Bio 6.4 PDF - The Lymphatic System

# Unit 6: The Circulatory System ## The Lymphatic System The lymphatic system is an entirely separate set of vessels that run alongside the circulatory system. It is a complex network of lymphatic vessels, lymph nodes, lymphoid organs, and other lymphatic tissue. The purpose of this system is to p...

# Unit 6: The Circulatory System ## The Lymphatic System The lymphatic system is an entirely separate set of vessels that run alongside the circulatory system. It is a complex network of lymphatic vessels, lymph nodes, lymphoid organs, and other lymphatic tissue. The purpose of this system is to provide your body with immunity to fight against illness and foreign invaders. Instead of blood, the fluid circulating in the lymphatic system is called lymph. Lymph is composed of extra fluids that drain from cells and are not absorbed by the capillaries. It contains proteins, lipids, and damaged cells. Excess fluid rejoins the circulatory system at the subclavian veins. This junction is also the connection between lipid digestion and the circulatory system: the lacteals, which absorbed the products of lipid digestion, drain into the lymphatic vessels before draining into the subclavian veins. Lymph also contains white blood cells, specifically lymphocytes which fight off infection. These are specialized white blood cells that respond to foreign objects and pathogens in the body. Without them, we would never be able to recover from simple illnesses. ## Lymphatic Structures ### 1. Lymph Vessels - Lymph vessels are similar to veins, ensuring the lymph only travels in one direction. They contain valves, which prevent fluids within the vessels from flowing backwards. There is no central "pump" like the heart powering the lymphatic system, and as such there are no arteries either. There are capillaries, which are nearly identical in structure to regular capillaries, and absorb excess fluid from tissue. ### 2. Lymph Nodes - Lymph nodes are small, round clusters of tissue dispersed around the body. They are connected to lymph vessels. - They help filter large particles out of lymph fluid. Nodes have the capacity to trap bacteria and cancer cells for destruction. - Lymph nodes can also produce lymphocytes. - When enough debris is trapped or lymphocytes are fighting bacteria in the nodes, they can swell up and become inflamed. This causes pain, but is also an indicator of immune system activity. If lymph nodes are swollen for extended periods of time, it may indicate a serious illness ### 3. Lacteals - Part of the digestive system, lacteals are blind sacs in the villi in the small intestine. - Lacteals absorb the products of fat Digestion (glyuvol + fatty acids), which make their way into the circulatory system at the subclavian veins. ### 4. Spleen - The spleen is the largest singular lump of lymphatic tissue in the body. It is in the left abdomen, above the stomach. - It also produces lymphocytes - In addition to making immune cells, it stores excess blood. It can help regulate blood pressure: - If blood pressure is too high, the spleen stores excess blood. - If blood pressure is too low, the spleen releases blood into the circulatory system. ### 5. Thymus Gland - The thymus is a bi-lobed structure situated between the lungs. It helps produce special types of lymphocytes called T cells by providing a site for maturation. It's kind of like college or university for lymphocytes! - It becomes smaller with age. What might be the result of this? Smaller thymus = less capacity to make lymphocytes. Less lymphocytes = less ability to fight infection. ### 6. Tonsils + Appendix - The tonsils are located on either side of the pharynx and contain lymphoid tissue. - Thought to help remove localized invading organisms, like bacteria and ## How does the Immune Response work? When a pathogen does invade the body, your immune system is well-equipped to fight off the threat. There are two main mechanisms used to fight invaders. 1. Lymphocytes continuously produce antibodies, antibodies which are designed to identify and bind to specific antigens. Antibodies circulate in the bloodstream. If a bacterial cell enters the body and an antibody binds to its antigen, an inactive complex is formed. This incapacitates the bacterial cell (causes agglutination) and alerts lymphocytes to travel to the area through the lymph capillary network. 2. Once lymphocytes arrive, they attack the bacterium. Many lymphocytes work by engulfing foreign invaders through phagocytosis. Many white blood cells die during this process. This usually occurs via apoptosis or contact with antigens. When dead white blood cells and bacteria and tissue clump up together, it forms a pus. ## Capillary Fluid Exchange - As we know, water, gases, nutrients and wastes are exchanged between blood and body tissues by osmosis and diffusion. Capillary walls contain small pores to allow this diffusion to occur, but there are other processes governing the movement of particles... - Hydrostatic pressure refers to the blood pressure within a vessel, while osmotic pressure refers to the amount of pressure needed to stop the flow of solutes across a membrane. Osmotic pressure is produced by high concentrations of salts and plasma proteins in the blood. The capillary walls allow water and small solutes to pass between its pores but do not allow proteins to pass through. The proteins help regulate osmotic pressure. - As blood enters the capillary bed on the arteriole end, the blood pressure in the capillary is greater than the osmotic pressure of the blood. Because the overall pressure in the capillary is higher than the tissues, the net result is that fluid moves from capillary into tissue cells. - At the middle of the capillary bed, blood pressure in the vessel equals the osmotic pressure of the blood in the vessel. The net result is that fluid passes equally between the capillary vessel and the body tissue. Gases, nutrients, & wastes are exchanged here. - On the venule end of the capillary bed, blood pressure in the vessel is less than the osmotic pressure blood in vessel. The net result is that fluids, CO₂, + wastes are drawn from the body tissue into the capillary vessel.