Lecture 4

Digestion Process

• Chewing food in the mouth breaks it down into smaller pieces, increasing the surface area for enzyme action.
• The pyloric sphincter, located between the stomach and small intestine, regulates the flow of food into the small intestine.

Stomach Function

• Pepsins, enzymes in the stomach, break down proteins into smaller peptides and amino acids.
• The stomach has a pH range of 1.5-3.5, creating an acidic environment for digestion.
• Mucous produced by epithelial cells covers the stomach surface, protecting it from HCl and potential damage.

Cellular Function in the Stomach

• G cells, enterochromaffin-like cells, and D cells respond to acetylcholine, histamine, and gastrin in the stomach, regulating digestion and secretion.
• Intrinsic factor, produced by parietal cells, helps absorb vitamin B12 in the stomach.

Small Intestine Function

• The pancreas secretes digestive enzymes into the small intestine to break down carbohydrates, proteins, and fats.
• Villi in the small intestine increase the surface area for nutrient absorption.
• Enterocytes, the absorptive cells lining the small intestine, are replaced every 2-4 days.

Fat Absorption

• After being absorbed in the small intestine, fat travels through lacteals, the lymphatic vessels, to the bloodstream.
• The lymphatic system plays a crucial role in fat absorption and transport.

Nutrient Absorption

• Nutrient absorption primarily occurs through facilitated diffusion and active transport in the small intestine.
• Lacteals, the lymphatic vessels, absorb dietary fats and transport them to the bloodstream.
• Glucose and amino acids, broken down in the small intestine, are absorbed into the bloodstream and transported to the liver for processing.