LYMPHATIC SYSTEM AND IMMUNITY

Transcription

1 LYMPHATIC SYSTEM AND IMMUNITY The Lymphatic System Consists of: Lymphatic vessels, Lymphatic tissues, Lymph (fluid), bone marrow Functions of the Lymphatic System are: - returns tissue fluid to the venous system - immunity (lymphocytes) - transports absorbed fats from intestine to blood Components Lymph Capillaries - close ended - in villi of GI called lacteals - have porous junctions that allow: - interstitial fluid, proteins, microorganisms, and absorbed fat to pass through - fluid once inside lymphatic capillaries is called lymph

2 - capillaries empty into lymphatics which empty into ducts after passing through nodes Two Main Ducts 1. The Thoracic duct empties into the left subclavian vein and drains lymph from: - the left side of the head, neck and chest - the left arm - the entire body below the ribs 2. The Right Lymphatic duct empties into the right subclavian vein and drains lymph from: - the upper right side of the head an neck - the right arm - the right side of the thorax, lung, and heart - part of the liver Lymphatic Tissue Lymphatic nodules - usually solitary - found in the lamina propria of the G.I., Respiratory airways, Urinary tract, and reproductive tracts - some are in large aggregates like: - pharyngeal tonsils - Peyer's patches Lymph Nodes - capsulated with extensions called trabeculae - composed of a: 1. Cortex with lymphocytes arranged in follicles including: - T cells, Macrophages, Follicular Dendritic Cells (activate T cells) - B cells 2. Medulla which contains: - macrophages - plasma cells (that secrete antibodies) 35

3 - lymph flow through the node is one way. Afferent lymphatic vessels > sinuses> efferent lymphatic vessels - nodes filter the lymph and trap antigens which are destroyed by immune cells Tonsils - are multiple aggregates of large lymphatic nodules - there are three types 1. Pharyngeal tonsils (adenoids) - found in the nasal pharynx 2. Palatine tonsils - found on the soft palate 3. Lingual tonsils - found on the base of the tongue - all function in protection against antigens passing through the oral and nasal cavity. Spleen a large gland with two kinds of tissue 1. White pulp - lymph tissue with lymphocytes. 2. Red Pulp - venous sinuses that contain splenic cords with macrophages, plasma cells, and granulocytes - functions: 1. Immunity - through B cells 2. Phagocytosis of old red blood cells and platelets via fixed macrophages 3. Stores and releases blood when needed. Thymus gland 36

4 - found in the mediastinum (the space between the lungs) in children only - capsulated - confers immunity on T cells. - secretes hormones that stimulate the immune system NONSPECIFIC IMMUNITY - provides a general response against a broad range of pathogens Skin and Mucous Membranes Mechanical Factors Epidermis of the skin - creates a physical barrier to the passage of microbes Mucous Membranes (including mucous and hair) - traps and filters microbes attempting to enter the body through a natural opening (nose, mouth, etc.) Cilia together with mucous traps microbes and dust particles in the respiratory tract Lacrimal apparatus, Saliva, and urine wash away microbes from the surface of the eyes, mouth and urethra. Defecation and vomiting removes microbes from the G.I. tract Chemical Factors Acid ph of the skin inhibits microbe growth Unsaturated fatty acids in sebum have antimicrobial substances Lysozyme - an antimicrobial substance found in tears, saliva, nasal secretions, and tissue fluids Hyaluronic acid in connective tissues prevents the spread of noxious agents in localized infections Gastric juice with its low ph destroys bacteria and most toxins Antimicrobial substances Interferons protect uninfected cells from viral infections Complement proteins that can lyse microbes, promote phagocytosis, and increase inflammation Natural Killer Cells kill a wide variety of microbes and tumor cells Phagocytes ingest microbes, toxins etc. Examples: neutrophils, eosinophils, and monocytes (macrophages) Inflammation confines and destroys microbes and aids in tissue repair Fever makes interferon work faster, inhibits microbe growth, and speeds up the bodies physiological responses to aid in repair Specific Immunity the bodies defense against specific pathogens such as: - Bacteria - viruses - foreign tissues - this specific resistance is called IMMUNITY - substances that the immune system recognizes as foreign are called antigens - two properties make immunity different from nonspecific defenses: 1. Specificity for one antigen and only one antigen 37

