Lymphatic System PDF

 LYMPHATIC SYSTEM The lymphatic system is a network of tissues, vessels and organs. ▪ Functions: ❑ Transport fluids from body tissues back to bloodstream. ❑ Play essential roles in body defense and resistance to disease. ▪ Consists of two semi-indepe...

 LYMPHATIC SYSTEM The lymphatic system is a network of tissues, vessels and organs. ▪ Functions: ❑ Transport fluids from body tissues back to bloodstream. ❑ Play essential roles in body defense and resistance to disease. ▪ Consists of two semi-independent parts : ❑ Lymphatic vessels ❑ Lymphoid tissues and organs  LYMPHATIC SYSTEM Lymph - excess tissue fluid carried by lymphatic vessels. - pale/clear white fluid, similar composition to blood plasma, but with more leukocytes, lymphocytes, and triglycerides.  LYMPHATIC SYSTEM Lymphatic Vessels ▪The lymphatic vessels, also called lymphatics, form a one way system, and lymph flows only toward the heart. ▪Function: carry lymph towards the heart (never away)  LYMPHATIC SYSTEM Lymphatic Vessels ▪ Fluid leaks into lymphatic capillaries from body tissue. ▪ Lymphatic collecting vessels collect it from lymph capillaries. ▪ Carries lymph to and away from lymph nodes. ▪ Returns fluid to circulatory veins near the heart. ▪ As lymph seeps into lymph capillaries, harmful materials are carried with it: bacteria, viruses, cancer cells, cell debris.  LYMPHATIC SYSTEM Lymphatic Vessels ▪ Lymph capillaries: The microscopic, blind-ended lymph capillaries weave between the tissue cells and blood capillaries in the loose connective tissues of the body and absorb the leaked fluid. ▪ Minivalves: They act as one-way swinging doors; the flaps, anchored by fine collagen fibers to surrounding structures, gape open when the fluid pressure is higher in the interstitial space, allowing fluid to enter the lymphatic capillary.  LYMPHATIC SYSTEM Lymphatic Vessels ▪ Lymphatic collecting vessels: Lymph is transported from the lymph capillaries through successively larger lymphatic vessels referred to as lymphatic collecting vessels, until it is finally returned to the venous system through one of the two large ducts in the thoracic region. ▪ Right lymphatic duct: The right lymphatic duct drains the lymph from the right arm and the right side of the head and thorax. ▪ Thoracic duct: The large thoracic duct receives lymph from the rest of the body; both ducts empty the lymph into the subclavian vein on their own side of the body.  LYMPHATIC SYSTEM Lymph Nodes The lymph nodes filter lymph before it is returned to the blood. They help protect the body by removing foreign material such as bacteria and tumor cells from the lymphatic stream and by producing lymphocytes that function in the immune response. ▪ Size and shape: Lymph nodes vary in size and shape, but most are kidney-shaped, less than 1 inch (approximately 2.5 cm) long, and “buried” in the connective tissue that surrounds them.  LYMPHATIC SYSTEM Lymph Nodes Leukocyte defense cells within lymph nodes: ▪Macrophage - engulf and destroy bacteria, viruses, and other foreign substances in the lymph before it is returned to the blood. ▪Lymphocytes – provide immune response to antigen  LYMPHATIC SYSTEM Lymph Nodes ▪ Trabeculae: Each node is surrounded by a fibrous capsule from which strands called trabeculae extend inward to divide the node into a number of compartments. ▪ Cortex: The outer part of the node, the cortex, contains collections of lymphocytes called follicles, many of which have dark-staining centers called germinal centers. ▪ Plasma cells: These centers enlarge when specific lymphocytes (the B cells) are generating daughter cells called plasma cells, which release antibodies.  LYMPHATIC SYSTEM Lymph Nodes ▪ T cells. The rest of the cortical cells are lymphocytes “in transit”, the so-called T cells that circulate continuously between the blood, lymph nodes and lymphatic stream, performing their surveillance role. ▪ Medulla. Phagocytic macrophages are located in the central medulla of the lymph node. ▪ Afferent lymphatic vessels. Lymph enters the convex side of a lymph node through the afferent lymphatic vessels. ▪ Efferent lymphatic vessels. It then flows through a number of sinuses that cut through the lymph node and finally exits from the node at its indented region, the hilum, via the efferent lymphatic vessels.  