Haem Physiology

Question 1

What are the components of blood?

Answer 1

Plasma (55%)
- Water (91%)
- Proteins: Albumin. Immunoglobulins, Fibrinogen
- Solutes: ions, nutrients, gases, waste
Buffy Coat (<1%)
- Leukocytes: Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils
- Thrombocytes (platelets)
Red Blood Cells

Question 2

How does albumin maintain osmotic pressure in the circulation?

Answer 2

• Capillaries are constantly leaking fluid into interstitium
• Albumin’s negative charge + inability to leak out of capillaries allow it to pull water back into capillaries

Question 3

What is hematocrit?

Answer 3

Relative vol of RBCs out of the total blood volume (Men: 46%, Women: 42%)

Question 4

Outline the steps of erythropoiesis.

Answer 4

Phase 1: Ribosome synthesis in early erythroblasts
Phase 2: HB accumulation in late erythroblasts & normoblasts
Phase 3: Ejection of nucleus from normoblasts, reticulocyte formation

Question 5

How are red blood cells destroyed?

Answer 5

• Aged and damaged RBCs are engulfed by macrophages of liver, spleen, bone marrow
• Haemoglobin broken down: heme broken into bilirubin and iron (stored as ferritin) and globin broken into amino acids
• Iron is bound to transferrin and released to blood from liver as needed for erythropoiesis
• Bilirubin picked up from blood by liver , secreted into intestine in bile, excreted into faeces
• Nutrients eg amino acids, Fe, B12, are absorbed from intestine and reenter blood

Question 6

What are the stages of haemostasis?

Answer 6

Vasoconstriction, platelet plug, fibrin clot

Question 7

What happens in the vasoconstriction stage of haemostasis?

Answer 7

• Initiated by sympathetic nerves, mediated by vascular smooth muscles
• Endothelial cells contract, exposing the basal lamina
• Triggered when there is damage, to reduce blood loss

Question 8

How is the platelet plug formed in haemostasis?

Answer 8

Platelet Adhesion
→ Mediated by von Willebrand’s Factor
- Plasma protein produced by platelets
- Binds platelets to exposed collagen
→ Adhesion activates platelets, resulting in morphological change – triggers release of granules containing platelet agonists, resulting in aggregation

Platelet Aggregation
→ Triggered by platelet agonists from granules (eg ADP, Thromboxane A2 etc)
- ADP attracts and activates more platelets
- Thromboxane A2 promotes aggregation & further vasoconstriction
→ Fibrinogen links platelets through glycoprotein receptors – linkages are weak, needing reinforcement from the fibrin clot

Question 9

List out the Coagulation Cascade.

Answer 9

Extrinsic: XII → XI → IX → X
Intrinsic: damaged tissue releases III → VII → X
Common: X → Prothrombin → Fibrinogem

Question 10

List the Clotting Factors.

Answer 10

I: Fibrinogen
II: Prothrombin
III: Tissue Factor
IV: Calcium ions
V: Procalcitonin (Labile Factor)
VI: -
VII: Proconvertin (Stable Factor)
VIII: Antihemophilic
IX: Plasma thromboplastin (Christmas Factor)
X: Stuart Prower Factor
XI: Hagoman Factor
XII: Fibrin-stabilizing Factor

Question 11

Outline the process of fibrinolysis.

Answer 11

→ During clot formation, plasminogen is trapped inside the clot.
→ Plasminogen is a plasma protein and protease precursor made by the liver
→ The surrounding tissue and vascular endothelial cells slowly release tissue plasminogen activator (tPA), which cleaves plasminogen to the protease plasmin – plasmin digests fibrin, thereby dissolving the clot
→ Macrophages remove the remains of the clot