digestion and absorption

• what is digestion?

  large biological molecules are hydrolysed into smaller molecules that can be absorbed across all cell membranes
• what enzymes are needed to hydrolyse carbohydrates into monosaccharides?

  amylases and membrane-bound disaccharides
• where is amylase produced?

  Pancreas and salivary glands.
• what does amylase do?

  hydrolyses polysaccharides into the disaccharide maltose by hydrolysing the glycosidic bonds
• what are the membrane bound enzymes?

  sucrase and lactase
• what do sucrase and lactase do?

  hydrolyse sucrose and lactose into monosaccharides
• what 3 enzymes hydrolyse proteins?

  endopeptidases, exopeptidases and membrane-bound dipeptidases
• what is the role of endopeptidases?

  hydrolyse peptide bonds between amino acids in the middle of a polymer chain
• what is the role of exopeptidases?

  hydrolyses peptide bonds between amino acids at the end of a polymer chain
• what is the role of membrane-bound dipeptidases?

  hydrolyse peptide bonds between 2 amino acids
• lipids are digested by what?

  lipase and the actions of bile salts
• where is lipase produced?

  Pancreas and small intestine.
• what is the role of lipase?

  hydrolyses ester bond in triglycerides to form monoglycerides and fatty acids
• where are bile salts produced?

  Liver
• what do bile salts do?

  emulsify lipids to form tiny droplets, micelles. this increases surface area for lipase to act on
• digesting lipids involves a physical stage, what is this?

  the emulsification and micelle formation, where lipids are coated in bile salt to create an emulsion and these many small droplet of lipids provide a large surface area to enable faster hydrolysis by lipase
• digestion of lipids involve a chemical stage, what is this?

  lipase hydrolyse lipids into glycerol and fatty acids
• what is the physical stage of lipid digestion?


  lipids are coated in bile salts to create an emulsion, many small droplets of lipids provide a larger surface area to enable faster hydrolysis action by lipase.
• what is the chemical stage in lipid formation?

  lipase hydrolyses lipids into glycerol and fatty acids
• what are micelles?


  water soluble vesicles formed of the fatty acids, glycerol, monoglycerides and bile salts.
• where do micelles delivers the fatty acids, glycerol, monoglyceride to?

  the epithelial cells of the ileum for absorption
• what is the ileum wall covered in?

  villi
• what are adaptations of the villi?

  thin walls, surrounded by a network of capillaries and epithelial cells have even smaller microvilli.
• how are monosaccharides and amino acids absorbed?

  co-transport
• why is co-transport required for glucose?

  there is more glucose in the epithelial cells
• what happens to the sodium ions in the epithelial cell?

  they are actively transports out of the epithelial cell into the blood, with the use of a carrier protein
• what happens to the sodium ion concentration in the epithelial cell when they are actively transported into the blood?

  decreases, so there is a higher concentration in the ileum now compared to the epithelial cell.
• what happens to the sodium ions in the ileum lumen?

  diffuse down their concentration gradient into the epithelial cell.
• what protein does the sodium ion diffuse through from the ileum into the epithelial cell?

  co-transporter protein
• what is a co-transporter protein?


  so either a glucose or amino acid can also attach and are transported into the epithelial cells against their concentration gradient
• what gradually happens to the concentration of glucose in the epithelial cell?

  increases
• how does glucose diffuse from the epithelial cell into the blood?


  by facilitate diffusion, down their concentration gradient
• why do the capillaries not have a build of glucose as they are being absorbed?

  blood flows and so carries away absorbed glucose
• why is active transport across a carrier protein possible?

  because when ATP is hydrolysed into ADP Pi, it causes the carrier protein to change shape and release molecules to the other side of the cell membrane
• describe the process involved in the absorption and transport of digested lipid from the ileum into lymph vessels?

  micelles contains bile salts and fatty acids/monoglycerides.

  make fatty acids/monoglycerides more soluble in water.

  fatty acids/monoglycerides absorbed by diffusion.

  triglycerides reformed in the cells.

  vesicles ( chylomicrons )move to cell membrane, drain into the lymphatic system.