Chap21 PPT

Chapter 21: The Lymphoid and Immune Systems

• Introduction

  • Microbiome: Microorganisms that reside on or in the human body.

    • Many are beneficial, but some can be harmful.

    • Body constantly exposed to harmful microorganisms from the external environment.

    • Body protection by the immune system.

  • Immune System: Not a single organ system but a population of cells across organs that defend against disease.

    • Concentrated in the lymphoid system: a network of organs and vessels.

    • Functions include fluid recovery, inspection for disease agents, and activation of immune responses.

The Lymphoid System

Functions

• Fluid Recovery: Fluid filters from blood capillaries into tissues; most is reabsorbed, remaining fluid enters lymphatic vessels (lymphedema occurs due to drainage interference).

• Immune Surveillance: Excess fluid collects foreign cells/chemicals, passes through lymph nodes where immune cells monitor and activate immune responses.

• Lipid Absorption: Lacteals in the small intestine absorb dietary lipids.

Components

• Lymph: Recovered fluid similar to plasma but low in protein.

• Lymphatic Vessels: Transport lymph throughout the body.

• Lymphoid Tissue: Aggregates of lymphocytes and macrophages populating multiple organs.

• Lymphoid Organs: Includes the red bone marrow, thymus, lymph nodes, tonsils, and spleen, each concentrated with lymphoid cells.

Major Lymphoid Organs

• Red Bone Marrow: Site of hematopoiesis; produces immune cells.

• Thymus: Houses developing T-cells, secretes hormones for T-cell maturation.

• Lymph Nodes: Filter lymph, sites for lymphocyte activation; numerous throughout the body.

• Spleen: Largest lymphoid organ; monitors blood for foreign antigens and removes old RBCs.

• Tonsils: Lymphoid patches guarding against ingested or inhaled pathogens.

Lymph and Lymphatic Vessels

Formation and Flow

• Lymph Formation: Originates from interstitial fluid; consists of various components based on location (like lipids in intestines).

• Lymph Flow: Occurs under low pressure; aided by contractions of lymphatic vessels and surrounding skeletal muscle; no central pump (heart) involved.

  • Pathway: Lymphatic capillaries → collecting vessels → trunks → ducts → subclavian veins.

• Lymphatic Structures: Capillary walls consist of overlapping endothelial cells allowing fluid/bacteria passage; valves prevent backflow.

Lymphocyte Types and Functions

• Neutrophils: Eat bacteria, release traps.

• Natural Killer (NK) Cells: Attack infected/diseased cells.

• T Lymphocytes (T-cells): Differentiate in thymus, involved in cellular immunity.

• B Lymphocytes (B-cells): Produce antibodies after activation.

• Macrophages: Large phagocytic cells, antigen-presenting cells (APCs).

• Dendritic Cells: APCs located in various tissues.

Adaptive Immunity

Types of Adaptive Immunity

• Cellular Immunity: T lymphocytes directly destroy infected/diseased cells.

• Humoral Immunity: Antibody-mediated response involving B lymphocytes.

Immune Memory

• The immune response develops memory for re-encounters with specific pathogens, resulting in rapid reactions.

Mechanisms of Action

• Immune Defenses: Include phagocytosis, cytotoxic effects, and the secretion of antibodies that neutralize pathogens; complement system enhances immune reactions.

Immune System Disorders

Hypersensitivity Types

• Allergic Reactions: Overreactions by the immune system to harmless substances.

• Autoimmunity: Immune system' inability to distinguish self from non-self, attacking body tissues.

Immunodeficiency**:

• Conditions like AIDS caused by HIV compromise immune function by targeting helper T cells, leading to increased susceptibility to infections.

COVID-19 and the Immune Response

• Emphasizes the impact of the SARS-CoV-2 virus, mechanisms of infection and inflammation, and the role of vaccinations in controlling spread and severity of disease.