Blood and Body Fluids

🟢 Lite — Quick Review (1h–1d)

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Blood and Body Fluids — Key Facts for NEET PG

• Blood volume: ~5–6 L in adults; plasma is ~55%, RBCs ~45% (hematocrit)
• Blood groups: ABO system (antibodies preformed), Rh system (anti-Rh antibodies only after sensitization)
• Hemostasis: Primary (platelet plug) → Secondary (coagulation cascade) → Fibrinolysis
• Coagulation cascade: Intrinsic (contact activation) and Extrinsic (tissue factor) pathways converge at Factor X
• ⚡ Exam tip: “8 is great, 10 is fine, 5 is dead” — Factors VIII, IX, X, XI, XII, XIII missing cause bleeding disorders

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🟡 Standard — Regular Study (2d–2mo)

Standard content for students with a few days to months.

Blood and Body Fluids — NEET PG Study Guide

Blood Composition

Plasma (55% of blood volume):

• Water: 90–92%
• Proteins: 6–8% (albumin 60%, globulins 36%, fibrinogen 4%)
• Electrolytes: Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, HCO₃⁻
• Nutrients: Glucose, amino acids, lipids
• Waste products: Urea, creatinine, bilirubin
• Gases: O₂, CO₂, N₂

Serum vs Plasma:

• Plasma: Blood with anticoagulant (contains fibrinogen)
• Serum: Plasma without fibrinogen (after clotting)

Packed RBCs: Prepared by centrifugation — volume remaining after plasma removal

Red Blood Cells (Erythrocytes)

Structure:

• Biconcave disc shape (↑ surface area for gas exchange)
• No nucleus, mitochondria, ribosomes
• Contain hemoglobin (Hb) — 2 α + 2 β chains
• Each Hb binds 4 O₂ molecules
• Lifespan: 120 days
• Destroyed in spleen (extravascular hemolysis)

RBC indices (for anemia classification):

Index	Normal Value	Formula
MCV	80–100 fL	PCV/RBC count
MCH	27–33 pg	Hb/RBC count
MCHC	32–36 g/dL	Hb/PCV
RDW	<14.5%	Anisocytosis measure

Anemia Types:

Type	MCV	Causes
Microcytic (<80 fL)	Low	Iron deficiency, thalassemia
Normocytic (80–100 fL)	Normal	Acute blood loss, hemolysis, chronic disease
Macrocytic (>100 fL)	High	B12/folate deficiency, alcohol, liver disease

⚡ Exam tip: Think “TAILS” for microcytic anemia: Thalassemia, Anemia of chronic disease, Iron deficiency, Lead poisoning, Sideroblastic anemia

White Blood Cells (Leukocytes)

Total count: 4,000–11,000/μL

Cell Type	%	Key Features
Neutrophils	50–70%	Segmented nuclei, phagocytosis, first responders
Lymphocytes	20–40%	T cells (cellular immunity), B cells (humoral immunity)
Monocytes	2–8%	Macrophage precursors, longest-lived
Eosinophils	1–4%	Bilobed nuclei, combat parasites
Basophils	<1%	Granules with histamine, heparin

Differential Count (NEET high-yield):

• Neutrophils: ↑ in bacterial infections
• Lymphocytes: ↑ in viral infections, chronic infections
• Eosinophils: ↑ in parasitic infections, allergies, asthma
• Basophils: ↑ in myeloproliferative disorders

⚡ Exam tip: “Band cells” (immature neutrophils) → left shift indicates acute infection/inflammation

Platelets

Normal count: 150,000–400,000/μL Lifespan: 8–10 days Structure: Anucleate fragments from megakaryocytes

Platelet Functions:

1. Maintain vascular integrity
2. Primary hemostasis (platelet plug formation)
3. Release reaction (PDGF for repair)
4. Provide phospholipid surface for coagulation

Blood Groups and Transfusion

ABO System:

Blood Type	Antigens	Antibodies	Can Donate To
A	A	Anti-B	A, AB
B	B	Anti-A	B, AB
AB	A and B	None (universal recipient)	AB
O	None	Anti-A and Anti-B	All (universal donor)

⚡ Exam tip: Blood group antibodies (anti-A, anti-B) are IgM — naturally occurring (NOT from previous transfusion)

Rh System:

• Rh-positive: D antigen present (85% population)
• Rh-negative: D antigen absent
• Erythroblastosis fetalis: Rh-negative mother with Rh-positive fetus → anti-D IgG production → hemolysis in subsequent pregnancies

Crossmatch: Always done before transfusion to ensure compatibility (minor antigens can cause reactions)

Hemostasis

Three Steps:

1. Primary Hemostasis (Vascular phase — 1–3 min):

   • Vasoconstriction
   • Platelet adhesion (via von Willebrand factor) → platelet plug
   • Platelet activation and release reaction

2. Secondary Hemostasis (Coagulation cascade — 5–10 min):

   • Intrinsic pathway: XII → XI → IX → VIII → X
     • Measured by aPTT (Activated Partial Thromboplastin Time)
   • Extrinsic pathway: Tissue factor → VII → X
     • Measured by PT (Prothrombin Time)
   • Common pathway: X → V → II (Prothrombin) → I (Fibrinogen → Fibrin)
   • Fibrin stabilization: XIII cross-links fibrin

