THE SPLEEN 23'.pptx

THE STRUCTURE AND FUNCTION OF THE SPLEEN AND TSS OKPUNU E.C.( MBBS, FMCPath) LECTURER @ AAUCOM AND CONSULTANT @ ISTH EDO STATE INTRODUCTION The spleen is an important organ in the body has a unique role in the function of the haemopoietic and immune systems. The spleen is directly involved in many d...

THE STRUCTURE AND FUNCTION OF THE SPLEEN AND TSS OKPUNU E.C.( MBBS, FMCPath) LECTURER @ AAUCOM AND CONSULTANT @ ISTH EDO STATE INTRODUCTION The spleen is an important organ in the body has a unique role in the function of the haemopoietic and immune systems. The spleen is directly involved in many diseases of the haemopoietic and immune systems. Numerous clinical features are associated with hypersplenism and hyposplenism. Anatomy of Spleen ANATOMY OF THE SPLEEN The spleen lies under the left costal margin Weighs about 150–250g Length of between 5 and 13 cm. Normally not palpable Becomes palpable at over 14 cm. The spleen is surrounded by a capsule which gives rise to trabeculae.This divide the parenchyma, into incomplete compartments. The capsule of the spleen is thickened at the hilum, where arteries, nerve fibers enter and veins, lymphatic vessels leave the spleen. Blood circulation in the spleen THE SPLEENIC CIRCULATION A minority of the splenic vasculature is closed forming sinuses In the closed system the arterial and venous systems are connected by capillaries with a continuous endothelial layer. Blood enters the spleen through the splenic artery. Splenic artery divides into trabecular arteries Trabecular arteries permeate the spleen and give rise to central arterioles. THE SPLEENIC CIRCULATION Most of the arterioles end in cords. The cords lack endothelial lining. It forms the open blood system. The open blood system is unique to the spleen. It has a loose reticular connective tissue network lined by fibroblasts and macrophages. THE SPLEENIC CIRCULATION The blood in the open system re-enters the circulation by passing across the endothelium of venous sinuses. From the sinusoids, blood proceeds to the red pulp veins that join together and enter the trabeculae, forming the trabecular veins Blood then passes from the trabecular veins into the splenic vein and back into the general circulation. THE SPLEENIC CIRCULATION There are both rapid (1–2 min) and slow (30–60 min) blood circulations through the spleen. The slow circulation becomes increasingly important in splenomegaly STRUCTURE OF THE SPLEEN The splenic pulp has two components,  The white pulp and the red pulp The cords and sinuses form the red pulp Red pulp is 75% of the spleen structure It monitors the integrity of red blood cells. STRUCTURE OF THE SPLEEN CONT’D The central arterioles are surrounded by a core of lymphatic tissue known as white pulp. The periarteriolar lymphatic sheath (PALS) lies directly around the arteriole containing T lymphocytes Follicles are found adjacent to the PALS and contains B-cells STRUCTURE OF THE SPLEEN CONT’D These are surrounded by the marginal and perifollicular zones. The marginal and perifollicular zones are rich in macrophages and dendritic cells. Lymphocytes migrate into white pulp from the sinuses of the red pulp or from vessels that end directly in the marginal and perifollicular zones. RED PULP The red pulp of the spleen is composed of splenic sinuses and splenic cords (of Billroth). The red pulp resembles a sponge The spaces within the sponge represent the sinuses and The sponge material among the spaces denotes the splenic cords. RED PULP CONT’D The splenic cords are composed of a loose network of reticular fibers The interstices are permeated by extravasated blood. Macrophages are particularly numerous in the vicinity of the sinusoids WHITE PULP The white pulp is composed of the Periarterial lymphatic sheath Lymphoid nodules The marginal zone Lymphoid nodules displays germinal centers, during antigenic stimulation WHITE PULP CONT’D The white pulp is surrounded by a marginal zone, that separates the white pulp from the red pulp. This zone is composed of plasma cells, T and B lymphocytes, macrophages, and interdigitating dendritic cells SPLEEN  FUNCTIONS OF THE Control of red cell integrity Phagocytosis: