The anatomy and circulation of the spleen • The spleen lies under the left costal margin, has a normal weight of 150 – 250 g and a length of between 5 and 13 cm. It is normally not palpable but becomes palpable when the size is increased to over 14 cm. • Blood enters the spleen through the splenic artery which then divides into trabecular arteries which permeate the organ and give rise to central arterioles . Te majority of the arterioles end in cords which lack an endothelial lining and form an open blood system unique to the spleen with a loose reticular connective tissue network lined by f ibroblasts and many macrophages.
• The blood re - enters the circulation by passing across the endothelium of venous sinuses . Blood then passes into the splenic vein and so back into the general circulation. • The cords and sinuses form the red pulp which forms 75% of the spleen and has an essential role in monitoring the integrity of red blood cells A minority of the splenic vasculature is closed in which the arterial and venous systems are connected by capillaries with a continuous endothelial layer. • The central arterioles are surrounded by a core of lymphatic tissue known as white pulp which has an organization similar to lymph nodes .
What is the function of spleen ❑ The spleen plays multiple supporting roles in the body . ± It acts as a filter for blood as part of the immune system . ± Old red blood cells are recycled in the spleen, and ± Platelets and white blood cells are stored there. ± The spleen also helps fight certain kinds of bacteria that cause pneumonia and meningitis.
The functions of the spleen : The spleen is the largest filter of the blood in the body and several of its functions are 1. Control of red cell integrity : The spleen has an essential role in the ‘ quality control ’ of red cells. Excess DNA, nuclear remnants severe haemolytic and megaloblastic anaemias. Extramedullary haemopoiesis may result either from reactivation of dormant stem cells within the spleen or homing of stem cells from the bone marrow to the spleen .
2. Immune f unction : The lymphoid tissue in the spleen is respond to antigens filtered from the blood and entering the white pulp. Macrophages and dendritic cells in the marginal zone initiate an immune response and then present antigen to B and T cells to start adaptive immune responses. This arrangement is highly ef cient at initiating immune responses to encapsulated bacteria and explains the susceptibility of hyposplenic patients to these organisms. 3. Extramedullary haemopoiesis : The spleen, like the liver, undergoes a transient period of haemopoiesis at around 3 – 7 months of fetal life but is not a site of erythropoiesis in the adult. However, haemopoiesis may be re – established in both organs as extramedually haemopoiesis , in disorders such as primary myelof brosis or in chronic severe haemolytic and megaloblastic anaemias. Extramedullary haemopoiesis may result either from reactivation of dormant stem cells within the spleen or homing of stem cells from the bone marrow to the spleen.
What are the symptoms of an enlarged spleen?
- Fall '19