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z:Physl 210A/B > GIT Lec 3: Stomach > Flashcards

GIT Lec 3: Stomach Flashcards

1
Q

Stomach (def.)

A

-muscular saclike organ between esophagus and small intestine

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2
Q

Functions of stomach

A
  • storage of food
  • mechanical breakdown of food
  • chemical breakdown of food
  • control rate food enters the small intestine
  • secretes intrinsic factor for vit B12 absorption in ileum
  • very little absorption
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3
Q

mechanical/chemical breakdown of food reduces

A

food to fragments of protein, polysacc., droplets of fat, salt, water chyme

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4
Q

chemical breakdown of food in the stomach involves

A
  • the secretion of pepsinogen (active form: pepsin)

- the secretion of HCl

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5
Q

HCl secretion in the stomach does these things:

A
  • dissolving food
  • partially digesting macromolecules
  • sterilization of food
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6
Q

Vit B12 is needed for

A
  • red blood cell production

- deficiency: pernicious anemia- red blood cell deficiency

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7
Q

Very little absorption occurs across stomach – exemptions

A
  • water
  • ethanol
  • lipophilic molecules
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8
Q

Parts of the stomach

A
  • fundus (top of layer)
  • body
  • antrum (bottom of layer)
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9
Q

Fundus + body

A
  • thin layer of smooth muscle

- secrete mucous, pepsinogen, HCl

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10
Q

Antrum

A
  • thicker layer of smooth muscle

- secrete mucous, pepsinogen, gastrin (hormone)

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11
Q

exocrine

A

-secreted onto an epithelial surface without passing into blood

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12
Q

Major exocrine secretion of stomach

A
  • mucous (protective coating over stomach epithelium to avoid self-digestion
  • HCl (hydrolysis of proteins)
  • pepsinogen (digestion of proteins)
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13
Q

Minor secretion of stomach

A
  • intrinsic factor - Vit B12
  • gastrin (endocrine)- stimulates HCl production + stomach motility
  • histamine (paracrine) - stimulates HCl production
  • somatostatin (paracrine) - inhibits HCl production
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14
Q

generalized gastric gland cells

A

-mucous cells (top), parietal cells, chief cells, enteroendocrine cells (G-cells), ECL cells, D-cells

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15
Q

Chief cells

A

found: gastric glands in all regions
secrete: pepsinogen (inactive precursor to pepsin)

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16
Q

pepsinogen + acid ( acid cleaves)

A

pepsin (increase protein digestion)

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17
Q

zymogen/proenzyme

A
  • inactive precursor of an enzyme

- requires a biochemical change for it to become an active enzyme

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18
Q

Enteroendocrine cells (G-cells)

A

found: gastric glands in antrum
secrete: gastrin

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19
Q

ECL cells

A

aka Enterochromaffin-like cells

found: all regions but especially antrum
secrete: histamine (paracrine) – HCl release

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20
Q

D-cells

A

found: all regions but more in antrum
secrete: somatostatin – inhibition of HCL release

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21
Q

Parietal cell (all expect specialized structure)

A
  • aka oxyntic cell
  • found in gastric glands in fundus/body regions
  • secrete: HCl +intrinsic factor
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22
Q

Parietal cell (specialized structure)

A
  • has canaliculi (apical side)- increase SA + secretion in stomach lumen
  • lot of mitochondria (acid secretion needs energy)
  • actively secreting cell have easy to see canaliculus
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23
Q

Acidification of stomach lumen

A
  • stomach secretes 2L of 0.1 M H+ Cl-/day

- lumen pH 1 vs cytosol (parietal cell) pH 7

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24
Q

Transporters in parietal cells acidify

A

the stomach + maintain neutral pH in cell

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25
Q

5 proteins important of acidification of stomach lumen

A
  1. Carbonic anhydrase (CA)
  2. H+/K+ ATPase
  3. Cl-/HCO3- exchanger
  4. K+ channels
  5. Cl- channels
26
Q

Carbonic anhydrase (CA)

A
  • in cytosol
  • catalyzes formation of H2CO3 = H2O + CO2
  • H2CO3 dissociates into H+ (for secretion into lumen) & HCO3-
27
Q

H+/K+ ATPase

A
  • luminal membrane
  • pumps H+ into lumen in exchange for K+ into cell
  • active transport (K+ in, H+ out), high [K] in , {H+] out
  • electroneutral
28
Q

Cl-/HCO3- exchanger

A
  • basolateral membrane
  • secondary active transport
  • maintains neural cellular pH
  • Cl- in , HCO3- out
29
Q

as [K+] increases in cell and reaches threshold

A
  • K+ channels open

- Cl- channels open

30
Q

K+ channels

A
  • recycled back into stomach lumen
  • diffusion through channel
  • loss of positive charge (compensated by Cl- secretion)
31
Q

