Lymph is derived from blood plasma and works to absorb excess proteins and fluid from the blood whilst also maintaining crucial defensive properties. Within lymphatic vessels, lymph travels to lymph nodes, small organs that filter lymph for harmful pathogens. Lymph drains into veins that enter the heart thus rejoining the cardiovascular system.
Cardiovascular System
The heart is a powerful pump, constantly contracting to maintain a double blood circulation around the body. One crucial responsibility of blood is to transport oxygen throughout the body, oxygenating tissues. Blood in the veins surrounding the lungs acquires oxygen when a person inhales. This blood returns to the heart within the pulmonary vein and supplies the left side of the heart with blood rich in oxygen. Subsequently, this blood is pumped via the aorta to tissues all around the body. Within the tissues, oxygen is removed from the blood and utilised by the tissues. The oxygen-poor blood returns to the right side of the heart via the vena cava and is pumped once again to the lungs within the pulmonary artery to replenish its oxygen supply.
Lymph Formation
Blood leaves the heart in arteries and travels at high pressure. Veins return blood to the heart at a smaller pressure. Arteries and veins are joined at capillaries. At the arterial end of the capillary, the high blood pressure forces fluid out of the artery into the space known as the interstitial space. At the venous end, the reduced pressure allows fluid to re-enter the vein. Any remaining fluid in the interstitial space is transported in the lymphatic system. Small amounts of protein constantly leak into the lymphatic system encouraging additional fluid to follow. Lymphatic vessels have valves that prevent backflow of lymph and flow is maintained by nearby muscles that squeeze the vessels when they contract.
Lymphatic Function
Almost all tissues in the body have additional channels that facilitate the flow of lymph. Lymph vessels range in size from the smallest lymph capillaries to the largest lymph ducts. Lymph vessels flow into small organs known as lymph nodes. Eventually lymph rejoins the blood flow by draining into the veins returning blood to the heart. The lymph system acts as an overflow system, transporting large proteins when there are too many in the blood. It also absorbs excess fluid from the blood and transports fats from the digestive system. More sinisterly it can also be a route for cancerous cell movement. However, it also has a defensive function as protective white blood cells are produced in the lymph nodes, through which lymph is filtered, and released into the circulation.
Lymph Nodes
Lymph nodes are bean-shaped and found distributed around the body and filter lymph for harmful pathogens. They contain many defensive white blood cells that are used to destroy pathogens and are released into the circulation if necessary. Lymph nodes can become swollen and palpable due to disease processes. The site of the swollen node can provide an indication towards the cause and location of the disease although it is not conclusive.
References
- MedlinePlus; "Swollen Lymph Nodes"; Linda J. Vorvick; May 2010
- Textbook of Medical Physiology; Arthur C, Guyton, et al.; 2005
