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Block D - Digestion and Metabolism > Physiology -- Gastric Secretion > Flashcards

Physiology -- Gastric Secretion Flashcards

1
Q

Volume of mixed gastric juice produced per day

A

1.5 - 2 L/d

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2
Q

Ionic composition of mixed gastric juice

A
  • Na+
  • K+
  • Cl-
  • H+

Isotonic*

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3
Q

pH of mixed gastric juice

A

1 - 2

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4
Q

Proteins found in mixed gastric juice

A
  • Pepsinogen
  • Intrinsic factor
  • Mucin
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5
Q

Composition of fluid secreted by cardiac and pyloric glands

A

Alkaline, mucin-rich fluid

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6
Q

Location of main gastric glands

A

Fundus and Corpus

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7
Q

Cells of gastric glands that secrete HCl

A

Parietal (oxyntic) cells

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8
Q

Cells of gastric glands that secrete pepsinogen

A

Chief cells (zymogenic)

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9
Q

Cells of gastric gland that secrete mucin

A

Mucous neck cells

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10
Q

Describe the ionic concentrations of the various maxied gastric juice ions based on the secretory rate of this substance

A
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11
Q

Explain the 2 component theory of gastric secretions

A

Comprised of non-parietal (secrete small volume) and parietal components (secrete large volume)

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12
Q

Ions secreted by non-parietal cells

A
  • Na+
  • K+
  • Cl-
  • HCO3-
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13
Q

Quantitty of Na+ secreted by non-parietal cells

A

150 mEq/L

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14
Q

Quantity of K+ secreted by non-parietal cells

A

10 mEq/L

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15
Q

Quantity of Cl- secreted by non-parietal cells

A

115 mEq/L

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16
Q

Quantity of HCO3- secreted by non-parietal cels

A

45 mEq/L

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17
Q

Resultant pH from non-parietal secretions

A

pH = 7.6

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18
Q

Quantity of H+ secreted by parietal cells

A

150 mEq/L

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19
Q

Quantity of Cl- secreted by parietal cells

A

150 mEq/L

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20
Q

Resultant pH of parietal secretions

A

pH = 0.8

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21
Q

At low rates, what is the contribution of parietal cells?

A

Low

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22
Q

At high rates of secretion, what is the contribution of parietal cells

A

High

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23
Q

Where does HCl secretion occur in the parietal cell?

A

Canaliculi

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24
Q

Describe the role of Cl- in the canaliculi

A

Cl- actively transported across canalicular membrane (yellow)

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25
Q

Describe the role of H+ in the canaliculi

A

H+ available from dissociation of intracellular water (green) is actively pumped into canaliculi in exchange for K+ (blue)

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26
Q

Consequence of H+ secretion on parietal cell pH and the response to this

A

Excess OH- = increased intracellular pH –> Increased CO2 diffusion from plasma (together with cellular metabolic CO2) combines with water in presence of carbonic anhydrase –> H2CO3- (red)

H2CO3- reacts with excess OH- to yield H2O and HCO3-. The latter diffuses into the circulation, restoring intracellular status quo and gives rise to increased alkalinity in the venous blood

27
Q

Effect of proton pump inhibitors

A

Block H+/K+ pump = suppression of acid secretion for up to 48 hours

28
Q

3 functions of HCl in stomach

A
  • Precipitates soluble proteins
  • Denatures proteins
  • Activates pepsin and provides optimal pH for its activity
29
Q

How is pepsinogen activated?

A

Acidic environment from HCl (pH<6) and autocatalysis from pepsin

30
Q

Pepsin function

A

Breakdown of protein to polypeptides (in an environment of pH 2 - 3)

31
Q

2 other gastric enzymes

A

Gelatinase

Lipase

32
Q

Function of intrinsic factor

A

Required for absorption of physiologically adequate amounts of Vitamin B12 (complexes in the small intestine for absorption in the ileum)

33
Q

What kind of molecule is intrinsic factor?

