Digestion And Absorption 6

Question 1

Digestion of carbohydrates

Answer 1

1. Starch hydrolysed by salivary amylase into maltose in mouth
2. Pancreatic amylase hydrolyses remaining starch into maltose
3. Complete hydrolysis of starch to glucose occurs in ileum by maltase, lactase and sucrase

Question 2

Digestion of lipids

Answer 2

Lipids are hydrolysed into glycerol, fatty acids and monoglycerides by lipase
Lipase hydrolyses the ester bonds in triglycerides
Rate of hydrolysis is increased by bile salts as they emulsify lipids causing them to form droplets increasing SA

Question 3

Digestion of proteins

Answer 3

Endopeptidases hydrolyse proteins into polypeptides by working inside amino acid chain
Exopeptidases hydrolyse polypeptides into dipeptides by working at the ends of amino acid chain
Dipeptidases hydrolyse dipeptides into amino acids

Question 4

Ileum is adapted for absorption of digested products..

Answer 4

Large SA due to length and villi and micro villi
Wall of villi consists of a layer of epithelial cells providing a short diffusion pathway
Villi contain bloody capillaries so maintain a high diffusion gradient
Lacteals (lymph vessels) in villi absorb digested lipids maintaining high diffusion gradient
Large number of mitochondria to supply ATP

Question 5

Absorption of digested lipids

Answer 5

Monoglycerides and fatty acids associate with bile salts and phospholipids to form micelles - transport poorly soluble monoglycerides and fatty acids to surface of epithelial cell, micelles break down next to epithelial cell which diffuse through bilayer
Short chained fatty acids diffuse from epithelial cells directly into blood
Long chained fatty acids, monoglycerides and glycerol are recombined to form triglycerides which are packaged into chylomicrons which are absorbed into lacteals in villi

Question 6

Absorption of monosaccharides and amino acids

Answer 6

Absorbed down a concentration gradient by facilitated diffusion

Question 7

Co-transport of monosaccharides and amino acids

Answer 7

Eventually conc of monosaccharides and amino acids in epithelial cells increases above the conc in lumen of ileum
1 sodium ions move into epithelial cells along conc gradient
2 to ensure uptake it is essential to maintain a lower conc of sodium ions in epithelial cells than in lumen
3 sodium ions therefore must be actively transported out of the other end of the cell and into bloody capillaries via carrier proteins
4 sodium continues to diffuse into epithelial cells from lumen through carrier protein. Glucose moves through carrier with sodium
5 glucose passes into bloody capillary by facilitated diffusion