Blood Formed Elements: Red Cells, White Cells, Platelets & Plasma

Formed Elements (Cellular Components)

When blood is centrifuged, formed elements constitute ~45% of volume (hematocrit). They include:

1. Erythrocytes (Red Blood Cells – RBCs)

• Function: Transport O₂ (via hemoglobin) and CO₂.
• Features: Anucleate, biconcave disc, ~7–8 µm diameter, lifespan ~120 days.
• Count: ~4.5–6.0 million/µL (men), ~4.0–5.5 million/µL (women).

2. Leukocytes (White Blood Cells – WBCs)

• Function: Immune defense.
• Total Count: ~4,000–11,000/µL.
• Five Types (Differential):
  • Neutrophils (50–70%) – acute bacterial infection, phagocytosis.
  • Lymphocytes (20–40%) – adaptive immunity (B/T/NK cells).
  • Monocytes (2–8%) – become macrophages/dendritic cells.
  • Eosinophils (1–4%) – parasites, allergies.
  • Basophils (<1%) – histamine release, allergic response.

3. Thrombocytes (Platelets)

• Function: Hemostasis—adhesion, aggregation, plug formation, coagulation support.
• Features: Cell fragments (2–3 µm), no nucleus, lifespan 7–10 days.
• Count: 150,000–450,000/µL.

Acellular Components (Plasma & Layers)

• Plasma (~55%): Straw-colored liquid matrix (90% water). Contains proteins (albumin, globulins, fibrinogen), electrolytes, nutrients, hormones, waste, gases. Serum = plasma minus clotting factors.
• Buffy Coat: Thin (~1%) whitish layer between packed RBCs and plasma after centrifugation; contains WBCs and platelets.

Key Ratios

Normal plasma:RBC ratio ≈ 55:45 (Hct ~45%). Dehydration ↑ Hct; anemia ↓ Hct.