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Physiology > GI 2 - Gastric Function > Flashcards

GI 2 - Gastric Function Flashcards

1
Q

what are the gastric functions

A

-temporary storage of ingested material
-production of chyme
-meter delivery of chyme to duodenum
- partially sterilize meal
-initiates protein digestion
- produces specialized secretions

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2
Q

what specialized secretions does the stomach produce

A

-HCl acid
-pepsinogen
- intrinsic factor
- mucus
- hormones/paracrines

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3
Q

what is the function in the fundus and body

A

secretion and resevoir

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4
Q

what is the function in the antrum

A

mixing and grinding

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5
Q

what are the 4 ways of gastric motility

A

-receptive relaxation
-peristalsis
- emptying
- migrating motility complex (MMC)

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6
Q

what is the function of receptive relaxation

A

-accommodate the volume of the meal
- reduce pressure prevents gastric reflux and premature gastric emptying

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7
Q

what is the function of peristalsis

A
  • chyme production
    -trituration
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8
Q

what is trituration

A

mix ingested nutrients with gastric secretions, breakdown large particles and increase SA for digestion

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9
Q

how much is emptied into the small intestine per hour

A

200 kcal/hour

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10
Q

what is function of MMC

A

sweep ingested solids that cannot be digested out of stomach and through intestinal tract

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11
Q

when does MMC occur

A

during fasting

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12
Q

how long does MMC take

A

90 mins to get from stomach to colon

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13
Q

what is gastric receptive relaxation initiated by

A

-stretch of gastric or duodenal wall
- protein or fat in duodenum

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14
Q

what hormone mediates receptive relaxation

A

CCK

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15
Q

describe the pathway of gastric receptive relaxation

A
  • stretch, fat, or protein causes CCK release which either does long vaso vagal reflex to the DVC or short ENS reflex using NO and VIP to relax
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16
Q

what is the function of gastric receptive relaxation

A

accommodate increased volume of food and slows emptying

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17
Q

what is gastric peristalsis/trituration generated by

A

pacemaker cells (interstitial cells of cajal) located in GI smooth muscle

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18
Q

describe how peristalsis happens

A

smooth muscle cells undergo spontaneous phases of deploarizations and repolarizations called basic electrical rhythm (BER) of the stomach

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19
Q

what is the frequency of peristalsis/trituration

A

3 times per minute

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20
Q

what are the functions of peristalsis/trituration

A
  • acts to mix and break down gastric contents
    -regulate gastric emptying
    -peristaltic wave forces chyme through pyloric sphincter
  • causes pyloric sphincter to contract reducing volume released to small intestine
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21
Q

what is the rate of gastric emptying influenced by

A
  • solid vs liquid
  • nutrient content
  • force of gastric contractions
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22
Q

how often is 50% of the stomach contents emptied

A

2.5-3 hours

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23
Q

how long does total emptying of the stomach take? small intestine?

A

stomach: 4-5 hours
small intestine: 3-5 hours

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24
Q

how long is transit through the colon

A

8-15 hours

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25
Q

what are factors that increase force of antral contractions which increase gastric empyting

A

-gastrin
- distension of stomach

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26
Q

what are factors that decrease force of antral contractions and decrease gastric empyting

A
  • contents of duodenum
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27
Q

what are enterogastrones

A

hormones secreted by duodenum in response to nutrients and acid in chyme

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28
Q

what are the enterogastrones and what do they each respond to

A
  • CCK: fat and protein
  • secretin: acid
  • GIP: carbohydrate
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29
Q

what is the pathway of how enterogastrones affect gastric emptying

A
  • high acidity, high fat, high AAs, hypertonicity, distension all increase secretion of enterogastrones and stimulate neural receptors
  • enterogastrones directly decrease gastric emptying
  • neural receptors decrease gastric emptying directly though enteric neurons OR long reflexes by increasing SNS efferents and decreasing PNS efferents to decrease gastric emptying
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30
Q

what is the MMC and when does it occur

A

-intervals of strong propulsive contractions that sweep the stomach and small intestine of indigestible material
-occurs in between meals (fasting state)

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31
Q

what hormone is involved in the MMC and what does it work through

A

intrinsic to ENS and involved motilin

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32
Q

when does the MMC stop

A

when meal is ingested

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33
Q

describe gastric glands

A
  • exocrine glands
  • produce gastric juice
    -variety of cell types and secretions
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34
Q

what type of cell is the parietal cell, what does it secrete and what is its function

