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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I now have comprehensive content from the textbooks covering all 13 topics. Let me now compile a thorough, well-organized answer for all topics.

Comprehensive Notes on All 13 Topics

1. Erythropoietin (EPO)

(Asked: 2010, 3 marks)

Definition: Erythropoietin (EPO) is a glycoprotein growth factor synthesized primarily in the kidneys (and to a lesser extent in the liver). It serves as the major stimulus for erythropoiesis by promoting differentiation of pro-erythroblasts into red blood cells.

Mechanism of Synthesis (triggered by hypoxia):

Decreased O2 delivery to the kidneys (hypoxia) - either from decreased hemoglobin concentration or decreased PaO2 - increases production of hypoxia-inducible factor-1α (HIF-1α)
HIF-1α acts on fibroblasts in the renal cortex and medulla → stimulates synthesis of mRNA for EPO
mRNA directs increased synthesis of EPO
EPO acts on proerythroblasts → causes differentiation into mature erythrocytes
Further maturation steps (after proerythroblast stage) do NOT require EPO

Why the kidney is ideal: The kidneys can distinguish decreased blood flow (causes decreased GFR → decreased Na+ reabsorption → decreased O2 consumption, so O2 delivery and consumption remain matched - no EPO needed) from decreased O2 content of blood (O2 consumption unchanged, delivery falls → EPO is released). This prevents unnecessary erythrocyte production during simple oligemia.

Clinical relevance:

Anemia of chronic renal failure: decreased functioning renal mass → decreased EPO synthesis → normocytic, normochromic anemia
Recombinant EPO therapy is used to treat anemia in CRF and some cancers

(Costanzo Physiology 7th Ed., p. 229)

2 & 5. Erythrocyte Sedimentation Rate (ESR)

(Asked: 2012, 2018 - 3 marks each)

Definition: ESR is the rate at which red blood cells settle (sediment) in a tube of anticoagulated blood over one hour, measured in mm/hr.

Principle: RBCs normally have a net negative charge (due to sialic acid residues) and repel each other (zeta potential), preventing rouleaux formation. In inflammation, acute-phase proteins - especially fibrinogen, and also globulins and acute-phase reactants - coat the RBCs and neutralize this charge, promoting rouleaux formation (RBCs stacking like coins). Larger rouleaux aggregates sediment faster due to greater mass-to-surface ratio.

Normal values:

Age/Sex	Normal ESR
0 to <1 month	≤2 mm/hr
1 month - 12 years	≤20 mm/hr
>12 years (male)	≤15 mm/hr
>12 years (female)	≤20 mm/hr

Westergren method: Anticoagulated blood in a 200 mm tube; read at 1 hour.

Causes of elevated ESR: Infections, inflammatory conditions (RA, SLE), malignancies, pregnancy, anemia, multiple myeloma (very high - due to paraprotein)

Causes of low ESR: Polycythemia, sickle cell disease, hypofibrinogenemia, congestive heart failure

Clinical use: Non-specific marker of inflammation; useful for monitoring disease activity in conditions like temporal arteritis, rheumatoid arthritis.

(Harriet Lane Handbook, 23rd Ed., p. 943)

3. Erythroblastosis Fetalis (Hemolytic Disease of the Newborn)

(Asked: 2016, 3 marks)

Definition: A disease of the fetus/newborn characterized by agglutination and phagocytosis of fetal RBCs due to maternal antibodies crossing the placenta.

Pathophysiology:

Classically: Rh-negative mother + Rh-positive father → Rh-positive baby
During first pregnancy (or at delivery), fetal RBCs enter maternal circulation (fetomaternal hemorrhage) → mother develops anti-Rh agglutinins (IgG antibodies)
In subsequent pregnancies, maternal IgG anti-Rh antibodies cross the placenta → attack fetal RBCs → agglutination and hemolysis

Incidence progression:

1st Rh+ baby: Usually no harm (insufficient anti-Rh agglutinin levels)
2nd Rh+ baby: ~3% affected
3rd Rh+ baby: ~10% affected (rises progressively)

Pathological effects on fetus:

