The lymphatic process
The lymphatic system is a one-way drainage system for the body, which is also known as the second circulatory system.
It consists of:
- Lymphatic vessels, eg capillaries, ducts and lacteals
- Lymph nodes or glands (up to 500)
- Lymphatic tissue, eg tonsils, adenoids, thymus, Peyer’s patches and the spleen
- Lymph fluid
Functions of the lymphatic system
- Returns excess fluid from peripheral tissue to the venous system
- Produces antibodies
- Removes unwanted materials
- Produces lymphocytes
- Absorbs digested fats in the villi of the intestines
The process of the lymphatic system
The tissues of the body are bathed with tissue fluid or interstitial fluid, which lies between the blood and the tissues. All interchange of waste and nourishment takes place within this interstitial fluid. Ten per cent of the body’s tissue fluid is returned through the lymphatic system – around 3.5 litres every day. The remaining 90 per cent of tissue fluid returns through the circulatory system. This is around 20.5 litres per day.
This process starts in the lymphatic capillaries, which are blind-ended single layer cells. These collect the excess fluid and waste that the blood is unable to take from the cells. The lymphatic capillaries allow large particles to pass through their walls, such as proteins, viruses, and bacteria.
Once the tissue fluid enters the lymphatic capillaries, it is called lymph. Lymph is a transparent watery fluid; it resembles blood plasma but has a lower concentration of plasma proteins.
The lymph leaves the capillaries and enters the larger lymphatic vessels and these then converge to form two large ducts (the thoracic and right lymphatic duct), which have valves to prevent backflow. These vessels are similar to veins as they rely on the muscles to contract in order to transport lymph through the system.
Throughout the body are lymph nodes, which cleanse the lymph. Lymph enters the lymph nodes via one of five afferent vessels, and is filtered of any unwanted material. Lymphocytes are produced in the lymph nodes, which help fight infection by destroying invading bacteria and viruses by engulfing the germs. Once the lymph is filtered, it passes out through the lymph node’s efferent vessel into the system.
The two main lymphatic ducts are the thoracic and right lymphatic ducts. These two ducts return the body’s lymph into the blood stream, creating a constant circulation between the tissue fluid, lymph in the capillaries and the blood stream.
The right lymphatic duct drains the right arm, head, neck and chest into the right brachiocephalic vein.
The larger, 15 inch thoracic duct drains the rest of the body, lower limbs and abdominal cavity into cistena chyli, from which the thoracic duct leads up to the left brachocephalic vein in the neck.
There are lymphatic vessels in the intestines through which all digested fats are absorbed. The lining of the intestines is covered with villi and each villus contains a lymphatic vessel called lacteals. The lymph from the intestines is milky in colour due to the fat content and is known as chyle. It passes into the cisterna chyli and then enters the thoracic duct.