A
  • exocrine
  • HCl; activation of pepsinogen and sterilization of meal
  • intrinsic factor; vitamin B12 absorption
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35
Q

what type of cell is a chief cell, what does it secrete and what is its function

A

-exocrine
- pepsinogen; protein digestion

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36
Q

what type of cell is a surface mucous cell, what does it secrete and what is its function

A
  • exocrine
  • mucus and HCO3-; gastroprotection
  • trefoil factors; gastroprotection
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37
Q

what type of cell is an ECL cell, what does it secrete and what is its function

A

-paracrine
- histamine
- regulation of gastric secretion

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38
Q

what type of cell is a G cell, what does it secrete and what is its function

A
  • endocrine
  • gastrin
  • regulation of gastric secretion
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39
Q

what do nerves release and what is its function

A

-gastrin releasing peptide; regulation of gastric secretion
- Ach; regulation of gastric secretion

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40
Q

what type of cell is a D cell, what does it release and what is its function

A

-paracrine
- somatostatin
- regulation of gastric secretion

41
Q

what type of cell is a Gr cell, what does it release and what is its function

A
  • endocrine
  • ghrelin
  • stimulates hunger
42
Q

what type of cells are found in corpus gastric glands

A
  • surface mucous cells
  • mucous neck cells
  • parietal cells
  • D cells
  • ECL cells
  • chief cells
43
Q

what is another name for corpus gastric glands

A

oxyntic gland

44
Q

what differentiates oxyntic glands and pyloric glands

A

-oxyntic glands have abundant amounts of parietal and chief cells
- pyloric glands have abundant mucus secreting cells and secrete hormones that regulate gastric function

45
Q

where are oxyntic glands found? pyloric glands?

A

-oxyntic: fundus
-pyloric: antral

46
Q

what is the mechanism of acid secretion by a cell

A
  • CO2 + H2O-> H2CO3 by carbonic anhydrase
    -carbonic acid splits and the HCO3- is transported across the basolateral membrane by the HCO3-/Cl- antiporter into the capillary and creates the alkaline tide
  • the H+ is transported across the apical membrane via the K+ H+ primary active antiporter
  • H+ combines with Cl- in the gastric gland lumen to form HCl
47
Q

what do oxyntic cells have receptors for and what do each hormone do

A

activate: gastrin, histamine, acetylcholine,
inhibit: somatostatin

48
Q

cells secrete up to ____ of HCl and

A

2 L/day; intrinsic factor

49
Q

where are proton pumps located in the oxyntic cell

A

apical membrane

50
Q

what is an example of synergism in the stomach

A

hormones that stimulate oxyntic cell function

51
Q

what does high levels of HCl negatively inhibit

A

gastrin secretion

52
Q

what does gastrin secretion stimulate

A

acid secretion by parietal cells and histamine secretion

53
Q

what does histamine secretion stimulate

A

acid secretion from parietal cells

54
Q

what is an example of an H2 receptor antagonist

A

ranitidine

55
Q

what is the stimulus for neural control of oxyntic cell function

A

stretch of gastric wall

56
Q

describe neural control mechanism of oxyntic cell function

A
  • stimulus causes short reflex using Ach to stimulate parietal cells and chief cells to release gastrin and acid in the oxyntic gland
  • stimulus causes long reflex of vaso vagal reflex to DVC which uses AcH to stimualte oxyntic gland and uses GRP to cause G cells to secrete gastrin
57
Q

what does somatostatin inhibit

A

parietal cells, ECL cells, and G cells

58
Q

what is the pathway of acid release by parietal cells

A
  • G cells release gastrin
  • gastric causes direct release of acid by parietal cells and acts on ECL cell to release histamine which causes acid secretion from parietal cell
59
Q

what are the phases of GI activation

A

-cephalic phase
- gastric phase
- intestinal phase

60
Q

what controls the cephalic phase and when does it occur

A
  • the vagus nerve
  • occurs before contents enter GI tract via vagus nerve
61
Q

what controls the gastric phase

A

-local nervous secretory reflexes
- vagal reflexes
- gastrin histamine stimulation

62
Q

what controls the intestinal phase

A
  • nervous mechanisms
  • hormonal mechanisms
63
Q

what are the stimulants for the cephalic phase of acid secretion

A

sight, smell, taste, thoughts of food

64
Q

what is the mechanism of the cephalic phase

A

-cephalic phase stimuli -> PNS preganglionic neurons -> enteric neurons -> AcH -> parietal cell acid release and stimulates G cell and ECL cell

