Special Pathology

Lymphoid System I. Components of the Lymphoid System 1. Lymphatic Vessels Structure : Composed of lymphatic capillaries, vessels, and nodes. Lymphatic Capillaries : Resemble blood capillaries. Have thin walls with a single endothelial cell layer. Highly permeable—allow passage of fluid, proteins, and particulate matter. Larger Lymphatics : Structurally similar to veins but with thinner muscle layers. More numerous valves than veins. Function : Drain excess tissue fluid (lymph). Return lymph to the bloodstream. Help in immune surveillance and transport of immune cells. 2. Lymph Nodes (Normal Structure) Gross Anatomy : Bean-shaped or oval. 1–2 cm in length. Covered by a fibrous capsule. Entry & Exit of Lymph : Afferent lymphatics enter at convex surface. Drain into subcapsular sinus → branches → exit via efferent lymphatic at the hilum. Internal Structure : Cortex : Contains B-cell rich lymphoid follic...

Laboratory Diagnosis of Leukemias I. Acute Myeloid Leukemia (AML) 1. Complete Blood Count (CBC) Anemia – normocytic, normochromic (↓ RBCs, Hb) Thrombocytopenia – ↓ platelet count Leukocytosis – ↑ WBC count (in most cases) Blast cells in peripheral smear – >20% blasts (WHO criterion) 2. Peripheral Blood Smear Myeloblasts – large cells with: High N:C ratio Fine chromatin 1–4 nucleoli Auer rods – (needle-like azurophilic granules; diagnostic of myeloid lineage ) 3. Bone Marrow Aspiration & Biopsy Hypercellular marrow >20% myeloblasts Suppressed normal hematopoiesis 4. Cytochemistry Myeloperoxidase (MPO) positive – (confirms myeloid origin) Sudan Black B (SBB) positive Non-specific esterase negative 5. Immunophenotyping (Flow Cytometry) CD13, CD33, CD117 – markers of myeloid lineage HLA-DR, CD34 (stem cell markers) 6. Cytogenetic & Molecular Studies t(8;21), inv(16), t(15;17) (PML-RARA in APL subtype) FLT3, NPM1 mutations (prognostic markers) ...

🦴 BONE MARROW & HAEMATOPOIESIS 📌 1. Bone Marrow and Blood Cell Formation Bone marrow contains pluripotent stem cells that give rise to: Non-lymphoid stem cells → form erythrocytes (RBCs) , granulocytes , monocytes , platelets . Lymphoid stem cells → form B cells , T cells , and Natural Killer (NK) cells . 🕒 2 . Lifespan of Blood Cells Cell Type Lifespan Neutrophils 6–8 hours Platelets ~10 days RBCs 90–120 days Production of these cells is tightly regulated to match the rate of loss. 🧬 3 . Haematopoiesis (Blood Cell Formation) Embryonic Sites of blood cell production: Yolk Sac → 1st few weeks. Liver & Spleen → 3rd month to 2 weeks after birth. Bone Marrow → Starts by 4–5 months, fully active by 7–8 months. In Adults : Active bone marrow remains in central skeleton : vertebrae, sternum, ribs, skull, pelvis, and ends of long bones. Fat replaces red marrow in long bones over time. In some diseases, liver a...