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Chap21 PPT

Chapter 21: The Lymphoid and Immune Systems

Overview

  • Understanding the lymphoid and immune systems is vital for human health.

  • The immune system protects the body from pathogens but also interacts with the human microbiome, which includes both beneficial and potentially harmful microorganisms.

Key Concepts

1. Immune System

  • Not a single organ system; a collection of cells residing in various body organs.

  • Responsible for defending against disease agents.

2. Lymphoid System

  • Composed of lymphatic vessels and tissues.

  • Functions include:

    • Fluid Recovery: Filters blood capillary fluid, returning excess (15%) to blood via lymphatic vessels.

    • Immune Surveillance: Lymph nodes inspect tissue fluid for disease agents.

    • Lipid Absorption: Small intestine lacteals absorb dietary lipids.

Lymph Fluid and Formation

Lymph Formation

  • Originates as tissue fluid absorbed through lymphatic capillaries:

    • Lymphatic Capillaries: Microscopic vessels, closed at one end, allowing entry of bacteria and larger particles.

  • Lymphatic Vessels: Transport lymph back to the bloodstream, comprising three layers:

    • Tunica interna: endothelial cells, valves.

    • Tunica media: elastic fibers, smooth muscle.

    • Tunica externa: connective tissue.

Flow and Structures

  • Path of lymph: Lymphatic capillaries → collecting vessels → lymphatic trunks → collecting ducts → subclavian veins.

  • Major lymphatic ducts:

    • Right lymphatic duct: drains right side of head, neck, arm.

    • Thoracic duct: larger, drains the majority of body fluid.

Components of the Lymphoid System

  • Key Cells:

    • Lymphocytes: B and T cells, key to adaptive immunity.

    • Macrophages: Phagocytes that engulf pathogens, presents antigens to lymphocytes.

    • Dendritic Cells: Antigen-presenting cells that process and present antigens to T cells.

Lymphoid Organs

  1. Bone Marrow: Produces blood cells including leukocytes.

  2. Thymus: Site of T cell maturation, shrinks with age.

  3. Lymph Nodes: Filter lymph, house immune cells such as B cells and T cells.

  4. Spleen: Largest lymphoid organ; monitors blood for pathogens, recycles old red blood cells.

  5. Tonsils: Protect against ingested or inhaled pathogens.

Immune Responses

1. Innate Immunity

  • First line of defense includes barriers (skin, mucous membranes).

  • Second line includes internal defenses (phagocytes, NK cells, inflammation).

2. Adaptive Immunity

  • Involves specific T and B lymphocytes that develop memory against specific antigens.

  • Humoral Immunity: Antibodies produced by activated B cells (plasma cells) that tag antigens for destruction.

  • Cellular Immunity: T cells directly kill infected or cancerous cells.

Disorders and Sensitivities

  • Hypersensitivity: An excessive response to harmless antigens (allergies).

    • Type 1: Immediate hypersensitivity leading to allergies.

    • Type 2: Antibody-mediated cell damage through complement activation.

  • Autoimmune Diseases: Occurs when the immune system mistakenly attacks the body’s own tissues.

  • Immunodeficiency: Weakened immune response (e.g., AIDS caused by HIV).

    • HIV infects and destroys helper T cells, compromising the immune response.

Key Notable Concepts

  • Memory Cells: Long-lived cells that provide quicker response during subsequent exposures to the same pathogen.

  • Inflammation: Body’s response to injury/infection; involves redness, heat, swelling, and pain.

  • Fever: Elevated body temperature that enhances immune function and inhibits pathogen growth.

Conclusion

  • Understanding the intricate structure and function of the lymphoid and immune systems is essential for comprehending how the body protects itself against diseases.