65
Q

what is the mechanism of the gastric phase

A
  • food in the stomach causes peptides -> G cell -> gastrin -> ECL cell -> histamine -> acid release from parietal cell
  • distenstion from food in the stomach activates neural reflexes -> enteric neurons -> ACh release -> parietal cell acid release and stimulates G cell and ECL cell
66
Q

what is the mechanism of the intestinal phase

A
  • increased H+, distension, osmolarity, fats in duodenum causes release of enterogastrones which inhibit acid release from parietal cell and inhibit G cells
  • increased H+, distension, osmolarity, fats in duodenum -> neural reflex -> ENS -> AcH -> increased acid release from parietal cell
67
Q

what happens during the interdigestive period (fasting)

A
  • acid is secreted at low levels
  • lack of buffer causes low pH in stomach
  • basal secretions stimulated by histamine and Ach
  • gastrin low due to low pH in gastric lumen
68
Q

what is the function of the events in the interdigestive period

A

possibly to sterilize gastric lumen

69
Q

what is the basal secretion rate

A

0-11 mEq/hr

70
Q

what is the stimulated secretion rate

A

10-63 mEq/hr

71
Q

what is the function of acid

A

-facilitates digestion of proteins
- protects against some pathogens
- increases absorption of B12, iron and calcium

72
Q

what are PPIs and what do they do

A
  • proton pump inhibitor
  • binds to and inhibits H+ K+ pump
  • nearly 100% inhibition
  • may have side effects related to functions of acid
    -prescribed to people with severe GERD
73
Q

what is intrinsic factor and what is it secreted by

A

glycoprotein secreted by oxyntic cells

74
Q

how is intrinsic factor secreted

A
  • exocytosis
  • secretion activated by same secretagogues that activate HCl secretion
    -mechanism unknown but different than acid secretion
75
Q

how do inhibitors of proton pump affect intrinsic factor

A

does not inhibit it but reduces its function

76
Q

what is intrinsic factor required for

A

vitamin B12 absorption

77
Q

what is vitamin B12 important in and what would a deficiency cause

A

RBC production
-pernicious anemia

78
Q

what is the function of chief cells

A

secretes pepsinogen by exocytosis to initiate digestion of protein

79
Q

what is pepsinogen activated to pepsin by

A

low pH

80
Q

what is pepsinogen activation to pepsin inactivated by

A

pH greater than 5

81
Q

what does pepsin do

A

protein digestion (not a significant amount)

82
Q

what is the main activation of chief cell function mediated through

A

local and vagal reflexes that release AcH

83
Q

describe the neural control of chief cell function

A

same as oxyntic cell function

84
Q

describe the pathway of activation of pepsinogen in the gastric lumen

A

chief cells secrete pepsinogen
- parietal cell secretes HCl and IF
- Pepsinogen is converted into Pepsin by HCl
- pepsin breaks down protein into peptides

85
Q

what are the stimuli for ghrelin

A

fasting and low body fat

86
Q

what does ghrelin secretion cause

A

-CNS to increase hunger and eating
- tissues to decrease metabolism

87
Q

what is ghrelin produced by

A

endocrine cells located in oxyntic glands

88
Q

what does ghrelin stimulate in the brain

A

hypothalamic NT neuropeptide Y

89
Q

when does ghrelin spike

A

before meal times

90
Q

compare ghrelin levels in someone who lost weight compared to someone who got gastric bypass

A
  • ghrelin levels are higher in someone who has lost weight
91
Q

why doesnt the stomach digest itself

A

gastric mucosal barrier

92
Q

what is the gastric mucosal barrier

A

two hydrophilic layers separated by hydrophobic barrier
- mucus is secreted by mucous cells onto surface of epithelium
- contains long chains of oligosachharides that expand and retain water
- viscoelastic substance that coats surface of gastric epithelial cells
- high pH produced by surface cell secretion of HCO3

93
Q

how does the gastric mucosal barrier limit diffusion of acid through the plane off the gel

A

via viscous fingering

94
Q

what is mucus secretion in the gastric mucosal barrier stimulated by

A

prostaglandins (NSAIDS)

95
Q

what helps stabilize the barrier in the gastric mucosal barrier

A

trefoil proteins

96
Q

where can ulcers be found in the GI tract

A

gastric and duodenal

97
Q

what are the 2 causes of ulcers and what do they do to cause the ulcer

A
  • helicobacter pylori- bacterial infection destroys the gastric diffusion barrier
  • zollinger-ellison syndrome- g cell tumor
98
Q

what is mucosal destruction

A

gastritis causing an ulcer
- mostly oxyntic gland mucosa

99
Q

what are the issues with emptying in gastric disfunction

A

-obstruction
- gastroparesis
- dumping

Physiology (41 decks)

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