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Anatomy & Physiology: Digestive System and Metabolism

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  • What are the main layers of the small intestine wall?

    The small intestine wall consists of the mucosa, submucosa, circular muscle, longitudinal muscle, and serosa.

  • What is the role of intestinal enteroendocrine cells in digestion?

    Enteroendocrine cells secrete hormones like cholecystokinin, secretin, and gastric inhibitory peptide that regulate digestive secretions and motility.

  • How is trypsinogen activated in the small intestine?

    Trypsinogen is activated to trypsin by enterokinase (enteropeptidase) in the small intestine, which then activates other pancreatic enzymes.

  • What are the main pancreatic enzymes secreted as inactive precursors?

    Trypsinogen, chymotrypsinogen, procarboxypeptidase, procolipase, and prophospholipase are secreted inactive and activated in the small intestine.

  • How is glucose absorbed in the small intestine?

    Glucose is absorbed by Na+-dependent active transport coupled with facilitated diffusion via GLUT2 transporters.

  • How are amino acids absorbed in the small intestine?

    Amino acids are absorbed by Na+ or H+ dependent active transport and small peptides by transcytosis across enterocytes.

  • What role do bile salts play in lipid digestion?

    Bile salts emulsify lipids by coating lipid droplets, increasing surface area for lipase action and aiding lipid absorption.

  • Describe the structure of a bile-acid-coated lipid droplet.

    The droplet has a hydrophobic side associating with lipids and a hydrophilic side associating with water, stabilizing emulsions.

  • What is the function of villi and microvilli in the small intestine?

    Villi and microvilli increase surface area for nutrient absorption and contain capillaries and lacteals for nutrient transport.

  • What is the role of mitochondria in enterocytes?

    Mitochondria provide ATP needed for active transport and metabolic processes in enterocytes during nutrient absorption.

  • What is glycolysis and where does it occur?

    Glycolysis is the cytosolic process converting glucose to pyruvate, producing 2 ATP and 2 NADH molecules.

  • What happens to pyruvate after glycolysis in aerobic respiration?

    Pyruvate enters mitochondria, is converted to acetyl CoA, and enters the citric acid cycle for further energy production.

  • What are the main products of the citric acid cycle per glucose molecule?

    The cycle produces 2 ATP, 6 NADH, 2 FADH2, and releases CO2 as a byproduct per glucose molecule.

  • How does the electron transport chain generate ATP?

    NADH and FADH2 donate electrons, creating a proton gradient that powers ATP synthase to produce ATP and water.

  • How are proteins digested and absorbed in the small intestine?

    Proteins are digested by pepsin and pancreatic proteases; amino acids are absorbed via active transport, peptides by transcytosis.

  • What is the role of chylomicrons in lipid absorption?

    Chylomicrons transport reassembled triglycerides from enterocytes through lymphatic vessels to the bloodstream.

  • How is fructose absorbed in the small intestine?

    Fructose is absorbed by facilitated diffusion through GLUT5 transporters independent of Na+.

  • What is the function of the myenteric and submucosal plexuses?

    The myenteric plexus controls GI motility; the submucosal plexus regulates secretion in the digestive tract.

  • What is the significance of the citric acid cycle intermediates like citrate and succinate?

    Intermediates participate in energy production and provide substrates for biosynthetic pathways.