and Immune System

LYMPHATIC SYSTEM FUNCTIONS Production, maintenance & distribution of lymphocytes Return of fluid & solutes from peripheral tissues to blood Distribution of hormones, nutrients & products from point of origin to general circulation

LYMPH CIRCULATION Arteries Capillaries Fluid exits circulation Heart Veins Capillaries Fluid exits circulation

Lymphatic Vessels Collect fluid from around tissues 1 2 3 4 Collect fluid from around tissues Transports fluid & solutes back to venous circulation Fluid moves from tissues into lymph capillaries; becomes lymph Lymph capillaries converge to form lymphatic vessels Lymph passes through lymph nodes Lymphatic vessels converge into larger vessels; valves prevent backflow 1

Lymphatic System Components Tonsils Lymphoid nodules (no capsule) Guard entrance to digestive & respiratory tracts Lymph Nodes Filter & purifies lymph Removes abnormal & foreign cells Surrounded by capsule Lymphatic Vessels Carry lymph back to venous

Thoracic duct (yellow) Thymus Thoracic duct (yellow) Collects lymph from left side above diaphragm & whole body below diaphragm Dumps lymph into venous circulation Right lymphatic duct (orange) Collects lymph from right side above diaphragm Thymus Site of T cell maturation

Spleen Removes abnormal blood cells & components Bone Marrow Hemocytoblasts produce lymphoid stem cells Lymphoid stem cells divide & differentiate into lymphocytes Appendix Contains lymphoid tissue

Immunity-Immune System Innate Immune defenses that are active immediately upon infection Response is the same whether you have seen the pathogen before or not. Adaptive Acquired immunity Activated in response to specific pathogens Differs from one person to another Slower than innate responses Strong defense against specific pathogens Ex. Vaccination (immunization) Made of harmless part of disease-causing pathogen (dead or weakened virus, piece of virus, inactivated bacterial toxin, surface proteins of virus) If you are exposed to what you have been vaccinated against, your immune system quickly responds.

Immunity Continued Active Passive Immune system is actively producing antibodies Passive Receive “premade” antibodies Mothers antibodies through placenta or via breast milk Injection of antibodies Ex injection a snakebite victim with antivenom (extracted from animals previously immunized against the venom) Temporary immunity Recipients immune system is not stimulated by antigens Lasts only as long as antibodies do (few weeks or months)

Lymphocytes Production Hemocytoblasts in bone marrow produce lymphoid stem cells Some stem cells remain in bone marrow & divide to produce B cells, T cells, & NK cells

B Cells Responsible for antibody-mediated immunity Lymphocytes 10 – 15% of circulating lymphocytes When activated divide & differentiate into: Plasma cells Memory B cells Responsible for antibody-mediated immunity

Natural Killer cells Lymphocytes 5 to 10% circulating • Responsible for cell-mediated immunity Attack foreign & abnormal cells Responsible for immunological surveillance Lyse and kill cancer cells and virus-infected cells.  

T Cells Responsible for cell-mediated immunity Some stem cells migrate to thymus & divide to produce T cells T Cells Lymphocytes Thymus 80% of circulating lymphocytes When activated divide and differentiate into: Helper T cells Cytotoxic T cells Memory T cells Suppressor T cells Responsible for cell-mediated immunity  

NONSPECIFIC DEFENSES Does not discriminate pathogens Present at birth (innate) Prevents approach or entry of pathogens

Skin Creates effective barrier (multiple layers, keratin coating, desmosomes hold cells tog.) Hairs (provide some protection against abrasion, keep hazardous materials & insects from contacting skin Secretions (oil, sweat & mucus): wash away pathogens & materials, contain chemicals that kill bacteria (lysozymes

Phagocytes Engulf & destroy pathogens & debris Neutrophil -Macrophage -Phagocytize cellular debris & invading bacteria Eosinophil -Target foreign compounds or pathogens coated with antibodies Macrophage   -Derived from monocytes -Large, active phagocytes

Immunological surveillance Destroys abnormal cells Constant monitoring of normal tissues Involves NK (natural Killer) cells NK cells sensitive to antigens characteristic of abnormal cell membranes.

INTERFERONS Small proteins Released by activated lymphocytes, macrophages & virus infected cells Increases resistance of other cells to viral infections

COMPLEMENT SYSTEM Several proteins that interact in chain reaction (cascade) Attacks & breaks down cell walls Attracts phagocytes Stimulates inflammation

INFLAMMATORY RESPONSE Mast Cells (and Basophils) release histamines Increases blood flow Activates phagocytes Increase capillary permeability Increases temperature Stimulates clotting Activates complement Activates specific immune responses

FEVER Body temperature rises above 37.2 oC (99 oF) Pyrogens – proteins that increase body temperature Mobilizes defenses Accelerates repair

What about allergies?

SPECIFIC DEFENSES

PROPERTIES OF IMMUNITY Specificity Specific defense activated by antigen Targets only that antigen Versatility Immune system produces millions of different lymphocytes Each lymphocyte has different antigen receptors Memory • Immune system remembers antigens it has encountered Tolerance When immune system does not respond to particular antigen Immune system ignores normal (self) & attacks foreign (nonself)

Cell-Mediated Immunity Provides defense against abnormal cells & pathogens that are inside living cells Involves T cells

Cytotoxic T cells Memory T cells Helper Suppressor T cells Macrophage • Engulfs antigen Breaks down antigen Presents antigen fragment on surface of cell membrane Specific T cell activated when contacts macrophage with antigen Activated T cell divides & differentiates Cytotoxic T cells Memory T cells   Helper Suppressor T cells

Antibody-mediated immunity (humoral) Provides defense against antigens & pathogens in body fluids Involves B cells

Helper T cell activates specific B cell by secreting cytokines Plasma cells Produce antibodies Helper T cell activates specific B cell by secreting cytokines Antibodies bind to antigen yellow) ( Antigen - antibody complex engulfed & destroyed by phagocytes Activated B cell divides & differentiates   Memory B Cells -held in reserve -Activated with 2nd exposure to antigen

ANTIBODY STRUCTURE Structure Antigen binding site Antigen binding site Structure -2 parallel polypeptide chains 2 heavy chains (red) -2 light chains (blue) -Each chain has constant segment (solid) variable segment (dashed) -Variable segment varies depending on targeted antigen   Action -Do not target the antigen -Targets portion of antigen called antigenic determinant site -Complete antigen must have 2 antigenic determinant sites – one for each arm of antibody