1. Erythropoietin.[3][2010] PAGE 77 2. ESR.[3][2012] PAGE 86-87 3. Erythroblastosis Fetalis.[3][2016] PAGE 105-106 4. Hemoglobinopathies.[3][2017] PAGE 81,82,75 5. ESR[3][2018] PAGE 86-87 6. Rh Incompatibility.[2019]37 7. Law of Landsteiner. [2014 supple.] 8. IgG[2013 supple.] PAGE 110-111 9. Humoralimmunity.[2015 supple.] PAGE 107,108 10. B and T lymphocytes. [2016 supple.] PAGE 108 11.Tissue macrophage system. [2017 supple.] 12.Megaloblastic anaemia. [2019 supple.] PAGE 78-79 13. Starling forces.[2024]
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Here is a complete, exam-ready write-up for all 13 topics from your question paper list, drawn from authoritative physiology and pathology textbooks.
Physiology Exam Answer Bank
1. Erythropoietin (EPO) [3 marks - 2010]
Definition: Erythropoietin is a glycoprotein growth factor synthesized primarily in the kidneys (and to a lesser extent in the liver) that serves as the major stimulus for erythropoiesis by promoting differentiation of pro-erythroblasts into red blood cells.
Mechanism of synthesis (steps):
- Decreased O₂ delivery to the kidneys (due to low hemoglobin or low PaO₂) causes increased production of hypoxia-inducible factor 1α (HIF-1α).
- HIF-1α acts on fibroblasts in the renal cortex and medulla → stimulates synthesis of EPO mRNA.
- EPO mRNA directs increased synthesis of EPO.
- EPO causes differentiation of proerythroblasts. Further maturation steps (to mature RBCs) do not require EPO.
Why kidneys are the ideal site: The kidney can distinguish between decreased blood flow (which lowers both O₂ delivery and consumption equally - no alarm) and decreased O₂ content of arterial blood (which lowers delivery without reducing consumption - alarm triggered).
Clinical note: In chronic renal failure, decreased renal mass → decreased EPO synthesis → normochromic normocytic anemia. Recombinant EPO is used therapeutically.
(Source: Costanzo Physiology 7th Edition)
2 & 5. ESR (Erythrocyte Sedimentation Rate) [3 marks - 2012, 2018]
Definition: ESR is the rate at which red blood cells settle (sediment) in a vertical glass tube of anticoagulated blood over 1 hour, expressed in mm/hour.
Normal values: ≤15 mm/hr (varies slightly by method: Westergren vs Wintrobe).
Mechanism:
- Any acute stress (trauma, infection, inflammation) triggers the acute-phase response → the liver rapidly synthesizes and secretes inflammatory proteins, most importantly fibrinogen.
- Fibrinogen (a large asymmetric protein) causes RBCs to aggregate into rouleaux (coin stacks) → increases effective particle density.
- Rouleaux sediment faster due to reduced surface area-to-volume ratio and increased downward gravitational force relative to upward plasma viscosity resistance.
Three stages of ESR:
- Aggregation phase (first ~10 min): rouleaux formation
- Sedimentation phase (next ~40 min): rapid, constant settling
- Packing phase (last ~10 min): RBCs pack at bottom
Factors increasing ESR: Elevated fibrinogen, globulins, paraproteins, anemia (fewer RBCs, less ionic cloud repulsion), macrocytosis, female sex, pregnancy, age.
Factors decreasing ESR: Polycythemia, sickle cell disease (abnormal shape prevents rouleaux), microcytosis, spherocytosis, hyperviscosity.
Clinical utility: Although nonspecific, ESR is widely used to assess the presence and severity of inflammation. Example: in lupus erythematosus, an elevated ESR with nonspecific complaints (fatigue, weakness) suggests disease reactivation rather than depression or poor sleep.
(Source: Medical Physiology - Boron & Boulpaep, Box 18-1)
3. Erythroblastosis Fetalis [3 marks - 2016]
Definition: A hemolytic disease of the fetus/newborn caused by maternal antibody-mediated destruction of fetal red blood cells, most commonly due to Rh incompatibility (also ABO).
Pathogenesis:
- Rh-negative mother sensitized by Rh-positive fetal blood (fetomaternal hemorrhage) → produces anti-D IgG antibodies.
- In subsequent pregnancies, maternal IgG (the only Ig class to cross the placenta) enters fetal circulation and destroys Rh-positive fetal RBCs → hemolytic anemia.
Consequences:
- Fetal anemia → bone marrow and extramedullary hematopoiesis → normoblastic hyperplasia (erythroblastosis).
