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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
Describe the role of H+ in the canaliculi
H+ available from dissociation of intracellular water (green) is actively pumped into canaliculi in exchange for K+ (blue)
26
Consequence of H+ secretion on parietal cell pH and the response to this
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
Effect of proton pump inhibitors
Block H+/K+ pump = suppression of acid secretion for up to 48 hours
28
3 functions of HCl in stomach
* Precipitates soluble proteins * Denatures proteins * Activates pepsin and provides optimal pH for its activity
29
How is pepsinogen activated?
Acidic environment from HCl (pH\<6) and autocatalysis from pepsin
30
Pepsin function
Breakdown of protein to polypeptides (in an environment of pH 2 - 3)
31
2 other gastric enzymes
Gelatinase Lipase
32
Function of intrinsic factor
Required for absorption of physiologically adequate amounts of Vitamin B12 (complexes in the small intestine for absorption in the ileum)
33
What kind of molecule is intrinsic factor?
Glycoprotein
34
Describe the layers of substances between the stomach lumen and the surface epithelial cells
* Mucous gel (muci-bicarbonate layer) * Gastric mucosal barrier (GMB) on apical surfaces and in tight functions
35
Describe the vicious cycle of damage to mucosal cells
36
3 barrier breakers of the GMB and mucous gel
* Aspirin * Ethanol * Bile
37
Consequence of damage to protective mucous layer and GMB in stomach
Disruption of: * Mast cells * Lysosomes * Capillary endothelium
38
4 protective mechanisms for the integirty of the gastric mucosa
* Muci-bicarb layer * Gastric mucosal barrier (most important) * Rapid cell turnover * Effective blood flow
39
5 trophic factors for re-epithelialization of gastric mucosa
* Non-gut hormones * Gut hormones * Nervous stimulation * Luminal nutrients * Prostaglandins
40
Function of prostaglandins in gastric mucosa protection (cytoprotection)
* Depress HCl secretion * Promote mucin and HCO3- secretion * Increase blood flow
41
What accounts for 35% of gastric ulcers?
Aspirin and other NSAIDs
42
How does aspirin cause gastric ulcers?
* Local destruction of GMB * Systemic inhibition of prostaglandin synthesis = loss of cytoprotection
43
Describe gastric secretions during fasting
Basal
44
Describe the causes of postprandial gastric secretions and by what proportion each component is responsible
* 30% cephalic (psychic and gustatory) * 60% gastric * 10% intestinal
45
Describe the neural regulation of gastric secretions
Vagal and sympathetic influences affecting parietal, peptic and mucous secretions + vasodilation
46
What mediates the cephalic phase of gastric secretions?
Vagus
47
Consequence of vagotomy to the stomach in terms of gastric secretions
Abolish the cephalic phase
48
3 mechanisms of the gastric phase of secretion
* Enteric reflex * Neural * Hormonal
49
Describe the enteric reflex of the gastric phase of secretions
Distention stimulates local enteric reflex
50
Describe the neural mechanism of the gastric phase of gastric secretions
Vago-vagal reflex in response to distension
51
Describe the hormonal mechanisms for the gastric phase of gastric secretions
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
Where is gastrin secreted from?
G cells
53
4 causes for gastrin release from G cells
* Secretagogues * Enteric reflexes * Vagal stimulation * Vago-vagal reflexes
54
When does maximal output of acid occur in the stomach?
Simultaneous stimulation of the parietal cells by both gastrin AND ACh
55
Define potentiation in terms of gastric secretions
Said to occur between 2 stimulants if the response to their simultaneous admnistration escheeds their macinal response when each is administered alone
56
Describe the self-regulating cycle of gastrin release
57
2 physiological roles of gastrin
HCl secretion Trophic effect
58
What substance is found in large proportions in the gastric mucosa?
Histamine
59
Effect of histamine administration on gastric secretions
Elicits large volume of gastric juice with lost of HCl
60
Describe the permissive hypothesis
Histamine is constantly released and [resented (in paracrine fashion) to the parietal cells as a tonic background, sensitizing them to other stimuli
61
Blocking the tonic background of histamine by H2-antagonists had what effect on secretions?
Inhibition of acid secretion in response to ACh and gasttin
62
Describe the duodenal excitatory component of gastric secretions
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
2 components of the intestinal phase of gastric secretions
* Enterogastric reflex * Enterogastrone hormonal complex Both INHIBITORY

Block D - Digestion and Metabolism (29 decks)

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