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ACVIM Specialty 2023 > GI: Physiology > Flashcards

GI: Physiology Flashcards

1
Q

What two neurologic plexuses lie within the GI tract and form the intrinsic nervous system? Where are they located?

A

Submucosal plexus: between the submucosa and the circular muscle layer
Myenteric plexus: between the circular muscle and longitudinal muscle

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2
Q

Postganglionic neurons of the parasympathetic nervous system have two classifications based on the neurotransmitter produced. Name them

A

Cholingergic: release acetylcholine
Peptidergic: release peptides such as substance P and vasoactive inhibitory peptide (VIP)

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3
Q

Name 3 effects of acetylcholine (parasympathetic stimulation) on the GI tract

A

Contraction of smooth muscle, relaxation of sphincters, increased secretion (salivary, gastric, and pancreatic)

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4
Q

Name 3 effects of norepinephrine (sympathetic stimulation) on the GI tract

A

Relaxation of smooth muscle, contraction of sphincters, increased salivary secretion

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5
Q

Name 2 effects of vasoactive intestinal peptide (VIP) on the GI tract

A

Relaxation of smooth muscle sphincters (receptive relaxation in the stomach, increased intestinal and pancreatic secretion

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6
Q

Name 2 effects of neuropeptide Y on the GI tract

A

Relaxation of smooth muscle (inhibits motility), decreased intestinal secretion

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7
Q

Name 2 effects of substance P on the GI tract

A

Secreted with parasympathetic stimulation: contraction of smooth muscle, increased salivary secretion

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8
Q

Name 4 gastrointestinal hormones:

A

Gastrin, cholecystokinin, secretin, GIP

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9
Q

Where is gastrin produced?

A

G cells in the antrum of the stomach

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10
Q

What stimulates gastrin secretion?

A

Ingestion of protein (small peptides, amino acids - phenylalanine and tryptophan most effective), distention of the stomach, vagal stimulation (gastrin releasing peptide)

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11
Q

Name 2 effects of gastrin

A
  • Increases H+ secretion by the parietal cells
  • Stimulates growth of the gastric mucosa
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12
Q

What inhibits gastrin secretion?

A

Low pH of gastric contents, somatostatin

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13
Q

What cells produce cholecystokinin (CCK)?

A

I cells of the duodenal and jejunal mucosa

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14
Q

What stimulates CCK production?

A
  • Monoglycerides and fatty acids (NOT triglycerides)
  • Small peptides and amino acids
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15
Q

Name the 5 actions of CCK

A
  1. Contraction of the gallbladder/relaxation of the sphincter of Oddi to eject bile
  2. Secretion of pancreatic enzymes
  3. Secretion of bicarbonate from the pancreas
  4. Growth of the exocrine pancreas and gallbladder
  5. Inhibition of gastric emptying
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16
Q

What cells produce secretin?

A

S cells of the duodenum

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17
Q

What stimulates secretion production?

A

H+ and fatty acids in the lumen of the small intestine

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18
Q

What is the function of secretin?

A
  • Promote secretion of pancreatic and biliary HCO3- to neutralize stomach acid
  • Inhibits effects of gastrin on parietal cells
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19
Q

Glucose-dependent insulinotropic peptide (GIP) is secreted by what cells?

A

K cells of the duodenal and jejunal mucosa

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20
Q

What stimulates GIP secretion?

A

All 3 major nutrients: glucose, amino acids, fatty acids

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21
Q

What is the effect of GIP?

A
  • Stimulation of insulin secretion by the pancreatic beta cells
  • Inhibition of gastric H+ secretion
  • Slows gastric emptying
  • Stimulates lipogenesis
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22
Q

Where is motilin secreted and what does it do?

A
  • Secreted from the upper duodenum during fasting states by M cells
  • Regulates interdigestive myoelectric complexes
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23
Q

What cells secrete somatostatin? In response to what stimulus?

A

D cells of the gastrointestinal mucosa in response to decreased luminal pH

24
Q

What is the effect of somatostatin?

A

Inhibits secretion of other GI hormones, inhibits gastric H+ secretion

25
Q

What are slow waves?

A

Oscillating depolarization and repolarization of the membrane potential of the GI smooth muscle - frequency varies along the tract and sets the frequency of contractions

26
Q

Where do slow waves originate?

A

In the interstitial cells of Cajal, within the myenteric plexus

27
Q

The parietal cells are located within the gastric oxyntic glands and produce what?

