The spleen is largest lymphoid tissue in the body and specialised as a been shaped organ for filtering blood. It is a highly vascular haemopoietic organ situated in the left hypochondrium directly beneath the diaphragm, above the left kidney and descending colon, behind the fundus of the stomach and weighing about 150 gms in adult. It also plays an important role in the metabolism and defence mechanism of the body. There are no afferent lymphatic vessels.
Structure of spleen: –
histological structure of a spleen shows i) capsule with its outer cooperating the peritoneum, ii) trabeculae with blood vessels or without blood vessels, iii) hilus, iv) White pulp scattered throughout the red pulp, v) the red pulp, vi) reticular meshwork, vii) blood vessels.
Spleen is covered by connective tissue capsule which is again, covered by a serous membrane, the peritoneum. The peritoneum is closely adherent to the outside of the capsule. The capsule is deeply indented and the medial aspect of the return and these indentation is known as the hilus of the spleen. Cruder hilus the blood vessels, lymphatic and nerves are passing. From the inner surface of the capsule and from the hilus many trabeculae radiate into the substance of the spleen and subdivide the organ to many communicating compartments of lobules. Each lobule is supplied with blood vessels that run along with the trabeculae. The lobules are not distinct because these are not completely surrounded by thetrabeculae.
An irregularly oval in shape the spleen is a solid organ. It is about 12 cm long and 7 cm broad. It Lies in theleft hypochondrium, behind the stomach, posteriorly, the spleen rests on the diaphragm opposite the ninth, tenth and eleventh ribs. Its Long axes correspond to that of the tenth rib. The spleen has a medial end with ease directed medially, up words and backwards; and a lateral end that is directed laterally, forwards and downwards. The medial end lies about 4 cm from the midline at the level of the spine of the tenth thoracic vertebra. The lateral end of the spleen reaches up to the midaxillary line. By the upper and lower border the medial and lateral ends are joined. The upper border is sharp, while the lower border is blunt.
Functions of spleen:
a) Blood formation: in the embryo, the spleen functions essay haemopoietic organ of some importance but in normal adult life never functions in the formation of RBC.
b) Blood destruction: the old red cells and white cells are destroyed by the RE
(Reticulo-Endothelial) cells on the spleen. The spleen has got some influence on the formation of platelets. In the post natal life, spleen acts as a filter, which removes the old useless cells and allows only the year-long active cells pass into the body circulation.
c) Blood reservoir: as a great reservoir of blood the action of spleen is well-known. It is observed that clean may release about 150 ml of blood to circulation.
d) Storage and metabolism: haemoglobin is broken down into haem and globin, and the haem is further split into iron and pigmented haematoidin, which forms Bilirubin of the plasma. So it is called the pigment metabolism. On the other side the iron which is liberated from haemoglobin is at first stored in the spleenic pulp cells. Then it is gradually transferred to other places, being carried by the monocytes and the detached RE cells. Specially it is taken to the liver for storage and to the bone marrow or had the haemoglobin synthesis. This system is known as iron metabolism.
e) Defensive action: many plasma cells are found in the spleenic red pulp and hence the spleen is a cheap site of immune the body formation. The RE cells overcome the attack of bacteria, parasites like those of bodies in Kala-azar and some foreign particles. The pulp cells unite with satin toxins, specially of diphtheria and remove them from the general circulation. The lymphoid cells of spleen also has the reaction against infections.
f) Haemolysin manufacturing: when red cells of one species be repeatedly injected in another, a specific haemolysin is formed in the spleen.