LYMPHATIC SYSTEM Other Lymphoid Organs Several organs contribute to lymphatic functions. These include: ▪Spleen ▪Thymus gland ▪Tonsils ▪Peyer’s patches ▪Appendix  LYMPHATIC SYSTEM Spleen The spleen is a soft, blood-rich organ that filters blood. ▪Location: The spleen is located on the left side of the abdominal cavity, just beneath the diaphragm, and curls around the anterior aspect of the stomach.  LYMPHATIC SYSTEM Spleen ▪ Function: ✔ Synthesizes antibodies, filters antibody-coated cells from blood ✔ Provides a site for lymphocyte proliferation and immune surveillance ✔ filters out and destroys worn-out red blood cells and return some of their breakdown products to the liver. ▪ Fetal spleen: In the fetus, the spleen is an important hematopoietic (blood cell-forming) site, but as a rule only lymphocytes are produced by the adult spleen.  LYMPHATIC SYSTEM Thymus Gland ▪ The thymus gland functions at peak levels only during youth. ▪ The thymus gland is a lymphoid mass found low in the throat overlying the heart. ▪ It produces thymosin to program (educate) certain lymphocytes so they can carry out their protective roles in the body.  LYMPHATIC SYSTEM Tonsils ▪ The tonsils are small masses of lymphoid tissue around the pharynx (the throat), where they are found in the mucosa. ▪ Function: to trap and remove bacteria or other foreign pathogens entering the throat. ▪ Tonsilitis. They carry out this function so efficiently that sometimes they become congested with bacteria and become red, swollen, and sore, a condition called tonsilitis.  LYMPHATIC SYSTEM Peyer’s Patches ▪ Peyer’s patches resemble the look of the tonsils found in the wall of the small intestine. ▪ Function: They capture and destroy bacteria (always present in tremendous numbers in the intestine) in the intestine. ▪ Peyer’s patches and the tonsils are part of the collection of small lymphoid tissues referred to as mucosa-associated lymphatic tissue (MALT) ▪ MALT acts as a sentinel to protect the upper respiratory and digestive tracts from the never-ending attacks of foreign matter entering those cavities.  LYMPHATIC SYSTEM Body defenses ▪ The body is constantly in contact with bacteria, viruses and fungi. ▪ The body has two defense systems for foreign materials: I. Nonspecific defense system ▪ Mechanisms protect against a variety of invaders ▪ Responds immediately to protect body from foreign materials II. Specific defense system ▪ Specific defense is required for each type of invader ▪ Also known as the immune system  LYMPHATIC SYSTEM Body defenses ▪ The body is constantly in contact with bacteria, viruses and fungi. ▪ The body has two defense systems for foreign materials: I. Nonspecific defense system II. Specific defense system  LYMPHATIC SYSTEM Body defenses I. Nonspecific defense system (Innate defense system) ▪ refers to the mechanical barriers that cover body surfaces and to the cells and chemicals that act on the initial battlefronts to protect the body from invading pathogens. ▪ Also called the non-specific defense system ▪ Mechanisms protect against a variety of invaders ▪ Responds immediately to protect body from foreign materials  LYMPHATIC SYSTEM Body defenses II. Specific defense system (Adaptive defense system) ▪ Sometimes referred to as the body’s third line of defense ▪ A functional system that recognizes foreign molecules (antigens) and acts to inactivate or destroy them.  LYMPHATIC SYSTEM I. Nonspecific defense system (Innate defense system) 1. First Line of Defense ▪ Body surface coverings and their secretions ▪ Surface Membrane Barriers a. Intact Skin – provides physical barrier to most microorganisms that swarm on the skin. b. Mucous membranes – include mucus, protein digesting enzymes, HCL (in stomach)  LYMPHATIC SYSTEM I. Nonspecific defense system (Innate defense system) 1. First Line of Defense ▪ Body surface coverings and their secretions c. Protective secretions Acidic pH of skin secretions (pH of 3-5) inhibits bacterial growth, and sebum contains chemicals that are toxic to bacteria; vaginal secretions of adult females are also very acidic Hydrochloric acid and protein-digesting enzymes, both kill pathogens Saliva and lacrimal fluid contain lysozyme, an enzyme that destroys bacteria Sticky mucus traps many microorganisms that enter digestive and respiratory passageways.  