Blood and Immune Cells

Lecture Overview

Lecture 19: Blood Cells and Immune Cells

Blood Composition

• Blood as a Tissue

  • Specialized fluid tissue composed of cells suspended in fluid matrix.

  • Functions include nutrient and oxygen transport, waste removal, and providing an adaptive immune response.

Blood Components

• Overall Composition

  • Plasma constitutes approximately 55% of blood volume, serving as the fluid portion.

  • Cellular components account for about 45%, which includes different types of blood cells.

Blood Plasma

• Composition

  • Composed of ~90% water with dissolved ions, known as electrolytes, which are crucial for various physiological processes.

  • Functions of Electrolytes

    • Regulate blood pH, ensuring optimal enzyme function and metabolic processes.

    • Help maintain osmotic balance, preventing water from moving in or out of cells excessively.

    • Ensure proper membrane permeability for cells to take in nutrients and expel waste.

• Key Plasma Proteins

  • Albumin: The major protein for maintaining osmotic balance and proper pH level in blood.

  • Immunoglobulins: Essential for immune defense, acting as antibodies that neutralize pathogens.

  • Apolipoproteins: Important for lipid transport, facilitating the movement of fats and cholesterol throughout the bloodstream.

  • Fibrinogen: Vital for blood clotting, converting to fibrin which forms the meshwork for clot formation during injury.

Cellular Components of Blood

• Origin

  • Cellular components originate from pluripotent hematopoietic stem cells in the bone marrow, influenced by various conditions and chemical signals that determine their fate.

• Myeloid Stem Cells

  • Differentiate into:

    • Erythrocytes (Red Blood Cells): The most abundant blood cells, critical for oxygen transport due to hemoglobin.

    • Platelets: Small cell fragments playing a key role in the clotting process.

    • Leukocytes (White Blood Cells): Integral components of the innate immune system, combating infections and foreign invaders.

• Lymphoid Stem Cells

  • Differentiate into:

    • Lymphocytes: Key players in the adaptive immune response, further classified into B and T cells.

Erythrocytes and Gas Exchange

• Role of Erythrocytes

  • Erythrocytes are specialized for gas exchange; they bind oxygen in the lungs and transport it to tissues, while also facilitating carbon dioxide removal.

  • EPO Hormone: Erythropoietin, secreted by the kidneys, stimulates erythrocyte production in response to low oxygen levels in the blood.

Blood Clotting Mechanism

• Platelets

  • Upon blood vessel injury, platelets become sticky, adhering to the site of damage and releasing factors that initiate the clotting cascade to prevent hemorrhage.

• Clotting Factors

  • A series of proteins that work together to transform fibrinogen into fibrin, forming a stable clot that seals the wound and facilitates healing.

Lipid Transport in Blood

• Apolipoproteins

  • Apolipoproteins serve as structural components for lipoproteins, which transport lipids, including fats and cholesterol, in the bloodstream.

  • Cholesterol Transport

    • LDL (Low-Density Lipoprotein): Carries excess saturated fats, often considered "bad cholesterol" due to its association with atherosclerosis.

    • HDL (High-Density Lipoprotein): Transports beneficial cholesterol back to the liver for recycling, often referred to as "good cholesterol" due to its protective cardiovascular effects.

Antigens and Immune Response

• Antigens

  • Structures that are recognized by the immune system as foreign, often consisting of proteins or glycoproteins on the surfaces of pathogens.

• Antibodies

  • Immunoglobulins produced by B lymphocytes that specifically bind to antigens, aiding in their neutralization or destruction.

• Blood Type Classification

  • Based on the presence or absence of specific antigens on the surface of erythrocytes, resulting in the following groups:

    • Group A: A antigens present; Anti-B antibodies in serum.

    • Group B: B antigens present; Anti-A antibodies in serum.

    • Group AB: Both A and B antigens present; no antibodies in serum.

    • Group O: No antigens present; has both Anti-A and Anti-B antibodies.

• Incompatibility in Blood Transfusions

  • Severe immune reactions can occur if mismatched blood types are transfused; for example, a patient with A- blood receiving B+ blood may provoke an immune attack against the B antigens, leading to hemolysis.

Immune System Overview

• Defensive Role

  • The immune system plays a crucial role in defending against pathogenic infections (e.g., bacteria, viruses) and abnormal cell proliferation (e.g., cancer cells).

• Innate Immunity

  • The first line of defense comprising physical barriers (skin, mucous membranes) and immune cells that react quickly to pathogens without prior exposure.

    • Features of Innate Immunity

      • Physical barriers ensuring pathogen entry is blocked.

      • Mobile immune cells, such as macrophages and neutrophils, which engage in phagocytosis and release toxins to destroy invaders.

• Adaptive Immunity

  • A highly specific response tailored to distinct pathogens, involving the generation of antibodies that can remember past infections.

    • Involvement of B and T Lymphocytes

      • B Lymphocytes: Responsible for the production of antibodies specific to foreign antigens.

      • T Lymphocytes: Target and destroy infected or cancerous cells, playing a critical role in cell-mediated immunity and regulating other immune cells.