Gastrointestinal Tract Physiology Part 2 Flashcards
(21 cards)
What is the stomach?
The stomach is a muscular, J-shaped organ in the upper left quadrant of the abdomen, located between the esophagus and the duodenum. It acts as a reservoir and initiator of digestion, particularly of proteins.
What is the main function of the stomach in digestion?
A: To store, mix, and begin digestion of food—especially proteins—before passing it to the small intestine as chyme.
What are the anatomical subdivisions of the stomach and their main roles?
• Fundus: Storage; receptive relaxation
• Body: Secretes acid, enzymes
• Antrum: Grinds food, secretes gastrin
• Pylorus: Controls emptying via the pyloric sphincter
What are the four layers of the stomach wall?
- Mucosa
- Submucosa
- Muscularis externa (with an extra oblique layer)
- Serosa
What do parietal cells secrete?
Hydrochloric acid (HCl) and intrinsic factor
What are the three muscular layers of the stomach?
- Inner oblique
- Middle circular
- Outer longitudinal
What is the function of HCL?
• Kills microbes, denatures proteins, activates pepsinogen
What is the function of intrinsic factor?
Essential for vitamin B12 absorption in the ileum
What do chief cells secrete?
Pepsinogen
It is Activated by HCl to form pepsin (active enzyme)
What do mucous neck cells secrete?
Protect mucosa from acid and autodigestion
What cells secrete histamine, and what is its effect?
ECL (enterochromaffin-like) cells – stimulate parietal cells to secrete acid
What hormone is secreted by G cells and what is its role?
Gastrin – stimulates acid secretion, gastric motility, and mucosal growth
What are the three phases of gastric secretion regulation?
- Cephalic phase – triggered by sight/smell/taste of food
- Gastric phase – triggered by food in stomach
- Intestinal phase – initially stimulatory, then inhibitory
What hormones inhibit gastric secretion during the intestinal phase?
Secretin, cholecystokinin (CCK), and GIP
What neurotransmitter mediates the cephalic phase?
Acetylcholine (ACh) via the vagus nerve
What mechanisms protect the gastric mucosa from self-digestion?
• Mucus-bicarbonate barrier
• Tight epithelial junctions
• Rapid cell turnover
• Prostaglandins (increase mucus & blood flow)
What is chyme?
A semi-liquid mixture of partially digested food and gastric secretions
What is the role of the pyloric sphincter?
Regulates the passage of chyme into the duodenum
What is Zollinger-Ellison syndrome?
A condition involving gastrin-secreting tumors, causing excessive acid production and ulcers
What causes pernicious anemia?
Autoimmune destruction of parietal cells → loss of intrinsic factor → vitamin B12 deficiency
What is gastritis and what are common causes?
Inflammation of the stomach lining; caused by H. pylori, NSAIDs, alcohol, stress, or infection