⚡ Exam tip: “Extrinsic = Tissue Factor (Factor III); Intrinsic = contact activation (XII)” — both converge at Factor X

3. Tertiary Hemostasis (Fibrinolysis):
   • Plasminogen → Plasmin (via tissue plasminogen activator/tPA)
   • Breaks down fibrin clots
   • FDPs (Fibrin Degradation Products) and D-dimer elevated in DIC

Coagulation Factors (Important for Exam)

Factor	Name	Notes
I	Fibrinogen	Converted to fibrin
II	Prothrombin	Vitamin K dependent
III	Tissue factor	Extrinsic pathway
IV	Calcium (Ca²⁺)	Required for multiple steps
V	Proaccelerin	Cofactor
VII	Proconvertin	Vitamin K dependent
VIII	Antihemophilic factor A	X-linked recessive (hemophilia A)
IX	Christmas factor	X-linked recessive (hemophilia B)
X	Stuart-Prower	Common pathway
XI	Plasma thromboplastin	Intrinsic pathway
XII	Hageman factor	Contact activation
XIII	Fibrin stabilizing	Cross-links fibrin

⚡ Exam tip: Vitamin K is needed for factors II, VII, IX, X (remember: “1972” or “2,7,9,10 — to K”)

Bleeding Disorders

Disorder	Defect	Lab Findings
Hemophilia A	Factor VIII deficiency	↑ aPTT, normal PT
Hemophilia B	Factor IX deficiency	↑ aPTT, normal PT
vWD	von Willebrand factor defect	↑ aPTT, bleeding time ↑
Christmas disease	Factor IX deficiency	↑ aPTT, normal PT
DIC	Consumptive coagulopathy	↓ platelets, ↑ PT/aPTT, ↑ D-dimer

Blood Disorders (High-Yield for NEET PG)

Sickle Cell Anemia:

• Point mutation in β-globin gene (Glu→Val at position 6)
• Autosomal recessive
• RBCs sickle in low O₂ conditions
• Complications: Vaso-occlusive crises, splenic sequestration, stroke

Thalassemia:

• α-thalassemia: Reduced α-globin chains (deletions)
• β-thalassemia: Reduced β-globin chains
• Microcytic, hypochromic anemia

Aplastic Anemia: Pancytopenia due to bone marrow failure

Polycythemia: ↑ RBC mass (primary = polycythemia vera; secondary = chronic hypoxia)

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🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for students on a longer study timeline.

Blood and Body Fluids — Comprehensive NEET PG Notes

Detailed RBC Physiology

Erythropoiesis:

• Site: Bone marrow (all bones in fetus; flat bones in adults)
• Stimulus: Hypoxia → kidney releases EPO (erythropoietin)
• Stages: Pronormoblast → Normoblast → Reticulocyte → RBC
• Reticulocyte count: Indicator of RBC production (normally <2%)
• Factors needed: Iron, B12, folate, B6, copper

Hemoglobin Metabolism:

• HbA (adult): α₂β₂ — 97%
• HbA₂ (adult): α₂δ₂ — 2–3%
• HbF (fetal): α₂γ₂ — <1% in adults
• Fetal Hb has higher O₂ affinity (displaces adult Hb at low O₂)
• Bilirubin: Product of heme breakdown → jaundice

RBC Breakdown:

• Extravascular (spleen): Macrophages phagocytose old RBCs
• Hemoglobin → Globin (amino acids) + Heme → Biliverdin → Bilirubin → Conjugated bilirubin → Excreted in bile
• Jaundice types:
  • Pre-hepatic: ↑ unconjugated bilirubin (hemolysis)
  • Hepatic: ↑ conjugated/unconjugated (liver disease)
  • Post-hepatic: ↑ conjugated bilirubin (obstruction)

WBC Function — Detailed

Neutrophils:

• First responders to infection
• Phagocytose bacteria and fungi
• Neutrophil extracellular traps (NETs): DNA webs to trap pathogens
• Leukocytosis with left shift in acute bacterial infection

Macrophages (from monocytes):

• Phagocytosis of debris, pathogens
• Antigen presentation to T lymphocytes
• Secrete cytokines (TNF-α, IL-1, IL-6)
• Activated by IFN-γ (delayed-type hypersensitivity)

Eosinophils:

• Defend against parasitic infections
• Major basic protein (MBP), eosinophil cationic protein (ECP)
• ↑ in allergic reactions and asthma

Basophils/Mast Cells:

• Release histamine, heparin, leukotrienes
• Mediate Type I hypersensitivity (IgE-mediated)

Lymphocytes:

• T cells: Cell-mediated immunity (thymus-dependent)
  • CD4⁺ helper T cells: Activate macrophages, help B cells
  • CD8⁺ cytotoxic T cells: Kill virus-infected cells
  • T regulatory cells: Suppress immune responses
• B cells: Humoral immunity (bone marrow-derived)
  • Differentiate into plasma cells (produce antibodies)
  • Memory B cells for secondary response
• NK cells: Innate lymphoid cells — kill virus-infected and tumor cells

