Lymphatic and Immune Systems Study Notes

Overview of the Lymphatic and Immune Systems

• Functions of the Lymphatic System:
  • Fluid Balance: Maintains fluid balance in the body.
  • Immune Protection: Helps protect the body from infections and diseases.
  • Fat Transport: Transports dietary fats from the intestines.

Lymphatic System Components

• Contains:
  • Organs: Red bone marrow, thymus, spleen, lymph nodes, diffuse lymphatic tissue.
  • Cells: Immune cells that are essential for the body’s defense.
  • Vessels: Network of vessels that transport lymph, a clear fluid similar to interstitial fluid.

Key Functions of the Lymphatic System

• Immunity:
  • Filters fluids from capillary beds, ready to respond to foreign invaders.
• Lipid Absorption:
  • Lacteals in the small intestine absorb dietary lipids.
• Fluid Recovery:
  • Absorbs excess plasma proteins and fluids (2-4 L/day) returning them to the bloodstream.
  • Impaired lymph drainage can lead to edema.

Lymph and Lymphatic Structures

• Lymph:
  • A clear, colorless fluid, similar to plasma but with less protein.
• Lymphatic Capillaries:
  • Closed at one end, anchored by filaments to tissues.
  • Allow bacteria and cells to enter, functioning as one-way valves based on interstitial fluid pressure.
  • Present throughout the body, except in avascular areas (e.g., cartilage).

Lymphatic Vessels

• Larger lymphatic vessels consist of three layers:
  • Tunica Interna: Endothelium and valves.
  • Tunica Media: Contains elastic fibers and smooth muscle.
  • Tunica Externa: The outer layer.

Route of Lymph Flow

• Flow Path:
  • Lymphatic capillaries → Collecting vessels → Lymphatic trunks → Collecting ducts (Right lymphatic duct and Thoracic duct).
  • The right lymphatic duct drains the right arm, right head and thorax into the right subclavian vein, while the thoracic duct drains everything else into the left subclavian vein.

Mechanisms of Lymph Flow

• Lymph moves at low pressure:
  • Rhythmic contractions of lymphatic vessels aid flow.
  • Skeletal muscle pump and thoracic pump assist with movement.
  • Exercise enhances lymphatic return.

Lymphatic Cells

• Types:
  • T Lymphocytes: Mature in the thymus; assist in cell-mediated immunity.
  • B Lymphocytes: Produce antibodies after activation.
  • Antigen Presenting Cells: Includes macrophages and dendritic cells.

Lymphatic Tissue

• Types:
  • Diffuse Lymphatic Tissue: Lymphocytes in mucous membranes and connective tissue.
  • Lymphatic Nodules: Dense masses of lymphocytes; examples include Peyer patches in the intestines.

Lymphatic Organs

• Key organs include:
  • Lymph Nodes: Filter lymph and contain lymphatic nodules.
  • Spleen: Filters blood and immune response, has red and white pulp.
  • Thymus: Site for T cell maturation.
  • Tonsils: Guard the entrance to the pharynx.

Immune Response Overview

• Innate Immunity: General defenses against pathogens such as skin and mucous membranes, phagocytes, and inflammation.
• Adaptive Immunity: Specific responses through T and B cells, generating memory against infections.

Characteristics of Antigens

• Antigens provoke an immune response; must possess immunogenicity and reactivity.
• Epitopes: Specific regions on antigens recognized by the immune system.

Antibodies and Their Functions

• Structure: Comprised of two heavy and two light polypeptide chains forming a specific shape.
• Classes of Antibodies:
  • IgG: Most abundant in blood, crosses the placenta.
  • IgA: Predominant in mucosal areas.
  • IgM: First response, found as a pentamer in blood.
  • IgE: Involved in allergic reactions.

The Immune Response Phases

• Primary Response: Initial exposure results in slow antibody production.
• Secondary Response: Faster and stronger due to memory cells.

Hypersensitivity Reactions

• Type I: Immediate allergic reactions, e.g., anaphylaxis.
• Type II: Antibody-dependent cytotoxic reactions, e.g., transfusion reactions.
• Type III: Immune complex-mediated reactions, e.g., lupus.
• Type IV: Delayed-type hypersensitivity, e.g., contact dermatitis.

Immunodeficiency Diseases

• Conditions like AIDS impair immune responses.
• Immunizations are crucial for those without a functioning spleen to protect against common infections.

Aging and the Immune System

• Immunosenescence leads to increased susceptibility to infections and reduced vaccine response.
• The thymus atrophies, leading to decreased T cell production.

Summary of Treatments & Vaccine Responses

• Strategies are in place to treat infections, including ART for HIV and immunotherapy for cancers.
• Vaccines stimulate adaptive immunity to provide long-term protection against diseases.