5 2. Memory for that same antigen should it reappear - carried out by two types of lymphocytes that develop from stem cells in the bone marrow: T cells and B cells - there are two types of immune responses: 1. Cell-mediated (cellular) immunity - T cells 2. Antibody-mediated (humoral) immunity - B cells Antigens - any chemical substance that the immune system can recognize as foreign - must have two important qualities: 1. Immunogenicity - or the ability to provoke and immune response 2. Reactivity - the ability to react with antibodies and form an antigen/antibody complex - antigens that have immunogenicity and reactivity are said to be complete antigens - some antigens have reactivity but not immunogenicity and are referred to as haptens - haptens can provoke an immune response if they attach themselves to a larger carrier molecule (ex: the pneumonia bacterium attaches to penicillin) - antigens have regions on their cell membranes that trigger immune responses. These regions are called antigenic determinant (epitopes) - most antigens have multiple determinant sites - the immune system can recognize over a billion antigen determinants. Cytokines - are a class of protein hormones that function as colony stimulating factors to 38

6 increase the production of white blood cells in the bone marrow. Antibodies - B cells when presented with an antigen differentiate and divide by mitosis to produce Memory cells and plasma cells - plasma cells secrete antibodies that are specific for the antigen presented to the B cell. - antibodies are Y shaped globulin proteins with two antigen binding sites (bivalent) - five classes of immunoglobins are recognized in humans: IgG, IgA, IgM, IgD, and IgE Cell-Mediated Immunity - T cells recognize a particular antigen - the T cell then undergoes proliferation and differentiation to become effector cells that carry out the immune response that results in elimination of the antigen How T Cells recognize antigens - the cell membrane of T Cells have T cell receptors that bind with specific antigens - when this occurs it is known as the first signal - T cells also need costimulators (like interleukin) to achieve activation - once activated or sensitized it Proliferates (divides) and differentiates to form clone cells that carry out different immune response. These clone cells include: Helper T cells - secrete cytokines which carry out a variety of immune responses (see exhibit 22.2 on page 703) Cytotoxic T cells - lyse antigens and inject lymphotoxin substances Delayed hypersensitivity T cells - release cytokines and active monocytes Suppressor T cells - may down regulate other T cells Memory T cells - are stored in lymphatic tissue - can remember the original invading antigen and respond to it more quickly upon second exposure 39

7 Antibody Mediated (Humoral) Immunity - B cells can respond to specific antigens - in the presence of antigens B cells become activated when an antigen binds to antigen receptors on the cells surface - B cells enlarge and divide to produce plasma cells or memory cells - plasma cells produce antibodies designed to specifically bond with the antigen that activated the B cell - the antibodies bind with the specific antigen and form antigen/antibody complexes which are immediately phagocytized by phagocytic cells - memory cells are stored in lymphatic tissues to await the return of the same antigen 40

8 Immunological Memory - the immune response is much faster the second time it is exposed to the same antigen - the first exposure or primary response takes the immune system several days to produce high levels of antibodies - when the same antigen returns (could be decades) later the secondary response occurs which results in the rapid production of antibodies that have a higher affinity for the antigen than the first response. This results in the immediate destruction of the antigen Self-Regulation 41

9 - your own T cells must be able to recognize your own body cells so they do not attack yourself. this is called self-regulation - T cells must not react to peptide fragments from your own body cells - this is known as immunological tolerance - B Cells also have these same capabilities - loss of immunological tolerance leads to autoimmune disorders 42