, EtOH]

41
Q

What are the 3 actions of secretin?

A
  • induces secretion HCO3 from pancreas/duodenum/bile duct = MAIN FUNCTION

also

  • inhibits gastrin release [and thus inhibits gastrin]
  • inhibits intestinal motility
42
Q

What hormone opposes the action of gastrin?

A

secretin

43
Q

What mech is secretin normally secreted?

A

as a hormone

44
Q

What family is secretin part of?

A

secretin/VIP/glucagon/GIP family

45
Q

What is vasoactive intestinal peptide [VIP]?

A

A neuromediator from enteric nervous system

46
Q

What are 3 possible actions of VIP?

A
  • stimulate epithelial cell contraction
  • stimulate smooth muscle [sphincter] relaxation
  • VIP-secreting tumors
47
Q

What are symptoms of a VIP-oma?

A
  • watery diarrhea
  • hypokalemia [low K]
  • achlorhydria [low gastric acid]
48
Q

What is glucagon? Where is it made

A

hormone
made by:
- pancreatic alpha cells
- cells of small intestine/colon [L cells]

49
Q

what is proglucagon? where is it broken down into which things?

A
  • precursor gene transcript
  • in pancreas: processed into glucagon
  • in small intestine: processed to GLP1/2 [glucagon-like peptides]
50
Q

What is function of glucagon?

A

regulate glucose homeostasis [with GLP-1]

51
Q

What is function of GLP-1?

A

regulate glucose homeostasis [with glucagon]

52
Q

What is function of GLP-2?

A

acts as intestinal growth factor, helps maintain GI mucosal mass

53
Q

What other 3 things are in same family as glucagon?

A

secretin/VIP/glucagon/GIP family

54
Q

What is glucose-dependent insulinotropic polypetide [GIP]? Where is it released from

A
  • a hormone

- released from small intestine [k cells]

55
Q

What stimulates GIP release?

A
  • released in response to hyperglycemia
56
Q

What is action of GIP?

A
  • stimulates pancreatic B cells to secrete insulin
57
Q

What x things are in the tachykinin family of proteins?

A
  • substance P

- Gastrin releasing peptide [GRP]

58
Q

what family is substance P? By what 2 mech does substance P act?

A
  • Tachykinin family
  • acts by neurocrine and paracrine
  • in CNS/PNS
59
Q

What are actions of substance P?

A
  • pain sensation [PRIMARY function]
  • pro-inflammation
  • inhibition of: somatostatin, biliary secretion
60
Q

What two things does substance P inhibit?

A
  • somatostatin

- biliary secretion

61
Q

What family is gastrin releasing peptide [GRP]? What is normal mech of release?

A
  • part of tachykinin family

- neurocrine, released by post-ganglionic parasympathetic

62
Q

What 2 actions of GRP?

A
  • mediates vagal release of gastrin

- stimulates pancreatic secretion and GI motility

63
Q

What is motilin? where is it released from? What family of proteins?

A
  • hormone
  • made in duodenum
  • motilin family of proteins
64
Q

What are actions of motilin?

A
  • binds receptors on smooth muscle through gut = pro-motility
  • increases phase III contraction of MMC [increases peristalsis]
65
Q

What drug is motilin agonist?

A

erythromycin

66
Q

What family of protein is grhelin? Where is it made?

A
  • part of motilin family

- made in gastric fundus [PD1 cells]

67
Q

What proteins are in motlin family?

A
  • motilin

- ghrelin

68
Q

Action of ghrelin?

A
  • increases food intake

- high levels during fasting, low levels when fed

69
Q

What is Prader-Willi syndrome?

A

extra high ghrelin [so always hungry]

70
Q

What family is pancreatic polypeptide [PP]? Where is it released from?

A
  • pancreatic polypeptide family

- released from pancreatic islet cells [PP cells]

71
Q

What stimulates pancreatic polypeptide release?

A
  • vagus
  • amino and fatty acids
  • gastrin/CCK
  • secretin
72
Q

What are functions of pancreatic polypeptide?

A

MAINLY: inhibit pancreatic exocrine secretion
also
- gall bladder contraction
- gut motility

73
Q

What family is peptide YY? WHere is it released from?

A
  • pancreatic polypeptide family

- released from distal small intestine [L cells]

74
Q

What stimulates PYY secretion?

A

meals, fat, bile acids

75
Q

What are the actions of PYY?

A
  • ileal break –> slow small intestine motility to increase absorption time
  • inhibits pancreatic and gastric acid secretion
76
Q

What is neuropeptide YY [NPY]

A
  • neurocrine homologue of PYY
  • found in CNS/PNS
  • binds sam receptors as PYY
77
Q

What is function of NPY?

A
  • mimics PYY [ileal break, inhibition pancreatic/gastric acid secretion]
  • also stimulates appetite
78
Q

What are 4 inhibitory signals of gastric emptying

A
  • low pH –> inhibits secretin
  • AA and fatty A –> inhibit cholecystokinin
  • osmolality –> inhibits vagal afferents
  • carbohydrates –> inhibit PYY
79
Q

Where is somatostatin made? [KNOW THIS CELL NAME]

A
  • D cells in antrum

- also less importantly: by cells in small intestine, pancreatic islets, enteric neurons

80
Q

What 3 things stimulate somatostatin release?

A
  • gastric acid in lumen
  • diet [protein, fat, glucose]
  • muscarinic stimulation
81
Q

What inhibits somatostatin?

A

high pH

82
Q

What are the major actions of somatostatin?

A

GLOBAL INHIBITOR

  • inhibits gastric acid [via G and parietal cells]
  • inhibits pancreatic secretion
  • reduces bile flow
  • slows motility
  • reduces splanchnic blood flow

Physiology Part 1 (37 decks)

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