Physiology
Gastrointestinal Physiology
Gastrointestinal physiology for MBBS and NEET-PG: gastric and pancreatic secretion, bile, gut hormones, digestion and absorption and gut motility, mapped to NMC codes PY4.
MedNext Academy | 3 min read
Gastrointestinal Physiology
Gastrointestinal physiology for MBBS and NEET-PG: gastric and pancreatic secretion, bile, gut hormones, digestion and absorption and gut motility, mapped to NMC codes PY4.
Gastrointestinal physiology covers how food is digested and absorbed and how the gut is controlled. It deals with gastric acid and enzyme secretion, the gut hormones, the role of bile and the pancreas, the absorption of carbohydrates, proteins and fats, and the nervous control of motility.
High-yield: Gastrointestinal Physiology
- The parietal cells of the stomach secrete hydrochloric acid and intrinsic factor.
- Intrinsic factor is essential for the absorption of vitamin B12 in the terminal ileum.
- Gastric acid secretion has cephalic, gastric and intestinal phases.
- Gastrin from G cells, histamine and vagal acetylcholine all stimulate acid secretion.
- The chief cells secrete pepsinogen, which is converted to active pepsin by acid.
- Cholecystokinin causes gallbladder contraction and pancreatic enzyme release and is triggered by fat and protein.
- Secretin stimulates the pancreas and bile ducts to release bicarbonate-rich fluid in response to acid.
- Bile salts emulsify fat and form micelles that carry lipids to the intestinal mucosa for absorption.
- Most nutrient absorption occurs in the small intestine, while the colon absorbs water and electrolytes.
- Carbohydrates are absorbed as monosaccharides, with glucose and galactose taken up by the sodium-dependent SGLT1 transporter.
- Proteins are absorbed as amino acids and small peptides across the enterocyte.
- Salivary amylase and pancreatic amylase digest starch, and pancreatic lipase digests fat.
- The enteric nervous system, with its myenteric and submucosal plexuses, controls gut motility and secretion.
- Segmentation mixes chyme in the small intestine while peristalsis propels it forward.
Key gut hormones
- **Gastrin:** From G cells. Stimulates acid secretion and gastric motility.
- **Cholecystokinin:** Gallbladder contraction and pancreatic enzyme release. Released by fat and protein.
- **Secretin:** Bicarbonate-rich pancreatic and biliary secretion in response to acid.
- **Intrinsic factor:** From parietal cells. Needed for vitamin B12 absorption in the ileum.
NMC competencies in this chapter
- **PY4.1:** Functional anatomy and innervation of the gut
- **PY4.2:** Salivary secretion and its regulation
- **PY4.3:** Gastric secretion and its regulation
- **PY4.4:** Pancreatic secretion and function
- **PY4.5:** Bile secretion and the functions of the liver
- **PY4.7:** Digestion and absorption of nutrients
- **PY4.8:** Gastrointestinal motility and its control
- **PY4.9:** Gastrointestinal hormones
Frequently Asked Questions
What stimulates gastric acid secretion?
Acid secretion by parietal cells is stimulated by gastrin from G cells, histamine from enterochromaffin-like cells, and acetylcholine from vagal nerve endings.
Why is intrinsic factor important?
Intrinsic factor from the parietal cells binds vitamin B12 so that it can be absorbed in the terminal ileum. Without it, B12 deficiency and pernicious anaemia develop.
What is the role of bile in digestion?
Bile salts emulsify dietary fat into small droplets and form micelles, which carry the products of fat digestion to the intestinal lining for absorption.
How are the carbohydrates absorbed?
Carbohydrates are broken down to monosaccharides, and glucose and galactose are absorbed into the enterocyte by the sodium-dependent SGLT1 transporter, while fructose uses GLUT5.
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