Hemolysis of fetal RBCs → release of hemoglobin → converted to bilirubin by macrophages
Jaundice (yellow skin)
Severe anemia → compensatory extramedullary hematopoiesis (liver, spleen enlarge)
Many nucleated RBCs (erythroblasts) flood circulation → hence the name "erythroblastosis"
Kernicterus: Bilirubin deposits in neurons → permanent brain damage, mental impairment, motor damage
In severe cases: Hydrops fetalis (congestive heart failure, generalized edema), intrauterine death

Detection in utero:

Kleihauer-Betke test / flow cytometry: detect fetal cells in maternal blood
Liley test: Amniotic fluid spectral analysis at 450 nm (ΔOD450) measures bilirubin
MCA Doppler: Now preferred screening for fetal anemia

Treatment:

Exchange transfusion with Rh-negative blood (replaces fetal Rh+ RBCs, removes bilirubin, removes maternal antibodies)
Intrauterine transfusion in severe cases

Prevention:

Rh immunoglobulin (anti-D): Given to Rh-negative mother at 28-30 weeks gestation AND within 72 hours of delivery of Rh+ baby
Mechanism: Anti-D antibody coats fetal D antigen on RBCs that enter maternal circulation → prevents maternal sensitization (B-lymphocyte antibody production is inhibited)

(Guyton & Hall Medical Physiology, p. 477)

4. Hemoglobinopathies

(Asked: 2017, 3 marks)

Definition: Hemoglobinopathies are genetic disorders of hemoglobin - either structural variants (qualitative) or defects in synthesis (quantitative/thalassemias).

Normal hemoglobin variants:

Hemoglobin A (HbA): α2β2 - normal adult hemoglobin
Hemoglobin A2 (HbA2): α2δ2 - minor adult component (~2.5%)
Hemoglobin F (HbF): α2γ2 - fetal hemoglobin; higher O2 affinity than HbA (facilitates O2 transfer from mother to fetus); gradually replaced by HbA in first year of life

Structural variants:

Variant	Defect	Effect
Hemoglobin S (HbS)	β-chain: glutamate→valine at position 6 (α2βS2)	Deoxygenated HbS forms sickle-shaped rods → sickling of RBCs → vaso-occlusion, pain crises; decreased O2 affinity
Methemoglobin	Iron in Fe3+ state (instead of Fe2+)	Cannot bind O2; caused by nitrites, sulfonamides, or congenital methemoglobin reductase deficiency

Sickle Cell Disease: Autosomal recessive; homozygous HbSS → severe disease; heterozygous HbAS (sickle trait) → generally asymptomatic, protective against falciparum malaria

O2-binding capacity:

1 g of HbA binds 1.34 mL O2
Normal hemoglobin concentration: 15 g/100 mL blood
O2-binding capacity: 15 × 1.34 = 20.1 mL O2/100 mL blood

(Costanzo Physiology 7th Ed., p. 225)

6. Rh Incompatibility

(Asked: 2019)

The Rh system centers on the D antigen (most immunogenic of the Rh antigens).

Rh-positive: Has D antigen on RBC surface (~85% of population)
Rh-negative: Lacks D antigen

Key feature: Unlike ABO antibodies, Rh antibodies do NOT pre-exist - they form only after exposure to Rh-positive blood.

Consequences:

Transfusion: Transfusing Rh+ blood to Rh- recipient → sensitization → anti-D IgG forms. A second transfusion with Rh+ blood → hemolytic transfusion reaction
Pregnancy: (see Erythroblastosis Fetalis above)

Rh agglutinins are IgG (can cross placenta, unlike IgM ABO antibodies which generally cannot)

Prevention: Anti-D immunoglobulin (RhoGAM) administered at 28 weeks and within 72 hours postpartum to Rh-negative women

(Guyton & Hall Medical Physiology, p. 477-478)

7. Law of Landsteiner (ABO Blood Groups)

(Asked: 2014 Supplementary)

Landsteiner's Law states: If an antigen (agglutinogen) is present on the RBCs, the corresponding antibody (agglutinin) is ABSENT in the plasma; and if the antigen is absent from the RBCs, the corresponding antibody IS present in the plasma.

