Lymphatic_system_and_immunity

Chapter 22: The Lymphatic System and Immunity

Learning Outcomes

  • Identify major components of the lymphatic system

  • Describe structure and functions of each component

  • Discuss the importance of lymphocytes

  • Distinguish between innate (nonspecific) and adaptive (specific) immunity

  • Explain the role of lymphocytes in immune response

  • List body’s innate defenses: components, mechanisms, and functions

  • Define adaptive defenses and distinguish between cell-mediated and antibody-mediated immunity

Introduction

  • Lymphatic System (Lymphoid System): Responsible for defending against environmental hazards and internal threats.

  • Immune System: Involves all cells and tissues in immunity, including lymphatic, integumentary, skeletal, cardiovascular, respiratory, and digestive systems.

  • Immunity: Ability to resist infection and disease.

  • Pathogens: Disease-causing organisms (viruses, bacteria, fungi, parasites).

Components of the Lymphatic System

  • Lymph: Fluid similar to plasma but lacks plasma proteins.

  • Lymphatic Vessels: Transport lymph from peripheral tissues to veins.

  • Lymphoid Cells: Include lymphocytes (T and B cells), phagocytes, etc.

  • Lymphoid Tissues: Connective tissues dominated by lymphocytes.

  • Lymphoid Organs: Organs where lymphocytes form, mature, or become activated.

Types of Lymphoid Tissues and Organs

  • Primary Lymphoid Organs: Sites of lymphocyte formation and maturation (e.g., red bone marrow, thymus).

  • Secondary Lymphoid Organs: Sites where lymphocytes are activated (e.g., tonsils, lymph nodes, spleen).

Functions of the Lymphatic System

  • Produce, maintain, and distribute lymphocytes.

  • Return excess fluid from tissues to bloodstream, maintaining blood volume.

  • Regulate interstitial fluid composition by transporting hormones, nutrients, and wastes.

Lymphatic Vessels

  • Structure: Carry lymph; start as capillaries that are closed at one end.

  • Lymphatic Capillaries: Thin walls, larger luminal diameter; act as one-way valves allowing entry of fluids and pathogens.

  • Meningeal Lymphatics: Drain cerebrospinal fluid (CSF) from dura mater.

  • Lymphatic Lacteals: Present in small intestine; transport absorbed lipids.

Lymphoid Cells

  • Phagocytic Cells: Include macrophages and microphages; engulf pathogens and debris.

  • Lymphocytes: Include T cells, B cells, and NK cells; respond to specific pathogens.

    • T Cells: Thymus-dependent; involve adaptive immune response.

    • B Cells: Bone marrow-derived; responsible for antibody production.

    • NK Cells: Natural killer cells; attack abnormal cells.

Lymphoid Organs

  • Lymph Nodes: Small organs filtering lymph; contain trabeculae and lymphatic vessels.

    • Function: Monitor infections, activate immune response, filter out pathogens.

  • Thymus: Lymphoid organ regulating T cell development; located in mediastinum.

    • Functions: Maturation of T cells, hormone production (thymosin).

  • Spleen: Filters blood for abnormal cells; involved in immune responses and storing iron.

Innate and Adaptive Immunity

  • Immunity: Body's ability to resist infectious organisms.

  • Innate Immunity: Nonspecific; includes physical barriers and internal defenses (present at birth).

  • Adaptive Immunity: Specific; involves B and T lymphocytes responding to specific pathogens.

Lymphocyte Production and Distribution

  • T Cells and B Cells: Formed in red bone marrow; migrate to peripheral lymphoid tissues for response.

  • Lymphocytopoiesis: The generation of lymphocytes involving stem cells in bone marrow and thymus.

Components of Innate Defenses

  • Physical Barriers: Skin, mucous membranes, and secretions (sweat, urine).

  • Phagocytes: Cells that consume pathogens (e.g., neutrophils, macrophages).

  • Immune Surveillance: NK cells identify and destroy abnormal cells.

  • Inflammation: Localized response to tissue injury; promotes healing and pathogen destruction.

  • Fever: Body's response raising temperature to fight infection.

Summary of Innate Defenses

  • Interferons: Proteins released as response to pathogens, important for antiviral defenses.

  • Complement System: Proteins that assist antibodies in pathogen destruction.

Adaptive Defenses

  • Cell-Mediated Immunity: Mediated by cytotoxic T cells; defends against infected or abnormal cells.

  • Antibody-Mediated Immunity: Mediated by B cells; defends against pathogens in body fluids.

Immune Response Mechanism

  • Involves antigen presentation, activation of T and B cells, and production of antibodies.