L3 physiology

White Blood Cells (WBCs) and Platelets

• WBCs, also known as leukocytes, are mobile units of the body's protective system.
• They are formed partly in bone marrow (granulocytes, monocytes) and lymph tissue (lymphocytes, plasma cells).
• WBCs are crucial for fighting infections and inflammation.
• They specifically travel to areas of infection or inflammation.
• There are six main types of WBCs:
  • Granulocytes: neutrophils, eosinophils, basophils
  • Agranulocytes: lymphocytes, monocytes.
• Polymorphonuclear cells have a granular appearance and are thus called granulocytes ("polys").
• The normal WBC count in an adult human is approximately 7000 per microliter of blood (ranging from 4,000 to 11,000/μ³).
  • Neutrophils make up approximately 62% of the total WBC count
• Functions of different types of WBCs:
  • Neutrophils: first line of defense, phagocytic cells
  • Eosinophils: involved in parasitic infections and allergic reactions
  • Basophils: involved in releasing histamine during allergic reactions
  • Lymphocytes: produce antibodies (B cells), and destroy viruses and cancer cells (T cells)
  • Monocytes: phagocytic cells called macrophages once they leave the blood.

Leucopoiesis

• Leucopoiesis is the process of formation of white blood cells
• The blood stem cells differentiate into either myeloid or lymphoid stem cells.
• Myeloid stem cells give rise to granulocytes and monocytes.
• Lymphoid stem cells give rise to lymphocytes.

Leukopenia

• A condition characterized by a low WBC count (less than 4000/mm³).
• Causes of leukopenia include:
  • Drugs (e.g., chloramphenicol)
  • Exposure to x-rays and certain radioisotopes
  • Bone marrow diseases
  • Severe chronic infections

Leukocytosis

• A condition characterized by an abnormally high WBC count (greater than 11,000/mm³).
• Causes of leukocytosis include:
  • Physiological conditions
  • Pregnancy, after meals, exercise
  • Pathological conditions such as tissue damage, pyogenic infections.

Leukemia

• A cancer characterized by uncontrolled proliferation of WBCs in bone marrow.
• Causes include:
  • Genetic predisposition
  • Exposure to chemicals (e.g., benzene derivatives, asbestos)
  • Cytotoxic drugs (e.g., chloramphenicol)
  • X-rays and radioisotopes

Platelets (Thrombocytes)

• Platelets are small, irregular-shaped cell fragments.
• Size: 1 to 4 micrometers in diameter
• They're produced in the bone marrow by megakaryocytes.
• Normal platelet count: 150,000 to 400,000 per microliter of blood (average 250,000/µL).
• Platelets are responsible for forming temporary plugs to stop bleeding from damaged blood vessels.

Thrombocytopenia

• A condition characterized by a low platelet count.
• Causes include:
  • Bone marrow failure
  • Immune system disorders (destroying platelets)
  • Spleen enlargement (holding excess platelets)
  • Combination of the above reasons

Hemostasis

• Hemostasis is the process that stops bleeding from damaged blood vessels.

How Hemostasis Works (Mechanism)

• 1. Local Vasoconstriction
• 2. Temporary Platelet Plug Formation
• 3. Definitive Platelet Plug Formation (blood coagulation)
• 4. Repair of Damaged Blood Vessels

Blood Coagulation

• Involves a cascade of proteins to form a fibrin clot.
  • Intrinsic pathway (inside the blood)
  • Extrinsic pathway (outside the blood)