B15 - The Liver

Question 1

What three main substances need to be excreted in mammals? And how are they excreted? (6)

Answer 1

CO2:
- excreted to lungs

Bile pigments:
- colour faeces
- from haemoglobin breakdown
- excreted in bile
- transported from liver to small intestine via bile duct.

Urea(nitrogenous waste):
- from excess amino acids breakdown
- secreted in urine by kidneys

Question 2

Which blood vessel supplies oxygenated blood to the liver from the heart? (1)

Answer 2

Hepatic artery

Question 3

What is the role of the hepatic portal vein? (2)

Answer 3

• supplies deoxygenated blood to liver from intestines
• contains products of digestion
• liver absorbs and metabolises nutrients
• supplies 75% of blood through the liver

Question 4

Describe the process of bile excretion (3)

Answer 4

• hepatocytes secrete bile from breakdown of haemoglobin into canaliculi.
• bile drained into bile ductules and is carried to the gall bladder.
• bile released into duodenum via bile duct
• then to small intestines

Question 5

State the role of sinusoids. (2)

Answer 5

• where blood from hepatic artery and hepatic portal vein is mixed.
• helps increase oxygen supply for hepatocytes’ needs.

Question 6

What are the macrophages of the liver called?

Answer 6

Kupffer cells

Question 7

What structures is the liver divided into?

Answer 7

Lobules

Question 8

What are the three main functions of the liver? (3)

Answer 8

• detoxification
• carbohydrate metabolism
• deamination of excess amino acids

Question 9

What harmful substances are detoxified by the liver? Explain their detoxification in as much detail as possible. (6)

Answer 9

Ethanol metabolism:
- hepatocytes have enzyme alcohol dehydrogenase which converts ethanol to ethanal
- ethanal –> ethanoate
- ethanoate used to store/build up fatty acids

Lactate metabolism:
- lactate converted to pyruvate
- some used for aerobic respiration
- some used as glucose and stored as glycogen to maintain BGC.

Hydrogen peroxide:
- hepatocytes contain enzyme catalase
- 2H202 —> 2H20 + 02

Question 10

Explain the importance of carbohydrate metabolism in the liver. (3)

Answer 10

• control blood glucose concentration.
• BGC increases therefore insulin levels increase, triggering glycogenesis to decrease glucose in bloodstream
• BGC decreases therefore glucagon levels increase, triggering glycogenolysis to increase glucose in bloodstream

Question 11

What is transamination? Why is it so important? (2)

Answer 11

• converting one amino acid into another.
• ensures diet has correct balance of amino acids.

Question 12

Describe the process of deamination. (3)

Answer 12

• amino group (NH2) group removed
• converted to very toxic ammonia
• converted to less toxic urea
• excreted by kidneys
• left over amino acids used in respiration or converted to lipids for storage.

Question 13

Why is deamination so important?

Answer 13

• hepatocytes synthesise most plasma proteins
• body cannot store proteins/ amino acids therefore must be deaminated - otherwise would just be excreted as waste.

Question 14

What does the ornithine cycle do?

Answer 14

Converts very toxic ammonia to less toxic/more manageable urea.

Question 15

What are the three main stages of liver cirrhosis? (3)

Answer 15

1) fatty liver
Fat filled vesicles replace nuclei of hepatocytes. Liver enlarges.

2) alcoholic hepatitis
fatty liver, damaged hepatocytes, narrowed sinusoids.

3) Alcoholic cirrhosis
Irreversible damage
Hepatocytes can’t divide/replicate.
Liver shrinks
Harder to detoxify substances