Immunity and Lymphatic System Overview

Immunity

• The immune system protects the body from bacteria, viruses, fungi, toxins, parasites, and cancer.
• The lymphatic system works with the immune system to remove disease-causing agents.
• Organs of the lymphatic system include the thymus, spleen, and lymph nodes.

Lymphatic System: Introduction

• The lymphatic system is a network of connecting vessels.
• It collects fluid (lymph) between cells and returns it to the bloodstream.
• This fluid carries protein-containing fluids from tissue spaces.
• The lymphatic system defends the body against pathogens by producing lymphocytes.

Lymphatic System: Pathways

• Lymphatic capillaries are larger than blood capillaries.
• They extend into interstitial spaces.
• They are permeable and thin-walled, picking up fluid and transporting it as lymph.
• Lymphatic vessels deliver lymph to lymph nodes where pathogens are removed and an immune response initiated.
• Lymph exits lymph nodes via efferent lymphatic vessels.
• Lymphatic trunks collect lymph from various parts of the body.
• Lymphatic collecting ducts drain lymph into the bloodstream.
• The thoracic duct collects lymph from the left side of the body and the right lymphatic duct collects lymph from the right side.

Lymphatic System: Nodes

• Lymph nodes are small, glandular structures located along paths of larger lymphatic vessels.
• Afferent lymphatic vessels bring lymph into the lymph node.
• Efferent lymphatic vessels transport lymph away from the node.
• Lymph nodes contain cells (macrophages and lymphocytes) that digest pathogens and initiate an immune response.

Lymphatic System: Organs

• Tonsils - Three groups of tonsils help protect against bacteria and other harmful substances. Types include Palatine, Pharyngeal (adenoids), and Lingual.
• Thymus - Located above the heart, it is large in children and shrinks with age. It produces T-cells and thymosin which stimulates lymphocyte production.
• Spleen - Largest lymphatic organ, located in the upper left quadrant of the abdomen. It filters blood, removes old red blood cells, and stores blood.

Defenses Against Disease

• Infection - presence of a pathogen in the body.
• Pathogen - A disease-causing agent.
• Innate immunity - Nonspecific defenses to protect against pathogens. Includes species resistance, mechanical barriers, chemical barriers, phagocytosis, fever, and inflammation.

Specific Defenses: Immunities

• Immunities - Protect against very specific pathogens.
• Antigens - Foreign substances in the body.
• Immunities use substances like proteins, antibodies, and WBCs (lymphocytes and macrophages) along with the lymph system and cytokines to help regulate the immune response.

Two Major Types of Lymphocytes

• B cells - Produce antibodies, providing immunity against circulating bacterial and viral infections.
• T cells - Come from the thymus gland, bind to antigens on cells, and directly attack them. Subtypes include cytotoxic T cells, helper T cells, and memory T cells.

T-cell Types

• Cytotoxic T cells - Protect the body against viruses and cancer cells.
• Helper T cells - Stimulate the production of killer T cells.
• Memory T cells - Remember how to get rid of a pathogen.

Antibodies

• Also called immunoglobulins.
• Different types: IgA, IgD, IgE, IgG, IgM.
• These antibodies play distinct roles in the body's defense mechanism

Immune Responses and Acquired Immunity

• Primary immune response - Occurs with the first exposure to an antigen; slow process producing memory cells.

• Secondary immune response - Occurs with subsequent exposure; response is quicker and carried out by memory cells. It frequently prevents the body from developing diseases from the antigen.

  • Naturally acquired active immunity - Natural exposure to the antigen (e.g., having an illness).
  • Artificially acquired active immunity - Injected with a pathogen (e.g., vaccines).
  • Naturally acquired passive immunity - Acquired from the mother (e.g., breast milk, placenta).
  • Artificially acquired passive immunity - Injected with antibodies (e.g., anti-venom).

Major Immune System Disorders

• Cancer - Uncontrolled growth of abnormal cells.
  • Stages 0-IV
• Allergies - Immune response to an allergen; IgE antibodies bind to allergens and trigger the release of histamine and heparin.
• Anaphylaxis - Severe allergic reaction with rapid onset and includes a rash, throat swelling, and low blood pressure—treated with epinephrine.
• Autoimmune diseases - Body attacks its own antigens (e.g., scleroderma, rheumatoid arthritis, multiple sclerosis, glomerulonephritis, Crohn's disease, type 1 diabetes).

Common IS Disorders: Other examples

• AIDS - Severe symptoms caused by the HIV virus which destroys lymphocytes leaving the immunity system weakened.
• Chronic fatigue syndrome (CFS) - Severe tiredness not relieved by rest and unrelated to illnesses.
• Lymphedema - Blockage of lymphatic vessels resulting in tissue swelling.

Word Building

• Splen/o + ectomy = Splenectomy (removal of spleen)
• Splen/o + megaly = Splenomegaly (enlargement of the spleen)
• Lymph/o + aden/o + it is = Lymphadenitis (inflammation of the lymph glands)

Abbreviations

• List of medical abbreviations (with explanations) is available.