Histology of Blood Cells

Study Notes

Blood is a specialized connective tissue composed of cells:
- Red blood cells (RBCs)
- White blood cells (WBCs or leucocytes)
- Blood platelets (thrombocytes) - 45% of blood volume
- Plasma (intercellular fluid) - 55% of blood volume
Originates from mesenchyme, which derives from the mesoderm.
Blood plasma consists of water, organic substances, inorganic substances, gases, hormones, and enzymes.

Normal range: 4.5 to 5.5 million cells per cubic millimeter.
Diameter: 7-9 µm (average 7.5 µm), thickness: 1.9 µm at edges, 1.1 µm at center.
Not true cells; lack nuclei and organelles.
Shape: rounded, biconcave discs.
In slow blood flow, they form aggregates called rouleaux due to surface tension.
Surrounded by a lipoprotein cell membrane.
Filled with hemoglobin, responsible for gas transport between lungs and tissues.

Colorless but appear white when aggregated.
Contain organelles and inclusions.
Exhibit amoeboid movement, allowing them to migrate through capillary walls for phagocytosis.
Count ranges from 4,000 to 11,000 cells per cubic millimeter, measurable by hemocytometer.
Five types of leucocytes:
- Granular:
  - Neutrophils
  - Eosinophils
  - Basophils
- Non-granular:
  - Lymphocytes
  - Monocytes

Comprise 60-75% of WBCs.
Diameter: 10-12 µm.
L/M: Single segmented nucleus with 2-5 segments; cytoplasm contains large azurophilic granules and small specific granules.
E/M: Few mitochondria, endoplasmic reticulum, and glycogen granules; azurophilic granules are lysosomes rich in hydrolytic enzymes, specific granules contain collagenase, alkaline phosphatase, and bactericidal substances.
Function: Phagocytosis and destruction of microorganisms.

Comprise 2-5% of WBCs.
Diameter: 12-14 µm.
L/M: Bilobed or horseshoe-shaped nucleus; cytoplasm contains coarse, specific acidophilic granules with a shiny red appearance.
E/M: Few mitochondria, small Golgi body, and endoplasmic reticulum; granules contain histaminase and sulphatase enzymes.
Function: Attracted to sites of allergic reactions.

Comprise 0-1% of WBCs.
Diameter: 10-12 µm.
L/M: Cytoplasm filled with large basophilic granules stainable with Giemsa; irregular (S-shaped) nucleus.
E/M: Electron-dense granules with a highly ordered internal structure.
Function: Related to the production and transport of histamine and heparin; exhibit slight phagocytic activity.

Classified by diameter into small and large lymphocytes.
Small Lymphocytes (15-20%):
- Diameter: 6-8 µm.
- L/M: Scanty cytoplasm with few azurophil granules; nucleus is small, dark-stained, and fills most of the cytoplasm.
- E/M: Covered by microvilli; contains free ribosomes and few organelles.
Large Lymphocytes (5-10%):
- Diameter: 10-15 µm.
- L/M: More abundant cytoplasm; less darkly stained nucleus.
- E/M: Abundant ribosomes, mitochondria, well-developed Golgi complexes; slightly indented nucleus.
Function: Play a crucial role in the immune response.