Types of Formed Elements in Blood

Types of Formed Elements

• Erythrocytes are red blood cells (RBCs) that primarily carry oxygen.
• Leukocytes are white blood cells (WBCs) crucial for immune defense.
• Platelets are cell fragments essential for blood clotting.

Erythrocytes Overview

• Function: Oxygen transport.
• Structure: Biconcave disks, essentially bags of hemoglobin, anucleate, with few organelles.
• Normal count: Approximately 5 million RBCs per cubic millimeter of blood.

Hemoglobin

• Composition: Iron-containing protein that binds oxygen.
• Structure: Each molecule has four oxygen-binding sites; each erythrocyte contains about 250 million hemoglobin molecules.
• Normal concentration: 12-18 g of hemoglobin per 100 mL of blood.

Anemia

• Definition: Decrease in the blood's oxygen-carrying capacity.

Sickle-cell Anemia (SCA)

• Cause: Abnormally shaped hemoglobin leads to distorted RBC shape.

Polycythemia

• Definition: Excessive increase in RBC count.
• Causes: Can result from bone marrow cancer (polycythemia vera) or adaptation to high altitudes (secondary polycythemia).
• Effect: Increased RBCs result in slower blood flow and higher viscosity, impairing circulation.

Leukocytes Overview

• Function: Defense against disease; complete cells with nuclei and organelles.
• Movement: Capable of diapedesis (moving out of blood vessels) and amoeboid motion.
• Response: Move toward damaged tissues through positive chemotaxis.
• Normal count: Ranges from 4,800 to 10,800 WBCs per cubic millimeter of blood.

Leukocytosis

• Definition: Elevated WBC count (above 11,000 cells/mm³), typically indicating infection.

Leukopenia

• Definition: Low WBC count, often due to drugs like corticosteroids and anticancer agents.

Leukemia

• Definition: Cancer of the bone marrow, producing excess WBCs.

Granulocytes

• Characteristic: Cytoplasmic granules can be stained; contain lobed nuclei.
• Types: Neutrophils, eosinophils, and basophils.

Agranulocytes

• Characteristic: Lack visible granules; nuclei are spherical, oval, or kidney-shaped.
• Types: Lymphocytes and monocytes.

Abundance of WBCs

• Order from most to least abundant:
  • Neutrophils → Lymphocytes → Monocytes → Eosinophils → Basophils.

Neutrophils

• Appearance: Pale pink cytoplasm, fine granules, deep purple lobed nucleus.
• Role: Act as phagocytes during infections.
• Normal count: 3,000-7,000 cells/mm³ (40-70% of WBCs).

Eosinophils

• Appearance: Red granules, bilobed nucleus.
• Role: Combat parasitic infections and mediate allergy responses.
• Normal count: 100-400 cells/mm³ (1-4% of WBCs).

Basophils

• Appearance: Sparse large blue-purple granules, U- or S-shaped nucleus.
• Function: Release histamine (a vasodilator) and contain heparin (an anticoagulant).
• Normal count: 20-50 cells/mm³ (0-1% of WBCs).

Lymphocytes

• Appearance: Pale blue cytoplasm and dark purple nucleus.
• Role: Integral to the immune system; B lymphocytes produce antibodies, T lymphocytes target tumors and viruses.
• Normal count: 1,500-3,000 cells/mm³ (20-45% of WBCs).

Monocytes

• Appearance: Largest WBCs with gray-blue cytoplasm, kidney-shaped nucleus.
• Role: Function as macrophages; important in chronic infection response.
• Normal count: 100-700 cells/mm³ (4-8% of WBCs).

Platelets

• Origin: Derived from ruptured megakaryocytes.
• Function: Essential for blood clotting processes.
• Normal count: 150,000 to 400,000 platelets/mm³, with 300,000 considered average.