BP104T Unit 4 – Hematology (Blood, Lymph & Hemostasis)
Unit 4 covers the anatomical organization of the lymphatic system, primary vs secondary lymphoid organs, innate vs adaptive immunity, cellular vs humoral immune responses, antibody structure (5 immunoglobulin classes), Gell and Coombs classification of Hypersensitivity reactions (Types I-IV), and autoimmune diseases.
📋 Prescribed Syllabus Topics
📖 Detailed Lecture Notes & Solved Examples
11. Lymphatic Anatomy & Primary vs. Secondary Lymphoid Organs
Dedicated Webpage➔The lymphatic system is a specialized vascular network that returns excess interstitial fluid (lymph) back to venous circulation, absorbs dietary lipids from the gastrointestinal tract via lacteals, and provides surveillance against invading pathogens. Lymphoid organs are classified into: (1) Primary Lymphoid Organs (Bone Marrow and Thymus) where lymphocytes are generated and undergo antigen-independent maturation and self-tolerance education, and (2) Secondary Lymphoid Organs (Lymph Nodes, Spleen, Tonsils, Peyer's Patches, and MALT) where mature, immunocompetent lymphocytes encounter foreign antigens and initiate adaptive immune responses.Lymphatic system shareer se extra fluid ko wapas khoon me lata hai aur bimariyon se ladta hai. Primary Organs (Bone Marrow me B-cells aur Thymus me T-cells mature hote hain). Secondary Organs (Lymph nodes aur Spleen me bacteria ko filter karke unpar attack kiya jata hai).
▶Anatomical Functions of Spleen and Lymph Nodes
Filtration and immune activation mechanisms.
- •Bone Marrow: Site of hematopoiesis and B-cell maturation.
- •Thymus: Site of T-cell maturation and positive/negative selection (Eliminates self-reactive T-cells).
- •Thoracic Duct: Drains lymph from entire lower body and left upper torso into the left subclavian vein.
22. Innate vs. Adaptive Immunity & Cell-Mediated vs. Humoral Responses
Dedicated Webpage➔Immunity is the body's defensive capacity to neutralize or eliminate foreign pathogens, toxins, and abnormal neoplastic cells. Innate (Non-Specific) Immunity is the first line of defense, present from birth, responding immediately without immunological memory. Adaptive (Specific) Immunity is acquired upon exposure, exhibits exquisite antigenic specificity, and develops long-lasting immunological memory. Adaptive immunity is divided into Humoral Immunity (mediated by B-lymphocytes differentiating into Plasma Cells that secrete Antibodies) and Cell-Mediated Immunity (mediated by T-lymphocytes: CD4+ Helper T-cells and CD8+ Cytotoxic T-cells).Innate immunity janam se milti hai (Skin, stomach acid, neutrophils jo turant attack karte hain bina memory ke). Adaptive immunity exposure ke baad banti hai: B-cells antibodies banakar bacteria ko maarte hain (Humoral), aur CD8+ T-cells virus se infected cell ko direct khatam karte hain (Cell-mediated).
▶MHC Antigen Presentation & T-Cell Activation Pathways
Major Histocompatibility Complex (MHC) restriction in cell-mediated immunity.
- •Innate Barriers: Physical (skin, mucous membranes), Chemical (gastric HCl, lysozyme in tears), Cellular (Neutrophils, Macrophages, NK cells), and Soluble (Complement system, Interferons).
- •Active Immunity: Body produces its own antibodies after infection or vaccination (Long-lasting memory).
- •Passive Immunity: Pre-formed antibodies are transferred directly (e.g. maternal IgG via placenta, Anti-tetanus serum; Immediate but transient protection with zero memory).
