130b/131b - Salivary Gland, Stomach, Pancreas Secretion Flashcards

1
Q

List 3 mechanism that prevent the stomach from digesting itself

A
  • Mucous barrier is impenetrable by acid
  • Any acid that gets neutralized by bicarbonate
  • Any acid that is not neutralized is washed away by blood flow
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2
Q

What is the most powerful stimulator of gastrin secretion in the gastric phase?

A

Stretch

  • Stretch
  • -> Vagus nerve relesases GRP
  • -> G cell stimulation
  • -> Gastrin release
    • -> Histamine release from ECL cells -> HCl from parietal
    • -> HCl from parietal
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3
Q

How does the composition of pancreatic secretion vary with flow rate?

A
  • Low flow
    • Low bicarbonate, high Cl- (iso-osmotic with plasma)
  • High flow
    • High bicarbonate, low Cl-

Higher flow = more stuff from stomach = need more HCO3-

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4
Q

Parietal cell receptor and second messenger pathway activated by ACh?

  • Receptor:
  • 2nd Messenger:
A
  • Receptor: M3 muscarinic
  • 2nd Messenger: Ca2+/IP3
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5
Q

Which hormone most strongly stimulates bicarbonate secretion from the pancreas?

A

Secretin (from S cells);
Released in response to HCl in the duodenum

  • ACh from the enteric nervous system also plays a role
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6
Q

What mechanisms convert pepsin to pepsinogen?

Does this vary depending on pH?

A
  • At pH 3.0-5.0: hydrolysis
  • At pH <3.5: Pepsin can cleave pepsinogen to pepsin
    • Self-activation
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7
Q

How does gastric secretion vary based on flow rate?

A
  • Low flow rate:
    • Surface epithelial cells secrete bicarbonate-enriched fluids
    • Less Cl- secreted
  • High flow rate:
    • Secretion from parietal cells dominates; lots of HCl
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8
Q

Salivary composition varies with secretory rate.

How will saliva compare to plasma at low secretory rates?

High secretory rates?

A

Saliva will always be hypotonic to plasma

  • Low secretory rate = more hypotonic
  • High secretory rate = more similar to plasma, but still hypotonic

*Note: secretions from salivary acinar cells are isotonic to plasma, but secretions are modified by ductal cells

(Ductal cells absorb Na+, Cl-, secrete K+, HCO3-)

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9
Q

Which ions are secreted by salivary ductal cells?

Which ions are absorbed?

A
  • Secreted = K+, HCO3-
  • Absorbed = Na+, Cl-
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10
Q

List 3 things that stimulate gastric acid secretion from the parietal cell

A
  • Histamine from ECL cells
    • Stimulated by ACh and Gastrin; the indirect pathway
  • Gastrin from G cells
    • Stimulated by GRP (released from CNX in response to stretch)
  • ACh from the vagus nerve
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11
Q

A patient is prescribe vitamin B12 shots for the rest of their life.

Loss of which cells in the GI tract might prompt this treatment?

A

Loss of parietal cells

Parietal cells secrete gastric acid and Intrinsic Factor (IF)

IF is needed for Vitamin B12 absorption

Possible causes of parietal cell loss:

Gastric bypass surgery, removal of the body and/or fundus of the stomach, chronic autoimmune gastritis

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12
Q

Parietal cell receptor and second messenger pathway activated by histamine?

  • Receptor:
  • 2nd Messenger:
A
  • Receptor: H2 histamine
  • 2nd Messenger: cAMP
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13
Q

What mechanism is responsible for the “alkaline tide” that occurs after a meal?

A

In response to a meal:

  • H+/K+ ATPase is upregulated to pump H+ into the stomach lumen (Cl- follows)
  • To maintain pH balance, OH- is sent to the interstitial space via HCO3-/Cl- exchanger

Remember, these gradients are set up by the Na+/K+ ATPase on the basolateral membrane

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14
Q

What are the effects of secretin on:

  • Gastric smooth muscle:
  • Parietal cells:
A
  • Gastric smooth muscle: relaxation
  • Parietal cells: decreased HCl secretion

Remember, secretin is released in response to HCl in the duodenum

Production of secretin is proportional to acid load, not concentration

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15
Q

What are the effects of CCK on the:

  • Gallbladder:
  • Pancreas:
  • Stomach:
  • Sphincter of Oddi:
A
  • Gallbladder: Contraction to release bile
  • Pancreas: Acinar secretion for digestive enzymes
  • Stomach: Reduced emptying so the duodenum isn’t overwhelmed
  • Sphincter of Oddi: Relaxation to allow bile and pancreatic secretions into the duodenum

Remember, CCK is released in response to nutrients in the duodenum

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16
Q

Parietal cell receptor and second messenger pathway activated by gastrin?

  • Receptor:
  • 2nd Messenger:
A
  • Receptor: CCK-B
  • 2nd Messenger: Ca2+/IP3
17
Q

In which phase of digestion are pancreatic cells most stronlgy stimulated?

A

Intestinal phase

  • Nutrients in the chyme stimulate S cells and I cells in the duodenum
    • S cells -> Secretin release -> HCO3- from ductal cells
    • I cells -> CCK release -> digestive enzymes from acinar cells

There is some stimulation from the vagus nerve during the cephalic and gastric phases

18
Q

Which hormone most strongly stimulates pancreatic acinar secretion?

A

CCK (from I cells)

  • CCK is released in response to fatty acids and protein in the duodenum