Hematology

Anatomy

Region: Medullary cavity of bones (axial skeleton in adults).
Key Structures: Hematopoietic stem cells → myeloid & lymphoid lineages; red (active) vs. yellow (fatty) marrow.
Clinical Correlation: Site of hematopoiesis and leukemias; biopsy from the posterior iliac crest; marrow failure → pancytopenia.

High-Yield Pearl

Adult hematopoiesis is mainly axial — aspirate marrow from the posterior iliac crest.

Region: Along lymphatic vessels throughout the body.
Key Structures: Cortex (B-cell follicles), paracortex (T cells), medulla; afferent → sinuses → efferent lymphatics.
Clinical Correlation: Reactive vs. malignant nodes; follicular hyperplasia (B-cell) vs. paracortical expansion (viral/T-cell); drainage localizes disease.

High-Yield Pearl

Follicles = B cells, paracortex = T cells — paracortical expansion suggests a viral infection.

Region: Left upper quadrant, under ribs 9–11.
Key Structures: Red pulp (filters senescent RBCs) + white pulp (lymphoid/immune); the largest lymphoid organ.
Clinical Correlation: Splenomegaly → sequestration & cytopenias; asplenia raises risk from encapsulated organisms.

High-Yield Pearl

After splenectomy, vaccinate against encapsulated bugs — pneumococcus, H. influenzae, meningococcus.