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Transcript
Lymphatic System Chapter 14 • -Part of the circulatory system • -2 major roles • 1) carries fluid from the extracellular environment into the bloodstream which helps with fluid balance • 2) immunity – defends the body against disease • -Parts included: lymphatic network (vessels, capillaries), lymph nodes, spleen, thymus, tonsils, Peyer’s patches Lymph network • -Interstitial fluid is plasma that is pushed through the walls of capillaries. It serves as a transport medium for gases, nutrients, and other molecules that travel between cells and blood • -90% of all interstitial fluid is returned to the blood stream; the rest slowly returns to the heart by way of the lymphatic vessels • -network includes lymphatic capillaries, vessels, trunks, and collecting ducts • Lymphatic capillaries • -found between cells and among capillary beds of nearly all tissues and organs • -not found in the brain, spinal cord, bone tissue, and epidermis • -made of a single layer of endothelium that overlaps at times; when pressure is greater in the capillaries, this overlap does not allow the lymph to leak back into the extracellular space • Lymphatic vessels • -formed when the capillaries merge w/ one another and are located closer to the heart • -thicker walls than the capillaries • -have valves to prevent the backflow of lymph (keep lymph traveling toward the heart) • -as the vessels extend toward the heart, they increase in size and form larger lymphatic trunks and collecting ducts; they lead to small oval organs called lymph nodes • -the lymph will pass through nodes and continue on its way Lymphatic Trunks and Collecting Ducts • • • • • • -formed from the merging of numerous lymphatic vessels - they drain lymph from a large part of the body (ex: right upper limb, pelvic region) -they merge and form one of the two collecting ducts: 1) thoracic duct 2) right lymphatic duct • Thoracic duct – main collecting vessel; drains the left side of the head, neck, and thorax, the left upper limb, the entire body below the diaphragm • It starts in the lower abdomen and travels up the back wall of the upper chest; unites with the left subclavian vein • Right lymphatic duct – drains lymph from the right side of the head, neck, and thorax, the right upper limb; empties into the right subclavian vein Movement of Lymph • lymph is moved by pressure gradients caused by accumulation of protein, skeletal muscle contraction and breathing movements Lymphatic Organs • Any structure that contains lymphoid tissue (connective tissue) is a lymphatic organ Lymph nodes • small oval masses of lymphoid tissue that lymph passes through on the way to the heart • clusters found in neck, armpit, groin, deep w/in abdominal cavity • vary in shape and size; frequently shaped like a kidney bean and 1 inch long Lymph Nodes • fibrous capsule – shell of connective tissue • lymph nodules – compact clusters of lymphocytes in the lymph node • cortex – outer area where lymphocytes mature • medulla – inner area where lymphocytes are arranged in strands called medullary cords • as lymph passes through nodes, it is filtered by WBC’s (lymphocytes + macrophages) to trap bacteria, viruses, and toxins Spleen • largest lymphatic organ located on the left side of the body under the diaphragm • contains both red pulp area (contains RBC’s) and white pulp area (contains WBC’s) • functions as a large filter; rids the blood of foreign particles, old/defective RBC’s + platelets • stores blood that is used in case of emergency (ex: trauma w/ major blood loss) Thymus gland • also functions in endocrine system • most active during ages 6 months to 5 years in immune response • by adulthood, it is replaced with fatty tissue and no longer active Tonsils • -3 kinds (palatine, pharyngeal, lingual) • -lymphatic tissue gathers and engulfs diseasecausing microorganisms in the mouth and throat regions • -removed if there are chronic infections Peyer’s patches • located in the walls of the distal end of the small intestine • believed to be a protective barrier between the walls of the intestine and abdominal cavity Defense Mechanisms of the Body • pathogen – disease-causing agents that include living bacteria, fungi, and protozoans • pathogens cause harm by destroying cells or releasing toxins (poisonus substances) that interfere w/ cell functioning • self-cells – cells that belong to the body • nonself cells – cells that do not belong to the body • WBC’s can tell the difference between the 2 b/c all self cells have specific marker proteins (MHC proteins) on the surface identifying them • MHC (majorhistocompatibility) complex – group of genes coding for marker proteins Nonspecific (Innate) Defense Mechanisms • -not selective • -defend against all foreign invaders • Physical/Mechanical Barriers – prevent substances from entering body – skin – 1st line of defense • mucous membranes line all body cavities (produce chemicals that can trap invaders) • infection – invasion by a pathogen that penetrates the body’s physical barriers • Chemical Barriers – fluid that contains a substance that destroys pathogens • gastric juice in stomach has low pH (HCl) and pepsin enzyme • tears contain lysozyme enzyme – destroys bacteria in eyes • sweat – kills some bacteria on skin • Phagocytosis – ingestion and destruction of particles by specialized cells called phagocytes – 1) extend pseudopod (cytoplasmic “foot”) to reach invader – 2) trap invader – 3) enzymes destroy invader • performed by most WBC’s • monocytes and neutrophils are most active b/c they can squeeze through blood vessels (diapedesis) and travel to sites of infection • monocytes become macrophages which attach to lymphatic vessels and organs • Natural Killer Cells • WBC’s that kill cancer cells and virus-infected cells by puncturing their membranes (lysis) • Proteins • 1) complement – a group of 20 types of plasma proteins – only active during infection – label invaders as unwanted so phagocytes can destroy them – help move phagocytes to area of infection • 2) interferons – proteins released by virus-infected cells – travel to surrounding cells and prevent virus from invading • Inflammation – response to body stress following an infection or physical injury • damaged cells release substances (histamine + serotonin) into bloodstream which causes 2 responses: • 1) Vasodilation – blood vessels widen – allows more blood flow to the site bringing clotting proteins, antibodies, and WBC’s (accumulates causing pus to form); results in redness and heat • 2) Increased permeability of blood vessels – pores in capillary walls widen which cause fluids to leak across capillary walls into extracellular space (edema); results in swelling and pain • Fever • increased temperature makes body inhospitable to pathogens • liver/spleen hold iron, making less iron in bloodstream; Iron is needed by bacteria and fungi to reproduce • phagocytic white blood cells are more active at higher temps. Specific Responses: The Immune Response • directed at a particular pathogen or toxin • immune response (immunity): state of resistance to infection • 2 types of immune response – Cell-mediated immunity (T-cells) – Humoral Immunity (antibodies and B-Cells) Components of Immunity • Antigens – substances that provoke an immune response when they enter the body – recognized as foreign by WBC’s • autoimmune response – immune failure when the immune system recognizes a person’s own cells as being foreign • Antibodies – a protein molecule produced in response to an antigen • antigen-antibody complex – when antigen binds to antibody and inactivates the toxic effects of the antigen • immunoglobulins (Ig) – family of proteins that antibodies belong to – 5 classes (IgG, IgA, IgM, IgD, IgE) p. 391 • Lymphocytes – most important WBC form in red bone marrow before birth: nonfunctional form – T cell line thymus gland (T-cells mature) – B cell line small intestine – spleen, stay in RBM • Lymph nodes and other lymphoid tissue • B and T cells are programmed to recognize self/non-self cells = immunocompetent • T cells – are immunocompetent shortly before/after birth – very active – destroy non-self cells in a # of ways – maintain the # of T cells by continuous mitosis (immunocompetent) – T cells become activated or sensitized (happens in lymphoid tissue) and form types of T cells Sensitization • macrophage identifies, phagocytizes, and processes an antigen • processed antigen is expressed on macrophage plasma membrane • macrophage presents processed antigen to a T cell, which enlarges and divides • 1) Killer (cytolytic) T-cells – destroy virus-infected cells, cancer cells, and foreign cells from transplants – binds to cells and releases lymphotoxins (toxic chemicals), causing cells to rupture • 2) Helper T-cells – stimulate/control defensive activities of other cells – release lymphokines (proteins) into bloodstream when they identify an antigen • 3) Suppressor T-cells – slow down and stop defense mechanisms controlled by helper T-cells – prevents unnecessary activity that can destroy healthy self cells • 4) Memory T-cells – remember antigens; T cells respond very fast when you are exposed to an antigen for a 2nd time • B cells – sensitization of B cells is same as for T cells – 1) Plasma cells – rest after they are formed and then produce antibodies (2000/second) – 2) Memory B cells – found in bone marrow, lymph nodes, and spleen – remember antigens so antibodies can be produced faster if exposed to antigen again (occurs w/in hours) – immunization – the ability of the immune response to activate itself quickly when exposed to a 2nd invasion The Allergic Response • • • • type of humoral response involving the release of antibodies by plasma cells allergic – intolerance to a certain antigen coming in contact with skin allergen – antigens that cause an allergic response an allergic individual secretes different antibodies (IgE) than nonallergic individuals (IgG or IgM) • IgE antibodies circulate in blood and eventually come in contact w/ a mast cell found throughout body, mainly in skin and mucous membranes; store chemicals that cause inflammation • when IgE binds to mast cells, chemicals are released and mucous membranes increate the rate of mucous production • Acquired Immunity - person’s ability to mount a defensive immune response b/c of previous contact w/ an antigen • Naturally Acquired Active Immunity – develops from exposure to pathogens or toxins during the course of daily living – symptoms of disease are expressed during 1st exposure • Naturally Acquired Passive Immunity – the transfer of antibodies from a person w/ immunity • during pregnancy, antibodies pass across the placenta to the fetus (last few months) – breast milk also passes antibodies to baby • Artificially Acquired Active Immunity – deliberate, artificial introduction of an antigen to stimulate the immune response • vaccine – killed or weakened living pathogen, or inactivated toxin • vaccination – process of introducing a vaccine • Artificially Acquired Passive Immunity – transferring human or animal antibodies to an individual by injection Homeostasis • immunodeficiency – impairment of the body’s ability to defend against pathogens and toxins due to damage or loss of WBC’s • Acquired Immunodeficiency Syndrome (AIDS) – lethal disease that acts by lowering a victim’s immunity, allowing a 2nd, unrelated infection to produce fatal symptoms • HIV (Human Immunodeficiency Virus) – virus that causes AIDS • blood test measures HIV antibodies produced by B cell lymphocytes in response to HIV exposure HIV: Mode of Infection • typical virus structure = RNA or DNA surrounded by proteins • HIV virus has an additional layer of lipids • Virus infects cells: – 1) Injects genetic information into host cell – 2) Host cell follows genetic information of virus and assembles new viruses – 3) Viruses burst host cell and infect nearby cells • • • • Development of AIDS helper T cells decline HIV activation suppresses cell-mediated immunity secondary diseases that commonly cause death: pneumonia, Kaposi’s sarcoma, hepatitis B, toxoplasmosis, HIV wasting syndrome, AIDS dementia • • • • Transmission and Prevention transmitted by transfer of blood or reproductive fluids outside the body, HIV is fragile cannot exist in air (20% oxygen), 135° water for 10 minutes, 30% hydrogen peroxide, rubbing alcohol, bleach