Body Fluids & Circulation – Blood Groups, Rh Factor & Erythroblastosis Foetalis (Lecture 04)

Composition of Blood

• Blood = Plasma + Formed elements (RBC, WBC, platelets)
• Plasma (~$55\%$ of blood volume)
  • $\approx 90\%$ water; $\approx 7\%$ proteins; $\approx 0.9\%$ salts; rest = nutrients, hormones, gases, wastes.
  • Major plasma proteins (all circulating in inactive form)
  • Albumins → osmotic balance
  • Globulins → antibodies
  • Fibrinogen & prothrombin → clotting factors
• Serum
  • Plasma − (fibrinogen + clotting factors)
  • Cannot undergo coagulation ➜ diagnostic use.
• Formed elements (~$45\%$)
  • Erythrocytes: $\approx 4.5 – 5.5\times10^{6}\,/\,\text{mm}^3$
  • Leukocytes: $\approx 6 – 8\times10^{3}\,/\,\text{mm}^3$
  • Thrombocytes (platelets): $\approx 1.5 – 3.5\times10^{5}\,/\,\text{mm}^3$

Blood Coagulation (Clotting Cascade)

• Trigger: Injury damages endothelium ➜ tissue factor + platelet factors released.
• Key sequential conversions
  • $\text{Prothrombin (inactive)} \xrightarrow[Ca^{2+}]{\text{Thrombokinase}} \text{Thrombin (active)}$
  • $\text{Fibrinogen (soluble)} \xrightarrow{\text{Thrombin}} \text{Fibrin (insoluble threads)}$
  • Fibrin network + trapped formed elements = clot (dark reddish-brown scab)
• Platelets provide phospholipids & serotonin (vasoconstriction).
• Vitamin $\mathbf K$ essential for hepatic synthesis of several factors.
• Delayed clotting → common causes
  • Thrombocytopenia (↓ platelets)
  • Defect in Castle’s intrinsic factor ➜ ↓ vitamin $\mathrm B_{12}$ ➜ faulty prothrombin synthesis
  • Folic-acid malabsorption

White Blood Cells & Their Special Roles

• Neutrophils ($50\,–\,70\%$) ➜ phagocytosis of microbes.
• Basophils ($0.5\,–\,1\%$) ➜ release histamine, serotonin, heparin ➜ inflammatory & allergic reactions.
• Eosinophils ($1\,–\,4\%$) ➜ combat parasites, modulate allergy (diagram in lecture; MCQ answer = eosinophil).
• Monocytes & lymphocytes ➜ immunity.

ABO Blood-Group System

• Based on two RBC surface antigens (agglutinogens) A & B.
• Plasma carries natural antibodies (agglutinins) formed without prior sensitisation.

• Consequences
  • Group $O$ = “universal donor” (no antigens to attack).
  • Group $AB$ = “universal recipient” (no antibodies).
• Transfusion rule: Match both antigen & antibody landscape to avoid haemolytic transfusion reactions (agglutination ↓ RBC → renal failure, death).

Rh (Rhesus) Blood-Group System

• Rh antigen (D-factor) present in $\approx 80\%$ humans ➜ $\text{Rh}^{+}$. Absence ➜ $\text{Rh}^{-}$.
• Unlike ABO, Rh antibodies are not natural; they are produced only after exposure to $\text{Rh}^{+}$ RBCs (transfusion or feto-maternal bleed).
• Before transfusion ➜ cross-match for Rh as well.

Erythroblastosis Foetalis (Haemolytic Disease of the New-Born, HDN)

• Pathogenesis sequence
  1. Mother $\text{Rh}^{-}$ × Father $\text{Rh}^{+}$ → Foetus $\text{Rh}^{+}$.
  2. First pregnancy: placental barrier prevents mixing; no problem.
  3. At delivery #1 some foetal $\text{Rh}^{+}$ RBCs enter maternal circulation.
  4. Mother’s immune system produces anti-Rh (IgG) antibodies (memory cells stored).
  5. Second & subsequent $\text{Rh}^{+}$ pregnancies: IgG crosses placenta (tiny size) ➜ bind foetal RBC ➜ agglutination & haemolysis.
• Clinical features in foetus/new-born
  • Severe anaemia (↓ RBC, ↓ $\mathrm{Hb}$)
  • Jaundice (↑ bilirubin & biliverdin from haem breakdown)
  • Hepatosplenomegaly, oedema (hydrops foetalis), possible intra-uterine or neonatal death.
• Prevention – Rhogam Protocol
  • Immediately (<$72$ h) after 1st delivery/abortion/amniocentesis, inject mother with anti-Rh $\gamma$-globulin (Rhogam).
  • Rhogam binds & destroys any foetal $\text{Rh}^{+}$ RBCs before mother is sensitised.
  • No immunological memory from Rhogam itself.

Lymph (brief touch, as per topic list)

• Ultrafiltrate of blood plasma; found in lymphatic vessels.
• Functions: returns interstitial fluid & proteins to blood, transports fats (lacteals), lymphocytes circulation, maintains tissue fluid balance.

Key MCQ / Assertion–Reason Points Discussed in Lecture

1. Plasma + formed elements constitute blood; serum cannot clot → BOTH TRUE.
2. "Fibrinogens, prothrombins are in active state" (F) & "fibrinogens themselves form clot mesh" (F) → BOTH FALSE.
3. Thrombin converts inactive fibrinogen to fibrin (answer: Fibrin).
4. Basophils cause inflammatory reactions via histamine/serotonin (answer: Basophils).
5. Injury triggers platelet/tissue factors → activates clotting; Reason correctly explains Assertion (A-type correct explanation).
6. Dark scab = fibrin network with trapped cells; both descriptive statements correct.
7. Diagram identification (3) Eosinophil – associated with allergy.
8. Erythroblastosis foetalis occurs in 2nd pregnancy; problem absent if foetus $\text{Rh}^{-}$ → BOTH STATEMENTS CORRECT.
9. Correct set about blood groups → I, II, V (O has both antibodies; B→A transfusion incompatible; anti-Rh after first child) .
10. ABO donor-compatibility figure: correct option (c) (AB receives from all, O donates to all).
11. Excessive bleeding delay → Thrombocytopenia (low platelets) probable cause.

Real-World & Clinical Significance

• Mandatory blood-group & Rh typing in blood banks, prenatal care, emergency transfusions.
• Universal donor/recipient concept simplifies mass-casualty triage.
• Rhogam availability has drastically reduced HDN incidence worldwide.
• Basophil-mediated inflammatory response forms basis for antihistamine therapy.
• Understanding cascade exploited pharmaceutically: anticoagulants (heparin, warfarin), fibrinolytics (streptokinase) in thrombosis management.

Ethical / Philosophical Angle

• Prenatal testing & Rh prophylaxis highlight preventive medicine ethics – treat mother to protect an unborn child.
• Blood donation campaigns rely on public altruism; universal donor group "O" individuals carry special responsibility.

Rapid-Revision Flash Facts

• $\text{O}$ = universal donor; $\text{AB}$ = universal recipient.
• Rh antigen present in $\approx 80\%$ population.
• Rh antibodies are IgG; can cross placenta.
• Rhogam: passive immunisation, no memory.
• Coagulation key ions: $Ca^{2+}$ and vitamin $K$.
• Basophil → histamine; Eosinophil → anti-parasitic + allergy; Neutrophil → phagocyte.
• Serum = plasma – clotting factors ➜ used in diagnostics & antiserum production.