Absorption

Question 1

How is the ileum adapted to its function?

Answer 1

Function of absorbing the products of digestion:
• Wall of the ileum is folded and possess finger like projections called villi
• Thin walls lined with epithelial cells on the other side of which has a rich network of blood capillaries
• Villi increase surface area, which increases the surface area of the ileum and therefore accelerate the rate of absorption

Question 2

Where are villi located?

Answer 2

Interface between lumen of the intestines and the blood and other tissues inside the body.

Question 3

How do villi increase efficiency of absorption?

Answer 3

• They increase surface area for diffusion
• Very thin walled, reducing distance over which diffusion takes place
• Contain muscle, therefore able to move, helps maintain diffusion gradients because movements mix contents of the ileum
• Well supplied with blood vessels and so that blood can carry away absorbed molecules and hence maintain a diffusion gradient
• Epithelial cells lining the villi possess microvilli, these further increase surface area

Question 4

How do villi muscles help maintain diffusion gradients?

Answer 4

• Through using muscles, able to move
• Movements mix contents of the ileum, which means as the products of digestion are absorbed from the food adjacent to the villi, new material rich in the products of digestion replaces it

Question 5

What does the digestion of proteins produce?

Answer 5

Amino acids

Question 6

What does the digestion of carbohydrates produce?

Answer 6

Monosaccharides:
• Glucose
• Fructose
• Galactose

Question 7

What happens to monoglycerides and fatty acids when formed during digestion?

Answer 7

• Remain in association with the bile salts that initially emulsified the lipid droplets
• Structures formed are called micelles

Question 8

What is the purpose of micelles?

Answer 8

• Through the movement of material inside the lumen of the ileum, micelles will come into contact with the epithelial cells lining the villi of the ileum
• Micelles break down, releasing the monoglycerides and fatty acids.
• These being non polar molecules, are able to easily diffuse across the surface membrane into the epithelial cells

Question 9

What happens to monoglycerides and fatty acids when passing into the epithelial cells?

Answer 9

• Monoglycerides and fatty acids are transported to the endoplasmic reticulum where where they are recombined to form triglycerides
• Starting in the ER and continuing in the golgi apparatus, the triglycerides associate with cholesterol and lipoproteins to form structures called chylomicrons

Question 10

What are chlyomicrons?

Answer 10

Special particles adapted for transport of lipids

Question 11

How do triglycerides reach the ER & golgi apparatus?

Answer 11

• monoglycerides and fatty acids will remain in association with the bile salts that initially emulsified the lipid droplets
• They will form structures that
• Through the movement of material inside the lumen of the ileum, micelles will come into contact with the epithelial cells lining the villi of the ileum
• Micelles break down, releasing the monoglycerides and fatty acids.
• These being non polar molecules, are able to easily diffuse across the surface membrane into the epithelial cells are called micelles
• Monoglycerides and fatty acids are transported to the endoplasmic reticulum where where they are recombined to form triglycerides
• Starting in the ER and continuing in the golgi apparatus, the triglycerides associate with cholesterol and lipoproteins to form structures called chylomicrons

Question 12

By which process do chlyomicrons move out of the epithelial cells?

Answer 12

• Exocytosis
• They enter lymphatic capillaries called lacteals that are found at the centre of each villus
• Chlyomicrons pass via lymphatic vessels into the blood system
• Triglycerides in the chylomicrons are hydrolysed by an enzyme in the endothelial cells of blood capillaries, from where they diffuse into cells

Question 13

How is glucose absorbed?

Answer 13

• Via active transport with sodium ions via a co transporter protein
• Galactose is absorbed in the same way using the same co transporter protein

Question 14

How are amino acids absorbed?

Answer 14

• Sodium ions are actively transported out of the epithelial cells into the ileum itself
• They then diffuse back into the cells through sodium dependent transporter proteins in the epithelial cell membranes carrying the amino acids with them