ABO Blood Group Table:

Blood Type	Agglutinogen on RBC	Agglutinin in Plasma
A	A	Anti-B
B	B	Anti-A
AB	A and B	Neither (Universal Recipient)
O	Neither	Anti-A and Anti-B (Universal Donor)

Genetics: Three alleles at the ABO locus: IA, IB, IO

IA and IB are codominant; IO is recessive
Six possible genotypes: IAIA, IAIO, IBIB, IBIO, IAIB, IOIO

Origin of agglutinins: Produced in response to small amounts of A and B antigens entering the body via food/bacteria after birth. Neonates have few or no agglutinins (formed almost entirely after birth). Agglutinins are mainly IgM and IgG gamma globulins.

Transfusion compatibility: Agglutinin in recipient's plasma reacts with agglutinogen on donor RBCs → agglutination and hemolysis. The donor's plasma agglutinins are diluted in the recipient's blood and are usually too weak to cause harm.

(Guyton & Hall Medical Physiology, p. 474)

8. IgG

(Asked: 2013 Supplementary, 3 marks)

IgG is the most abundant immunoglobulin in serum (~75% of all immunoglobulins) and the only immunoglobulin that crosses the placenta.

Structure:

Two heavy (H) chains + two light (L) chains linked by disulfide bonds
Each chain has a variable region (V) at one end (antigen-binding site) and a constant region (C)
The variable regions of one H-chain and one L-chain together form one antigen-binding site (Fab)
IgG has 2 antigen-binding sites (bivalent)
The constant region of the H-chain forms the Fc region - determines biological properties

Properties of IgG:

Molecular weight: ~160,000 Da
Only Ig to cross the placenta → provides passive immunity to newborn for ~3-6 months
Activates the classical complement pathway
Promotes opsonization (Fc receptors on phagocytes bind Fc region)
Produced in secondary immune response (memory response) - higher affinity than IgM
Four subclasses: IgG1, IgG2, IgG3, IgG4

Antibody-antigen bonding forces:

Hydrophobic bonding
Hydrogen bonding
Ionic attractions
Van der Waals forces

Five Ig classes: IgM (primary response, pentamer, 10 binding sites), IgG (secondary response), IgA (secretions), IgD (B cell receptor), IgE (allergies/parasites)

(Guyton & Hall Medical Physiology, p. 465)

9. Humoral Immunity

(Asked: 2015 Supplementary)

Definition: Humoral immunity is the component of the adaptive immune response mediated by B lymphocytes and their secreted antibodies (immunoglobulins) - protects primarily against extracellular pathogens, toxins, and bacteria.

Steps of humoral immune response:

Antigen entry → processed and presented by APCs (macrophages, dendritic cells) via MHC class II to CD4+ helper T cells
T-helper cell activation → releases cytokines (IL-2, IL-4, IL-5, IL-6) → stimulates B cell proliferation
B cell activation → clonal expansion → differentiation into:
- Plasma cells (antibody-secreting factories)
- Memory B cells (long-lived; rapid response on re-exposure)
Antibody production → antibodies bind antigens and mediate:
- Neutralization
- Opsonization (coating antigen for phagocytosis)
- Complement activation (classical pathway via IgM/IgG)
- Agglutination
- Precipitation

Complement system effects (classical pathway):

Opsonization (C3b)
Chemotaxis (C5a) → attracts neutrophils and macrophages
Mast cell/basophil activation (C3a, C4a, C5a) → release histamine, heparin, serotonin
Lysis via Membrane Attack Complex (MAC, C5b-9) → creates pores in bacterial membranes
Agglutination and neutralization of viruses

Primary vs. Secondary immune response:

Primary: Slow (days to weeks), lower antibody titer, mainly IgM
Secondary (anamnestic): Rapid (hours to days), high antibody titer, mainly IgG (due to memory cells and class switching)

(Guyton & Hall Medical Physiology, p. 462-467)

10. B and T Lymphocytes

(Asked: 2016 Supplementary)

Lymphocytes constitute 20-30% of all leukocytes and are the central players of the adaptive immune system.

