Different Blood Groups and Blood Clotting Process

Composition of Blood

  • Overall makeup
    • Plasma: 55%55\% (liquid portion)
    • Formed elements ("corpuscles"): 45%45\%
    • Red Blood Cells (RBCs / erythrocytes): 41%41\% of whole blood volume
    • White Blood Cells (WBCs / leukocytes) and Platelets (thrombocytes): combined 4%4\% of whole blood volume
  • Functional overview
    • Blood constantly circulates, providing nutrition, oxygen delivery, and waste removal for every tissue
    • Two-phase system (plasma + cells) allows simultaneous transport of dissolved molecules and cellular payloads
    • Ethical / medical relevance: accurate knowledge of composition is critical for transfusion medicine, diagnostics, and managing hemorrhage

Plasma (Liquid Component)

  • Appearance: straw-colored, mostly water
  • Principal constituents & significance
    • Water: solvent that carries heat (thermoregulation) and materials
    • Proteins
    • Clotting factors (e.g.
      • Fibrinogen → becomes fibrin during coagulation)
    • Carrier proteins (albumin, globulins) for hormones, lipids, metal ions
    • Nutrients: glucose, amino acids, lipids
    • Inorganic ions: \text{Na^+}, \text{K^+}, \text{Ca^{2+}}, \text{Cl^-}, \text{HCO_3^-}
    • Wastes: urea, creatinine, bilirubin (to be excreted by kidneys/liver)
    • Dissolved gases: O<em>2\text{O<em>2}, CO</em>2\text{CO</em>2}, \text{N_2}
  • Practical implication: plasma can be separated and transfused ("fresh frozen plasma") to treat clotting-factor deficiencies

Formed Elements

Red Blood Cells (Erythrocytes)

  • Morphology
    • Biconcave, anucleate discs → increased surface area / volume ratio for gas diffusion, flexibility through capillaries
  • Pigment
    • Hemoglobin (Hb) gives red color; each Hb binds 4\text{4} \text{O_2} molecules via heme iron
  • Function
    • Transport O<em>2\text{O<em>2} from lungs to tissues; carry CO</em>2\text{CO</em>2} back as carbamino-Hb or dissolved \text{HCO_3^-}
  • Life span & turnover
    • Average life: 44 months (≈ 120120 days)
    • Bone marrow replaces ≈ 2 million2\ \text{million} RBCs every second (remarkable metabolic demand)
  • Clinical notes
    • Anemia: ↓ number/function of RBCs leads to tissue hypoxia
    • Polycythemia: ↑ viscosity, risk of thrombosis

White Blood Cells (Leukocytes)

  • General traits
    • Have nuclei; < 1%1\% of blood volume but essential for immunity
    • Two major classes
    • Granulocytes (cytoplasmic granules)
    • Agranulocytes (no visible granules)
Granulocytes
  1. Neutrophils
    • Most numerous; first responders
    • Phagocytose and digest bacteria/fungi
    • Elevated in acute bacterial infections
  2. Eosinophils
    • Attack parasites and cancer cells; moderate allergic responses by degrading histamine
  3. Basophils
    • Rarest WBC; release histamine & heparin → vasodilation, anticoagulation
    • Act as "alarms" initiating inflammatory/immune cascade
Agranulocytes
  1. Lymphocytes
    • B cells → produce antibodies (humoral immunity)
    • T cells → kill infected cells, coordinate immune response
    • NK cells → innate cytotoxic defense against tumors/viruses
  2. Monocytes
    • Largest WBC; long life span
    • Become tissue macrophages → phagocytosis, antigen presentation, cleanup of debris/bacteria

Platelets (Thrombocytes)

  • Description
    • Cytoplasmic fragments of megakaryocytes; lack nuclei
  • Normal count: 150,000150{,}000 – 400,000400{,}000 per μL\mu\text{L} of blood
  • Primary function: initiate hemostasis by clumping at vascular injury, interacting with clotting proteins
  • Clinical correlation: thrombocytopenia (< 150,000150{,}000) → bleeding risk; thrombocythemia (> 450,000450{,}000) → clot risk