A

Glycoprotein

34
Q

Describe the layers of substances between the stomach lumen and the surface epithelial cells

A
  • Mucous gel (muci-bicarbonate layer)
  • Gastric mucosal barrier (GMB) on apical surfaces and in tight functions
35
Q

Describe the vicious cycle of damage to mucosal cells

A
36
Q

3 barrier breakers of the GMB and mucous gel

A
  • Aspirin
  • Ethanol
  • Bile
37
Q

Consequence of damage to protective mucous layer and GMB in stomach

A

Disruption of:

  • Mast cells
  • Lysosomes
  • Capillary endothelium
38
Q

4 protective mechanisms for the integirty of the gastric mucosa

A
  • Muci-bicarb layer
  • Gastric mucosal barrier (most important)
  • Rapid cell turnover
  • Effective blood flow
39
Q

5 trophic factors for re-epithelialization of gastric mucosa

A
  • Non-gut hormones
  • Gut hormones
  • Nervous stimulation
  • Luminal nutrients
  • Prostaglandins
40
Q

Function of prostaglandins in gastric mucosa protection (cytoprotection)

A
  • Depress HCl secretion
  • Promote mucin and HCO3- secretion
  • Increase blood flow
41
Q

What accounts for 35% of gastric ulcers?

A

Aspirin and other NSAIDs

42
Q

How does aspirin cause gastric ulcers?

A
  • Local destruction of GMB
  • Systemic inhibition of prostaglandin synthesis = loss of cytoprotection
43
Q

Describe gastric secretions during fasting

A

Basal

44
Q

Describe the causes of postprandial gastric secretions and by what proportion each component is responsible

A
  • 30% cephalic (psychic and gustatory)
  • 60% gastric
  • 10% intestinal
45
Q

Describe the neural regulation of gastric secretions

A

Vagal and sympathetic influences affecting parietal, peptic and mucous secretions + vasodilation

46
Q

What mediates the cephalic phase of gastric secretions?

A

Vagus

47
Q

Consequence of vagotomy to the stomach in terms of gastric secretions

A

Abolish the cephalic phase

48
Q

3 mechanisms of the gastric phase of secretion

A
  • Enteric reflex
  • Neural
  • Hormonal
49
Q

Describe the enteric reflex of the gastric phase of secretions

A

Distention stimulates local enteric reflex

50
Q

Describe the neural mechanism of the gastric phase of gastric secretions

A

Vago-vagal reflex in response to distension

51
Q

Describe the hormonal mechanisms for the gastric phase of gastric secretions

A

Amino aicds or partially digested proteins form secretagogues that stimulate the release of gastrin into the portal blood, which stimulates parietal cells to secrete HCl

52
Q

Where is gastrin secreted from?

A

G cells

53
Q

4 causes for gastrin release from G cells

A
  • Secretagogues
  • Enteric reflexes
  • Vagal stimulation
  • Vago-vagal reflexes
54
Q

When does maximal output of acid occur in the stomach?

A

Simultaneous stimulation of the parietal cells by both gastrin AND ACh

55
Q

Define potentiation in terms of gastric secretions

A

Said to occur between 2 stimulants if the response to their simultaneous admnistration escheeds their macinal response when each is administered alone

56
Q

Describe the self-regulating cycle of gastrin release

A
57
Q

2 physiological roles of gastrin

A

HCl secretion

Trophic effect

58
Q

What substance is found in large proportions in the gastric mucosa?

A

Histamine

59
Q

Effect of histamine administration on gastric secretions

A

Elicits large volume of gastric juice with lost of HCl

60
Q

Describe the permissive hypothesis

A

Histamine is constantly released and [resented (in paracrine fashion) to the parietal cells as a tonic background, sensitizing them to other stimuli

61
Q

Blocking the tonic background of histamine by H2-antagonists had what effect on secretions?

A

Inhibition of acid secretion in response to ACh and gasttin

62
Q

Describe the duodenal excitatory component of gastric secretions

A

Secretagogues in the duodenum may cause secretion of gastrin and entero-oxyntin in the portal blood to stimulate parietal cells into making more HCl

63
Q

2 components of the intestinal phase of gastric secretions

A
  • Enterogastric reflex
  • Enterogastrone hormonal complex

Both INHIBITORY

Block D - Digestion and Metabolism (29 decks)

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