Blood Composition and Hematology Essentials

Primary Functions of Human Blood

Blood performs several critical roles in the body:

• Transport: Nutrients, oxygen, carbon dioxide, and hormones.
• Immune Defense: Protecting against toxins and pathogens.
• Waste Elimination: Removing metabolic waste products.
• Homeostasis: Controlling pH levels and ion concentrations.
• Fluid Regulation: Restricting fluid loss at injury sites.
• Temperature Regulation: Maintaining stable body temperature.

Blood Composition and Volume

Blood consists of plasma (46–63%) and formed elements (37–54%).

• Plasma: Composed of water (92%), plasma proteins (7%), and other solutes (1%).
• Formed Elements: Composed of red blood cells (99.9%), white blood cells (0.1%), and platelets (0.1%).

Blood Volume:

• Males: 5–6 liters (approximately 46% of body mass).
• Females: 4–5 liters (approximately 42% of body mass).

Plasma Proteins and Serum

• Albumins (60%): Transport nutrients and minerals.
• Globulins (35%): Function as antibodies.
• Fibrinogens (4%): Essential for blood clotting.

Serum is the component of blood that is neither a blood cell nor a clotting factor; it is blood plasma with the fibrinogens removed. Serum includes all proteins not used in blood clotting (coagulation), as well as electrolytes, antibodies, antigens, hormones, and exogenous substances such as drugs and microorganisms.

Red Blood Cells and Erythropoiesis

The average lifespan of a red blood cell (RBC) is 120 days.

Erythropoiesis is the process by which red blood cells (erythrocytes) are produced. This process is caused by the hormone erythropoietin, which stimulates the proliferation and differentiation of red cell precursors, leading to increased erythropoiesis.

Types of White Blood Cells

• Neutrophils: Provide the fastest response of all WBCs to bacteria and parasites. They release lysozymes to digest bacteria, defensive proteins that act as natural antibiotics, and strong oxidants to destroy pathogens.
• Basophils: Involved in inflammatory and allergic reactions. They release heparin, histamine, and serotonin to heighten the inflammatory response. Heparin is a potent anticoagulant that prevents clotting within vessels.
• Eosinophils: Release histaminase to slow down inflammation caused by basophils. They attack parasitic worms and phagocytize antibody-antigen complexes.
• Monocytes: Take longer to reach the site of infection but arrive in larger numbers. Once they leave the capillaries, they become wandering macrophages that destroy microbes and clean up dead tissue.
• Lymphocytes: There are three primary types:
  • B cells: Destroy bacteria and toxins; they turn into plasma cells that produce antibodies.
  • T cells: Attack viruses, fungi, transplanted organs, and cancer cells.
  • Natural Killer (NK) cells: Attack various microbes and tumor cells through direct attack.

Differential WBC Count and Diagnostics

A Differential WBC Count detects changes in the percentages of circulating white blood cells. This diagnostic tool helps identify infections, poisoning, leukemia, chemotherapy effects, parasites, or allergic reactions.

Normal WBC Percentages:

• Neutrophils (60–70%): Increased during bacterial infections.
• Lymphocytes (20–25%): Increased during viral infections.
• Monocytes (3–8%): Increased during fungal or viral infections.
• Eosinophils (2–4%): Increased during parasitic infections or allergic reactions.
• Basophils (<1%): Increased during allergic reactions.