⚡ Exam tip: CD4 count drops in HIV — opportunistic infections occur when CD4 <200 cells/μL

Platelet Physiology

Platelet Activation Phases:

1. Adhesion: vWF binds to collagen → GP Ib-IX-V receptor binds vWF
2. Activation: Shape change, granule release (ADP, serotonin, TxA₂)
3. Aggregation: GP IIb/IIIa binds fibrinogen → platelet plug
4. Procoagulant activity: Phospholipid exposure for coagulation cascade

Platelet Granules:

• Dense granules: ADP, ATP, serotonin, Ca²⁺
• α-granules: vWF, fibrinogen, PDGF, PF4
• Lysosomes: Degradative enzymes

Antiplatelet Drugs (NEET important):

• Aspirin: Irreversibly inhibits COX → ↓ TxA₂
• Clopidogrel: Blocks ADP receptor (P2Y12) on platelets
• GP IIb/IIIa inhibitors: Abciximab, eptifibatide

Detailed Transfusion Medicine

Transfusion Reactions:

Type	Mechanism	Signs	Management
Hemolytic (acute)	ABO incompatibility	Fever, chills, flank pain, hemoglobinuria	Stop transfusion, fluids, supportive
Hemolytic (delayed)	Minor antigen antibodies	2–10 days post-transfusion	Monitor
Febrile non-hemolytic	Cytokine release, anti-leukocyte antibodies	Fever, chills	Acetaminophen
Allergic	IgE-mediated	Urticaria, pruritus	Antihistamines
Anaphylactic	IgA deficiency with anti-IgA	Hypotension, bronchospasm	Epinephrine
TRALI	Donor antibodies against recipient WBC	Acute respiratory distress	Stop transfusion, oxygen

⚡ Exam tip: TRALI (Transfusion-Related Acute Lung Injury) is the leading cause of transfusion-related death — donor plasma contains antibodies against recipient WBC

Blood Component Therapy:

Component	Indication
Packed RBCs	Anemia, blood loss
Fresh Frozen Plasma	Coagulopathy, warfarin reversal
Platelets	Thrombocytopenia, platelet dysfunction
Cryoprecipitate	Hypofibrinogenemia, vWD, Hemophilia A
Whole blood	Massive hemorrhage

Detailed Hemostasis — Coagulation Cascade

Vitamin K-Dependent Factors: II, VII, IX, X (and Proteins C, S, Z)

Coagulation Cascade — Step by Step:

Intrinsic Pathway:

1. XII activated by collagen/exposure (contact activation)
2. XIIa activates XI
3. XIa activates IX
4. IXa + VIIIa + PL + Ca²⁺ → activates X

Extrinsic Pathway:

1. Tissue factor (III) exposed by damaged tissue
2. TF + VIIa + Ca²⁺ → activates X

Common Pathway:

1. Xa + Va + PL + Ca²⁺ → converts II (prothrombin) to IIa (thrombin)
2. Thrombin converts I (fibrinogen) to Ia (fibrin monomers)
3. XIIIa stabilizes fibrin clot

Natural Anticoagulants:

• Antithrombin III: Inhibits thrombin and factors IXa, Xa, XIa
• Protein C and S: Inactivate Va and VIIIa
• Tissue factor pathway inhibitor (TFPI): Inhibits TF-VIIa complex
• Heparin cofactor II: Inhibits thrombin

⚡ Exam tip: Heparin works by enhancing antithrombin III activity

Tests of Coagulation:

Test	Pathway Measured	Normal Time
PT	Extrinsic (VII, X, V, II, I)	11–13.5 sec
aPTT	Intrinsic (XII, XI, IX, VIII, X, V, II, I)	25–35 sec
Thrombin time	Fibrinogen → fibrin conversion	14–19 sec
Bleeding time	Platelet function	2–7 min

Body Fluid Distribution

Gibbs-Donnan Equilibrium:

• Impermeant anions (proteins) on one side create electrochemical imbalance
• At equilibrium: [Cl⁻]₁ × [Na⁺]₁ = [Cl⁻]₂ × [Na⁺]₂
• Clinical application: Plasma protein loss → edema (nephrotic syndrome)

Edema Mechanisms:

1. Increased capillary hydrostatic pressure: Heart failure
2. Decreased plasma oncotic pressure: Hypoalbuminemia (liver disease, nephrotic syndrome)
3. Increased capillary permeability: Inflammation, allergy
4. Lymphatic obstruction: Lymphedema (filariasis)

Practice Questions for NEET PG

1. A patient has prolonged PT but normal aPTT. Which pathway is affected and why?
2. A Rh-negative mother delivered a Rh-positive baby. She was given Rhogam. Explain the immunological basis.
3. Classify anemia based on MCV with causes for each type.
4. Describe the steps of platelet plug formation.
5. What is DIC? Explain its pathophysiology and lab findings.
6. Compare hemolytic, anaphylactic, and TRALI transfusion reactions.
7. A patient on warfarin has INR of 4.5. What clotting factors are affected and which vitamin is involved?

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