Practice 5 structured short- and long-answer medical questions on Weekly Year 2: GIT Physiology Exam - May 29, 2026 (Sections B & C). Review model answers fo...
Answer: Bile salts emulsify large fat globules into smaller droplets, increasing the surface area for lipase action. They also form micelles with fatty acids and monoglycerides, which are soluble in the aqueous environment of the intestinal lumen, facilitating their absorption across the brush border membrane.
Answer: Pepsinogen is secreted by chief cells in the stomach. It is an inactive zymogen precursor. In the acidic environment of the stomach (pH < 2), pepsinogen is auto-activated to pepsin, the active enzyme. Pepsin then initiates protein digestion by breaking peptide bonds.
Answer: The hepatic portal system transports nutrient-rich blood from the gastrointestinal tract (stomach, intestines, spleen, pancreas) directly to the liver. This allows the liver to process absorbed nutrients, detoxify harmful substances, and synthesize essential proteins before they enter general circulation.
Answer: Hunger is stimulated by signals such as ghrelin (a hormone from the stomach), low blood glucose levels, and empty stomach distension. Satiety is promoted by signals like leptin (from adipose tissue), CCK, and GLP-1 from the gut, as well as distension of the stomach and duodenum, and nutrient presence in the small intestine.
Answer: Carbohydrate absorption involves digestion of polysaccharides into monosaccharides (glucose, fructose, galactose) by brush border enzymes. Monosaccharides are absorbed via secondary active transport (e.g., SGLT1 for glucose and galactose) and facilitated diffusion (e.g., GLUT5 for fructose) into enterocytes, then transported into the portal circulation via GLUT2. Protein absorption involves digestion of proteins into amino acids and small peptides by proteases. Amino acids are absorbed by various active transport systems and cotransporters (e.g., Na+-dependent transporters). Small peptides are absorbed via PepT1 and then intracellularly broken down to amino acids. Lipids are digested by lipases into fatty acids and monoglycerides, which form micelles. Micelles deliver lipids to the enterocyte brush border where they diffuse across. Inside the enterocyte, they are re-esterified into triglycerides, packaged into chylomicrons, and released into the lymphatic system (lacteals).