Chapter 20/21: Lymphatic System & Lymphoid Organs/Tissues & Immunity

Describe the functions of the lymphatic system and the primary lymphatic structures.

Functions

• Drain interstitial fluid

• Transport dietary fats

• Carry out immune responses

Primary lymphatic organs

Organs where immune cells become immunocompetent

• Red bone marrow

• Thymus

Secondary lymphatic organs: lymph nodes, spleen, lymphatic nodules

Describe location, structure, and functions of the spleen, thymus, and lymph nodes.

Lymph nodes

• Principal secondary lymphoid organs of the body; hundreds found throughout the body

• Act as lymph “filters”

  • Macrophages remove and destroy microorganisms and debris that enters lymph

  • Prevents unwanted substances from being delivered to the blood

• Immune system activation: offers a place for lymphocytes to become activated and mount an attack against antigens

• Can become secondary cancer site if metastasizing cancer cells become trapped in the node

Spleen

• Blood-rich organ located in the left side of the abdominal cavity, just below the stomach; largest lymphoid organ

  • Site of lymphocyte proliferation and immune surveillance and response

  • Cleanses blood of aged blood cells and platelets; macrophages remove debris

  • Has thin capsule, so direct blow or severe infection may cause it to rupture, spilling blood into the peritoneal cavity

    • Splenectomy: surgical removal of the ruptured spleen

Thymus

• Small gland in the lymphatic system between the lungs; key immune system regulator

  • Site of production and maturation of T lymphocytes (immune cells)

Discuss the formation of lymph from tissue fluid and lymph flow through the major lymph vessels.

Flow of lymph

Interstitial fluid → lymphatic capillary → afferent lymphatic vessel → lymphatic node → efferent lymphatic vessel → lymphatic trunk → lymphatic duct → subclavian vein

• Blood plasma is filtered from the blood capillaries into interstitial spaces to become interstitial fluid

• Lymphatic capillaries absorb interstitial fluid and pass lymph to afferent lymphatic vessels

• Afferent lymphatic vessels carry lymph from lymphatic capillaries to lymph nodes

• Lymph nodes remove foreign substances through reactions

• Efferent lymphatic vessels carry lymph from lymph nodes

• Lymphatic vessels pass lymph to lymphatic ducts

• Lymphatic ducts empty lymph into the junction of jugular and subclavian veins of the cardiovascular system

Briefly describe the structure and function of the immune system and distinguish between antigens and antibodies.

Two lines of defense

1. Skin and mucous membranes: first line

   • Mechanical defenses: skin, mucous membranes, tears, saliva, mucus, cilia, epiglottis, vomiting

   • Chemical defenses: sebum (sebaceous gland has specific pH that can kill some bacteria), lysozyme, gastric juice

2. Internal defenses: second line

   • Antimicrobial proteins, phagocytes, natural killer cells, inflammation, fever'

     • Phagocytosis is composed of neutrophils and monocytes

Antigens: foreign substances or molecule that triggers an immune response

• Reactivity: antigen’s ability to bind

• Immunogenicity: antigen’s ability to activate an immune response

• Typically, just certain small parts (epitopes) of a large antigen molecule act as the trigger for immune responses

Antibodies (immunoglobulins): proteins produced by the immune system in response to antigens, specially designed to recognize and bind to them

• IgG: most abundant (80%); protects against bacteria/virsues by enhancing phagocytosis

• IgA: found in sweat, tears, saliva, breast milk

• IgM: first to increase under infection

• IgD: mainly found on surfaces of B cells as antigen receptors

• IgE: involved in allergic and hypersensitivity reactions; protection against parasitic worms

Describe the body’s three lines of defense against pathogens, including the difference between nonspecific (innate) and specific (adaptive) defenses.

3 lines of defense: skin and mucous membrane, internal defense, adaptive immune response

Nonspecific resistance (innate immunity): present at birth; includes defense mechanisms that provide general protection against invasion by a wide range of pathogens

Immunity (adaptive immunity): involves activation of specific lymphocytes that combat a particular pathogen or other foreign substance

• Has both specificity and memory and is divided into 2 types

  • Cell-mediated: T-lymphocyte

  • Antibody-mediated: B-lymphocyte (secretion of antibodies)

  • B and T cells produce memory cells (artificial immunity in vaccines that help body experience exposure to possible pathogens

Explain the function of T and B cells in specific immune defenses. Discuss active and passive immunity (natural and artificial). Provide examples of each.

T-cells

• Active T-cells leave lymphatic tissue to attack invading antigens

• Directed against intracellular pathogens, some cancer cells, and tissue transplants

B-cells

• Antibodies bind to and activate antigens in body fluids

• Directed against extracellular pathogens

Natural immunity: stimulated by environment or mother

Artificial immunity: stimulated by medical intervention

Active immunity: person produces own antibodies; delayed protection that is permanent

Passive immunity: person receives antibodies from outside source (instant protection that is temporary)

Examples

• Natural active immunity: person encounters pathogen directly and has strong primary immune response (sickness)

• Natural passive immunity: baby receives antibodies through placenta or breastmilk

• Artificial active immunity: person receives vaccine and has weak primary immune response

• Artificial passive immunity: person receives antibodies through shot (antiserum); protection lasts until those antibodies break down (2-3 weeks)