33. Immunoglobulin Architecture & The 5 Classes of Antibodies
Dedicated Webpage➔Antibodies (Immunoglobulins - Igs) are Y-shaped glycoprotein molecules synthesized by plasma cells. An individual antibody consists of four polypeptide chains: two identical Heavy (H) chains and two identical Light (L) chains joined by interchain disulfide bonds. The antibody molecule is functionally divided into the Fab region (Fragment antigen-binding, containing the variable $V_H$ and $V_L$ domains that form the antigen-combining paratope) and the Fc region (Fragment crystallizable, which binds to immune cell Fc receptors and activates the classical complement cascade). Human immunoglobulins are classified into 5 distinct isotypes based on heavy chain structure: IgG, IgM, IgA, IgE, and IgD.Antibody ka shape 'Y' jaisa hota hai (2 Heavy + 2 Light chains). Inhe yaad rakhne ka short formula hai 'GAMED': (1) IgG sabse jyada hoti hai aur placenta cross karti hai, (2) IgM sabse badi pentamer hoti hai aur pehle banti hai, (3) IgA maa ke doodh aur saliva me mucosal protection deti hai, (4) IgE allergy aur asthma me histamine release karwati hai, (5) IgD B-cell surface par hoti hai.
▶Distinctive Biological Roles of the 5 Immunoglobulin Classes
Structural and clinical properties of IgG, IgM, IgA, IgE, and IgD.
| Ig Class | Physical Structure | Serum Half-Life | Crosses Placenta? | Primary Clinical Function |
|---|---|---|---|---|
| IgG | Monomer | ~21 - 23 days | YES (Only class) | Long-term immunity, opsonization, neutralization of toxins |
| IgM | Pentamer with J-chain | ~5 days | NO | Primary acute response, agglutination, complement fixation |
| IgA | Dimer + Secretory piece | ~6 days | NO | Mucosal mucosal surface protection, present in colostrum |
| IgE | Monomer | ~2 days | NO | Allergic immediate hypersensitivity, anti-parasitic defense |
| IgD | Monomer | ~3 days | NO | B-lymphocyte surface antigen recognition receptor |
- •IgG: Crosses placenta; dominant in secondary booster immune responses.
- •IgM: Pentameric structure; first antibody produced during acute infection.
- •IgA: Secretory dimer; protects mucous membranes and infant gut via breast milk.
- •IgE: Reaginic antibody responsible for anaphylaxis and asthma.
44. Gell and Coombs Classification of Hypersensitivity Reactions (Types I - IV)
Dedicated Webpage➔Hypersensitivity refers to exaggerated, inappropriate, or damaging immune responses against harmless environmental antigens (allergens) or self-antigens, causing tissue damage, inflammation, or death. Gell and Coombs (1963) established the definitive four-tier classification system based on underlying immunological mechanisms.Hypersensitivity ka matlab hai immune system ka zaroorat se jyada react karna (ACID mnemonic): Type I = Anaphylaxis/Allergy (IgE + Mast cell histamine release jaise Penicillin allergy); Type II = Cytotoxic (blood transfusion reaction); Type III = Immune Complex (SLE, Arthritis); Type IV = Delayed (24-72 ghante baad hone wali T-cell reaction jaise TB Mantoux skin test).
▶Detailed Gell and Coombs Hypersensitivity Mechanisms
Etiology, mediators, and clinical examples.
| Type | Descriptive Name | Key Immune Mediators | Onset Speed | Prototypic Clinical Examples |
|---|---|---|---|---|
| Type I | Immediate / Anaphylactic | IgE, Mast cells, Histamine, Leukotrienes | 2 - 30 minutes | Penicillin anaphylaxis, Asthma, Urticaria |
| Type II | Cytotoxic / Tissue-specific | IgG, IgM, Complement, Macrophages | Hours to days | Rh incompatibility, Transfusion reaction, Myasthenia |
| Type III | Immune Complex | Antigen-Antibody complexes, Neutrophils | 3 - 8 hours | SLE, Serum sickness, Rheumatoid arthritis |
| Type IV | Delayed / Cell-Mediated | Sensitized T-cells (Th1, CD8+), Macrophages | 24 - 72 hours | Tuberculin skin test, Contact dermatitis (Nickel) |
- •Types I, II, and III are Immediate and strictly Antibody-mediated.
- •Type IV is Delayed (24-72 hours) and strictly T-Cell-mediated.
- •Mnemonic (ACID): Type I = Anaphylactic / Allergic, Type II = Cytotoxic, Type III = Immune Complex, Type IV = Delayed.
- In a 10-mark question on Hypersensitivity, explain all 4 Gell and Coombs types with complete immunological mechanisms and clinical examples.
- Draw the Y-shaped structure of an antibody labeling Heavy chains, Light chains, Disulfide bonds, Fab region, and Fc region.