Composition and Functions of Blood

Blood Composition

  • Blood is composed of cells (42%) and fluid matrix (plasma).

  • Average blood volume: 4.5 to 5.5 liters; males generally have more blood than females.

Blood Component Separation

  • Centrifugation separates blood components:

    • Red blood cells at the bottom,

    • Plasma at the top,

    • Buffy coat in between (contains white blood cells and platelets).

Plasma Composition

  • Plasma:

    • 92% water,

    • 1% small molecules (amino acids, glucose, lipids, ions, vitamins, gases),

    • 77% proteins (mainly albumin, globulins, fibrinogen).

  • Albumin: Maintains colloid osmotic pressure, keeping blood within vessels.

Blood Cells

  • Types of blood cells:

    • Red blood cells (RBCs): transport oxygen and CO2.

    • White blood cells (WBCs): immune response.

    • Platelets: clotting.

Hematopoiesis

  • Blood cell formation process.

  • Prenatal and postnatal stages.

  • Hematopoietic stem cells give rise to all blood cells.

White Blood Cells Subtypes

  • Lymphocytes, phagocytes (monocytes, neutrophils), granulocytes (neutrophils, basophils, eosinophils).

Locations of Blood Cell Production

  • Early production: yolk sac, then liver, spleen, thymus.

  • Postnatal: primarily in bone marrow, particularly after age 5.

Blood Cell Lifespan

  • RBCs: ~120 days,

  • Neutrophils: ~6 hours,

  • Lymphocytes: up to ~200 days,

  • Platelets: 9-12 days.

Cytokines and Hematopoiesis Control

  • Key cytokines:

    • Erythropoietin (stimulates RBC production),

    • Thrombopoietin (stimulates platelet production),

    • Colony-stimulating factors (various WBC types).

Erythropoiesis

  • Process of RBC formation initiated by EPO from kidney, responding to hypoxia.

Blood Testing Parameters

  • Common tests include RBC count, hemoglobin levels, hematocrit, etc.

  • Reference values:

    • Males: RBC count 4.7 to 6.1 million/mcL.

    • Females: RBC count 4.2 to 5.4 million/mcL.

Blood Type and Compatibility

  • Based on ABO and Rh systems.

  • Important for transfusions to avoid hemolysis.

  • Universal donor: Type O, universal recipient: Type AB.

Hemoglobin Structure

  • Composed of four heme groups, binds oxygen;

  • Oxyhemoglobin (with oxygen) vs. Deoxyhemoglobin (without oxygen).

Blood Test Interpretation

  • Evaluate absolute number of RBCs, hemoglobin concentration, hematocrit and mean corpuscular volume.