Cl- channels

A
  • leaks back in stomach lumen
  • diffusion through channel
  • compensated for loss of positive charge through K+ channels
32
Q

4 chemical messengers regulate insertion of H+/K+ ATPase in luminal membrane

A
  • gastrin (hormone)
  • acetylcholine (neurotransmitter)
  • histamine (paracrine)
  • somatostatin (paracrine)
32
Q

Histamine potentiates (increase)

A

the effects of gastrin + ACh

33
Q

Pepsinogen secretion +activation

A
  • secreted by chief cells, stimulated by ENS (enteric nervous system) -parallel release of HCl
  • cleaved by acidic pH= pepsin
  • inactive form= prevents autodigestion
  • unactivated when it enters small intestine
34
Q

The phases of Gastric secretion

A

1) Cephalic phase
2) Gastric phase
3) Intestinal phase

35
Q

Cephalic phase of Gastric secretion

A
  • anticipatory, excitatory

- via vagus nerve

36
Q

Gastric phase of Gastric secretion

A
  • major phase, excitatory

- via gastrin

37
Q

Intestinal phase of Gastric secretion

A

-inhibitory due to the presence of acid, fat, hypertonic solution in duodenum

38
Q

Regulation of gastric secretion: directly increase acid secretion

A
  • ACh
  • gastrin
  • histamine
39
Q

Regulation of gastric secretion: directly decrease acid secretion

A

-somatostatin

40
Q

Regulation of gastric secretion: indirectly increase acid secretion

A
  • Ach stimulates gastrin from G-cells
  • Ach stimulates histamine from ECL cells
  • Ach inhibits somatostatin from D-cells
  • Gastrin stimulates histamine
41
Q

When acid secretion is high

A
  • parasymp. input is reduced (cephalic pause)
  • acid inhibits release of gastrin
  • somatostatin released
42
Q

Somatostatin release increases due to

A
  • reduced parasymp. inhibition of D cell

- acid secretion

43
Q

high Somatostatin concentration

A
  • inhibits acid secretion from parietal cell
  • inhibits histamine release from ECL cell
  • inhibits gastrin release from G cell
44
Q

empty stomach size

A
  • small diameter (50 ml)

- slightly larger than small intestine

45
Q

stomach size (meal)

A
  • meal +smooth muscle relaxation

- stomach can increase to 1.5L with increasing pressure

46
Q

smooth muscle relaxation (stomach)

A

-mediated by parasym. nerves to ENS

47
Q

peristaltic waves stimulated by … and involve

A

food

  • weak contractions in body of stomach
  • powerful contractions in antrum
48
Q

powerful contractions in antrum

A

-mixes luminal contents +causes closure of pyloric sphincter

49
Q

closure of pyloric sphincter

A
  • small amounts of contents released to duodenum

- most contents forced back to body of stomach to mix with enzymes + acid

50
Q

electrical basis of stomach motility

A
  • stomach has pacemaker cells- set basic electrical rhythm

- excitatory hormones +neurotransmitters determine strength of contraction

51
Q

Vomiting centre is in

A

-medulla

52
Q

vomiting centre (medulla) affected by

A
  • pressure of CNS, psychogenic (sights, smells)
  • motion sickness/inner ear infection
  • GIT disturbances
  • alcohol
  • toxins on chemoreceptors
53
Q

vomiting action

A

-nausea, saliva, breath held in mid-inspiration
-glottis closes off trachea
-lower esophageal sphincter + esophagus relaxes
-diaphragm + abdominal muscles contract
-reverse peristalsis moves upper intestinal contents into stomach into esophagus +mouth (soft palate raised)
vomit

54
Q

Benefits of vomiting

A

removal of harmful substances before absorption, less likely to take substance again

55
Q

Negative consequences of vomiting

A

dehydration, loss of slats, metabolic alkalosis to loss of H+, acid erosion off tooth enamel

56
Q

Ulcer (defintion)

A

-damaged/eroded area of GIT mucosa, usually in acidic regions (esophagus, stomach, duodenum-most common)

57
Q

Ulcers physiological cause

A

-imbalance of acid/pepsin + mucous/HCO3-

58
Q

Ulcers physiological cause affected by

A
  • helicobacter pylori infection
  • NSAIDS -aspirin,ibuprofen (decrease prostaglandins)
  • smoking
  • excessive alcohol
  • stress (unlikely)
  • gastrinomas (rare)
59
Q

Ulcers treatment

A
  • antibiotics
  • H+/K+ ATPase inhibitor
  • Histamine (H2) antagonist
  • prostaglandin type drugs
60
Q

Gastric bypass surgery

A

-stomach bypass (also duodenum avoided)

61
Q

Gastric bypass surgery consequences

A
  • lack of intrinsic factor
  • acid treatment of food
  • nutrients reaches large intestine (gas)

z:Physl 210A/B (28 decks)

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