Digestion and absorption

Question 1

Digestion def

Answer 1

Process where large molecules are hydrolysed to smaller molecules by enzymes to be absorbed.

Question 2

Carbohydrate hydrolysation process

Answer 2

Amylase, produced in salivary glands, pancreas and small intestine, hydrolyses starch to maltose.
Maltase, produced in linings of ileum, hydrolyses maltose to glucose.

Question 3

Carbohydrate digestion in mammals

Answer 3

Salivary amylase mixed with starch during mastication. pH maintained neutral by salts as it is optimum pH.
Acid in stomach denatures salivary amylase to prevent further hydrolysis of starch.
Pancreatic juice containing pancreatic amylase hydrolyses remaining starch to maltose in small intestine, salts keep pH neutral.
Muscles in intestine wall push food along ileum and membrane-bound disaccharidase, maltase hydrolyses maltose to a-glucose.

Question 4

Lipid hydrolysation process and digestion in mammals

Answer 4

Lipases produce in pancreas hydrolyse ester bond in triglycerides to form fatty acids and monoglycerides (glycerol + 1 fatty acid).
Micelles emulsified from lipids by bile salts produced in liver to increase SA for action of lipases.

Question 5

Protein hydrolysation process and digestion in mammals

Answer 5

Endopeptidases hydrolyse peptide bonds between amino acids in centre of protein molecule to form series of peptide molecules.
Exopeptidases hydrolyse peptide bonds on last amino acids in each peptide chain to release dipeptides and amino acids.
Dipeptidases hydrolyse peptide bonds in dipeptides. This is membrane bound and part of epithelial cell surface membrane in ileum.

Question 6

Ileum structure

Answer 6

Villi between lumen and blood vessels/tissues increase SA and rate of absorption.
Thin walled, reducing diffusion distance.
Contain muscle so can move to maintain diffusion gradients by mixing contents of ileum.
Well supplied with blood vessels to maintain diffusion gradient.
Microvilli increase SA for absorption.

Question 7

Absorption of amino acids and monosaccharides

Answer 7

Sodium ions actively transported out of epithelial cells into blood by sodium-potassium pump in protein carrier molecule to maintain high conc of Na+ in lumen of intestine relative to epithelial cells.
Sodium ions diffuse into epithelial cells from lumen through different protein-carrier into epithelial cells while carrying glucose or amino acids.
Glucose/amino acids pass into blood plasma by facilitated diffusion.

Question 8

Absorption of triglycerides

Answer 8

Lipids are emulsified by bile salts made by liver to make micelles containing monoglycerides and fatty acids.
These are brought to lining of ileum and are absorbed by diffusion into these cells. The triglycerides are reformed in the cell and move in vesicles to cell membrane.