ABO Blood Groups

  • Discovered by Karl Landsteiner (Austrian, 19001900; Nobel Prize 19301930)
  • Antigens = glycoproteins on RBC membrane; antibodies = immunoglobulins in plasma
  • Four phenotypes
    1. Type A
    • Antigen: A
    • Plasma antibody: Anti-B
    • Compatible donations: A, O
    • Cannot receive: B, AB
    1. Type B
    • Antigen: B
    • Plasma antibody: Anti-A
    • Compatible donations: B, O
    1. Type AB (universal recipient)
    • Antigens: A + B
    • Plasma antibody: none
    • Compatible donations: A, B, AB, O (all types)
    1. Type O (universal donor)
    • Antigen: none
    • Plasma antibodies: Anti-A & Anti-B
    • Compatible donations: only O to receive; can donate to everyone
  • Clinical / ethical relevance
    • Mistyped transfusion → acute hemolytic reaction (potentially fatal)
    • Population genetics: studying distribution aids anthropology & epidemiology

Rh (D) Factor

  • Protein antigen discovered in Rhesus monkeys; genetically inherited
  • Status
    • If antigen present → Rh$^+$
    • If absent → Rh$^-$
  • Epidemiology: ≈ 85%85\% of humans are Rh$^+$
  • Transfusion rule of thumb
    • Rh$^+$ recipients can receive Rh$^-$ blood
    • Rh$^-$ recipients must NOT receive Rh$^+$ (risk of sensitization & hemolysis)
  • Obstetric importance
    • Hemolytic Disease of the Newborn (erythroblastosis fetalis): Rh$^-$ mother carrying Rh$^+$ fetus; prevented with anti-D immunoglobulin

RBC Compatibility Summary (simplified from table)

  • O$^-$: universal donor; can only receive O$^-$
  • O$^+$: can donate to all Rh$^+$ types; receive O$^-$ or O$^+$
  • A$^-$: donate to A$^-$, A$^+$, AB$^-$, AB$^+$; receive O$^-$, A$^-$
  • A$^+$: donate to A$^+$, AB$^+$; receive O$^-$, O$^+$, A$^-$, A$^+$
  • B and AB follow analogous logic (based on presence/absence of A, B, and Rh antigens)

Blood Clotting (Hemostasis / Coagulation)

  • Purpose: prevent exsanguination while maintaining fluidity elsewhere
  • Phases (cascade of physical + biochemical events)
    1. Vascular spasm
    • Immediate vasoconstriction after endothelial injury to reduce blood flow
    1. Platelet plug formation
    • Injury exposes subendothelial collagen → platelets adhere (via vWF\text{vWF}) and activate
    • Platelets release ADP, serotonin, thromboxane \text{A_2} → recruit more platelets (positive feedback)
    1. Coagulation (conversion of blood from liquid to gel)
    • Key biochemical steps described in transcript:
      a. Platelet disintegration converts inactive Thromboplastinogen\text{Thromboplastinogen} → Thromboplastin\text{Thromboplastin} (a.k.a. Tissue Factor)
      b. Thromboplastin+Ca2+\text{Thromboplastin} + Ca^{2+} ions transform inactive Prothrombin\text{Prothrombin} → active enzyme Thrombin\text{Thrombin}
      c. Thrombin\text{Thrombin} catalyzes soluble Fibrinogen\text{Fibrinogen} → insoluble Fibrin\text{Fibrin} threads
      d. Fibrin threads weave into a meshwork that traps RBCs & platelets → definitive clot (red connective-tissue mass)
  • Clot retraction & repair (not in slides but conceptually linked)
    • Actomyosin in platelets contracts, shrinking clot and pulling wound edges together
    • Endothelial & fibroblast proliferation then rebuild vessel wall
  • Fibrinolysis (clot removal)
    • Plasminogen → plasmin (via tPA) dissolves fibrin once repair is sufficient
  • Clinical tie-ins
    • Vitamin KK required for synthesis of several clotting factors (II, VII, IX, X)
    • Warfarin inhibits vitamin KK recycling → anticoagulation
    • Hemophilia: genetic deficiency of factor VIII or IX → impaired cascade
    • Deep-vein thrombosis & embolism: pathological clotting; treated with heparin or DOACs

Integrated Perspective & Real-World Connections

  • Matching blood type and Rh status is mandatory for safe transfusions, organ transplants, and obstetric care
  • Understanding WBC subsets guides diagnosis (e.g., neutrophilia in bacterial infections, eosinophilia in parasitic or allergic conditions)
  • Platelet function & coagulation cascade underpin surgical hemostasis, trauma management, and pharmacologic manipulation (antiplatelet drugs, anticoagulants)
  • Public health dimension: blood-donor screening ensures adequate supply of O$^-$ (universal donor) and AB$^+$ plasma (universal plasma donor)
  • Historical insight: Landsteiner’s discovery revolutionized medicine, reducing transfusion mortality and enabling modern surgery