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GI System > Regulation of gastric acid secretion > Flashcards

Regulation of gastric acid secretion Flashcards

1
Q

What is gastric acid?

A

Colourless liquid secreted by glands in the lining of the stomach

constituents include:

  • pepsin
  • rennin
  • HCl
  • mucus
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2
Q

What are the Fundus and Body Secretions?

A

Mucus
pepsinogen

body and fundic glands also have parietal cells whcich secrete HCl and intrinsic factor

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3
Q

What are the antrum secretions?

A

secretes less HCl

more gastrin

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4
Q

What is the role of the Cardiac and pyloric glands?

A

secrete mainly mucus

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5
Q

What is the role of gastric glands?

A

contain chief cells which create gastric juice

contain parietal cells which secrete gastric acid (HCl) and intrinsic factor

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6
Q

Describe the process of Production of Gastric Acid (HCl).

A

1) Bicarbonate concentration in parietal cell increases
2) Bicarbonate leaves basal cell membrane of parietal cell into capillary blood in exchange for chloride (blood draining from stomach is more alkaline than arriving in it)
3) ATP binds to K+/H+ ATPase which transports K+ into the parietal cell and H+ into stomach lumen
4) Excess Cl- diffuses into the stomach through chloride channels
5) Net flow of H+ and Cl- out of the parietal cell and into the stomach lumen, binding together to form HCl.

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7
Q

What is the Effect of gastrin, Ach and histamine on HCl secretion?

A

Promote HCl secretion

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8
Q

What is the Effect of secretin on HCl secretion?

A

Neutralises secreted HCl

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9
Q

What is the Effect of somatostatin on HCl secretion?

A

Block HCl secretion

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10
Q

What are the functions of gastrin secretions?

A

Mucus- protection layer (alkaline due to high bicarbonate levels)

Rennin- aids in digestion of milk proteins (replaced by pepsin as we get older)

Lipase- digests triglycerides

Intrinsic Factor- prevents pernicious anaemia as it absorbs Vit B12

HCl- kills bacteria and denatures digested food. Also activates pepsinogen to pepsin

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11
Q

What are the 3 phases of gastric secretion?

A

Cephalic phase
Gastric phase
Intestinal phase

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12
Q

What is the cephalic phase of gastric secretion?

A
  • Occurs before food enters the stomach and stimulated by sight, smell, taste and chewing
  • Ach and GRP are released from nerve endings
    Ach binds directly

Ach binds directly to parietal cells, stimulating HCl release.
Ach binds to ECL cells, releasing histamine which then binds to parietal cells stimulating HCl release.

GRP binds directly to parietal cells causing HCl secretion.

GRP acts on G cells, releasing gastrin, which binds ECL cells, releasing histamine and binds to parietal cells stimulating HCl secretion.

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13
Q

Explain the gastric phase of gastric secretion.

A

Stimulated by distention of the stomach and by raising pH of its contents:

distention of the stomach activates neural reflexes, stimulating more Ach for HCl secretion

peptides and amino acids directly stimulate G cells to secrete even more gastrin for HCl secretion

peptides also buffer stomach acid and increase pH to prevent stimulation of somatostatin secretion, allowing for more gastrin secretion and therefore HCl secretion

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14
Q

Explain the intestinal phase of gastric secretion.

A

Is controlled by the entrance of acidic chyme into duodenum

moderates gastric activity via hormones and nervous reflexes

acid secretion is inhibited in this phase via short (local) and long (extrinsic) reflexes and also via hormones:

-secretin, CCK and GIP inhibit acid secretion

  • increased sympathetic (inhibitory) activity
  • decrease parasympathetic (excitatory) activity
  • decreased contractions (NO and VIP involved)

inhibitions are acid secretion by parietal cells and gastrin secretion by G cells

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15
Q

What are the effects of PGE2 (prostaglandin E2) on HCl secretion?

A

PGE2 negatively regulates HCl secretion by promoting bicarbonate

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16
Q

Name the factors that increase acid secretion.

A 
histamine
Ach
gastrin
caffeine
alcohol
NSAIDs (aspirin)
nicotine
H.pylori
Zollinger-Ellison syndrome (acid secreting tumour)
stress
bile salts
genetic
17
Q

What is hypochlorhydria/achlorhydria?

A

Production of gastric acid (HCl) in stomach is low or absent, causing failure of protein digestion

18
Q

Describe Pepsinogen secretion.

A

Parallels between acid secretion and pepsinogen secretion

Inputs to chief cells from nerve plexus stimulates secretion of pepsinogen

19
Q

Describe the Activation of pepsinogen.

A

pepsinogen activated to pepsin if H+ concentration is high (acidic environment) through an autocatalytic feedback process

20
Q

Describe pepsinogen inactivation.

A

Upon entry of food, pepsinogen is inactivated as bicarbonate and peptides neutralise the H+, therefore no acidic environment for activation of pepsin

pepsin is degenerated in conditions of hypoacidity

21
Q

Pepsin digests proteins into peptides. Other enzymes that digest proteins are:

A

trypsin
chymotrypsin
elastase

GI System (15 decks)

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