A

HCl and intrinsic factor (dogs)

28
Q

The chief cells are located within the gastric oxyntic glands and produce what?

A

Pepsinogen

29
Q

Describe the function of carbonic anhydrase

A

Converts CO2 and H2O to H2CO3

30
Q

How is H+ secreted into the gastric lumen?

A

Intracellular CO2 and H2O combine to form H2CO3, which dissociates into H+ and HCO3-. H+ is secreted into the lumen through H+-K+ ATPase

31
Q

How is Cl- secreted into the gastric lumen?

A

HCO3- is transported into the blood via HCO3-Cl- exchanger. Cl- then follows the concentration gradient out into the lumen

32
Q

What 3 substances stimulate H+ secretion?

A

Acetylcholine, histamine (most important), and gastrin

33
Q

What is the effect of acetylcholine on the LES? What is the effect of nitric oxide?

A

Acetylcholine - increases LES contraction
NO - relaxes the LES

34
Q

Name 3 causes of cobalamin deficiency?

A
  1. EPI (cats - failure to make intrinsic factor)
  2. Small intestinal bacterial overgrowth (bacteria consume B12)
  3. Malabsorption
35
Q

What gene mutation is responsible for congenital cobalamin deficiency? What breeds is it found in?

A

Cubam receptor mutation - Border Collies, Beagles, Australian shepherd, Giant Schnauzer, Shar Pei

36
Q

Name two effects of histamine on the GI tract

A

Stimulates synthesis and insertion of H+/K+ ATP on parietal cells
Stimulates HCL release

37
Q

The most important determinant of time and rate for gastric muscle contraction is:

A

Rate of the slow waves

38
Q

What gastric cell type is responsible for production of histamine?

A

Enterochromaffin cells

39
Q

What effect do prostaglandins have on the stomach?

A

Modulate blood flow, mucus, and HCO3 production

40
Q

What is the major source of energy for enterocytes of the small intestine?

A

Glutamate

41
Q

Where are B lymphocytes present within the GI tract?

A

Peyer’s patches, LNs
Plasma cells are throughout the pericryptal lamina propria

42
Q

In the dog’s lamina propria, which T cell predominates? In cats?

A

Dogs: CD4+
Cats: CD8+

43
Q

Dendritic cells that induced Tregs are positive for what marker?

A

CD103+

44
Q

What are the purpose of CD4+ Th1 cells? Name 2 cytokines they secrete

A

Mediate cellular immunity in response to intracellular pathogens or cancer - activate CD8+ cells and macrophages. Secrete IFNgamma and IL-2

45
Q

What are the purpose of CD4+ Th2 cells? Name 2 cytokines they secrete

A

Promote B cell activation, class switching and differentiation to plasma cells. Secrete IL-4, 5, 6 and 13

46
Q

Treg cells are positive for what markers? What cytokine do they predominately secrete?

A

CD25+FoxP3+, IL-10

47
Q

What are the 3 signals needed to activate a B cell?

A
  1. Recognition of antigenic epitopes by the B cell receptor
  2. Direct intercellular molecular interactions with T cells
  3. Th2 cytokines acting on a B cell cytokine receptor
48
Q

How is IgA transported to the luminal surface of enterocytes?

A

Binds to the polymeric immunoglobulin receptor (pIgR) on the basolateral surface, passes through the enterocyte, and is delivered to the luminal surface, where pIgR is cleaved to form the secretory component, which stays with IgA to protect it from degradation

49
Q

How does IgA function on mucosal surfaces?

A

Binds to its respective antigen and neutralizes it

50
Q

What receptor does IgE bind to on mast cells to result in mast cell degranulation?

A

Fc-epsilon-R1

51
Q

What cells produce glucagon?

A

Pancreatic islet alpha cells

52
Q

What effect does glucagon have on the liver’s handling of carbohydrates?

A

Causes glycogenolysis and gluconeogenesis (opposite of insulin)

53
Q

What do the pancreatic F cells (aka PP cells) produce?

A

Pancreatic polypeptide

54
Q

What do the pancreatic delta cells produce?

A

Somatostatin

55
Q

What do the pancreatic epsilon cells produce?

A

Ghrelin

56
Q

What is the function of pancreatic polypeptide?

A

Inhibits pancreatic secretion of fluid and enzymes, stimulates gastric acid secretion (antagonist of CCK)

ACVIM Specialty 2023 (38 decks)

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