B Lymphocytes

Mature in bone marrow
Surface receptors: B-cell receptors (BCRs) = membrane-bound antibodies
Function: Humoral immunity - become plasma cells (secrete antibodies) and memory B cells
Recognize intact, native antigens (no need for MHC presentation)
Produce all 5 classes of immunoglobulins (IgM, IgG, IgA, IgD, IgE)

T Lymphocytes

Mature in thymus (undergo positive and negative selection)
Surface receptors: T-cell receptors (TCRs) - recognize antigen only when presented by MHC molecules on APCs
Three main subsets:

Subset	Marker	Function
Helper T cells (Th)	CD4+	Activate B cells; coordinate immune response via cytokines (IL-2, IL-4, etc.)
Cytotoxic T cells (Tc)	CD8+	Kill virus-infected/tumor cells by releasing perforin and granzymes (cell-mediated immunity)
Regulatory T cells (Tregs)	CD4+CD25+	Suppress immune responses; prevent autoimmunity

Clonal expansion: Both T and B cells can undergo rapid proliferation within 5-7 days upon antigen exposure. Specific clones persist as memory cells for years.

Thymic tolerance (negative selection): Autoreactive T cells (those that react to self-antigens) are destroyed in the thymus - prevents autoimmunity.

NK cells (natural killer cells): Are lymphocytes but part of innate immunity; kill cells with abnormal MHC expression (virus-infected/tumor cells); express CD16 (FcγRIII receptor for IgG) → antibody-dependent cellular cytotoxicity (ADCC)

(Roitt's Essential Immunology; Guyton & Hall Medical Physiology, p. 462-470)

11. Tissue Macrophage System (Mononuclear Phagocyte System / Reticuloendothelial System)

(Asked: 2017 Supplementary)

Definition: The tissue macrophage system (formerly called the reticuloendothelial system) consists of macrophages fixed in various tissues throughout the body. They derive from bone marrow monocytes that migrate into tissues and differentiate.

Distribution of tissue macrophages:

Tissue	Macrophage Name
Liver	Kupffer cells
Lung	Alveolar macrophages
Brain	Microglia
Bone	Osteoclasts
Spleen (red pulp)	Splenic macrophages
Connective tissue	Histiocytes
Lymph nodes	Sinus macrophages
Peritoneum	Peritoneal macrophages

Functions of tissue macrophages:

Phagocytosis: Engulf and destroy bacteria, foreign particles, cellular debris, old/abnormal RBCs (especially in spleen and bone marrow)
Antigen presentation: Present antigens via MHC class II molecules to T helper cells → initiate adaptive immune responses
Cytokine secretion: Upon PRR engagement (TLRs, NOD-like receptors), secrete:
- Pro-inflammatory: IL-1, IL-6, TNF-α, IL-12
- G-CSF, GM-CSF, M-CSF → stimulate bone marrow granulocyte/monocyte production
Increase vascular permeability via cytokines/chemokines → allows plasma proteins and neutrophils to enter tissues
Activate complement, coagulation pathways
Wound healing and tissue repair

Spleen macrophages specifically: Blood passes through red pulp cords → macrophages line venous sinuses and trabeculae → phagocytize old/abnormal RBCs, bacteria, and debris from blood

Consequences of loss (asplenia/hyposplenism): Increased susceptibility to encapsulated organisms (Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis)

(Guyton & Hall Medical Physiology, p. 455-456)

12. Megaloblastic Anaemia

(Asked: 2019 Supplementary)

Definition: A macrocytic anemia caused by impaired DNA synthesis leading to large, immature, hypersegmented RBC precursors (megaloblasts) in the bone marrow.

