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Functions of Lymphatic System

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Functions of Lymphatic System Lymphatic system The lymphatic system contains three parts, a network of lymphatic vessels, a fluid inside of the vessels called lymph, and lymph nodes that cleanse the lymph while it passes through. Functions of Lymphatic system: 1. Draining excess interstitial fluid-It is responsible for the removal of interstitial fluid from tissues 2. Transporting dietary lipids-It absorbs and transports fatty acids and fats as chyle from the digestive system 3. Carrying out immune response- It transports white blood cells to and from the lymph nodes into the bones. The lymph transports antigen-presenting cells, such as dendritic cells, to the lymph nodes where an immune response is stimulated. 4. The lymphatic system returns fluids that have leaked from the blood (vascular system) back to the blood. Without it, our cardiovascular and immune systems would begin to shut down. FLOW OF LYMPH Lymphatic Capillaries Lymphatic capillaries merge together into larger lymphatic vessels to carry lymph through the body. The structure of lymphatic vessels closely resembles that of veins: they both have thin walls and carrying fluids under low pressure. Lymph is transported through lymphatic vessels by the skeletal muscle pump— contractions of skeletal muscles constrict the vessels to push the fluid forward. Check valves prevent the fluid from flowing back toward the lymphatic capillaries. The sequence of fluid flow is blood capillaries (blood) interstitial spaces (interstitial fluid) lymphatic capillaries (lymph) lymphatic vessels (lymph) lymphatic ducts (lymph) junction of the internal jugular and subclavian veins (blood). The interstitial fluid picked up by lymphatic capillaries is known as lymph. Lymph very closely resembles the plasma found in the veins: it is a mixture of about 90% water and 10% solutes such as proteins, cellular waste products, dissolved gases, and hormones. Lymph may also contain bacterial cells that are picked up from diseased tissues and the white blood cells that fight these pathogens. In late-stage cancer patients, lymph often contains cancerous cells that have metastasized from tumors and may form new tumors within the lymphatic system. A special type of lymph, known as chyle, is produced in the digestive system as lymph absorbs triglycerides from the intestinal villi. Due to the presence of triglycerides, chyle has a milky white coloration to it. Lymphatic Ducts All of the lymphatic vessels of the body carry lymph toward the 2 lymphatic ducts: the thoracic duct and the right lymphatic ducts. These ducts serve to return lymph back to the venous blood supply so that it can be circulated as plasma. Thoracic duct. The thoracic duct connects the lymphatic vessels of the legs, abdomen, left arm, and the left side of the head, neck, and thorax to the left brachiocephalic vein. Right lymphatic duct. The right lymphatic duct connects the lymphatic vessels of the right arm and the right side of the head, neck, and thorax to the right brachiocephalic vein. Rate of Lymph Flow About 100 milliliters per hour of lymph flows through the thoracic duct of a resting human, and approximately another 20 milliliters flows into the circulation each hour through other channels, making a total estimated lymph flow of about 120 ml/hr or 2 to 3 liters per day. Effect of Interstitial Fluid Pressure on Lymph Flow. Normal lymph flow is very little at interstitial fluid pressures more negative than the normal value of -6 mm Hg. Then, as the pressure rises to 0 mm Hg (atmospheric pressure), flow increases more than 20-fold. Relation between interstitial fluid pressure and lymph flow lymph flow reaches a maximum when the interstitial pressure, PT, rises slightly above atmospheric pressure (0 mm Hg). Therefore, any factor that increases interstitial fluid pressure also increases lymph flow if the lymph vessels are functioning normally. Such factors include the following: . Elevated capillary pressure . Decreased plasma colloid osmotic pressure . Increased interstitial fluid colloid osmotic pressure . Increased permeability of the capillaries All of these cause a balance of fluid exchange at the blood capillary membrane to favor fluid movement into the interstitium, thus increasing interstitial fluid volume, interstitial fluid pressure, and lymph flow all at the same time. Special structure of the lymphatic capillaries that permits passage of substances of high molecular weight into the lymph. Structure of lymphatic capillaries and a collecting lymphatic, showing also the lymphatic valves. In addition to the pumping caused by intrinsic intermittent contraction of the lymph vessel walls, any external factor that intermittently compresses the lymph vessel also can cause pumping. In order of their importance, such factors are: Contraction of surrounding skeletal muscles Movement of the parts of the body Pulsations of arteries adjacent to the lymphatics Compression of the tissues by objects outside the body The lymphatic pump becomes very active during exercise, often increasing lymph flow 10- to 30-fold. Conversely, during periods of rest, lymph flow is sluggish, almost zero. DISEASES OF LYMPHATIC SYSTEM Edema results when tissue fluid accumulates faster than the lymphatic system can remove it. Ascites, pleural, and pericardial effusions are localized fluid collections formed by similar mechanisms. Lymphoedema is defined as accumulation of lymph in the extracellular space as a result of lymphatic block or dysfunction. The early edema seen in surgically transposed free flaps, or transplanted visceral organs, for example bowel, lungs, and heart, is in part a result of accumulation of lymph as a result of transected lymphatics. Acute lymphoedema has been shown to affect the heart and lungs following thoracic surgery. It can depress myocardial function and cause pulmonary hypertension as a result of perivascular oedema. Acute lymphoedema typically settles over a few days. Chronic lymphoedema is usually seen as a complication of radical cancer surgery or radiotherapy in the Western world. Lymph slowly accumulates in the tissues distal to the site of damage over weeks, months or years. In the initial stage the oedema is soft, pitting and temporarily reduced by elevation and a compression bandage . Pain may occur from stretching of soft tissues and be related to conditions such as infection, thrombosis, and nerve entrapment syndromes. If left untreated, an inflammatory state develops with collagen deposition and soft tissue overgrowth. At this stage, the tissue becomes less pitting, more firm or brawny, and elevation of the limb no longer results in reduction of the oedema. Metastatic Cancers metastasis is when cancer cells break free of original tumor and travel to other sites in the body. lymph nodes are common sites of metastatic cancer since lymphatic capillaries are so permeable, cancer cells can easily enter and travel in the lymph. Hodgkin Disease lymph node malignancy early symptoms: enlarged, painful nodes, especially in neck; fever, anorexia, weight loss, night sweats, severe itching often progresses to neighbouring lymph nodes. Non-Hodgkin Lymphoma lymphoma similar to above but more common more widespread distribution in body with higher mortality rate. .
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