digestion and absorbtion 3.3.3

• define digestion

  enzymes hydrolyse

  large insoluble molecules into small soluble molecules
• define co - transport

  • products of digestion are transported through the epithelial cell lining the small intestine
  • using channel and carrier proteins
  • transported into the blood
• order of digestion

  • mouth
  • salivary glands
  • stomach
  • small intestine
  • gall bladder
  • pancreas
  • large intestine
• What is the first step in carbohydrate digestion?

  Salivary amylase in the mouth
• What does salivary amylase hydrolyze in starch?

  Alternate glycosidic bonds
• What is the optimum pH for salivary amylase?

  Neutral pH
• Why does carbohydrate digestion stop in the stomach?

  Acidic conditions denature amylase
• What is mixed with remaining starch in the duodenum?

  Pancreatic juice
• What does pancreatic juice contain that aids in carbohydrate digestion?

  Pancreatic amylase and alkaline salts
• What is the role of alkaline salts in pancreatic juice?

  Neutralizes acidic conditions
• Where are membrane-bound disaccharidases located in the small intestine?

  Epithelial cells of the ileum
• What does maltase hydrolyze maltose into?

  Alpha glucose
• How does alpha glucose cross the ileum wall into the blood?

  By co-transport
• What are the main stages of carbohydrate digestion?

  1. Mouth: Salivary amylase hydrolyzes starch
  2. Stomach: Acidic conditions denature amylase
  3. Small intestine (duodenum): Pancreatic juice neutralizes acid
  4. Small intestine (ileum): Maltase hydrolyzes maltose into glucose
• protein digestion

  • endopeptidases - hydrolyse the peptide bond between amino acids in the central region of a protein molecule forming smaller polypeptide molecules
  • exopeptidases - hydrolyse the peptide bonds at the terminal ends of the polypeptide to remove amino acids
  • dipeptiases - hydrolyse the peptide bonds between the two amino acids of a dipeptide
• describe how proteins are digested in the human gut (4)

  • endopeptidases hydrolyses peptide bonds in polypeptide to form shorter polypeptide molecules ,, which increases the surface area
  • exopeptidase hydrolyses the peptide bonds on the terminal ends of the polypeptide forming dipeptides in the small intestine
  • dipeptidases - membrane bound enzymes which hydrolyse peptide bonds in dipeptides forming amino acids ready for absorption
• lipid digestion

  • most lipid / triglyceride digestion occurs in the small intestine - duodenum
  • lipids form a suspension of large droplets
  • lipids are split up into smaller droplets by bile salts which are produced by the liver.
  • this process is called emulsification and increases the surface area for lipase action
  • so faster hydrolysis of lipids
  • lipases are produced in the pancreas and they hydrolyse the ester bonds found in triglycerides to form fatty acids and glycerol
  • the fatty acids and glycerol are carried to the epethlial cells lining the small intestine in the form of micelles
• define digestion

  • enzymes hydrolyse large insoluble molecules
  • into smaller soluble molecules
  • ready for absorbtion
• define absorbtion

  • products of digestion are transported through the epethilial cell lining the small intestine (ileum)
  • using channel and carrier proteins
  • transported into the blood
• define ingestion

  • food is taken to the mouth
  • chewed and mixed with saliva and swallowed
• explain what is meant by the human digestive system

  • the human digestive system is made up of a long muscular tube and its associated glands
  • the glands produce enzymes that hydrolyse large molecules into smaller soluble molecules ready for absorbtion
  • the digestive system is therefore an exchange surface through which food substances are absorbed
• dipeptidases

  • located in the surface membrane of cells lining the small intestine
  • hydrolyse dipeptides into amino acids
  • final products of protein digestion are amino acids
  • which are then absorbed by cells lining the ileum of the small intestine
• to be used as passive immunity, an anti toxin antibody would have to be injected. If it was given by mouth it would be digested, describe how the anti-toxin antibody would be digested.

  • peptide bonds hydrolysed
  • endopeptidases break internal peptide bonds
  • exopeptidases break terminal peptide bonds
  • membrane bound dipeptidases break dipeptides to amino acids
• thin epethilial cells (ileum)

  • reduces the distance in which diffusion has to take place
• many mitochondria (ileum)

  • produces ATP to release energy for active transport
• Microvilli (ileum)

  • finger-like projections of the cell surface membrane that increases the surface area
• many carrier / channel proteins

  • allow facillitated diffusion to occur , as well as active transport and co-transport
• membrane bound enzymes (ileum)

  • allows the hydrolysis of disacharides into glucose during digestion
  • maintains the concentration gradient
• What process is involved in the absorption of amino acids and glucose?

  Co-transport
• Where does the absorption of glucose and amino acids occur?

  In the small intestine
• What mechanisms are used for the absorption of glucose and amino acids?

  Facilitated diffusion and active transport
• From where are glucose and amino acids moved into the blood?

  From the lumen of the ileum
• What type of proteins are involved in the transport of glucose and amino acids?

  Co-transport carrier proteins
• Where are co-transport carrier proteins located?

  In the cell surface membranes of epithelial cells
• How do co-transport carrier proteins function?

  They transport glucose or amino acids with sodium ions
• What is the role of sodium ions in the absorption process?

  They help transport glucose or amino acids
• How are sodium ions maintained in the epithelial cells?

  They are actively transported out into the blood
• What pump is used to transport sodium ions out of the epithelial cells?

  The sodium-potassium pump
• How do glucose and amino acids move out of the epithelial cells into the blood?

  By facilitated diffusion
• How does the sodium-potassium pump contribute to the absorption of nutrients?

  It maintains a steep concentration gradient for sodium