- Hemoglobin catabolism → unconjugated bilirubin; placenta normally removes this, so jaundice is not seen in utero, but amniotic fluid bilirubin rises.
- Severe cases: hydrops fetalis (congestive heart failure, massive edema, intrauterine death).
- After birth: bilirubin rises rapidly → kernicterus (bilirubin encephalopathy).
Diagnosis:
- Kleihauer-Betke test or flow cytometry to detect fetal cells in maternal blood.
- Amniotic fluid spectrophotometry: measurement of ΔOD₄₅₀ (net bilirubin absorbance at 450 nm) - the Liley test - to assess severity.
- Now largely replaced by MCA Doppler (middle cerebral artery peak systolic velocity) as a non-invasive measure of fetal anemia.
Management: Anti-D immunoglobulin (RhoGAM) given prophylactically to Rh-negative mothers at 28 weeks and within 72 hours of delivery.
(Source: Henry's Clinical Diagnosis and Management by Laboratory Methods)
4 & part of 6. Hemoglobinopathies [3 marks - 2017]
Definition: A group of genetic disorders affecting the structure or production of hemoglobin chains.
Classification:
| Type | Mechanism | Examples |
|---|---|---|
| Structural hemoglobinopathies | Abnormal globin chain sequence (qualitative) | Sickle cell disease (HbS), HbC, HbE |
| Thalassemias | Reduced/absent synthesis of normal globin chains (quantitative) | α-thalassemia, β-thalassemia |
Sickle Cell Disease (HbS):
- Mutation: Glu→Val at position 6 of β-globin chain.
- Deoxygenated HbS polymerizes → sickling of RBCs → hemolysis, vaso-occlusion, painful crises.
- Protects against falciparum malaria (heterozygous advantage).
β-Thalassemia:
- Decreased (β⁺) or absent (β⁰) β-globin chain synthesis.
- Excess α-chains precipitate in RBCs → ineffective erythropoiesis, hemolysis, bone marrow expansion.
- Thalassemia major (Cooley's anemia): severe, transfusion-dependent; skeletal deformities ("crew-cut" skull X-ray, chipmunk facies).
HbF: Fetal hemoglobin (α₂γ₂) - high O₂ affinity, present until ~6 months of age. Its persistence (HPFH) ameliorates sickle cell and β-thalassemia.
Lab findings (common): Microcytic hypochromic anemia, target cells, elevated HbA₂ (β-thalassemia trait), Hb electrophoresis diagnostic.
(Sources: Murray & Nadel's Respiratory Medicine; Robbins Pathologic Basis of Disease)
6. Rh Incompatibility [2019]
Rh System Basics:
- The Rh (Rhesus) antigen, specifically the D antigen, is the most clinically important. ~85% of people are Rh-positive (carry D antigen).
- Unlike ABO antibodies, anti-D antibodies are not naturally occurring - they develop only after exposure (transfusion or pregnancy).
Mechanism of sensitization:
- Rh-negative (D-negative) mother carries Rh-positive fetus.
- Fetomaternal hemorrhage (especially at delivery) → fetal Rh-positive RBCs enter maternal circulation.
- Maternal immune system responds → produces anti-D IgG (primary response, usually too late to affect first pregnancy).
- In subsequent Rh-positive pregnancies: maternal IgG crosses placenta → erythroblastosis fetalis (see topic 3 above).
ABO incompatibility is usually milder because anti-A and anti-B are IgM (cannot cross placenta) and because ABO antigens are expressed on many tissues.
Prevention: Anti-D immunoglobulin (passive immunization) given within 72 hours of delivery, miscarriage, or amniocentesis - destroys fetal cells before sensitization can occur.
7. Law of Landsteiner [2014 Supple]
Landsteiner's Law (1900-1901): States that if a blood group antigen is absent from the red blood cell surface, the corresponding antibody (agglutinin/isoantibody) will be present in the serum.
ABO Blood Group System:
| Blood Group | RBC Antigen | Serum Antibody | Genotype |
|---|---|---|---|
| A | A | Anti-B | AA or AO |
| B | B | Anti-A | BB or BO |
| AB | A and B | Neither | AB |
| O | Neither | Anti-A and Anti-B | OO |
Key points:
- Anti-A and anti-B are IgM antibodies (naturally occurring, do not require prior sensitization, do not cross placenta).
- ABO antigens are also present on most body tissues (not just RBCs).
- This law governs blood transfusion compatibility: mismatched transfusion causes acute hemolytic transfusion reaction (intravascular hemolysis, DIC, renal failure).
