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🩸 Important Topics in Blood Physiology - First Year MBBS

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⭐ MUST-KNOW TOPICS (Most Exam-Frequent)

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1. Erythropoiesis (RBC Formation)

• Sites: yolk sac (embryo) → liver/spleen (fetus) → red bone marrow (adult)
• Stages: Proerythroblast → Basophilic erythroblast → Polychromatophilic erythroblast → Orthochromatophilic erythroblast → Reticulocyte → Mature RBC
• Requirements: Iron, Vitamin B12, Folic acid, Erythropoietin (EPO)
• EPO: Produced mainly by the kidneys (85%), triggered by hypoxia
• EPO shortens erythropoiesis from ~7 days to ~4 days

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2. Hemoglobin

• Structure: 4 globin chains + 4 heme groups; each heme has 1 Fe²⁺ ion
• Types: HbA (α2β2) - normal adult; HbA2 (α2δ2); HbF (α2γ2) - fetal; HbS - sickle cell
• Normal values: Males ~15-16 g/dL; Females ~14-15 g/dL
• O₂-Hemoglobin Dissociation Curve (very important): sigmoid shape, P50 = 26 mmHg
• Bohr Effect: Increased CO₂/decreased pH → RIGHT shift → more O₂ released to tissues
• Haldane Effect: Oxygenation of Hb promotes CO₂ release from blood
• Right shift (↓O₂ affinity): ↑temp, ↑CO₂, ↑H⁺ (↓pH), ↑2,3-DPG
• Left shift (↑O₂ affinity): ↓temp, ↓CO₂, ↓H⁺, HbF, CO poisoning

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3. Blood Groups (ABO and Rh)

• Antibodies are agglutinins (IgM), antigens are agglutinogens
• Transfusion reactions: intravascular hemolysis, fever, renal failure

• Rh-positive = has "D" antigen; Rh-negative = no D antigen
• Erythroblastosis Fetalis (HDN): Rh-negative mother + Rh-positive fetus → anti-D IgG crosses placenta in subsequent pregnancies → hemolysis in baby
• Prevention: Anti-D immunoglobulin (RhoGAM) given to Rh-negative mothers

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4. Hemostasis and Blood Coagulation

1. Vascular spasm - immediate smooth muscle contraction (Thromboxane A2 from platelets)
2. Platelet plug - primary hemostasis (ADP, serotonin, TXA2 cause aggregation; vWF links platelets to collagen)
3. Coagulation cascade - secondary hemostasis → fibrin clot
4. Fibrous tissue formation - permanent repair

• Extrinsic pathway: Tissue Factor (TF) + Factor VII → activates Factor X (quicker, ~15 sec)
• Intrinsic pathway: Factor XII activation (contact activation) → slower (~1-2 min)
• Common pathway: Factor X + Va → Prothrombinase → Prothrombin → Thrombin → Fibrinogen → Fibrin
• Factor XIII cross-links fibrin (stable clot)

• Antithrombin III (inhibits thrombin + Xa)
• Protein C & S (inactivate Va and VIIIa)
• Tissue Factor Pathway Inhibitor (TFPI)
• Prostacyclin (PGI₂) from endothelium - inhibits platelet aggregation

• PT (Prothrombin Time): tests extrinsic + common pathway (Factors I, II, V, VII, X) - normal 12-15 sec
• aPTT: tests intrinsic + common pathway - normal 25-35 sec
• Bleeding time: platelet function - normal 2-7 min
• Clotting time: normal 5-8 min

• Hemophilia A: Factor VIII deficiency
• Hemophilia B (Christmas disease): Factor IX deficiency
• Both: ↑aPTT, normal PT

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5. White Blood Cells (Leukocytes)

• Neutrophilia: bacterial infection
• Eosinophilia: allergy/parasites
• Lymphocytosis: viral infections
• Monocytosis: chronic infections

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6. Plasma Proteins

• Normal total plasma proteins: 6.5 - 8.5 g/dL
• Albumin: 3.5 - 5 g/dL
• A:G ratio: ~1.5-2.5:1 (reversal suggests chronic liver disease/nephrotic syndrome)
• Plasma vs. Serum: Serum = Plasma minus clotting factors (no fibrinogen)

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7. Anemia - Types and Classification

• Microcytic (MCV <80): Iron deficiency anemia, thalassemia
• Normocytic (MCV 80-100): Aplastic anemia, hemolytic anemia, acute blood loss
• Macrocytic (MCV >100): B12/folate deficiency (megaloblastic anemia)

• Iron deficiency: most common anemia worldwide; hypochromic microcytic
• Pernicious anemia: lack of intrinsic factor → B12 malabsorption
• Sickle cell: HbS (valine replaces glutamate at position 6 of beta chain)

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📋 IMPORTANT SHORT QUESTIONS

1. Differences between plasma and serum
2. Erythropoietin - production site, stimulus, mechanism
3. Universal donor and universal recipient blood groups
4. Erythroblastosis fetalis - mechanism and prevention
5. Bohr effect vs Haldane effect
6. 2,3-DPG and its role in O₂ delivery
7. Positive and negative chemotaxis in WBCs
8. Fibrinolysis - plasminogen → plasmin (by t-PA)
9. Differences between Hemophilia A and B
10. Functions of the spleen in blood physiology

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🧠 QUICK REVISION - IMPORTANT NUMBERS

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📌 EXAM STRATEGY FOR TOMORROW

1. Hemostasis & Coagulation cascade (always a long question)
2. Blood Groups (ABO + Rh + erythroblastosis fetalis)
3. Hemoglobin structure + O₂ dissociation curve
4. Erythropoiesis + EPO
5. WBC types and functions
6. Plasma proteins + A:G ratio
7. Anemia classification