digestion and absorption

• what is the function of the oeseophagus?

  carries food from the mouth to the stomach
• what is the stomach?

  a muscular sac with an inner layer that produces enzymes. stores and digests food
• what is the ileum?

  a long muscular tube that further digests food by enzymes produced by the ileum walls and by secretions produced on the ileum wall
• how is the ileum adapted for absorption?

  Very long so there is enough time for absorption to occur. -The inner walls are highly folded, giving a much larger surface area for absorption. -Has villi which increases surface area and microvilli which increases the surface area further-Thin membrane-Good blood supply
• what is the pancreas?

  A large gland situated below the stomach that produces a secretion called pancreatic juicesecretions contains proteases to hydrolyse proteins, lipases to hydrolyse lipids and amylase to hydrolyse starch
• what is physical disgestion?

  The body crushing and churning food to break it into small chunks giving it a larger SA for enzymes to act on-by teeth in the mouth-food is churned by the muscles in the stomach wall
• what is chemical digestion?

  Hydrolysis of large insoluble molecules into smaller, soluble molecules using enzymes
• what do carbohydrases do?

  Hydrolyse carbohydrates into monosaccharides
• what to lipases do?


  Hydrolyse lipids into glycerol and fatty acids
• what do proteases do?

  hydrolyse proteins to amino acids
• Carbohydrate digestion in humans

  1. Saliva containing salivary amylase enters the mouth and is mixed with the food during chewing

  2. Salivary amylase begins to hydrolyse starch to maltose

  3. Food is swallowed and enters the stomach where conditions are acidic, denaturing the amylase

  4. Food passes into the small intestine where it mixes with pancreatic juice containing pancreatic amylase

  5. Pancreatic amylase continues to hydrolyse any remaining starch to maltose

  6. Muscles in the intestinal wall push the food along the ileum

  7. Epithelial lining produces maltase (a membrane-bound disaccharidase) which hydrolyses the maltose into α-glucose
• where is maltase found?

  in the lining of the ileum, membrane bound disaccharidase.
• what hydrolyses sucrose?


  sucrase - a membrane bound disaccharidaseinto glucose and fructose
• what hydrolyses lactose?


  lactase - a membrane bound disaccharidaseinto glucose and galactose
• where are lipases produced?


  pancreas
• what bond do lipases hydrolyse?

  ester bonds
• what are lipids hydrolysed into?

  monoglycerides and fatty acids
• what is a monoglyceride?

  A glycerol molecule with a single fatty acid molecule attached
• where are bile salts produced?

  liver
• where are endopeptidases secreted from?

  stomach
• where are exopeptidases secreted from?

  pancreas
• how do the properties of the villi increase the efficiency of absorption?

  thin wall so diffusion distance is reduced, blood supply to maintain concentration gradient, microvilli to increase surface area
• how are amino acids and monosaccharides absorbed?

  sodium ions are actively transported into the blood from the epithelial cells-this creates a conc gradient between the epithelial cell and the lumen of the small intestine-so sodium ions diffuse from the lumen into the epithelial cells with glucose or amino acids through a co-transport protein-the glucose/amino acid will now be at a greater concentration in the epithelial cell than in the blood so glucose can move by facilitated diffusion through a channel protein
• what is the role of micelles in the absorption of fats into the cell lining of the ileum?

  micelles include bile salts and fatty acids-make the fatty acids more soluble in water-release fatty acids at the lining of the ileum where they are absorbed by diffusion-also maintain a higher concentration gradient of fatty acids to the lining of the ileum