Physiology
Haematology
Haematology for MBBS and NEET-PG: blood composition, erythropoiesis, haemoglobin, white cells, blood groups and coagulation, mapped to NMC codes PY2.
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Haematology
Haematology for MBBS and NEET-PG: blood composition, erythropoiesis, haemoglobin, white cells, blood groups and coagulation, mapped to NMC codes PY2.
Haematology covers the composition of blood and its formed elements. It deals with red cell production and haemoglobin, the white cells and immunity, the blood groups and transfusion, and the mechanisms of haemostasis and coagulation that stop bleeding.
High-yield: Haematology
- Blood makes up about 8 percent of body weight, with plasma forming roughly 55 percent and cells about 45 percent.
- Erythropoietin from the kidney drives red cell production in response to hypoxia.
- The normal haemoglobin is about 13 to 17 grams per decilitre in men and 12 to 15 in women.
- One gram of haemoglobin carries about 1.34 millilitres of oxygen when fully saturated.
- Red cells live about 120 days and are removed by the spleen and reticuloendothelial system.
- Adult haemoglobin is HbA with two alpha and two beta chains, while fetal haemoglobin is HbF with two alpha and two gamma chains.
- The ABO blood groups depend on A and B antigens, and group O is the universal donor for packed red cells.
- Rh incompatibility can cause haemolytic disease of the newborn when an Rh negative mother carries an Rh positive fetus.
- Platelets are formed from megakaryocytes and live about 7 to 10 days.
- Primary haemostasis is platelet plug formation, and secondary haemostasis is the coagulation cascade forming fibrin.
- The intrinsic pathway is measured by the activated partial thromboplastin time and the extrinsic by the prothrombin time.
- Vitamin K is needed for factors two, seven, nine and ten and for proteins C and S.
- Plasma proteins include albumin, which maintains oncotic pressure, and globulins, which include antibodies.
- Neutrophils are the most numerous white cells and lead the acute response to bacterial infection.
Coagulation pathway tests
- **Prothrombin time:** Tests the extrinsic and common pathway. Prolonged by warfarin.
- **aPTT:** Tests the intrinsic and common pathway. Prolonged by heparin and haemophilia.
- **Vitamin K factors:** Factors 2, 7, 9, 10 and proteins C and S.
- **Universal donor:** Group O negative for packed red cells; AB is universal plasma donor.
NMC competencies in this chapter
- **PY2.1:** Composition and functions of blood
- **PY2.2:** Plasma proteins and their functions
- **PY2.3:** Erythropoiesis and its regulation
- **PY2.4:** Haemoglobin structure, types and functions
- **PY2.6:** White blood cells and immunity
- **PY2.8:** Blood groups and transfusion
- **PY2.10:** Platelets and haemostasis
- **PY2.11:** Coagulation and anticoagulants
Frequently Asked Questions
What controls red blood cell production?
Erythropoietin, a hormone released by the kidney in response to low oxygen, stimulates the bone marrow to make more red cells.
What is the difference between the PT and the aPTT?
The prothrombin time assesses the extrinsic and common pathways and is prolonged by warfarin, while the activated partial thromboplastin time assesses the intrinsic and common pathways and is prolonged by heparin and haemophilia.
Why is group O called the universal donor?
Group O red cells lack the A and B antigens, so they are not attacked by anti-A or anti-B antibodies in a recipient of any ABO group.
Which clotting factors depend on vitamin K?
Factors two, seven, nine and ten, along with the natural anticoagulants protein C and protein S, need vitamin K for their production.
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