Digestion and absorption

• What is the role of the mouth in digestion?

  Mechanical digestion and introduction of salivary amylase
• Where does starch digestion begin?

  In the mouth
• What do salivary glands produce?

  Salivary amylase
• What type of digestion occurs in the stomach?

  Mechanical digestion by churning
• What begins in the stomach?

  Protein digestion
• What does the pancreas produce?

  Exopeptidases, pancreatic amylase, lipase
• What does the liver produce?

  Bile salts
• What happens in the ileum?

  Production of dipeptidases, disaccharidases, absorption
• Why is digestion important for cells?

  It allows absorption of soluble molecules
• How does enzyme specificity relate to protein structure?

  Each enzyme's tertiary structure is specific
• What do digestive enzymes do?

  Catalyse hydrolysis of long polymers
• What bonds in starch are hydrolysed by amylase?

  Glycosidic bonds
• What does maltose get hydrolysed into?

  Glucose
• What does sucrase hydrolyse?

  Sucrose
• What does lactase hydrolyse?

  Lactose
• How do endopeptidases and exopeptidases work together?

  Endopeptidases increase ends for exopeptidases
• What is the role of bile salts in digestion?

  Emulsify lipids to increase surface area
• What does lipase hydrolyse?

  Ester bonds in triglycerides
• What do micelles contain?

  Bile salts, fatty acids, and monoglycerides
• How do micelles aid in lipid absorption?

  Increase concentration of fatty acids near cells
• How are fatty acids and monoglycerides absorbed?

  By diffusion into epithelial cells
• What happens to fatty acids in the cells?

  They are reassembled into triglycerides
• What are chylomicrons?

  Vesicles containing reassembled triglycerides
• How do chylomicrons leave epithelial cells?

  By exocytosis
• What are the key events in digestion and their organ roles?

  • Mouth: Mechanical digestion, salivary amylase, starch digestion
  • Salivary glands: Produce salivary amylase
  • Oesophagus: Transports food to stomach
  • Stomach: Mechanical digestion, endopeptidases, protein digestion
  • Pancreas: Produces exopeptidases, pancreatic amylase, lipase
  • Liver: Produces bile salts
  • Ileum: Produces dipeptidases, disaccharidases, absorption
  • Large intestine: Absorbs water
  • Rectum: Stores faeces before egestion
• What is the process of starch digestion?

  1. Amylase hydrolyses glycosidic bonds in starch to produce maltose.
  2. Maltose is hydrolysed by maltase to produce glucose.
• What is the process of disaccharide digestion?

  1. Sucrose is hydrolysed by sucrase to produce glucose and fructose.
  2. Lactose is hydrolysed by lactase to produce glucose and galactose.
• How do endopeptidases and exopeptidases work together in protein digestion?

  • Endopeptidases hydrolyse internal peptide bonds.
  • Exopeptidases hydrolyse peptide bonds at the ends.
  • This increases the number of ends for exopeptidases to act on.
• What is the role of bile salts in lipid digestion?

  • Emulsify lipids to increase surface area.
  • Increase lipase activity.
  • Form micelles with fatty acids and monoglycerides.
• What are the adaptations of intestinal epithelial cells for absorption?

  • Folded cell surface/microvilli for large surface area.
  • Many co-transporter and channel proteins for faster absorption.
  • Numerous mitochondria for ATP production.
  • Membrane-bound digestive enzymes to maintain concentration gradient.
• How do amino acids and glucose get absorbed against a concentration gradient?

  • Sodium ions are actively transported to create a gradient.
  • Amino acids and glucose are co-transported with sodium ions.
  • They move by facilitated diffusion into the capillary.
• What is the role of micelles in lipid absorption?

  • Micelles contain bile salts, fatty acids, and monoglycerides.
  • They increase solubility of fatty acids and monoglycerides.
  • They facilitate absorption by breaking apart near ileum cells.
• What happens to fatty acids and monoglycerides after absorption?

  • They are reassembled into triglycerides.
  • Formed into chylomicrons for transport.
  • Chylomicrons leave cells by exocytosis.