Absorption of the products of digestion

Question 1

How is the illeum adapted to its function by having villi?

Answer 1

The wall of the illeum is folded in order to have villi , which have thin walls, lined with epithelial cells on the other side of which is a rich network of blood capilaries, the villi increase SA of the illeum therfore increasing the rate of absorption

Question 2

How does the intestines having villi increase the efficiency of absorption

Answer 2

• Inc SA for diffusion
• Thin walled reducing the diffusion distance
• They contain muscle and are able to move helping maintain diffusion gradients because their movements mixes the contents of the illeum ensuring that when the products of digestion are absorbed from the food adjacent to the villi new material rich in the products of digestion replaces it
• Well supplied with blood vessels so blood can carry away absorbed molecules and maintain a conc gradient
• Epithelial cells that line this possess microvilli which further inc the SA of absorption

Question 3

How are the products of hydrolysed carbohydrates and proteins absorbed by the illeum?

Answer 3

Carbohydrates hydrolyse into monosacharides such as glucose and fructose
These are absorbed by co transport and diffusion

Question 4

How are the products of lipid digestion absorbed by the ileum?

Answer 4

• Monoglycerides and fatty acids remain in association with bile salts that digested them, forming micelles ( 4nm diameter)
• These micelles then encounter the epithelial wall and break down back to monoglycerides and fatty acids, these are non polar meaning they can easily diffuse across the cell surface membrane into epithelial cells
• Inside the E cells they go to the endoplasmic recticulum where they are recombined to form triglycerides
• Triglycerides reassociate with cholesterol and lipoproteins to form chilomicrons which are particles adapted for transport of lipids
• Chilomicrons move out of E cells in exocytosis entering the lymphatic capillaries called lacteals found at the centre of each villus
• Lymphatic vessles then enter the blood stream where these triglycerides are hydrolysed by an enzyme in the endothelial cells of blood cappilaries

Question 5

Describe the role if micelles in absoption of fats lnto cells lining the illeum

Answer 5

• Micelles consist of fatty acids and bile salts
• This makes the fatty acids more soluble in water
• Brings and releases fatty acids into cells lining the illeum
• Maintains a high conc of fatty acids at the cells lining the ileeum
• Fatty acids are then abrobed by diffusion

Question 6

Describe the role of enzymes in the digestion of proteins in a mammal

Answer 6

• Endopeptidase act in the middle of a peptide chain hydrolysing peptide bonds to form individual peptides
• Exopeptidase act at the ends of peptide chains producing dipeptides and amino acids
• Dipeptidase acts on a dipeptide hydrolysing the bond to give 2 single amino acids

Question 8

Describe the advantages of lipid droplet and micelle formation

Answer 8

• Droplets increase the surface area for more lipase action so faster hydrolysis of lipids
• Micelles carry fatty acids and monoglycerides through the membrane into the intestinal epithelial cell

Question 9

How is the golgi body involved in the absorption of lipids

Answer 9

• It posesses triglycerides
• Combines triglycerides with proteins
  -Packages them by forming vesicles for excoytosis