LYMPHATIC SYSTEM I. Nonspecific defense system (Innate defense system) 1. First Line of Defense ▪ Body surface coverings and their secretions d. Structural modifications ▪ Mucus-coated hairs inside the nasal cavity trap inhaled particles ▪ Respiratory tract mucosa is ciliated; the cilia sweep dust- and bacteria-laden mucus superiorly toward the mouth, preventing it from entering the lungs.  LYMPHATIC SYSTEM I. Nonspecific defense system (Innate defense system) 2. Second Line of Defense ▪ For its second line of defense, the body uses an enormous number of cells and chemicals to protect itself. ▪ Internal Defenses: Cells and Chemicals a. Phagocytes (like macrophages) - engulf and digest foreign particle b. Natural killer (NK) cells – lyse and destroy cancerous or virus infected cells  LYMPHATIC SYSTEM I. Nonspecific defense system (Innate defense system) 2. Second Line of Defense ▪ Internal Defenses: Cells and Chemicals c. Antimicrobial proteins c.1 Complement is a group of plasma proteins that lyses microorganisms, enhances phagocytosis and intensifies inflammatory response. c.2 Interferons are proteins released by virus-infected cells that protect uninfected tissue cells from viral takeover and mobilize immune system. c.3 Urine has a normally acidic pH that inhibits bacterial growth, and cleanses the lower urinary tract as it flushes from the body.  LYMPHATIC SYSTEM I. Nonspecific defense system (Innate defense system) 2. Second Line of Defense ▪ Internal Defenses: Cells and Chemicals d. Inflammatory response The inflammatory response is a nonspecific response that is triggered whenever body tissues are injured; the four most common indicators of an acute inflammation are redness, heat, swelling, and pain. e. Fever Fever, or abnormally high body temperature, is a systemic response to invading microorganisms; normally the body’s “thermostat” is set at approximately 37 degrees Celsius, but it can be reset upward in response to pyrogens (chemicals secreted by white blood cells and macrophages exposed to foreign cells or substances in the body).  LYMPHATIC SYSTEM II. Specific defense system (Adaptive Body Defenses) Third Line of Defense ▪ The specific defense system is a functional system that recognizes foreign molecules (antigens) and acts to inactivate or destroy them. ▪ 3 important aspects: 1. It is Antigen-specific - recognizes and acts against particular pathogens or foreign substances 2. It is Systemic - immunity is not restricted to the initial infection site. 3. It has “memory“ - it recognizes and mounts even stronger attacks on previously encountered pathogens.  LYMPHATIC SYSTEM Antigens ✔ An antigen (Ag) is any substance capable of mobilizing our immune system and provoking an immune response. They are foreign intruders or nonself. a. Foreign intruders.- An almost limitless variety of substances can act as antigens, including virtually all foreign proteins, nucleic acids, many large carbohydrates, and some lipids; proteins are the strongest antigens. b. Self-antigens - your own cells have variety of protein molecules or self-antigens; self-antigens do not trigger an immune response in a person but they are strongly antigenic to other people. c. Hapten / incomplete antigen – as a rule, small molecules are not antigenic, but when they link up with our own proteins, the immune system may recognize the combination as foreign and mount an attack that is harmful rather than protective.  LYMPHATIC SYSTEM Third Line of Defense: Cells of the Immune System A. Lymphocytes ▪ Lymphocytes originate from hemocytoblasts in red bone marrow. ▪ The immature lymphocytes released from the marrow are essentially identical- B lymphocytes (B cells) and T lymphocytes (T cells). ▪ Maturation of T cells: T cells arise from lymphocytes that migrate to the thymus, where they undergo a maturation process of 2 to 3 days, directed by thymic hormones. ▪ Maturation of B cell - B cells develop immunocompetence in bone marrow, but less is known about the factors that regulate B cell maturation.  