BIO212 Module 9 PPT1 (Chapter 21 10th Edition AP1)

Chapter Overview

  • Title: The Lymphoid and Immune Systems

  • Author: Kenneth S. Saladin

  • Edition: Tenth Edition

  • Publisher: McGraw Hill LLC

Introduction

Microbiome

  • Microorganisms residing on and in the human body

    • Beneficial: Many are helpful to human health

    • Harmful: Some have the potential to cause illness

  • The body is constantly exposed to potentially harmful microorganisms from external environments.

Immune System

  • Not a distinct organ system, but a collection of cell populations throughout the body that defends against disease.

  • Concentrated in the lymphoid system, which:

    • Recovers fluid

    • Inspects for disease agents

    • Activates immune responses

    • Returns fluid to the bloodstream

The Lymphoid System

Expected Learning Outcomes

  1. List the functions of the lymphoid system.

  2. Explain lymph formation and its return to the bloodstream.

  3. Identify major cells of the lymphoid system and their functions.

  4. Describe types of lymphoid tissue.

  5. Explain the structure and function of red bone marrow, thymus, lymph nodes, tonsils, and spleen.

Basic Components of the Lymphoid System

  • Lymphatic Vessels: Penetrate nearly every tissue and transport lymph.

  • Fluid Recovery:

    • Fluid continually filters from blood capillaries into tissue spaces.

    • Capillaries absorb 85% of the fluid; remaining 15% enters lymphatic vessels.

    • Lymphedema: Swelling due to impaired lymphatic drainage.

Functions of the Lymphoid System

  • Immune Surveillance:

    • Excess filtered fluid collects foreign cells and chemicals.

    • Passes through lymph nodes, activating immune response against pathogens.

  • Lipid Absorption:

    • Lacteals in the small intestine absorb dietary lipids not taken by blood capillaries.

Components of the Lymphoid System

  • Lymph: Clear, colorless fluid similar to plasma but low in protein.

  • Lymphatic Vessels: Transport lymph.

  • Lymphoid Tissue: Aggregates of lymphocytes and macrophages.

  • Lymphoid Organs: Concentrated lymphoid cells surrounded by connective tissue.

Structure of Major Lymphoid Organs

1. Red Bone Marrow

  • Soft, loose, highly vascular material, involved in hematopoiesis and immune responses.

2. Thymus

  • Bilobed, located in superior mediastinum.

  • Maturation site for T cells, secretes hormones for regulation.

3. Lymph Nodes

  • Bean-shaped organs that cleanse lymph and activate lymphocytes.

  • About 450 in a typical young adult.

4. Spleen

  • Body's largest lymphoid organ.

  • Red Pulp: Blood reservoir and site of erythrocyte graveyard.

  • White Pulp: Monitors blood for antigens.

Lymphatic Vessels

Overview

  • Lymphatic Capillaries: Microscopic vessels that penetrate tissues, collecting interstitial fluid.

    • Structure: Endothelial cells form valves to facilitate lymph entry.

  • Larger Lymphatic Vessels: Composed of three layers—tunica interna, tunica media, and tunica externa.

  • Flow of Lymph: Moves due to contraction of vessels, pressure from surrounding skeletal muscles, and thoracic pump.

Lymphoid Cells

  • Neutrophils: Antibacterial action.

  • Natural Killer (NK) Cells: Attack infected and cancerous cells.

  • T Lymphocytes (T Cells): Recognize and respond to pathogens.

  • B Lymphocytes (B Cells): Produce antibodies upon activation.

  • Macrophages and Dendritic Cells: Antigen-presenting cells (APCs).

Lymphoid Tissues

  • Diffuse Lymphoid Tissue: Scattered lymphocytes, prevalent in open body passages.

  • Lymphoid Nodules: Clusters of lymphocytes and macrophages; can be temporary or permanent.

Innate Immunity

First Line of Defense

  • External Barriers: Skin and mucous membranes.

Second Line of Defense

  • Cellular Defenses: Includes leukocytes like neutrophils, eosinophils, and macrophages.

Third Line of Defense

  • Adaptive Immunity: Specific responses against pathogens, characterized by memory.

Types of Hypersensitivity

  • Type 1: Acute allergic reactions, mediated by IgE.

  • Type 2: Antibody-dependent cytotoxicity (e.g., blood transfusion reactions).

  • Type 3: Immune complex diseases (e.g., systemic lupus erythematosus).

  • Type 4: Delayed hypersensitivity (e.g., poison ivy).

Immune Disorders

Autoimmune Diseases

  • Result from immune system targeting the body’s own tissues.

  • Examples include lupus and rheumatoid arthritis.

Immunodeficiency Diseases

  • Conditions like SCID and AIDS lead to decreased immune response.