2 - Digestion and Absorption

Question 1

What is rate of passive diffusion based on?

Answer 1

Hydrophobicity (charge) and concentration gradient

Question 2

List the three types of transporters

Answer 2

• Uniporters (oft in facilitated diffusion)
• Symporters
• Antiporters

Question 3

What happens to maltose, sucrose and lactose in the brush border enzymes of the duodenum?

Answer 3

Maltose -> glucose

Lactose -> galactose

Sucrose -> glucose/fructose

Question 4

How is glucose absorbed?

Answer 4

A symporter transports glucose and sodium ions into the villi where there is a high concentration of glucose

A glucose channel (uniport) then facilitates transport of glucose into the blood where there is a low concentration of glucose

Question 5

Describe pepsin activation

Answer 5

Pepsinogen autocatalytically cleaved to pepsin in low pH. Pepsin can then go on to cleave more pepsinogens (a zymogen)

Question 6

What is the role of enterocytes in protein digestion?

Answer 6

Secrete enterokinases which cleaves trypsinogen to trypsin (active) in the duodenum

After cleavage of proteins to short peptides and amino acids they can be absorbed into the enterocytes by facilitated diffusion

Question 7

Describe the broad steps of lipid digestion

Answer 7

1. Lingual lipase breaks down free fatty acids
2. Emulsification in the stomach
3. Bile and lipases in the small intestine
4. Bacterial digestion in jejunum

Question 8

What is the function of bile salts?

Answer 8

Allows water soluble molecules to attach the lipids

Question 9

How are lipids absorbed?

Answer 9

Transported by chylomicrons into central lacteals of villi

Question 10

WHere is most water absorbed?

Answer 10

1. Small intestine

2. Large intestine