Gastric Secretion Flashcards
What are the glands present in the stomach?
Gastric gland
Pyloric gland
Location of the gastric gland
Proximal 80% of stomach (Fundus and body)
Secretions of the gastric gland
Hydrochloric acid
Pepsinogen
Intrinsic factor
Mucus
Location of the pyloric gland
Distal 20% of stomach (antrum and pylorus)
Secretions of the pyloric gland
Mucus
Gastrin hormone (from G cells)
Somatostatin (from D cells)
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
Characteristics of gastric secretions
2500ml/day
Colorless
pH of 1 to 3.5 (acidic)
Composition: 99.5% water and 0.5% solids
Types of solid components of gastric secretion
Inorganic: HCl, K+, Na+, Mg++ and HPO4
Organic: Mucus, enzymes (e.g, pepsinogen, lipase) and intrinsic factor
What are the phases of gastric secretion?
Cephalic phase
Gastric phase
Intestinal phase
Cephalic phase is caused by …
… sight, smell, thought and taste of food
Cephalic phase account for how much gastric secretion
30%
Origin of cephalic phase
Cerebral cortex and in the appetite centers of the amygdala and hypothalamus
When does the gastric phase occur?
When food enters the stomach
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
Gastric phase accounts for how much of the gastric secretion?
60%
When does the intestinal phase occur?
When food enters the duodenum
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 H2receptors 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 Gireceptors 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 Gireceptors
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)