LYMPHATIC SYSTEM Lymphocyte Differentiation and Activation The process of differentiation and activation of lymphocytes include the following: ▪ Immunocompetence. Lymphocytes destined to become T cells migrate from bone marrow to the thymus and develop immunocompetence there; B cells develop immunocompetence in the bone marrow. ▪ Activation. After leaving the thymus or bone marrow as naive immunocompetent cells, lymphocytes “seed/migrate” to the lymph nodes and spleen and loose connective tissues, where the antigen challenge occurs and the lymphocytes become fully activated. ▪ Circulation. Activated (mature) lymphocytes circulate continuously in the bloodstream and lymph, and throughout the lymphoid organs of the body.  B - Lymphocytes T - lymphocytes They mature in BONE They mature in THYMUS MARROW GLAND They produce antibody They directly attack the against antigen. antigen or attach B cells to produce antibody They do not respond to They respond to organ organ transplantation. transplantation.  LYMPHATIC SYSTEM II. Specific defense system (Adaptive Body Defenses) Third Line of Defense B. Macrophages ▪ Macrophages arise from monocytes, formed in the bone marrow. ▪ Macrophages tend to remain fixed in the lymphoid organs, but lymphocytes, especially T cells circulate continuously through the body. ▪ A major role of macrophages is to engulf foreign particles and rid them from the area; they also present fragments of those antigens.  LYMPHATIC SYSTEM II. Specific defense system (Adaptive Body Defenses) Third Line of Defense B. Macrophages ▪ Macrophages also secrete cytokines proteins that are important in the immune response. ▪ Activated T cells, in turn, release chemicals that causes macrophages to become killer macrophages.  LYMPHATIC SYSTEM Antibodies (G-A-M-E-D) ▪ Antibodies, also referred to as immunoglobulins, or Igs, constitute the gamma globulin part of blood proteins. ▪ Antibodies are soluble proteins secreted by activated B cells or by their plasma-cell offspring in response to an antigen and they are capable of binding specifically with that antigen. ▪ There are five major immunogloblin classes- IgM, IgA, IgD, IgG, and IgE.  LYMPHATIC SYSTEM Third Line of Defense Humoral (Antibody Mediated) Immune Response ▪ Primary humoral response. The resulting family of identical B cells descended from the same ancestor cell is called a clone, and clone formation is the primary humoral response to that antigen. ▪ Most of the B cell clone members, or descendants, become plasma cells. ▪ B cell clone members that do not become plasma cells become long-lived memory cells capable of responding to the same antigen at later meetings with it. ▪ Memory cells are responsible for the immunological memory, and these later immune responses, called secondary humoral responses,  LYMPHATIC SYSTEM Humoral (Antibody Mediated) Immune Response Active and Passive Humoral Immunity A. Active immunity: When your B cells encounter antigen and produce antibodies against them, you are exhibiting active immunity. B. Passive immunity: In passive immunity, the antibodies are obtained from the serum of an immune human or animal donor; as a result, the B cells are not challenged by the antigen, immunological memory does not occur, and the temporary protection provided by the “borrowed antibodies” ends when they naturally degrade in the body.  ACQUIRED ACTIVE Immunity IMMUNITY PASSIVE Antibodies are Antibodies are obtained developed inside the from the serum of an body immune human or animal Long lasting donor Short period Active Antibodies made Antibodies transmitted Passive Natural after exposure to NATUR from mother to baby Natural Immunity an active infection AL (via placenta and Immunity breastmilk) Antigens Antibodies Active ARTIFICI Passive administered acquired from an Aritificial Artificial to stimulate AL immune serum Immunity Immunity antibody e.g. from animal to vaccination human  LYMPHATIC SYSTEM Third Line of Defense Cellular (Cell-Mediated) Immune Response ▪ Like B cells, immunocompetent T cells are activated to form a clone by binding with a “recognized” antigen; However, T cells are not able to bind with free antigens. Instead, the antigens must be “presented” by macrophages, and a double recognition must occur.