Causes:

Vitamin B12 (Cobalamin) deficiency
- Dietary deficiency (strict vegans)
- Pernicious anemia (lack of intrinsic factor from gastric parietal cells → B12 not absorbed in terminal ileum)
- Gastrectomy, terminal ileum resection, Crohn's disease
- Fish tapeworm (Diphyllobothrium latum) competition
Folate (Folic acid) deficiency
- Poor dietary intake (alcoholics, elderly)
- Increased demand: pregnancy, hemolysis
- Drugs: methotrexate, trimethoprim, phenytoin (inhibit dihydrofolate reductase or folate absorption)
- Malabsorption (celiac disease)

Pathophysiology:

Both B12 and folate are required for synthesis of thymidine (a DNA building block)
Deficiency → impaired DNA replication → cells grow but cannot divide → large cells (megaloblasts)
Ineffective erythropoiesis: Most megaloblasts destroyed in bone marrow before release (intramedullary hemolysis)
Results in macro-ovalocytes (large oval RBCs) and hypersegmented neutrophils (>5 lobes in >5% of neutrophils - a hallmark)
Pancytopenia may develop (WBC and platelets also affected)

B12 additionally: Needed for myelin synthesis via methylmalonyl-CoA pathway → subacute combined degeneration of the spinal cord (dorsal columns + lateral corticospinal tracts) - this does NOT occur in folate deficiency alone

Schilling test: Used to diagnose pernicious anemia

Laboratory findings:

MCV >100 fL (macrocytic)
Hypersegmented neutrophils
Low reticulocyte count (relative to anemia)
Elevated serum LDH and bilirubin (intramedullary hemolysis)
Low serum B12 or folate

Treatment:

B12 deficiency: IM cyanocobalamin (especially if pernicious anemia - oral absorption impossible)
Folate deficiency: Oral folic acid
Important: Always replace B12 before or with folate in combined deficiency - giving folate alone can unmask or worsen subacute combined degeneration of spinal cord

13. Starling Forces (Capillary Fluid Exchange)

(Asked: 2024)

Starling's Law of the Capillaries describes the movement of fluid across the capillary wall based on the balance of opposing hydrostatic and oncotic (colloid osmotic) pressures.

Four Starling Forces:

Force	Direction	Value (typical)
Capillary hydrostatic pressure (Pc)	Outward (filtration)	Arterial end: ~35 mmHg; Venous end: ~15 mmHg
Interstitial fluid hydrostatic pressure (Pi)	Inward (opposes filtration)	~-3 mmHg (slightly subatmospheric)
Plasma oncotic (colloid osmotic) pressure (πp)	Inward (reabsorption)	~28 mmHg (mainly albumin)
Interstitial oncotic pressure (πi)	Outward (opposes reabsorption)	~8 mmHg

Net filtration pressure (NFP) formula:

NFP = (Pc + πi) - (Pi + πp)

Or: NFP = (Pc - Pi) - (πp - πi)

At arterial end: NFP = (35 + 8) - (3 + 28) = 43 - 31 = +12 mmHg → net filtration (fluid leaves capillary)

At venous end: NFP = (15 + 8) - (3 + 28) = 23 - 31 = -8 mmHg → net reabsorption (fluid enters capillary)

Net result: Slightly more fluid is filtered than reabsorbed. The excess (~10%) is returned to the blood via the lymphatics.

Edema occurs when:

Capillary hydrostatic pressure rises (e.g., heart failure, venous obstruction)
Plasma oncotic pressure falls (e.g., hypoalbuminemia from nephrotic syndrome, liver failure, malnutrition)
Capillary permeability increases (e.g., inflammation, burns)
Lymphatic obstruction (e.g., filariasis)

Glomerular filtration (Starling forces in kidney): GFR = Kf × [(PGC - PBS) - (πGC - πBS)] where PGC = glomerular capillary hydrostatic pressure, PBS = Bowman's space pressure, πGC = glomerular oncotic pressure, πBS = oncotic pressure in Bowman's space (~0)

(Guyton & Hall Medical Physiology; Medical Physiology by Boron & Boulpaep)

Sources used: Guyton and Hall Textbook of Medical Physiology; Costanzo Physiology 7th Edition; Roitt's Essential Immunology; Henry's Clinical Diagnosis and Management; Harriet Lane Handbook 23rd Ed.; Medical Physiology (Boron & Boulpaep)

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