This topic will provide an overview of hematology, including the study of blood, blood-forming tissues, and blood-related disorders. It will cover the components of blood, functions of blood cells, and basic hematological terms.
Introduction to Hematology – Study Notes
1. What Is Hematology?
- Definition: The branch of medicine that deals with the study of blood, the organs that produce blood, and blood‑related diseases.
- Key Components of Blood:
- Plasma – liquid matrix (≈55% of blood volume) containing water, electrolytes, proteins, hormones, and waste products.
- Cellular elements – red blood cells (RBCs), white blood cells (WBCs), and platelets (thrombocytes).
2. Major Blood‑Forming Organs (Hematopoietic System)
| Organ / Tissue |
Primary Function |
Notes |
| Bone Marrow |
Site of hematopoiesis (production of all blood cells) |
Red marrow active in children; becomes yellow (fatty) in adults except in axial skeleton |
| Spleen |
Filters blood, removes aged cells, immune surveillance |
Reservoir for platelets; produces some lymphocytes |
| Thymus |
Maturation of T‑lymphocytes |
Involutes after puberty |
| Lymph Nodes |
Immune response coordination |
Filter lymph, house B‑ and T‑cells |
| Liver |
Fetal hematopoiesis; stores iron; produces clotting factors |
Can resume hematopoiesis in severe disease (extramedullary hematopoiesis) |
3. Blood Cell Types & Functions
| Cell Type |
Normal Count (per µL) |
Main Functions |
Life Span |
| Red Blood Cells (Erythrocytes) |
4.5–5.9 M (men), 4.0–5.2 M (women) |
Transport O₂ (via hemoglobin) & CO₂ |
~120 days |
| Neutrophils |
1.5–8.0 K |
Phagocytosis of bacteria; first line of defense |
6–8 hrs (circulating) |
| Lymphocytes |
1.0–4.8 K |
Adaptive immunity (B‑cells produce antibodies; T‑cells mediate cellular immunity) |
Weeks–years |
| Monocytes |
0.2–0.8 K |
Phagocytosis, antigen presentation; become macrophages in tissues |
1–3 days (circulating) |
| Eosinophils |
0.04–0.5 K |
Combat parasites, modulate allergic responses |
8–12 hrs |
| Basophils |
0.02–0.1 K |
Release histamine & heparin; role in allergy & inflammation |
1–2 hrs |
| Platelets (Thrombocytes) |
150–400 K |
Initiate clot formation, release growth factors for wound healing |
7–10 days |
4. Basic Hematologic Tests
| Test |
What It Measures |
Clinical Use |
| Complete Blood Count (CBC) |
RBC, WBC, platelet counts; hemoglobin, hematocrit, indices (MCV, MCH, MCHC) |
Screening for anemia, infection, leukemia, thrombocytopenia |
| Peripheral Blood Smear |
Morphology of cells |
Identify abnormal shapes, parasites, blasts |
| Reticulocyte Count |
Immature RBCs |
Assess marrow response to anemia |
| Coagulation Panel ( |
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