Biochemical aspects of liver metabolism

Question 1

What is the livers principle roles?

Answer 1

Final destination of absorbed products from the liver 
Bile production 
Elimination of unwanted molecules 
Secretion of plasma proteins 
Storage of important molecules 
Regulation of metabolism

Question 2

Describe the plasma proteins?

Answer 2

Albumin
Alpha globulins
Beta globulins
Gamma globulins (immunoglobulins)

Question 3

What allows separation of proteins by size - plasma proteins?

Answer 3

Electrophoresis

Question 4

What are the main functions of plasma proteins?

Answer 4

Maintenance of oncotic or colloid osmotic pressure 
Transport of hydrophobic substances 
pH buffering 
Enzymatic 
Immunity

Question 5

What is the function of alpha goblin?

Answer 5

Transports lipids, bilirubin, lipoproteins and some dietary metals

Retinol binding protein - transports Vitamin A

Question 6

What is the function of beta globulins?

Answer 6

Transferrin - transports Fe3+, indicator of iron deficiency

Fibrinogen - inactive form of fibrin, clotting of the blood

Question 7

What does transferrin do?

Answer 7

Transports Fe3+ - indicator of iron deficiency

Question 8

What does fibrinogen do?

Answer 8

Inactive form of fibrin

Clotting of the blood

Question 9

Describe albumin?

Answer 9

Most abundant plasma protein - main determinant of plasma oncotic pressure

Question 10

What stimulates the production of albumin?

Answer 10

Insulin stimulates the production of albumin

Question 11

What causes a decrease of albumin levels?

Answer 11

Starvation/low protein diet

Question 12

What does albumin transport?

Answer 12

Endogenous lipophilic substances
Fatty acids
Bilirubin
Thyroid hormones

Exogenous
Drugs like aspirin

Question 13

What is bilirubin the breakdown product of?

Answer 13

Breakdown product of haem

Question 14

What is iron transported as?

Answer 14

Ferric iron Fe3+

Question 15

What is Ferric iron Fe3+ bound to when being transported?

Answer 15

Transferrin

Question 16

Where is iron stored?

Answer 16

In cells bound to ferritin

Question 17

What is copper bound to when transported in the blood?

Answer 17

Ceruoplasmin

Question 18

What is copper essential for?

Answer 18

The regulation of redox reactions, transport and use of iron

Question 19

What is a deficiency of copper called?

Answer 19

Wilsons disease

neurological symptoms and liver pathology due to copper accumulation in tissues…. [Cu2+] is not bound by ceruloplasmin and so is improperly metabolised and excreted

Question 20

What are steroid hormones derived from?

Answer 20

Cholesterol

Question 21

What is thyroxine transported in the blood?

Answer 21

Bound to thyroid-binding globulin

Question 22

What is cortisol transported in the blood?

Answer 22

Bound to cortisol-binding globulin

Question 23

Describe lipoproteins?

Answer 23

Core of hydrophobic lipids
Surround by a shell (phospholipid, and apoproteins)
Free cholesterol dispersed throughout

Fat transport between organs and tissue

Question 24

What is the function of HDL?

Answer 24

Reverse cholesterol transport

Question 25

What is the function of LDL?

Answer 25

Cholesterol transport to peripheral tissues

Question 26

Describe reverse cholesterol transport by HDL?

Answer 26

It removes excess cholesterol from cells

Question 27

What is the liver the only organ capable of metabolising and excreting?

Answer 27

Cholesterol

Question 28

When cholesterol is esterifed with fatty acids and transported back to the liver what does the liver do?

Answer 28

It excretes it as bile salts via the biliary system or faeces

Question 29

What does the liver store?

Answer 29

Vitamins A, D and B12 | Iron

Question 30

Where does the iron stored in the liver come from?

Answer 30

The breakdown of haemoglobin, soared associated with ferritin

Question 31

What is cholesterol as essential component of?

Answer 31

Mammalian cell membranes - increases the rigidity

Question 32

What is cholesterol the precursor for?

Answer 32

Three important classes of biologically active compounds - bile acids - steroid hormones - Vit D

Question 33

Where is cholesterol stored?

Answer 33

It can be incorporated into lipoproteins and thus solubilised (located in the core of the molecule) IT can be stored in lipid droplets Majority of it is esterified to a wide range of long chain fatty acids 30% is circulating in free form

Question 34

Where is cholesterol synthesised?

Answer 34

In virtually all cells | Mainly in the liver

Question 35

What does synthesis of 1mol of cholesterol require?

Answer 35

Source of C atoms - 18mol of acetly-CoA Source of reducing power - 16 mol of NADPH Significant amounts of energy - 36mol of ATP

Question 36

What does HMG-CoA reductase do?

Answer 36

Catalyses the irreversible formation of mevalonic acid It is a rate limiting enzyme

Question 37

What is HMG-CoA reductase a target for?

Answer 37

Cholesterol lowering drugs - statins

Question 38

What is cholesterol synthesis controlled by?

Answer 38

Hormones HMG-CoA reductase

Question 39

Describe steroid hormones as a product of cholesterol?

Answer 39

Three groups Corticosteroids (adrenal cortex) Androgens (testis) Estrogens (ovary)

Question 40

What is the main metabolic product of cholesterol?

Answer 40

Bile salts

Question 41

Where are bile salts synthesises and secreted by?

Answer 41

The liver

Question 42

What do bile salts act as?

Answer 42

Dtgergents for emulsifying ingested lipids

Question 43

What are bile salts recycled by?

Answer 43

The enterohepatic circulation