Digestion & Absorption

• Definition of digestion

  The hydrolysis of large biological molecules into small biological molecules with the use of enzymes.
• Definition of absorption 


  The movement of molecules from the lumen of the ileum, through the ileum lining into the bloodstream.
• What are membrane-bound disaccharidases?

  Enzymes that are attached to the cell membrane of epithelial cells lining the ileum which help to break down disaccharides into monosaccharides.
• Why is emulsification useful?


  It increases surface area of the lipids so that the action of lipases is sped up.
• What are the adaptations of villi?

  • Very thin-walled
  • Rich blood supply
  • Further increase absorption
• What are chylomicrons?


  Special particles adapted for the transport of lipids.
• Suggest how chylomicrons leave the epithelial cell.

  By exocytosis since they’re too large to leave through the cell membrane.
• Explain how low FEV1 could cause difficulty walking upstairs in emphysema.

  Less CO2 removed, less O2 uptake, less aerobic respiration/ ATP.
• What is the definition of digestion?

  The hydrolysis of large biological products to small biological molecules with the use of enzymes
• What is the definition of absorption?


  The movement of the molecules from the lumen of the ileum, through the ileum lining into the bloodstream
• How is food digested in the human body?

  • Buccal cavity: mechanical digestion and mastication
  • Saliva contains mucin, salivary amylase, and mineral salts
  • Peristalsis pushes food down the oesophagus
  • Food travels from mouth to stomach in 4-8 seconds
  • Stomach: mechanical digestion and mixing with gastric juice
  • Early small intestine: input of pancreatic juices
  • Large intestine absorbs water, minerals, and vitamins
  • Faeces stored in the rectum and egested through the anus
• What components are found in saliva and their functions?

  Saliva contains mucin (binds food), salivary amylase (digests starch), and mineral salts (regulates pH around 7)
• What role does peristalsis play in digestion?

  Peristalsis contracts and relaxes to push food down the digestive tract
• How long does it usually take for food to travel from the mouth to the stomach?

  Between 4 and 8 seconds
• What happens in the stomach during digestion?

  • Mechanical digestion occurs through churning
  • Food mixes with gastric juice
  • Gastrin is produced by the stomach wall
• What is the function of pancreatic juices in digestion?

  Pancreatic juices contain enzymes that continue the hydrolysis of starch to maltose
• What is the role of the large intestine in digestion?

  The large intestine absorbs water, minerals, and vitamins
• Where are faeces stored before egestion?

  In the rectum
• How are carbohydrates digested in the mouth?

  Salivary amylase hydrolyzes glycosidic bonds in starch to form maltose
• What happens to salivary amylase in the stomach?

  The acid in the stomach denatures the amylase and prevents further hydrolysis of starch
• What is the role of pancreatic amylase in carbohydrate digestion?

  Pancreatic amylase continues the hydrolysis of remaining starch to maltose in the small intestine
• What maintains the optimal pH for amylase in the small intestine?

  Alkaline salts produced by the pancreas and intestinal wall
• What are membrane-bound disaccharidases?

  Enzymes like maltase that are part of the cell-surface membrane of the epithelial cells in the ileum
• How are lipids digested in the small intestine?

  Bile salts emulsify lipids into micelles, increasing their surface area for lipase action
• What is the function of lipases in lipid digestion?

  Lipases hydrolyze the ester bond in triglycerides to form fatty acids and monoglycerides
• Why is emulsification useful in lipid digestion?

  It increases the surface area of lipids, speeding up the action of lipases
• How are proteins digested in the stomach?

  Endopeptidases hydrolyze peptide bonds in the middle of polypeptides
• What maintains the optimum pH for enzymes in the stomach?

  Hydrochloric acid (HCl) in the stomach
• What happens to polypeptides in the ileum?

  Exopeptidases released from the pancreas hydrolyze peptide bonds at the ends of polypeptides
• What is the role of membrane-bound dipeptidases in protein digestion?

  Dipeptidases hydrolyze the peptide bonds within dipeptides to form amino acids
• What are the adaptations of the villi in the small intestine?

  • Very thin-walled to reduce diffusion distance
  • Contain muscle to maintain diffusion gradient
  • Rich blood supply to carry away absorbed molecules
  • Microvilli increase absorption surface area
• How are triglycerides absorbed in the small intestine?

  1. Micelles help move monoglycerides and fatty acids to the epithelium
  2. Monoglycerides and fatty acids diffuse across the epithelial cell membrane
  3. They are transported to the ER and combine to form triglycerides
  4. Triglycerides associate with cholesterol and lipoproteins to form chylomicrons
  5. Chylomicrons enter lacteals by exocytosis and drain into the bloodstream near the heart
• What are chylomicrons?

  Special particles adapted for the transport of lipids
• How do chylomicrons leave the epithelial cell?

  By exocytosis, as they are too large to pass through the membrane
• How does a low FEV1 affect physical activity in individuals with emphysema?

  A low FEV1 leads to less CO2 removal, less oxygen uptake, and less aerobic respiration, making activities like walking upstairs difficult
• What is the definition of digestion?

  The hydrolysis of large biological products to small biological molecules with the use of enzymes
• What is the definition of absorption?


  The movement of the molecules from the lumen of the ileum, through the ileum lining into the bloodstream
• How is food digested in the human body?

  • Buccal cavity: mechanical digestion and mastication (chewing)
  • Saliva contains mucin, salivary amylase, and mineral salts
  • Peristalsis pushes food down the oesophagus
  • Food travels from mouth to stomach in 4-8 seconds
  • Stomach: mechanical digestion and mixing with gastric juice
  • Early small intestine: input of pancreatic juices
  • Large intestine absorbs water, minerals, and vitamins
  • Faeces stored in the rectum and egested through the anus
• What components are found in saliva and their functions?

  Saliva contains mucin (binds food), salivary amylase (digests starch), and mineral salts (regulates pH around 7)
• What role does peristalsis play in digestion?

  Peristalsis contracts and relaxes to push food down the digestive tract