Spleen

The spleen is the largest organ of the lymphatic system, it is closely associated with the circulatory system. The function of the spleen include the formation of antibodies and the removal of cell waste products and worn out red blood cells. Most vertebrates have a spleen, but it is not essential to life. The human spleen is located in the abdominal cavity below the diaphragm, behind and the left of the stomach. Its size and weight depend on the amount of blood. It is storing and its immune functions.

The organ consist of white pulp, red pulp and marginal zones. Nodules of the white pulp, which contain lymphatic sheaths and lymph follicles, are scattered throughout the organ. The lymphatic sheaths, loose meshes of tissue surrounding a central artery, are composed predominantly of small lymphocytes. The red pulp consist of thin walled sinuses and cords, which hold blood. Marginal zones between the red pulp and white pulp are the end point for many arteries and contain blood cells from the arterial vessels, macrophages, and lymphocytes. In all animals except human the spleen surrounded by smooth muscle, which enables, it to contract and expel blood from reservoir during period of blood loss.

All of the blood in the human body passes through the spleen approximately every 90 minutes. Blood flow through the spleen via two routes. Most blood passes into the cord of the red pulp, where it travel throughout the organ before emptying into the sinuses. A small portion of blood entering the spleen goes directly to the sinuses. The blood in the red pulp is collected by veins and transported back out of the spleen. The nerve of the spleen follow along the path of the blood vessels.

In adult human the spleen functions both as an immunologically active organ and as a filter for white and red blood cells. Lymphocytes and plasma cells are manufactured in the white pulp, which can also store circulating antigens and produce antibodies. The filtration system of the marginal zone and the red pulp allows macrophages to ingest cellular waste transported into the spleen by the blood.

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