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Lymphatic system

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The lymphatic system is a biological system that produces and transports lymph fluid from tissues to the circulatory system and is a major part of the immune system. The major components of the lymphatic system are lymphatic vessels, lymph, lymph nodes, and some other lymphatic organs. The system is comprised of tissues and organs that produce, store, and carry white blood cells that fight infections and other diseases. Major components include the bone marrow, spleen, thymus, lymph nodes, and lymphatic vessels. Lymphatic vessels branch, like blood vessels, into all the tissues of the body. Lymphatic vessels carry lymph, a colorless liquid, throughout the body. Along lymph vessels are small bean-shaped glandular nodules called lymph nodes.[1]

Functions

The lymphatic system has three primary functions. First of all, it returns excess interstitial fluid to the blood. Of the fluid that leaves the capillary, about 90 percent is returned. The 10 percent that does not return becomes part of the interstitial fluid that surrounds the tissue cells. Small protein molecules may "leak" through the capillary wall and increase the osmotic pressure of the interstitial fluid. This further inhibits the return of fluid into the capillaries, and fluid tends to accumulate in the tissue spaces. If this continues, blood volume and blood pressure decrease significantly and the volume of tissue fluid increases, which results in edema (swelling). Lymph capillaries pick up the excess interstitial fluid and proteins and return them to the venous blood. After the fluid enters the lymph capillaries, it is called lymph.[2]

The second function of the lymphatic system is the absorption of fats and fat-soluble vitamins from the digestive system and the subsequent transport of these substances to the venous circulation. The mucosa that lines the small intestine is covered with fingerlike projections called villi. There are blood capillaries and special lymph capillaries, called lacteals, in the center of each villus. The blood capillaries absorb most nutrients, but the fats and fat-soluble vitamins are absorbed by the lacteals. The lymph in the lacteals has a milky appearance due to its high fat content and is called chyle.[2]

Immune System

Main Article: Immune System

The third and probably most well known function of the lymphatic system is defense against invading microorganisms and disease. The organs of your immune system are connected with one another and with other organs of the body by a network of lymphatic vessels. Lymph nodes and other lymphatic organs filter the lymph to remove microorganisms and other foreign particles. Lymphatic organs contain lymphocytes that destroy invading organisms. [2]

Lymphocytes can travel throughout the body using the blood vessels. The cells can also travel through a system of lymphatic vessels that closely parallels the body's veins and arteries. Cells and fluids are exchanged between blood and lymphatic vessels, enabling the lymphatic system to monitor the body for invading microbes. The lymphatic vessels carry lymph, a clear fluid that bathes the body's tissues.[3]

Small, bean-shaped lymph nodes sit along the lymphatic vessels, with clusters in the neck, armpits, abdomen, and groin. Each lymph node contains specialized compartments where immune cells congregate and encounter antigens.

Immune cells and foreign particles enter the lymph nodes via incoming lymphatic vessels or the lymph nodes' tiny blood vessels. All lymphocytes exit lymph nodes through outgoing lymphatic vessels. Once in the bloodstream, they are transported to tissues throughout the body. They patrol everywhere for foreign antigens, then gradually drift back into the lymphatic system to begin the cycle all over again.[4]

Organs

Lymphatic organs are:

  • Tonsil: clusters of lymphatic tissues just under the mucous membranes that line the nose, mouth, and pharynx.
  • Spleen: it is similar to a lymph node in shape and structure but it is much larger.
  • Thymus: a soft organ with two lobes that is located anterior to the ascending aorta and posterior to the sternum.
  • Peyer patch: lymphoid tissue on the visceral surface of the small intestine.

Tonsils

Main Article: Tonsils

The tonsils are immune system organs comprised of masses of lymph tissue located in the back of one's throat that play an uncertain role in the lymphatic system. Tonsillitis is a common childhood illness and can create recurrent health problems such as fever, sore throat, and ear aches. The tonsils are one of the few organs that a person safely may have removed and the removal of them poses no risk to one's medical health. Interestingly, within the first thirty minutes of the removal of the tonsils they are able to bounce higher than that of a rubber ball of similar size [5]. The medical world has yet to come to an agreement on the importance of tonsils, but has recently strayed away from the removal of them (tonsillectomy) and is now suggesting to patients with throat problems and discomfort to try to wait out the problem instead [6]. However, doctors are recommending tonsillectomies to those battling sleep apnea. The percentage of tonsillectomies performed due to an infection in the throat is currently only twenty percent, and the other eighty percent who receive tonsillectomies struggle with sleep problems. Tests are also beginning to show that a tonsillectomy may also help improve a child's behavior and focus in school. [7]

"Fewer tonsillectomies are performed today than in the past because it is now known that the tonsils remove many of the pathogens that enter the pharynx; therefore, they are a first line of defense against invasion of the body" Inquiry into Life 10th edition, Mader, McGraw Hill, copyright 2003 p293

Spleen

Main Article: Spleen

The spleen is an organ of the lymphatic system that is located in between the 9th and 12th thoracic ribs on the left side of the body.[8] It is composed of masses of lymphoid tissue and twisted veins and fibers, and plays an important role in the immune system, constantly storing blood platelets and white blood cells. In an average adult up to 30% of blood platelets are stored away by the spleen.[9] Your spleen also helps control the amount of blood in your body, and destroys old and damaged cells. Although once thought to have been a non-vital organ, the importance of this organ in immune defense is vital. However, due to many circumstances, the spleen may become enlarged and start to provide problems for the human body, but this is often solved by removal of the organ (splenectomy).

Disease

References

  1. lymphatic system Dictionary of Cancer Terms. by the National Cancer Institute.
  2. 2.0 2.1 2.2 Introduction to the Lymphatic System by the National Cancer Institute.
  3. Understanding Cancer Series: The Immune System - Slide 6 Lymphatic System by the National Cancer Institute.
  4. Understanding Cancer Series: The Immune System - Slide 7 Lymph Node by the National Cancer Institute.
  5. Tonsils. De Brain.
  6. Tonsil removal has no major benefits over watchful waiting in children with throat infections or enlarged tonsils and adenoids. The Medical News. September 9, 2004
  7. Tonsillectomy Facts in the U.S.: From ENT Doctors American Academy of Otolaryngology — Head and Neck Surgery
  8. Sonographic Evaluation of Spleen Size in Tall Healthy Athletes Spielmann, Audrey L., David M. DeLong, and Mark A, Kliewer, American Journal of Roentgenology. 2005.
  9. Splenectomy By Surgeryencyclopedia.com. Accessed 17 February 2011.