Liver Physiology

Question 1

What are the functions of the liver

Answer 1

• Filtration/storage of blood
• Metabolism of CHO/fats/proteins/foreign chemicals/ammonia
• Bile formation
• Storage of iron and vitamins
• Formation of blood proteins (e.g. albumin)

Question 2

Describe the contents of the hepatic artery and portal vein.

Answer 2

Hepatic artery is O2 rich - supplies liver with blood.

Portal vein is nutrient rich: products of digestion first pass through the liver via the portal vein.

Question 3

What are Kupffer cells?

Answer 3

Contain macrophages.

Removal >99% git BACTERIA.

Question 4

How does sympathetic tone impact blood flow to liver?

Answer 4

High sympathetic tone limits blood flow to liver and vice-versa.

Noradrenaline causes vasoconstriction of portal vein and hepatic artery, diverting blood away from liver.

Question 5

What are the vasodilator fibres in the liver.

Answer 5

Trick question- there are no vasodilator fibres of the liver.

All dilation is due to local control: adenosine produced by liver causes vasodilation.

Question 6

Describe the functionality of the counter-current flow of bile.

Answer 6

Bile with high concentration of extracted compounds requires the MOST energy to put more stuff in - so this is next to the highest concentration blood.

Question 7

What do the relative pressures of porta and hepatic supplies cause ?

Answer 7

Portal venous pressure = 10mmHg

Hepatic venous pressure = 5mmHg

Hepatic arterial pressure = 90mmHg

Large difference in pressure creates fluid production (lymph), which is drained into the lymphatic duct.

Question 8

How does the liver provide a blood glucose buffer?

Answer 8

Too much glucose = liver can convert glucose into glycogen.

Too little glucose = liver can break down glycogen into glucose.

Question 9

What roles does the liver play in fat metabolism?

Answer 9

• Primary site of beta-oxidation
• Synthesise fats from CHO/AA, cholesterol from acetyl-CoA
• Catabolises cholesterol to form bile salts
• Storage and formation of lipoproteins.

Question 10

What vitamins does the liver store?

Answer 10

Vitamin A (5-10month supply)

Vitamin B12 (1yr supply)

Vitamin D

Vitamin K

Question 11

Describe the storage of iron in the liver (Hint: Fe2+ and Fe3+)

Answer 11

Iron is bound to ferritin.

Ferroxidase converts Fe2+ to Fe3+ (safe storage)

Ferroductase converts Fe3+ to Fe2+ (soluble release)

Elevated levels of Fe causes release of hepcidin, closing ferroportin channels.

Question 12

What is the function of bile?

Answer 12

• Bile salts - emulsification and absorption of fats
• Excretion of waste products from blood into bile (e.g. bilirubin, drugs, toxins, cholesterol)

Question 13

How is bilirubin formed, and how is it taken up the liver.

Answer 13

BIlirubin is formed from the breakdown of haem. Bilirubin binds to albumin i in the blood, and is taken up by OATP. It dissociates and is conjugated to form glucuronic acid (can’t diffuse back across). Forms bilirubin di-gluconoride (BG2)

Question 14

How is bilirubin reabsorbed?

Answer 14

Bacterai convert bilirubin di-glucoronide into urobilinogens.

Small intesteine and colon is permeable to urobilinogens and free bilirubin, but IMPERMEABLE to BG2 and conjugated bilirubin.

Question 15

What are the two broad causes of excess bilirubin?

Answer 15

Haemolytic cause (excessive RBC destruction) and hepatic causes (impaired uptake and processing)

Question 16

Why do newborns often have jaundice, and how is it treated?

Answer 16

Newborn have poorly formed bilirubin conjugating enzymes, so jaundice is common.

Can use phototherapy to promote bilirubin into a photo-isomer which is easy to excrete.