68. blood. blood plasma. antibodies

blood

Blood is a specialized form of connective tissue that plays several vital roles in the body. It is composed of blood cells (the "formed elements") and plasma, the liquid component.

Composition of Blood

• Blood Cells (Formed Elements): These make up about 45% of blood.

  • Erythrocytes (Red Blood Cells, RBCs): Comprise about 96% of the formed elements.

    • Function: Transport oxygen (O₂) from the lungs to the tissues and carbon dioxide (CO₂) from the tissues to the lungs.

  • Leukocytes (White Blood Cells, WBCs): Comprise about 3% of the formed elements.

    • Function: Play a critical role in the immune response, defending the body against infection and foreign substances.

  • Thrombocytes (Platelets): Comprise about 1% of the formed elements.

    • Function: Involved in blood clotting (hemostasis), preventing excessive bleeding (hemorrhage).

• Blood Plasma: Makes up about 55% of blood.

  • Definition: The liquid intercellular substance of blood, serving as the medium for transporting blood cells and other components throughout the body.

  • Composition:

    • Water: 92%

    • Proteins: 7-8%

      • Albumins: 58% of plasma proteins; maintain osmotic pressure and transport hormones, vitamins, and drugs.

      • Globulins: 37% of plasma proteins; involved in immune responses (e.g., antibodies) and transport.

      • Fibrinogen: 4% of plasma proteins; a key protein involved in blood clotting.

      • Regulatory Proteins: Less than 1%; includes enzymes and hormones.

    • Other Components: 1-2%

      • Electrolytes, nutrients, vitamins, gases, and metabolic waste products.

• Hematocrit (HCT): The percentage of erythrocytes (RBCs) in a blood sample.

  • Normal HCT Values:

    • Men: 40-50%

    • Women: 35-45%

• Total Blood Volume: Approximately 4-6 liters in an adult body, accounting for about 7-8% of body weight.

functions of blood

1. Transport:

   • Carries nutrients, gases (O₂ and CO₂), hormones, and metabolic waste products to and from cells.

2. Regulation:

   • Helps regulate body temperature, pH (buffering capacity), and fluid balance (homeostasis).

3. Defense:

   • Protects the body against infections through leukocytes (white blood cells) and antibodies.

4. Clotting:

   • Platelets and clotting factors in plasma prevent excessive bleeding by forming blood clots.

blood plasma

• Definition: Blood plasma is the clear, straw-colored liquid portion of blood that remains after blood cells, platelets, and clotting factors have been removed.

• Serum: Plasma without fibrinogen (the clotting factor). It contains antibodies, electrolytes, antigens, hormones, and exogenous substances like drugs.

• pH: Blood plasma has a slightly alkaline pH, ranging from 7.35 to 7.45.

antibodies

• Definition: Antibodies, also known as immunoglobulins (Ig), are large Y-shaped proteins produced by B-lymphocytes (a type of white blood cell).

• Function:

  • Identify and bind to specific antigens (foreign molecules like bacteria and viruses) to neutralize them.

  • Promote agglutination (clumping) of antigens, making it easier for phagocytes to engulf and destroy pathogens through phagocytosis.

• Classes of Antibodies:

  • IgA: Found in mucosal areas, such as the gut, respiratory tract, and urogenital tract, as well as in saliva, tears, and breast milk.

  • IgG: The most abundant antibody in the blood and extracellular fluid; provides long-term protection.

  • IgE: Involved in allergic reactions and defense against parasitic infections.

  • IgD: Functions mainly as a receptor on B cells that have not been exposed to antigens.

  • IgM: The first antibody produced in response to an infection; primarily found in the blood and lymph fluid.

key blood cells

• Red Blood Cells (RBCs): Biconcave disc-shaped cells without a nucleus, primarily responsible for oxygen transport.

• White Blood Cells (WBCs): Several types, including:

  • Neutrophils: First responders to infection; involved in phagocytosis.

  • Eosinophils: Fight against parasitic infections and participate in allergic responses.

  • Basophils: Release histamine during allergic reactions.

  • Monocytes: Differentiate into macrophages and dendritic cells in tissues; involved in phagocytosis and antigen presentation.

  • Lymphocytes: Include B-cells (produce antibodies), T-cells (kill infected cells and regulate immune response), and natural killer (NK) cells.

• Platelets: Small, disc-shaped cell fragments involved in clotting and wound repair.