White Blood Cells, Red Blood Cells, Plasma

Functions of Blood

  • Three main functions:

    • Transport: Blood delivers nutrients, gases, hormones, etc.

    • Regulation: Helps maintain temperature, pH, and fluid volume.

    • Protection: Prevents blood loss through clotting and infection via immune components.

Composition of Blood

  • Blood as Fluid Tissue:

    • The only fluid tissue in the body, classified as connective tissue.

  • Components:

    • Plasma: nonliving fluid matrix (~55% of blood).

    • Formed Elements: living blood cells suspended in plasma, which includes:

      • Erythrocytes (RBCs)

      • Leukocytes (WBCs)

      • Platelets

  • Blood Composition:

    • Erythrocytes on bottom (~45% of whole blood):

    • Hematocrit: percentage of blood volume that is RBCs.

    • Normal hematocrit values:

      • Males: 47% ± 5%

      • Females: 42% ± 5%

    • WBCs and platelets in Buffy coat (<1%): thin layer between RBCs and plasma.

Physical Characteristics of Blood

  • Physical Characteristics:

    • Sticky, opaque fluid with metallic taste.

    • Color varies with oxygen content:

      • High O2 levels: scarlet red

      • Low O2 levels: dark red

    • pH: 7.35–7.45.

    • Blood makes up ~8% of body weight.

    • Average volume:

      • Males: 5–6 L

      • Females: 4–5 L

Blood Plasma

  • Plasma Characteristics:

    • Straw-colored, sticky fluid (~90% water).

    • Contains over 100 dissolved solutes: nutrients, hormones, waste, proteins, inorganic ions.

    • Most abundant solutes are plasma proteins:

      • Albumin: makes up 60% of plasma proteins; functions as a carrier, blood buffer, and contributor to osmotic pressure.

      • Globulins: constitute 36% of plasma proteins; they are involved in immune responses, functioning as antibodies and transport proteins for various substances.

        • Alpha: produced by liver and transport proteins for lipids and fat-soluble vitamins, playing a crucial role in lipid metabolism.

        • Beta: produced primarily in the liver, these globulins play a significant role in transporting iron and maintaining proper osmotic balance within the bloodstream.

        • Gamma (antibodies): produced by plasma cells, these globulins act as antibodies in the immune response, helping to protect the body against infections and foreign pathogens.

      • Fibrinogen: 4% of plasma proteins, synthesized by the liver, is essential for blood clotting as it is converted into fibrin during the coagulation process, forming a stable mesh that helps in sealing wounds and preventing excessive bleeding.

Formed Elements

  • Elements: erythrocytes (RBCs), leukocytes (WBCs), and platelets.

  • Only WBCs are complete cells with nuclei and organelles.

  • RBCs lack nuclei and organelles, survive in bloodstream only a few days, originate in bone marrow.

Erythrocytes (Red Blood Cells)

  • Structure:

    • Small diameters (7.5 μm), biconcave disc shape, anucleate, filled with hemoglobin (Hb).

    • Contain proteins such as spectrin for flexibility.

  • Function:

    • Dedicated to respiratory gas transport; Hb binds with O2.

    • Normal values for Hb:

      • Males: 13–18 g/100 ml

      • Females: 12–16 g/100 ml.

  • Hemoglobin Structure:

    • Comprised of heme pigments and globin protein (four polypeptide chains).

  • Gas Transport:

    • Each Hb molecule can transport four O2.

    • Also facilitates CO2 transport as carbaminohemoglobin.

Production of Erythrocytes

  • Hematopoiesis: Formation of all blood cells primarily in red bone marrow.

  • Stages of Erythropoiesis:

    • Process takes about 15 days, begins with hematopoietic stem cells.

    • Transformation stages from hemocytoblast to reticulocyte, indicating rate of RBC formation.

Regulation and Requirements of Erythropoiesis

  • Red Blood Cell Lifespan: 100–120 days.

  • Hormonal Control: Erythropoietin (EPO) stimulates RBC production.

    • Released in response to hypoxia (low oxygen levels).

  • Dietary Requirements:

    • Amino acids, lipids, carbohydrates.

    • Iron and vitamins B12 and folic acid critical for RBC production.

Fate and Destruction of Erythrocytes

  • Breakdown: Old RBCs get trapped in the spleen, where macrophages engulf and break them down.

  • Products of Breakdown:

    • Iron is stored or reused, heme is converted to bilirubin and eventually excreted.

    • Globin is broken down into amino acids.

Erythrocyte Disorders

  • Anemia: Low O2-carrying capacity; caused by blood loss, insufficient RBC production, or excessive destruction.

    • Types of Anemia:

      • Hemorrhagic Anemia: Rapid loss due to severe wounds.

      • Iron-Deficiency Anemia: Caused by insufficient iron; results in microcytes.

      • Pernicious Anemia: Autoimmune condition affecting B12 absorption.

      • Thalassemias: Genetic disease affecting hemoglobin.

      • Sickle-Cell Anemia: Genetic mutation causing RBC deformation.

      • Polycythemia: Excess RBC; can result from primary bone marrow disease or secondary to hypoxia.

Leukocytes (White Blood Cells)

  • General Structure:

    • Complete cells with nuclei, <1% of blood volume (4,800–10,800 WBCs per µl blood).

  • Functions: Defense against disease; can exit capillaries (diapedesis) and move via amoeboid motion.

  • WBC Types: Granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes (T cells and B cells), monocytes).

    • Mnemonic for abundance: "Never let monkeys eat bananas."

Production and Life Span of Leukocytes

  • Leukopoiesis: Production of WBCs stimulated by chemical signals.

    • All originate from hemocytoblasts, with pathways diverging to lymphocytes and myeloid cells.

  • Granulocyte and Agranulocyte Production: Involves multiple immature forms culminating in mature leukocytes.

Leukocyte Disorders

  • Leukemias: Result from abnormal WBC proliferation.

    • Named by the type of WBC involved; treatment includes irradiation and antileukemic drugs.

  • Infectious Mononucleosis: Caused by Epstein-Barr virus; characterized by increased atypical agranulocytes.