Lymphatic System and Immune System

Learning Objectives

By the end of this lesson, the learner should be able:

• Identify the components and anatomy of the lymphatic system
• Discuss the role of the innate immune response against pathogens
• Describe the power of the adaptive immune response to cure disease
• Explain immunological deficiencies and over-reactions of the immune system
• Discuss the role of the immune response in transplantation and cancer
• Describe the interaction of the immune and lymphatic systems with other body systems

Overview of the Lymphatic System

Function: Protects the body against invading pathogens including bacteria, viruses, fungi, and protists.

Lymphatic System: Lymph, lymph capillaries, lymph vessels, lymph nodes.

• Skeletal muscle contractions move the lymph one way through the lymphatic system to lymphatic ducts
  • Dump back into venous supply via lymph nodes
• Red marrow- produces blood cells
• Leukocytes- WBC

Lymph Nodes: located in neck, armpit, and groin

• Small swellings in the lymphatic system where lymph is filtered and lymphocytes are formed

Lymph Tissue: Tonsils, adenoids, thymus, spleen, peyer's patches

• Tonsils: Located in pharynx
  • Protect against pathogens entering via mouth or throat
• Thymus: Maturation chamber for immune T Cells formed in bone marrow
• Spleen: Cleans blood of dead cells and pathogens
• Peyer's Patches: Located in ileum of Sm. Intestine.
  • Protects GI tract from pathogens

Lymphatic system:

• A collection of cells and biochemicals that travel in lymphatic vessels
• Contains a network of vessels that assist in circulating fluids
• Closely associated with the cardiovascular system

3 functions of the lymphatic system

• Transports excess interstitial fluid away from the interstitial spaces, and returns it to the bloodstream
• Absorbs lipids from digestive system, and transports them to the bloodstream; accomplished by lymphatic capillaries called lacteals
• Defends the body against diseases, and allows humans to live in world with other organisms
• The term “immune system” refers to the fact that many cells of the lymphatic system provide both defense against disease and permanent immunity against future infections

Lymphatic Pathways

General Immune Defenses

• Skin: Primary barrier (intact)
• Ciliated Mucous Membranes: Cilia protect respiratory system
• Glandular Secretions: Exocrine- destroy bacteria
• Gastric Secretions: Gastric Acid destroys pathogens
• Normal Bacterial Populations: Compete with pathogens in gut and vagina

3 Types of WBC

• Macrophage: Phagocytes that alert T-Cells to the presence of foreign substances
  • Largest, longest living phagocyte
  • Engulf and destroy pathogens
  • Found in lymph
• T Lymphocytes: Directly attack cells infected by viruses and bacteria
  • Helper T, Killer T, Memory T, Suppressor T
• B Lymphocytes: Target specific bacteria for destruction
  • Plasma Cells: Antibody production.

Other Immune Cells

• Helper T-Cells: Activate B-Cells to make Antibodies and other chemicals
• Suppressor T-Cells: Stop other T-Cells when the battle is over
• Memory T-Cells: Remain in blood on alert incase invader attacks again
• Killer/Cytotoxic T-Cells: Destroy Cells infected with a pathogen, virus, or tumor

Leukocytes: WBC- Produced in Red Marrow

• Monocyte
  • Macrophage
  • Dendritic Cell: Present antigens to T Cell
• Granulocyte
  • Neutrophil: Short living phagocyte; responds quick to invaders
  • Basophil: Alerts body of invasion
  • Eosinophil: Large, long living phagocyte; Defend against multicellular invaders
• T Lymphocyte
• B Lymphocyte
• Natural Killer Cell

Antibody Mediated Response: Response is to an antigen

Cellular Mediated Response: Response is to an already infected cell

Antigen: Foreign particle that stimulates the immune system

• Typically a protein on the surface of bacteria, virus, or fungi Antibody: A blood protein that counteracts a specific antigen

Steps of Immune System

1. Macrophage engulfs antigen and presents fragments of antigen on its surface
2. A Helper T Cell joins the Macrophage
3. Killer/Cytotoxic T Cells and B Cells are activated
4. Killer/Cytotoxic T Cells search and destroy cells presenting the same antigen
5. B Cells differentiate into Plasma Cells and Memory Cells

Innate Immune System

• Born with it
• Non Specific response
• EX) Skin, hair, mucus, earwax, secretions, normal flora, antimicrobials, inflammation, interferons, complement, NK Lymphocytes, phagocytes

Adaptive Immune System

• Responds to specific antigens
• Vaccinations or previous encounters
  • Reaction: Cytotoxic T Cells kill pathogen
  • Prevention: B Cells produce Antibodies
• Activated by Antigen and Helper T Cells
• Helper T Cells activated by Antigen Presenting Cells (APC)

Types of Immunity

Naturally Acquired Active Immunity: Exposure to pathogen without immunization

Naturally Acquired Passive Immunity: Occurs during pregnancy and during breast feeding

• Antibodies are passed from mother to child
• Provides protection from infancy to childhood

Artificially Acquired Active Immunity: Build immunity via Vaccination

Artificially Acquired Passive Immunity: Immunization given during an outbreak or emergency

• Quick, short lived protection
• Antibodies come from another person or animal