- Universal donor: Group O (no antigens, safe RBCs for all).
- Universal recipient: Group AB (no antibodies, accepts all).
8. IgG [2013 Supple]
Structure: IgG is a monomer with two heavy (γ) chains and two light chains joined by disulfide bonds. MW ~150 kDa. Has an Fc region and two Fab regions (antigen-binding).
Unique properties of IgG:
| Feature | Detail |
|---|---|
| Most abundant immunoglobulin | ~80% of total serum immunoglobulins |
| Secondary immune response | Copiously produced; long-lasting memory |
| Complement activation | Via classical pathway (needs ≥2 IgG molecules); IgG3 > IgG1 > IgG2 most effective |
| Opsonization | Fc region binds Fc receptors on macrophages and neutrophils → enhanced phagocytosis |
| ADCC | NK cells bearing Fc receptors kill IgG-coated target cells |
| Only Ig to cross placenta | Fc receptor-mediated transcytosis through syncytiotrophoblast; provides passive immunity to neonate until ~6 months |
| High diffusion coefficient | Distributes into extravascular spaces; major defense in tissues |
4 subclasses: IgG1 (most abundant), IgG2, IgG3 (most effective complement activator), IgG4 (cannot activate complement by classical pathway). All except IgG2 cross the placenta.
Clinical importance: IgG deficiency → recurrent bacterial infections. In autoimmune disease (e.g., Graves', myasthenia gravis), pathogenic IgG autoantibodies cross the placenta → transient neonatal disease.
(Source: Henry's Clinical Diagnosis and Management by Laboratory Methods)
9. Humoral Immunity [2015 Supple]
Definition: The arm of adaptive immunity mediated by antibodies (immunoglobulins) produced by B lymphocytes/plasma cells. Effective primarily against extracellular pathogens (bacteria, free viruses, toxins).
Key steps:
- Antigen recognition: B cells recognize antigen via surface immunoglobulin (B cell receptor).
- T cell help: For most antigens (T-dependent antigens), activated CD4+ T helper cells (Th2) provide costimulatory signals (CD40L-CD40 interaction) and cytokines (IL-4, IL-5, IL-6).
- B cell activation and proliferation.
- Class switching (isotype switching): Cytokines direct which Ig class is produced (IgM → IgG, IgA, or IgE).
- Somatic hypermutation and affinity maturation in germinal centres → higher-affinity antibodies.
- Differentiation into:
- Plasma cells: Effector cells secreting large amounts of antibody.
- Memory B cells: Long-lived; rapid secondary response on re-exposure.
Effector mechanisms of antibodies:
- Neutralization: Block pathogen binding to host cells (viruses, toxins).
- Opsonization: IgG/IgM coat pathogens → enhanced phagocytosis (Fc receptor and C3b receptor-mediated).
- Complement activation (classical pathway): IgM and IgG → lysis, opsonization, inflammation.
- ADCC: IgG-coated cells killed by NK cells.
- Mast cell degranulation: IgE cross-linking on mast cells → immediate hypersensitivity.
Deficiency: Hypogammaglobulinemia (e.g., Bruton's XLA) → recurrent pyogenic infections beginning after maternal IgG wanes (~6 months).
(Sources: Cellular and Molecular Immunology; Medical Microbiology 9e)
10. B and T Lymphocytes [2016 Supple]
B Lymphocytes
- Origin & maturation: Bone marrow (both origin and maturation). Express surface immunoglobulin (sIgM, sIgD).
- Function: Precursors of antibody-secreting plasma cells. Mediate humoral immunity.
- Markers: CD19, CD20, CD21, MHC Class II, surface Ig.
- Subsets: Follicular B cells (classical adaptive), Marginal zone B cells (rapid response), B1 cells (produce natural IgM against bacterial polysaccharides).
- On activation with T cell help → class switching, affinity maturation, memory formation.
T Lymphocytes
- Origin: Bone marrow; maturation in thymus (positive and negative selection).
- Markers: CD3 (all T cells), CD4 (helper), CD8 (cytotoxic).
- Recognize antigen only when presented by MHC molecules (MHC restriction).
- CD4+ Helper T cells (Th):
- Th1: activate macrophages, CD8+ T cells → cell-mediated immunity (intracellular pathogens, TB, viral infections). Cytokines: IFN-γ, TNF.
- Th2: help B cells, activate eosinophils → humoral immunity, allergy. Cytokines: IL-4, IL-5, IL-13.
