digestion ,enzymes and absorption

Question 1

Describe how glucose is absorbed from the ilium into the blood

Answer 1

Na+ (sodium ions) are actively transported out of epithelial cell into the blood (by sodium potassium pump);
This creates a concentration gradient of Na+ (between lumen of the ilium and the epithelial cell)
(Cotransporter proteins have 2 binding sites complementary to Na+ and glucose.
Na+ and glucose enter by facilitated diffusion using a complementary cotransporter protein
Na+ diffuse into the cell down its concentration gradient.
Glucose moves into the cell against its concentration gradient / down an electrochemical gradient
Glucose moves into the blood by facilitated diffusion

Question 2

Describe and explain the role of enzymes in the complete digestion of polypeptide chains

Answer 2

Endopeptidases hydrolyse peptide bonds within the polypeptide producing shorter polypeptides.
This increases surface area for exopeptidases to act on.
Exopeptidases hydrolyse peptide bonds at the end of peptides producing amino acids (or dipeptides)
Dipeptidases hydrolyse the peptide bond in a dipeptide producing two amino acids.
Amino acids can be absorbed

Question 3

Describe the purpose of bile salts in lipid digestion.

Answer 3

Smaller droplets have a larger surface area to volume ratio
More surface for lipase to act
faster hydrolysis of triglycerides into glycerol, fatty acids and monoglycerides.

Question 4

Describe the role of micelles in absorption of fats into cells of the ileum

Answer 4

1.Micelles are bile salts and fatty acids
2.Make the fatty acids more soluble in water
3.carry fatty acids to cell lining of the ileum
4.Maintain higher concentration of fatty acids at cell lining than inside the cell.
5.Fatty acids (only) absorbed by simple diffusion

Question 5

Describe how and where triglycerides are reformed and absorbed.

Answer 5

1. Fatty acids and glycerol recombine to form triglycerides at Smooth endoplasmic reticulum.
2. Triglycerides are modified by addition of proteins to make chylomicrons and then packaged into vesicles at the golgi apparatus.
3. Chylomicrons are transported into lymph/lacteal vessel by exocytosis.