5. Liver: Biosynthetic Functions

Question 1

What are the functions of the liver?

Answer 1

Metabolism
Synthesis
Excretion and detoxification: bilirubin, amino acids and NH3, Cholesterol, steroid hormones, drugs, toxins

Question 2

Name a reaction in the liver that is compartmentalised

Answer 2

Ammonia detoxification

Question 3

What metabolism is carried out in the liver?

Answer 3

glycogenesis, glycogenolysis, gluconeogenesis and fatty acid metabolism

Question 4

What substances are made by the liver?

Answer 4

plasma proteins, coagulation factors, haem, lipoproteins, bile acids

Question 5

What substances are excreted and detoxified by the liver?

Answer 5

bilirubin, amino acids and NH3, Cholesterol, steroid hormones, drugs, toxins

Question 6

What determines the rate of production of albumin?

Answer 6

Physiological stress

Concentration of colloids in hepatic interstitium

Question 7

What are the functions of albumin?

Answer 7

Transportation of substances

Oncotic pressure

Question 8

Describe the production of albumin

Answer 8

1. Preproalbumin has a 24 AA extension at the N terminal end
2. AA extension signals insertion into ER membrane
3. 18 AAs cleaved in lumen=proalbumin
4. Proalbumin moved to glogi apparatus, 6AA removed
5. Albumin secreted immediately

Question 9

What conditions can increase albumin loss from plasma?

Answer 9

Nephrosis

Lymphoedema

Question 10

Where in the body can albumin be stored?

Answer 10

Vascular compartments of skin, muscle, liver, gut

Question 11

What is the structure of alpha and beta globulins?

Answer 11

Glycoproteins

Question 12

What are alpha and beta globulins cleared by?

Answer 12

Asialoglycoprotein receptors on surface of hepatocytes

Question 13

What are the functions of alpha and beta globulins?

Answer 13

Transport
Protease inhibitors
Clotting factors

Question 14

What might decreased alpha and beta globulins indicate?

Answer 14

Genetic disorder

Malnutrition

Question 15

What might increased alpha and beta globulins indicate?

Answer 15

Post-inflammation or trauma

Question 16

What is the structure of haem?

Answer 16

Ferrous iron is chelated onto a porphyrin ring

Question 17

Name 4 examples of haemoproteins

Answer 17

Haemoglobin
Myoglobin
Cytochrome P450 proteins
Catalase

Question 18

What is the first enzyme involved in haem synthesis?

Answer 18

ALA synthase

Question 19

Where is ALA synthase found?

Answer 19

Mitochondria

Question 20

What is ALA synthase inhibited by?

Answer 20

Non-protein bound haem by negative feedback

Question 21

Where is ALA dehydratase found?

Answer 21

Cytoplasm

Question 22

What is the function of ALA dehydratase?

Answer 22

Converts 2 ALA molecules to PBG

Question 23

Which enzyme is sensitive to inhibition by lead?

Answer 23

ALA dehydratase

Question 24

What is the function of Uropophyrinogen synthase 1?

Answer 24

Converts 4 PBG to uroporphyrinogen

Question 25

What are the porphyrias?

Answer 25

Group of metabolic disorders caused by partial defects in one of the haem biosynthetic enzymes

Question 26

What is Acute Intermittent Porphyria a defect in?

Answer 26

Uroporphyrinogen synthase 1

Question 27

What does Acute Intermittent Porphyria result in?

Answer 27

Accumulation of ALA and PBG

Question 28

What is the treatment for AIP?

Answer 28

Haematin respresses ALA synthase

Switches off pathway

Question 29

What are the features of Porphyria Cutanea Tarda?

Answer 29

Itching, erythema, blistering

Question 30

What is the cause of PCT?

Answer 30

Deficiency of uroporphyrinogen decarboxylase

Question 31

What are the consequences of PCT?

Answer 31

Accumulation of porphyrins and porphyrinogens