- Th17: IL-17, IL-22 → mucosal immunity, autoimmunity.
- T-regulatory (Treg): FoxP3+, suppress immune responses, prevent autoimmunity.
- CD8+ Cytotoxic T cells (CTL): Kill virus-infected cells and tumor cells via perforin/granzyme and Fas-FasL pathway. Restricted to MHC Class I (expressed on all nucleated cells).
Comparison:
| Feature | B Cells | T Cells |
|---|---|---|
| Maturation site | Bone marrow | Thymus |
| Receptor | Surface Ig (BCR) | T cell receptor (TCR) |
| Antigen recognition | Free/soluble antigen | MHC-presented peptides only |
| Effector | Plasma cells → antibodies | Cytokines, cytotoxicity |
| Immunity type | Humoral | Cell-mediated |
(Sources: Robbins Basic Pathology; Junqueira's Basic Histology)
11. Tissue Macrophage System [2017 Supple]
Also called the Mononuclear Phagocyte System (MPS) (formerly reticuloendothelial system).
Definition: A network of phagocytic cells derived from bone marrow monocytes that mature into tissue-resident macrophages in virtually every organ.
Components and tissue locations:
| Tissue Macrophage Name | Location |
|---|---|
| Kupffer cells | Hepatic sinusoids (liver) |
| Alveolar macrophages | Lung alveoli |
| Microglia | Central nervous system |
| Osteoclasts | Bone |
| Langerhans cells | Skin epidermis |
| Mesangial cells | Kidney glomerulus |
| Splenic macrophages | Splenic red pulp (remove senescent RBCs) |
| Peritoneal/pleural macrophages | Body cavities |
Functions:
- Phagocytosis and killing of microorganisms (bacteria, fungi, parasites).
- Antigen presentation via MHC Class II → activate CD4+ T cells (bridge innate and adaptive immunity).
- Removal of senescent/damaged cells (e.g., aged RBCs cleared by splenic and hepatic macrophages).
- Blood cleansing: Kupffer cells phagocytose gut-derived bacteria from portal blood in <0.01 seconds - <1% of intestinal bacteria reach systemic circulation.
- Secretion of cytokines: TNF-α, IL-1, IL-6, IL-12 → inflammation, fever.
- Wound healing and tissue remodeling.
- Lipid metabolism: Foam cell formation (lipid-laden macrophages in atherosclerotic plaques).
Activation states:
- M1 (classical activation): IFN-γ + LPS → pro-inflammatory, microbicidal.
- M2 (alternative activation): IL-4, IL-13 → anti-inflammatory, tissue repair.
(Sources: Guyton and Hall Textbook of Medical Physiology; Medical Microbiology 9e; Junqueira's Basic Histology)
12. Megaloblastic Anaemia [2019 Supple]
Definition: A macrocytic anemia caused by impaired DNA synthesis (due to B₁₂ or folate deficiency), leading to nuclear-cytoplasmic asynchrony and ineffective erythropoiesis.
Causes:
Vitamin B₁₂ deficiency:
- Decreased intake: strict vegetarians/vegans
- Decreased intrinsic factor: pernicious anemia (autoimmune gastritis, anti-IF antibodies), gastrectomy
- Malabsorption: ileal disease/resection (terminal ileum is absorption site), bacterial overgrowth, fish tapeworm (Diphyllobothrium latum)
Folate deficiency:
- Decreased intake: alcoholism, poverty, infancy, pregnancy (↑ requirement)
- Malabsorption: celiac disease, tropical sprue
- Drugs: methotrexate (DHFR inhibitor), phenytoin, oral contraceptives
- Increased demand: hemolytic anemia, disseminated cancer
Pathophysiology: B₁₂ and folate are cofactors for synthesis of thymidine (a DNA base). Deficiency → impaired DNA synthesis → cells continue to grow (RNA/protein synthesis intact) but cannot divide → large cells with immature nuclei (nuclear-cytoplasmic asynchrony).
Morphology:
- Peripheral blood: Macro-ovalocytes, anisocytosis, poikilocytosis, low reticulocytes, hypersegmented neutrophils (≥5 lobes - pathognomonic), pancytopenia in severe cases.
- Bone marrow: Hypercellular; megaloblasts at all stages; giant metamyelocytes; nuclear chromatin remains fine (does not condense normally).
B₁₂ vs Folate deficiency - key distinguishing feature:
- B₁₂ deficiency ONLY causes subacute combined degeneration of spinal cord (posterior and lateral columns) due to demyelination → paresthesias, ataxia, spastic paraparesis.
