Lymphatic system

[samreen]

Lymphatic system

The lymphatic system is a complex network of lymphoid organs, lymph nodes, lymph ducts, lymph tissues, lymph capillaries and lymph vessels that produce and transport lymph fluid from tissues to the circulatory system. The lymphatic system is a major component of the immune system.

The lymphatic system has three interrelated functions: (1) removal of excess fluids from body tissues, (2) absorption of fatty acids and subsequent transport of fat, chyle, to the circulatory system and, (3) production of immune cells (such as lymphocytes, monocytes, and antibody producing cells called plasma cells).

Lymph originates as blood plasma that leaks from the capillaries of the circulatory system, becoming interstitial fluid, and filling the space between individual cells of tissue. Plasma is forced out of the capillaries by oncotic pressure gradients, and as it mixes with the interstitial fluid, the volume of fluid accumulates slowly. Most of the fluid is returned to the capillaries by hydrostatic pressure gradients. The proportion of interstitial fluid that is returned to the circulatory system by osmosis is about 90% of the former plasma, with about 10% accumulating as overfill. The excess interstitial fluid is collected by the lymphatic system by diffusion into lymph capillaries, and is processed by lymph nodes prior to being returned to the circulatory system. Once within the lymphatic system the fluid is called lymph, and has almost the same composition as the original interstitial fluid.

Lymphatic circulation
The lymphatic system acts as a secondary circulatory system, except that it collaborates with white blood cells in lymph nodes to protect the body from being infected by cancer cells, fungi, viruses or bacteria. Unlike the circulatory system, the lymphatic system is not closed and has no central pump; the lymph moves slowly and under low pressure due to peristalsis, the operation of semilunar valves in the lymph veins, and the milking action of skeletal muscles. Like veins, lymph vessels have one-way, semilunar valves and depend mainly on the movement of skeletal muscles to squeeze fluid through them. Rhythmic contraction of the vessel walls may also help draw fluid into the lymphatic capillaries. This fluid is then transported to progressively larger lymphatic vessels culminating in the right lymphatic duct (for lymph from the right upper body) and the thoracic duct (for the rest of the body); these ducts drain into the circulatory system at the right and left subclavian veins.

Function of the Fatty Acid Transport System
Lymph vessels, called lacteals, are present in the lining of the gastrointestinal tract. While most other nutrients absorbed by the small intestine are passed on to the portal venous system to drain, via the portal vein, into the liver for processing, fats are passed on to the lymphatic system, to be transported to the blood circulation via the thoracic duct. The enriched lymph originating in the lymphatics of the small intestine is called chyle (not chyme). The nutrients that are released to the circulatory system are processed by the liver, having passed through the systemic circulation. The lymph system is a one-way system, transporting interstitial fluid back to blood

Lymphoid organs

The thymus, spleen, lymph nodes, peyer's patches, tonsils, vermiform appendix, and red bone marrow are accessory lymphoid tissues that comprise the lymphoid organs. These organs contain a scaffolding that support circulating B- and T-lymphocytes and other immune cells like macrophages and dendritic cells. Another sub-component of the lymphatic system is the reticuloendothelial system. When micro-organisms invade the body or the body encounters other antigens (such as pollen), the antigens are transported from the tissue to the lymph. The lymph is carried in the lymph vessels to regional lymph nodes. The lymph nodes filter the lymph fluid and remove foreign material, such as bacteria and cancer cells. Specialized cells called macrophages and dendritic cells phagocytose pathogens, process them, and present antigens to lymphocytes. When these pathogens are recognized, the lymph nodes enlarge as additional immune cells are produced to help fight the infection.

SourceFrom Wikipedia, the free encyclopedia

[dr.junaid]

Hodgkin’s Disease
Hodgkin’s Disease or Hodgkin's Lymphoma, less severe form of two types of cancer that arise in the lymphatic system (network of small vessels that carry lymph, a fluid containing white blood cells of the immune system). The other form is non-Hodgkin's lymphoma. Hodgkin's disease is characterized by usually painless but progressive enlargement of lymph nodes (or glands) and other lymphoid tissue. The American Cancer Society estimates that about 7,400 new cases of Hodgkin’s disease are diagnosed in the United States annually. Hodgkin's disease more commonly occurs in people 15 to 35 years of age and over 50. Generally the first symptom of the disease is swelling of lymph nodes in the neck, armpit, or groin. Later many other lymph nodes become involved, and the spleen becomes enlarged. Secondary symptoms include fever, chills, night sweats, weight loss, fatigue, and loss of appetite. The cause has remained unknown since the British physician Thomas Hodgkin first described the condition in 1832. Some researchers have suggested that macrophages (large immune cells that ingest foreign bacteria) may play a role in causing Hodgkin's disease.

Diagnosis of Hodgkin's disease is made with a biopsy (removal of a small tissue sample for examination under a microscope). Hodgkin's disease is primarily distinguished from non-Hodgkin's lymphoma by the presence of Reed-Sternberg cells, large cells that contain several nuclei. If the disease is diagnosed at an early stage and has not metastasized (spread to other areas of the body, see Metastasis), radiation therapy is commonly used. With advanced cases, the doctor will usually prescribe chemotherapy (anti-cancer drugs) for approximately six months, often in combination with radiation therapy. For patients with disease resistant to conventional treatments, or for patients who have relapses (reappearance of symptoms after an apparent cure), doctors may try high-dose chemotherapy and bone-marrow transplants. The chemotherapy destroys all of the patient's unhealthy bone marrow in preparation for the transplantation of healthy bone marrow, so the body can once again produce healthy white blood cells. The healthy bone marrow is injected into the bloodstream and, if successful, the cells find their way to the bones and begin to grow. Approximately 90 percent of Hodgkin's patients who are diagnosed at an early stage are cured. Advanced cases of the disease are cured 50 to 80 percent of the time.

[dr.junaid]

Elephantiasis
Elephantiasis, disease of the lymphatic system, characterized by an enormous enlargement of the infected area. The hardened skin of this area resembles the hide of an elephant. The disease is usually the result of blockage of the lymphatic system by threadlike filarial worms, usually Wuchereria bancrofti. The parts of the body most frequently affected are the limbs and the genitals. The disease is treated with the antifilarial drug diethylcarbamazine (Hetrazan) and with surgery.