Cardiac Biochemistry

Question 1

Describe a lipoprotein

Answer 1

A lipoprotein is formed from a protein and lipids.

Hydrophobic lipids are seen at the core and hydrophilic at the exterior.

Phospholipids, apoproein, cholesterol and triglycerides form lipoproteins

Question 2

Describe the composition of different lipoproteins

Answer 2

Chylomicron, VLDL, IDL, LDL and HDL

Decrease in their protein content and increase in their cholesterol content.

Major lipid in chylomicrons and VLDL is TG. Cholesterol is the major lipid in the others.

They also vary in the type of apoprotein.

Question 3

Describe the importance of triglycerides

Answer 3

Formed from 3 fatty acids and a glycerol molecule.

They act as energy storage. Lipolysis and subsequent beta-oxidation of the fatty acids provides an energy source for the body.

Question 4

Describe the importance of cholesterol

Answer 4

Functions:

• Steroid hormone synthesis
• Bile synthesis
• Precursor of vitamin D
• Component of plasma membrane

All carbons in cholesterol are derived from acetate

Question 5

Describe lipoprotein metabolism

Answer 5

Question 6

Give examples of way to reduce triglyceride and cholesterol levels

Answer 6

• Decrease intake of saturated foods, cholesterol and sugar
• Moderate alcohol intake
• Exercise
• Lose weight
• Increase intake of insoluble fibres (plant sterols decrease cholesterol levels)

Ultimately, this prevents overload of the system and subsequently lipid deposits in vessels and tissues.

Question 7

Define embolus and thrombus

Answer 7

Thrombus: A blood clot adhered to the vessel wall which occludes the vessel

Embolus: A blood clot which travels to a distal site and occludes a vessel

Question 8

Give examples of inherited defects of haemostasis

Answer 8

• Sickle cell anaemia
• Mutations in clotting factors
• Mutations in platelet associated genes
• Conditions that impair bone marrow formation (source of platelets)
• Defects in collagen production

Question 9

Give examples of how nutrient defects cause defects in haemostasis

Answer 9

• Vitamin C deficiency (reduced production of collagen)
• Vitamin K deficiency
• Iron deficiency

Question 10

Describe the vessels role in haemostasis

Answer 10

• Endothelium secretes NO for vasodilation
• Smooth muscle cells perform vasoconstriction
• The basement membrane is exposed. Blood is not exposed to collagen.
• Exposure of the vessel wall, exposing the blood to activating factor
• Lysed cells secrete ADP

Question 11

Describe the platelets role in haemostasis

Answer 11

Platelets allow for clotting of blood. A fibrin mesh is created.

Question 12

Describe the fibrinolytic cascade’s role in haemostasis

Answer 12

Plasminogen is converted to plasmin, a serine protease. Plasmin acts to breakdown fibrin clots. This acts to decrease occlusion of vessels.

• Streptokinase activates plasmin
• Urokinase activates plasmin
• Alteplase activates plasmin

Question 13

Explain how blood clots form and resolve

Answer 13

Form: Clots form through the activation of the coagulation cascade. This allows fibrin to be generated. Fibrin creates a mesh for platelets. A platelet plug is formed to limit blood loss.

Resolution occurs via plasmin mediated breakdown of the clots.

Question 14

Molecules secreted by platelets: Explain the functions of ADP, Von Willebrand factor, serotonin and TXA₂

Answer 14

ADP: Activates other platelets

Von Willebrand Factor: Allows adhesion of platelets

Serotonin: Vasocontriction (can also act to vasodilate, as seen in inflammation)

TXA₂: Vasocontriction

Question 15

Describe the mechanisms by which platelets are activated

Answer 15

1. Binding to ADP
2. Platelet activating factor (released from vessel walls)
3. Collagen (vessel ECM)
4. Thrombin
5. Immune complexes
6. High physical shear force