Lymphatic

Chapter 22: The Lymphatic System and Immunity

1. Learning Outcomes

  • 22-1 Understand major components of the lymphatic system, their structure, functions, and the significance of lymphocytes.

  • 22-2 Differentiate between innate (nonspecific) and adaptive (specific) immunity, and describe lymphocytes' roles in the immune response.

  • 22-3 Outline innate defenses and their components, mechanisms, and functions.

  • 22-4 Define adaptive defenses and differentiate between cell-mediated and antibody-mediated immunity.

  • 22-5 Discuss types of T cells, their roles in adaptive immunity, and T cell activation/differentiation.

  • 22-6 Explain B cell activation, antibody structure, and primary and secondary responses to antigens.

  • 22-7 Discuss immunocompetence development, stress effects on immune function, and examples of immune disorders/allergies.

  • 22-8 Describe aging's impact on the lymphatic system and immune response.

  • 22-9 Provide examples of interactions between the lymphatic system and other body systems, including influence from the nervous and endocrine systems.

2. Introduction to the Lymphatic System

  • Pathogens: Microscopic organisms causing diseases such as viruses, bacteria, fungi, and parasites.

  • Lymphatic System: Protects against disease by responding to pathogens, toxins, and abnormal cells (cancers).

    • Lymphocytes: Key immune system cells that identify and attack pathogens.

  • Immune System: Involves all body cells and tissues in producing immunity, not just the lymphatic system.

3. Components of the Lymphatic System

a. Core Components

  • Lymph: Fluid similar to plasma without plasma proteins.

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

  • Lymphoid Tissues and Organs: Scattered throughout the body.

  • Lymphoid Cells: Include lymphocytes and phagocytes.

b. Major Organs and Tissues

  • Lymph Nodes: Act as filters for lymph, containing macrophages and lymphocytes.

  • Thymus: Located in the mediastinum, essential for T cell maturation.

  • Spleen: Filters blood, recycles iron, and initiates immune responses.

  • Mucosa-associated lymphoid tissue (MALT): Helps protect mucous membranes within digestive, respiratory, urinary, and reproductive tracts.

4. Functions of the Lymphatic System

  • Produce, maintain, and distribute lymphocytes.

  • Return excess fluid to bloodstream and maintain blood volume.

  • Transport hormones, nutrients, and wastes.

5. Lymphatic Vessels Characteristics

  • Flow Direction: From lymphatic capillaries to larger vessels, equipped with one-way valves.

  • Capillary Differences:

    • Closed at one end, larger luminal diameters, thinner walls compared to blood capillaries.

    • Overlapping endothelial cells create one-way valves for fluid entry while preventing exit.

6. Lymphocyte Types and Development

  • T Cells: Produced in the thymus; crucial for cell-mediated immunity.

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

  • NK Cells: Natural killer cells that respond to infected or cancerous cells.

  • Development:

    • Primary lymphoid organs: Red bone marrow and thymus for production.

    • Secondary lymphoid organs: Tonsils, MALT, lymph nodes, and spleen for activation.

7. Adaptive Immunity

a. Types of Immunity

  • Innate Immunity: Non-specific and inborn defenses that respond consistently to any pathogens.

  • Adaptive Immunity: Specific and acquired post-exposure, reliant on lymphocytes (B and T cells).

b. T Cells and B Cells Responses

  • T Cells: Activated through antigen presentation by MHC proteins, leading to responses against cells presenting foreign antigens.

  • B Cells: Differentiate into plasma cells for antibody production, adopting memory cells for future responses.

8. Immune Response Mechanisms

  • Innate Defenses: Include physical barriers, phagocytes, interferons, complement systems, inflammation, and the fever response.

  • Antibody Operation: Involves binding to antigens, neutralizing them, activating complement pathways, and recruiting phagocytes.

9. Immune Disorders and Aging

  • Immunodeficiency: Can stem from congenital issues, infections, or treatments.

  • Hypersensitivities: Rapid, excessive reactions to antigens, leading to conditions like allergies.

  • Aging: Results in decreased immune responses, increasing susceptibility to infections and diseases.