Composition of Blood and Erythrocytes

Composition of Blood

• Blood is a complex fluid connective tissue.
• It comprises plasma, a yellowish liquid, and formed elements (cells and cell fragments).
• Plasma accounts for about 55% of blood volume.
• Plasma is mostly water (90-92%), with dissolved proteins (albumin, globulins, fibrinogen), electrolytes (e.g., sodium, potassium, calcium), nutrients, waste products, and hormones.
• Formed elements include erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets).
• Erythrocytes are the most numerous blood cells and are responsible for oxygen transport.
• Leukocytes are involved in the immune response and defense mechanisms.
• Thrombocytes are essential for blood clotting.

Erythrocytes (Red Blood Cells)

• Erythrocytes are biconcave discs, lacking a nucleus in mammals.
• They are filled with hemoglobin, a protein that binds oxygen.
• Hemoglobin gives blood its red color.
• Function primarily in oxygen transport from the lungs to the body tissues and carbon dioxide transport from tissues to the lungs.
• Erythrocytes have a lifespan of about 120 days.
• Their breakdown occurs in the spleen and liver.

Leukocytes (White Blood Cells)

• Leukocytes are crucial components of the immune system.
• They defend the body against pathogens and foreign substances.
• Leukocytes are classified into granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes).
• Granulocytes have granules in their cytoplasm, while agranulocytes do not.
• Neutrophils are phagocytic cells that engulf and destroy microorganisms.
• Eosinophils combat parasitic infections and allergic reactions.
• Basophils release histamine and heparin, playing a role in inflammation.
• Lymphocytes (T cells and B cells) are key players in adaptive immunity, mediating specific responses to antigens.
• Monocytes differentiate into macrophages, which engulf cellular debris and pathogens.

Thrombocytes (Platelets)

• Thrombocytes are small cell fragments derived from megakaryocytes.
• They play a vital role in blood clotting (hemostasis).
• Platelets release clotting factors and promote the formation of a platelet plug at the site of injury.
• They participate in the coagulation cascade, leading to the conversion of fibrinogen to fibrin, forming a stable clot.

Blood Types

• Blood is categorized into different types based on the presence or absence of specific antigens on the surface of red blood cells.
• The most common blood typing system is the ABO system (A, B, AB, O) and the Rh system (positive or negative).
• Blood transfusions must be carefully matched to prevent a harmful immune response, an important consideration in healthcare.

Blood Functions

• Blood plays an essential transport role, delivering oxygen and nutrients to tissues and removing waste products.
• Blood also regulates body temperature, pH, and fluid balance.
• Blood protects the body by carrying antibodies and cells involved in the immune response.
• The clotting mechanism protects the body from excessive blood loss.