- Serum methylmalonic acid (MMA) is elevated in B₁₂ deficiency only.
- Folate deficiency: no neurological involvement; serum homocysteine elevated (in both).
Treatment: IM hydroxocobalamin (B₁₂ deficiency); oral folic acid (folate deficiency). Note: giving folate to B₁₂-deficient patients may mask anemia but will not prevent neurological damage.
(Source: Robbins, Cotran & Kumar Pathologic Basis of Disease)
13. Starling Forces [2024]
The Starling Equation governs fluid movement across capillary walls:
Jv = Kf [ (Pc - Pi) - (πc - πi) ]
Where:
- Jv = Net fluid movement (mL/min); positive = filtration (out of capillary), negative = absorption (into capillary)
- Kf = Hydraulic conductance (water permeability of capillary wall)
- Pc = Capillary hydrostatic pressure (force favoring filtration)
- Pi = Interstitial hydrostatic pressure (force opposing filtration; normally ≈ 0 or slightly negative)
- πc = Capillary oncotic pressure (force opposing filtration; due to plasma proteins)
- πi = Interstitial oncotic pressure (force favoring filtration; normally very low)
The four Starling forces at a typical capillary:
| Force | Value | Direction |
|---|---|---|
| Pc (capillary hydrostatic) | 30 mm Hg (arteriolar end) → 15 mm Hg (venous end) | Filtration ← |
| Pi (interstitial hydrostatic) | ~1 mm Hg | Absorption → |
| πc (plasma oncotic) | ~26 mm Hg | Absorption → |
| πi (interstitial oncotic) | ~3 mm Hg | Filtration ← |
- At the arteriolar end: Net pressure = +6 mm Hg → net filtration
- At the venous end: Net pressure = -5 mm Hg → net absorption
- Small net excess of filtration over absorption is drained by lymphatics back to circulation
Each parameter explained:
- Kf varies with capillary type (highest in glomerulus, lowest in brain). Increases in burns/toxin injury → edema.
- Pc is raised by increased venous pressure (more than arterial). It falls along capillary length due to filtration.
- πc falls with hypoproteinemia (e.g., nephrotic syndrome, liver disease) → increased filtration → edema.
- πi rises when protein leaks out of capillary (capillary injury) → further worsens edema.
Causes of edema (changes in Starling forces):
| Cause | Mechanism |
|---|---|
| Heart failure | ↑ venous/capillary hydrostatic pressure (Pc↑) |
| Hypoalbuminemia (nephrotic/cirrhosis) | ↓ capillary oncotic pressure (πc↓) |
| Burns/inflammation | ↑ Kf (capillary permeability ↑) + πi↑ |
| Lymphatic obstruction | Impaired return of excess filtrate |
| Filariasis | Lymphatic blockade → massive edema (elephantiasis) |
(Source: Costanzo Physiology 7th Edition)
Quick Summary Table
| # | Topic | Key Points to Remember |
|---|---|---|
| 1 | Erythropoietin | Kidney (HIF-1α) → EPO → proerythroblast differentiation; fails in CRF |
| 2/5 | ESR | Fibrinogen → rouleaux → settles faster; non-specific inflammation marker |
| 3 | Erythroblastosis Fetalis | IgG anti-D crosses placenta; ΔOD₄₅₀, MCA Doppler; prevent with RhoGAM |
| 4 | Hemoglobinopathies | Structural (HbS, HbC) vs quantitative (thalassemia); Hb electrophoresis diagnostic |
| 6 | Rh Incompatibility | D antigen; sensitization at delivery; affects subsequent pregnancies |
| 7 | Landsteiner's Law | Absent antigen → antibody present; ABO table; natural IgM antibodies |
| 8 | IgG | Most abundant; crosses placenta; opsonization; ADCC; complement; 4 subclasses |
| 9 | Humoral Immunity | B cell → plasma cell → antibodies; neutralization, opsonization, complement |
| 10 | B & T Lymphocytes | B: bone marrow maturation, antibodies; T: thymus maturation, CD4/CD8, MHC restriction |
| 11 | Tissue Macrophage System | MPS; Kupffer cells, microglia, alveolar macrophages; phagocytosis, APC function |
| 12 | Megaloblastic Anaemia | B₁₂/folate → impaired DNA; macro-ovalocytes, hypersegmented neutrophils; B₁₂ = neurological features |
| 13 | Starling Forces | Jv = Kf[(Pc-Pi)-(πc-πi)]; filtration at arteriolar end, absorption at venous end; edema mechanisms |
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