Blood: Components, Properties, and Blood Typing

General Properties of Blood

Blood is a specialized fluid connective tissue essential for transporting substances throughout the body. It consists of cells suspended in a liquid extracellular matrix called plasma.

• Volume: Adults typically have 4 to 6 liters of blood.

• Composition: Blood is made up of plasma and formed elements (cells and cell fragments).

• Plasma: The matrix of blood, a clear, light yellow fluid that makes up about 55% of blood volume.

• Formed Elements: Includes red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).

• Hematocrit: The percentage of blood volume occupied by erythrocytes, typically about 44% in adults.

Formed Elements of Blood

The formed elements are the cellular components of blood, each with specialized functions.

• Erythrocytes (Red Blood Cells, RBCs): Responsible for oxygen transport via hemoglobin.

• Platelets (Thrombocytes): Cell fragments involved in blood clotting, derived from megakaryocytes in bone marrow.

• Leukocytes (White Blood Cells, WBCs): Key players in immune defense, divided into two main categories:

  • Granulocytes: Contain visible cytoplasmic granules when stained.

    • Neutrophils: Multi-lobed nucleus (3-5 lobes), phagocytize bacteria, most abundant WBC.

    • Eosinophils: Bilobed nucleus, reddish granules, combat parasitic infections and participate in allergic responses.

    • Basophils: S-shaped nucleus, dark purple granules, release histamine during inflammatory responses.

  • Agranulocytes: Lack visible granules in cytoplasm.

    • Lymphocytes: Spherical nucleus, thin rim of cytoplasm, involved in adaptive immune responses (B and T cells).

    • Monocytes: U-shaped nucleus, abundant cytoplasm, differentiate into macrophages for phagocytosis of debris.

Hemoglobin and Oxygen Transport

Hemoglobin is the oxygen-carrying protein in erythrocytes. Each hemoglobin molecule can bind up to four oxygen molecules.

• Structure: Composed of four polypeptide chains, each with a heme group that binds oxygen.

• Function: Transports oxygen from lungs to tissues and facilitates carbon dioxide transport back to the lungs.

Blood Typing and Antigens

Blood type is determined by specific glycoprotein antigens present on the surface of red blood cells (RBCs). The most clinically significant blood group systems are the ABO and Rh systems.

• ABO System:

  • Type A: Has A antigens on RBCs; produces anti-B antibodies.

  • Type B: Has B antigens on RBCs; produces anti-A antibodies.

  • Type AB: Has both A and B antigens; produces neither antibody (universal recipient).

  • Type O: Has neither antigen; produces both anti-A and anti-B antibodies (universal donor).

• Rh System:

  • Rh-positive (Rh+): Has the Rh antigen (D antigen) on RBCs.

  • Rh-negative (Rh-): Lacks the Rh antigen; can develop anti-Rh antibodies if exposed to Rh+ blood.

Table: ABO Blood Types and Compatibility

Blood Transfusion Compatibility

Transfusion reactions occur if incompatible blood is transfused, leading to hemolysis (destruction of donor RBCs). Compatibility depends on matching both ABO and Rh antigens.

• Universal Donor: Type O- (no A, B, or Rh antigens)

• Universal Recipient: Type AB+ (has all antigens, so no antibodies against A, B, or Rh)

• Rh Considerations: Rh- individuals should not receive Rh+ blood unless previously sensitized.

• Antibodies in Recipient: Always consider the antibodies present in the recipient's plasma, as these can attack donor RBC antigens.

Processing of Donated Blood

Before transfusion, donated whole blood is processed to separate its components and reduce the risk of reactions.

• Centrifugation: Blood is spun to separate into red cells, platelets, and plasma.

• Leuko-reduction: Removal of white blood cells to minimize immune reactions in recipients.

• Component Packaging: Each component is packaged as a standardized "unit" for clinical use.

• Plasma Processing: Plasma may be further processed into products like cryoprecipitate, which aids in clotting.

Summary Table: Characteristics of Leukocytes

Key Equations

• Hematocrit Calculation:

Example: Blood Type Compatibility

• Example: A type AB donor and a type O- recipient are incompatible. The recipient's anti-A and anti-B antibodies would attack the donor's RBCs.

Additional info: For more practice with blood typing, online simulations and videos are recommended. Always review pre-lab materials before laboratory sessions.