Gastric Secretion Flashcards by John Jonah Jameson Jr.

What are the glands present in the stomach?

Gastric gland
Pyloric gland

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Location of the gastric gland

Proximal 80% of stomach (Fundus and body)

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Secretions of the gastric gland

Hydrochloric acid
Pepsinogen
Intrinsic factor
Mucus

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Location of the pyloric gland

Distal 20% of stomach (antrum and pylorus)

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Secretions of the pyloric gland

Mucus
Gastrin hormone (from G cells)
Somatostatin (from D cells)

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Functions of each cell of the gastric/oxyntic gland

Mucus neck cells secretesmucus and bicarbonate
Peptic (or chief) cells secretes pepsinogen
Parietal (or oxyntic)cells secreteshydrochloric acidandintrinsic factor.
Enterochromaffin-like(ECL)cellssecretes histamine

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Characteristics of gastric secretions

2500ml/day
Colorless
pH of 1 to 3.5 (acidic)
Composition: 99.5% water and 0.5% solids

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Types of solid components of gastric secretion

Inorganic: HCl, K+, Na+, Mg++ and HPO4
Organic: Mucus, enzymes (e.g, pepsinogen, lipase) and intrinsic factor

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What are the phases of gastric secretion?

Cephalic phase
Gastric phase
Intestinal phase

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Cephalic phase is caused by …

… sight, smell, thought and taste of food

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Cephalic phase account for how much gastric secretion

30%

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Origin of cephalic phase

Cerebral cortex and in the appetite centers of the amygdala and hypothalamus

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When does the gastric phase occur?

When food enters the stomach

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What occurs in the gastric phase?

Long vagovagal reflexes from the stomach to the brain and back to the stomach
Local enteric reflexes
Gastrin and histamine release

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Gastric phase accounts for how much of the gastric secretion?

60%

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When does the intestinal phase occur?

When food enters the duodenum

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Intestinal phase accounts for how much of gastric secretion?

10%

Where is mucus secreted from?

Neck
Surface mucous cells
Gastric and pyloric glands

Function of mucus

Forms mucus-bicarbonate barrier

What can a distruption in the mucus-bicarbonate barrier cause?

Peptic ulcer

Which cells secrete HCl?

Parietal cells

What are the functions of hydrochloric acid?

PROBE ATTACK
Has a protective function against bacteria ingested with food
Breaks down and degrades food into smaller molecules
Activates pepsinogen into pepsin
Promote the absorption of calcium & iron

Which cells secrete pepsinogen?

Cheif cells/Peptic cells

HCl activates pepsinogen into pepsin

What are the functions of pepsin

Digestion of proteins

Which cells secrete intrinsic factor?

Parietal cells

What are the functions of intrinsic factor?

Absorption of Vitamin B12

What does the absence of intrinsic factor cause?

Pernicious anemia

Function of gastrin?

Stimulates gastric secretion and motility

Function of somatostatin?

Inhibits gastric secretion and motility

Describe the mechanism of HCL formation

**Stage 1**: H₂O and CO₂ use carbonic anhydrase enzyme to form H₂CO₃ (a week acid) which dissociates into H⁺ and HCO₃^- **Stage 2**: H⁺ is secreted in exchange with K⁺ by H⁺-K⁺-ATPase proton pump at the luminal border **Stage 3**: HCO₃ is reabsorbed to the blood stream in exchange with Cl^- at the basolateral border **Stage 4**: Cl^- is secreted into the luminal border by CFTR channel

What factors stimulate HCl production?

ACh (parasympathetic stimulation), gastrin and histamine

What factors inhibit HCL secretion?

Somatostatin, prostaglandin, secretin and GIP

How does parasympathetic stimulation affect HCl secretion?

**Directly** ACh acts on M3 receptor on the parietal cells and stimulate HCL secretion and inhibit somatostatin **Indirectly** Through stimulation of ECL cell to secrete histamine Through stimulation of G cell to secret gastrin via release of gastrin releasing peptide (GRP)

How does gastrin affect HCl secretion?

Stimulation by eating and by vagal stimulation Increases H+ through cholecystokinin B (CCKB) Gq-coupled receptors on parietal cells Also a stimulator of histamine release from ECL cells

How does histamine affect HCl secretion?

Binds H2 receptors on parietal cells to increase H+ through Gs-coupled receptors Histamine release can be increased by ACh and gastrin, or it can be decreased by somatostatin

How does somatostatin affect HCl secretion?

**Directly** inhibits parietal cells via Gi receptors in a paracrine and endocrine fashion. This means it affects both its neighboring cells as well as distant cells **Indirectly** it is an important blocker of histamine and gastrin release

How do prostaglandins affect HCl secretion?

Inhibitor of acid secretion at parietal cells and also act via Gi receptors

What is a peptic ulcer?

It is due to breakdown of the barrier that protects stomach mucosa

What are the causes of a peptic ulcer?

Infection with the bacterium Helicobacter pylori Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs), which inhibit the production of prostaglandins Zollinger-Ellison syndrome (gastrinoma)

What are the treatments for a peptic ulcer?

H2 blocker (ranitidine) Proton pump inhibitors (omeprazole) prostaglandins analogues (misoprostol)