Lymphatic System PDF

THE LYMPHATIC SYSTEM and IMMUNITY Lymphatic System The lymphatic system consists of several structures and organs that contain lymphatic tissue, bone marrow, and a fluid called lymph that flows within lymphatic vessel  Function of Lymphatic system The lymphatic system funct...

THE LYMPHATIC SYSTEM and IMMUNITY Lymphatic System The lymphatic system consists of several structures and organs that contain lymphatic tissue, bone marrow, and a fluid called lymph that flows within lymphatic vessel  Function of Lymphatic system The lymphatic system functions to: Drain interstitial fluid Transport dietary fats Carry out immune responses  LYMPHATIC VESSELS Lymphatic vessels begin as lymphatic capillaries, which are closed on one end Lymphatic capillaries are located between cells of many tissues Lymphatic capillaries merge to form lymphatic vessels, which have thin walls and many valves Lymph Trunks and Ducts From the lymphatic vessels, lymph passes through lymph nodes and then into lymph trunks Lymph trunks then merge to form either the thoracic duct or the right lymphatic duct Routes of Drainage Flow of Lymph Interstitial fluid  lymph capillaries  lymph vessels  lymph trunks  lymph ducts  subclavian veins Lymphatic Organs and Tissues Primary lymphatic organs are organs where immune cells become immunocompetent Red bone marrow Thymus  Secondary lymphatic organs and tissues include: Lymph nodes Spleen Lymphatic nodules Lymphatic nodules lymph nodes in particular 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. Particularly large clusters are found in the inguinal, axillary, and cervical regions of the body Within the lymph nodes are macrophages, which engulf and destroy bacteria, viruses, and other foreign substances in the lymph before it is returned to the blood.  Lymph nodes vary in shape and size, but most are kidney-shaped, less than 1 inch (approximately 2.5 centimeters [cm]) long, and “buried” in the connective tissue that surrounds them. Each node is surrounded by a fibrous capsule from which strands called trabeculae extend inward to divide the node into a number of compartments The outer part of the node, its cortex, contains collections of lymphocytes called follicles, many of which have dark-staining centers called germinal centers. These centers enlarge when specific lym phocytes (the B cells) are generating daughter cells called plasma cells, which release antibodies.  Phagocytic macrophages are located in the central medulla of the lymph node. Lymph enters the convex side of a lymph node through afferent lymphatic vessels. It then flows through a number of sinuses that meander through the lymph node and finally exits from the node at its indented region, the hilum via efferent lymphatic vessels. SPLEEN s a soft, blood-rich organ that filters blood. It is located in the left side of the abdominal cavity, just beneath the diaphragm, and curls around the anterolateral aspect of the stomach. Instead of filtering lymph, the spleen filters and cleanses blood of bacteria, viruses, and other debris. provides a site for lymphocyte proliferation and immune surveillance, but its most important function is to destroy worn-out red blood cells and return some of their breakdown products to the liver. Other functions of the spleen include storing platelets and acting as a blood reservoir (as does the liver). THYMUS which functions at peak levels only during youth, is a lymphoid mass found low in the throat overlying the heart. TONSILS small masses of lymphoid tis sue that ring the pharynx (the throat), where they are found in the mucosa. Their job is to trap and remove any bacteria or other foreign pathogens entering the throat. They carry out this function so efficiently that sometimes they become congested with bacteria and become red, swollen, and sore, a condition called tonsillitis. PEYER’S PATCHES Peyer’s patches, which resemble tonsils, are found in the wall of the distal part of the small intestine. Lymphoid follicles are also heavily concentrated in the wall of the appendix, a tubelike offshoot of the first part of the large intestine. The macrophages of Peyer’s patches and the appendix are in an ideal position to capture and destroy bacteria (always present in tremendous numbers in the intestine), thereby preventing them from penetrating the intestinal wall. Peyer’s patches, the appendix, and the tonsils are part of the col lection of small lymphoid tissues BODY DEFENSES INNATE IMMUNITY  SURFACE MEMBRANE BARRIERS The acidic pH of skin secretions and usually of urine (pH of 3 to 5) inhibits bacterial growth, and sebum contains chemicals that are toxic to bacteria. Vaginal secretions of adult females are also very acidic  The stomach mucosa secretes 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. INTERNAL DEFENSES its second line of defense, the body uses an enormous number of cells and chemicals to protect itself. These defenses rely on the destructive powers of phagocytes and natural killer cells, on the inflammatory response, and on a variety of chemical substances that kill pathogens and help repair tissue. NATURAL KILLER CELLS Natural killer (NK) cells roam the body in blood and lymph. They are a unique group of aggressive lymphocytes that can lyse and kill cancer cells, virus-infected body cells, and some other nonspecific targets well before the adaptive arm of the immune system is enlisted in the fight. natural killer cells are far less picky. They can act spontaneously against any such target by recognizing certain sugars on the “intruder’s” surface as well as its lack of certain “self” cell surface molecules. NK cells are not phagocytic. INFLAMMATORY RESPONSE 5 cardinal signs of Inflammation: Pain (Dolor) Heat (calor) Redness (Rubor) Swelling (Tumor) Loss of function (Functio laesa) The inflammatory response prevents the spread of damaging agents to nearby tissues, disposes of cell debris and pathogens, and sets the stage for repair. 1. Neutrophils, responding to a gradient of diffusing inflammatory chemicals, enter the blood from the bone marrow and roll along the blood vessel walls following the “scent. 2. At the point where the chemical signal is the strongest, they flatten out and squeeze through the capillary walls, a process called diapedesis 3. Still drawn by the gradient of inflammatory chemicals, the neutrophils gather in the precise site of tissue injury (a process called positive chemotaxis), and within an hour after injury has occurred, they are busily devouring any foreign material present ADAPTIVE BODY DEFENSES The immune system’s response 3 important aspects of the to a threat, called the immune response, involves tremendously adaptive defense: increased internal nonspecific 1. It is antigen specific it defenses (inflammatory recognizes and acts against responses and others) and also provides protection that is particular pathogens or carefully targeted against specific foreign substances. antigens. 2. It is systemic immunity is referred to as the body’s third not restricted to the initial line of defense, the specific infection site. defense system is a functional system that recognizes foreign 3. It has “memory” to molecules (antigens) and acts to recognizes and mounts inactivate or destroy them. even stronger attacks on Normally it protects us from a previously encountered wide variety of pathogens, as pathogens. ANTIGEN is any substance capable of mobilizing our immune system and provoking an immune response. Most antigens are large, complex molecules that are not normally present in our bodies. they are foreign intruders, or nonself. END