Lymphatic System and Immunity Lymphatic System n n

Lymphatic System and Immunity:

Lymphatic System n n n n Lymphatic vessels Lymphatic tissue Lymphatic nodules Lymph nodes Tonsils Spleen Thymus

Lymphatic Vessels n n Carry lymph away from tissues Lymphatic capillaries n n More permeable than blood capillaries Epithelium functions as series of one-way valves

Functions of the Lymphatic System n Fluid balance n n Fat absorption n n Excess interstitial fluid enters lymphatic capillaries and becomes lymph Absorption of fat and other substances from digestive tract Defense n Microorganisms and other foreign substances are filtered from lymph by lymph nodes and from blood by spleen

Lymphatic Vessels n n Carry lymph away from tissues Lymphatic capillaries n n More permeable than blood capillaries Epithelium functions as series of one-way valves

Lymphatic Vessels Lymphatic capillaries join to form n Lymphatic vessels n n Have valves that ensure one-way flow Lymph nodes: Distributed along vessels and filter lymph n Lymphatic trunks: Jugular, subclavian, bronchomediastinal, intestinal, lumbar n Lymphatic ducts: Right and thoracic which connect to large veins n

Lymph Drainage Into Veins

Lymphatic Tissue and Nodules n Lymphatic tissue n n n Consists mainly of lymphocytes Encapsulated or not Lymphatic nodules n Numerous in loose connective tissue of digestive (Peyer’s patches), respiratory, urinary, reproductive systems

Tonsils n n n Large groups of lymphatic nodules in nasopharynx and oral cavity Provide protection against bacteria and other harmful material Groups n Palatine Pharyngeal n Lingual n

Lymph Nodes n n n Organized in cortex and medulla Substances removed by phagocytosis or stimulate lymphocytes or both Only structures to filter lymph n Afferent and efferent vessels

Spleen n Located in left superior side of abdomen n n Blood flows through at 3 different rates n n Can be ruptured in traumatic abdominal injuries resulting in bleeding, shock, death Fast (most), slow, intermediate Functions Destroys defective RBCs n Detects and responds to foreign substances n Limited reservoir for blood n

Spleen

Thymus n n n Located in superior mediastinum Divisions: Cortex and medulla Site of maturation of T cells

Immunity n n Ability to resist damage from foreign substances as microorganisms and harmful chemicals Categories n Innate or nonspecific resistance n n Mechanical mechanisms: Prevent entry or remove microbes Chemical mediators: Promote phagocytosis and inflammation Cells: Involved in phagocytosis and production of chemicals Adaptive or specific immunity n n Specificity: Ability to recognize a particular substance Memory: Ability to remember previous encounters with a particular substance and respond rapidly

Innate immunity

Inflammatory Response n n n Tissue injury regardless of type can cause inflammation Response initiated by chemical mediators that produce vasodilation, chemotactic attraction, increased vascular permeability Types n n Local: Symptoms are redness, heat, swelling, pain, loss of function Systemic: Symptoms are increase in neutrophil numbers, fever and shock

Inflammatory Response

Normal Microcirculation Flow

Exudate Formation

Leukocyte Margination and Migration

Diapedesis

Chemotaxis

Innate Immunity: Cells n White blood cells n n Most important cellular components of immune system Methods n n n Chemotaxis Phagocytosis n n n Phagocytic and first cells to enter infected tissue Promote inflammation Eosinophils n n Monocytes that leave blood, enter tissues Large phagocytic cells Basophils and mast cells n Neutrophils n Macrophages Reduce inflammation Natural killer cells n Lyse tumor and virusinfected cells

Antigenic Determinants n Antigenic determinants n n Specific regions of a given antigen recognized by a lymphocyte Antigenic receptors n Surface of lymphocyte that combines with antigenic determinant

C 3 a stimulates mast cells and basophils, which then secrete inflammatory mediators

Adaptive Immunity n n Involves the ability to recognize, respond to, and remember a particular substance Stimulants n Antigens: Large molecules n n Foreign: Not produced by body, introduced from outside Self-antigens: Produced by body Haptens: Small molecules and capable of combining Types n n Humoral or Antibody-mediated: B cells Cell-mediated: T cells

Origin and Development of Lymphocytes n B and T cells n n n Originate in red bone marrow Move to lymphatic tissue from processing sites and continually circulate Clones are small groups of identical lymphocytes

Origin and Development of Lymphocytes n Positive selection n n Negative selection n n Ensures survival of lymphocytes that react against antigens Eliminates lymphocytes that react against selfantigens Primary lymphatic organs (red bone marrow, thymus) n n Where lymphocytes mature into functional cells Secondary lymphatic organs n Where lymphocytes produce an immune response

Major Histocompatability Complex (MHC) n Most lymphocyte activation involves glycoproteins of cell surfaces called MHC molecules Class I molecules display antigens on surface of nucleated cells, resulting in destruction of cells n Class II molecules display antigens on surface of antigen-presenting cells, resulting in activation of immune cells n

Antigen Processing

MHC class I

Phagocytosis n n n Phagocytosis also involves membrane invagination. This process does not involve clathrin. Pseudopods extend around a particle, forming a phagosome. Phagosome will fuse with a lysosome, containing digestive enzymes. There are smaller transport mechanisms in the wall of the secondary lysosome.

Costimulation

Proliferation of Helper T Cells

Proliferation of B Cells

Lymphocyte Inhibition n Tolerance: To prevent the immune system from responding to self-antigens n Provoked by n Deletion of self-reactive lymphocytes n Preventing activation of lymphocytes n Activation of suppressor T cells

Antibody-Mediated Immunity n Antibodies or Immunoglobulins (Ig) n n Classes: Ig. G, Ig. M, Ig. A, Ig. E, Ig. D Structure n n Variable region: Part that combines with anitgenic determinant of antigen Constant region: Responsible for activities

Actions of Antibodies

Antibody Production

Cell-Mediated Immunity n n n Antigen activates effector T cells and produces memory T cells Cytotoxic T cells lyse virus-infected cells, tumor cells, and tissue transplants Cytotoxic T cells produce cytokines, which promote phagocytosis and inflammation

of Innate and Adaptive Immunity

Ways to Acquire Adaptive Immunity

Effects of Aging Little effect on lymphatic system n Decreased ability of helper T cells to proliferate in response to antigens n Decreased primary and secondary antibody responses n Decreased ability of cell-mediated immunity to resist intracellular pathogens n

Immune System Problems Hypersensitivity reactions n Autoimmune disease n Severe combined immunodeficiency disease (SCID) n Transplantation n Acute rejection n Chronic rejection n