lymphatic system

Introduction to the Lymphatic System

• The lymphatic system is an essential part of the body's immune system.

• It consists of several components:

  • Lymph

  • Lymphatic vessels

  • Lymphatic tissues and organs

Composition of Lymph

• Lymph:

  • Contains interstitial fluid (the fluid between cells)

  • Comprises lymphocytes (a type of white blood cell)

  • Contains macrophages (cells that engulf and digest debris and pathogens)

• Lymphatic Vessels:

  • Function by passing through lymphatic tissues and organs

  • Deliver lymph to venous circulation

Lymphatic Structures

• Primary Lymphatic Structures:

  • Thymus: Site of T cell maturation

  • Red Bone Marrow: Produces blood cells, including lymphocytes

• Secondary Lymphatic Structures:

  • Tonsils: Lymphoid tissues that protect against pathogens entering through the mouth and nose

  • Lymph Nodes: Filter lymph and house lymphocytes

    • Found in various regions: axillary, lumbar, pelvic, inguinal

  • Spleen: Filters blood, removes old red blood cells and pathogens

  • Mucosa-associated lymphoid tissue (MALT): Associated with various tracts (digestive, respiratory, urinary, reproductive)

Functions of the Lymphatic System

• Production and Maintenance of Lymphocytes:

  • Cells vital for immune defense

  • Includes differentiation of T cells, B cells, and NK cells

• Maintaining Blood Volume and Composition:

  • Returns interstitial fluid to the bloodstream to maintain blood volume

• Transport of Substances:

  • Provides an alternative route for hormones, nutrients, and waste transport

Hemodynamics and Lymphatic Flow

• Blood Pressure:

  • Approximately 35 mm Hg in capillaries, forcing solutes into interstitial fluid

• Fluid Entry into Lymphatics:

  • Excess interstitial fluid enters lymphatic capillaries

  • The lymphatic system returns this fluid to the venous system

Structure of Lymphatic Vessels

• Lymphatic Capillaries:

  • Larger and have thinner walls compared to blood capillaries

  • Irregular outlines and greater permeability for fluid accumulation

  • Anchoring filaments connect to surrounding tissue to maintain open structures

• Larger Lymphatic Vessels:

  • Have valves like veins to prevent backflow

  • Contain larger lumens compared to comparable veins

Major Lymphatic Collecting Vessels

• Superficial Lymphatics:

  • Located in subcutaneous tissues and mucosal linings

• Deep Lymphatics:

  • Collect lymph from skeletal muscles and various organs

• Lymphatic Trunks:

  • Major trunks include:

    • Lumbar

    • Intestinal

    • Bronchomediastinal

    • Subclavian

    • Jugular

Lymphatic Ducts

• Thoracic Duct:

  • Drains into the left subclavian vein

  • Collects lymph from regions inferior to the diaphragm and the left side of the body

• Right Lymphatic Duct:

  • Drains into the right subclavian vein

  • Drains lymph from the right arm, head, and neck

Lymphocytes: Key Player in the Immune System

• Types of Lymphocytes:

  • T Cells: Matures in thymus, critical for cell-mediated immunity

    • Includes cytotoxic, helper, regulatory, and memory T cells

  • B Cells: Develop in bone marrow, produce antibodies

  • NK Cells: Provide rapid responses to virally infected cells and cancer cells

Lymphocyte Production and Function

• Lymphocytopoiesis:

  • Process of lymphocyte production in red bone marrow and thymus

  • T Cells mature via exposure to thymosin, while B cells produce antibodies against antigens

Immune Response Mechanisms

• Cell-Mediated Immunity:

  • Involves T cells directly attacking pathogens

• Antibody-Mediated Immunity:

  • Involves B cells producing antibodies that lock onto pathogens to mark them for destruction

Aging and the Lymphatic System

• As people age, T and B cell responsiveness to antigens decline

• The number of helper T cells decreases, leading to increased vulnerability to infections and cancer

• The thymus gland diminishes in size, impacting T cell production