Removal of red cells containing excess DNA, nuclear remnants (Howell–Jolly bodies) and siderotic granules in the red pulp by macrophages. FUNCTIONS OF THE SPLEEN CONT’D  Immunologic function The lymphocytes in the spleen respond to antigens from the blood 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 response to encapsulated bacteria FUNCTIONS OF THE SPLEEN CONT’D This explains the susceptibility of hyposplenic patients to these organisms. These organism include Strep. pneumonia H. influenzae type b Neisseria meningitidis, Viral infections Intra-erythrocyte parasitic infection like plasmodium FUNCTIONS OF THE SPLEEN CONT’D Extramedullary haemopoiesis In disorders such as Primary myelofibrosis Chronic severe haemolytic anaemia 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. FUNCTIONS OF THE SPLEEN CONT’D  Phagocytosis Uptake of none viable cells and foreign matter by the macrophages. It is irreversible in the presence of metabolically active macrophages the densely packed red cells are deprived of O2 & glucose and causes increase in membrane rigidity This rigidity reduces natural deformability of the biconcave cell FUNCTIONS OF THE SPLEEN CONT’D The above effect is marked in the following conditions: -Red cell metabolic system abnormality -Red cells coated with antibody -Fragmented cells In these states they remain trapped in cord space and undergo phagocytosis FUNCTIONS OF THE SPLEEN CONT’D Sequestration A reversible process whereby cells are held up temporarily before returning into circulation eg reticulocytes Cells are temporarily trapped by adhesion to the reticular meshwork of the cords on their passage through the spleen FUNCTIONS OF THE SPLEEN CONT’D During this process, there is removal of inclusions from the red cells before returning to the circulation by culling or pitting These inclusions include: Siderotic granules  Howell-Jolly (DNA) bodies Nuclear reminant Heinz bodies. SPLENOMEGALY Splenic size >14cm Measurement of spleen clinically is unreliable because: Minor enlargement is undetectable by palpation Grossly enlarged spleen may be missed in obese patients SPLENOMEGALY Splenomegaly is usually felt under the left costal margin. Massive splenomegaly may be felt as far as the right iliac fossa The spleen moves with respiration and a medial splenic notch may be palpable in some cases. SPLENOMEGALY CONT’D In developed countries the most common causes of splenomegaly are: Infectious mononucleosis Haematological malignancy Portal hypertension. Malaria and schistosomiasis are more prevalent on a global scale SPLENOMEGALY CONT’D  Causes of massive splenomegaly Chronic myeloid leukaemia Primary myelofibrosis Malignant Lymphoma Gaucher disease, Malaria-TSS Leishmaniasis and Schistosomiasis SPLENOMEGALY CONT’D  Methods of reliable detection of splenomegaly USS MRI CT SPLENOMEGALY CONT’D  Pathologic basis of splenomegaly Reactive increase of white pulp in inflammation and infection Congestive expansion of the red pulp Increased blood pool Increased macrophage function/compartment SPLENOMEGALY CONT’D Proliferative cellular infiltration Extramedullary haemopoiesis Storage disease, cysts, solid tumour. HYPERSPLENISM Approximately 5% (30–70 mL) of the total red cell mass is present in the spleen Up to half of the total marginating neutrophil pool and 30% of the platelet mass are located in the spleen. As the spleen enlarges, up to 40% of the red cell mass, 90% of platelets may be pooled in an enlarged spleen. CONT’D HYPERSPLENISM A clinical syndrome seen in any form of splenomegaly. Characterized by Splenomegaly. Reduction of at least one cell line in the blood  Presence of normal bone marrow function. Rapid improvement in the peripheral blood count after splenectomy HYPOSPLENISM Functional hyposplenism is characterized by PBF findings of Howell–Jolly bodies or Pappenheimer bodies (siderotic granules on iron staining) Common causes:  Surgical removal of the spleen,following traumatic rupture. Sickle cell anaemia Gluten-induced enteropathy Amyloidosis SPLENECTOMY Surgical removal of the spleen Indications  Treatment of haematological disorders  Splenic rupture  Splenic tumours or cysts Splenectomy can be performed by Open abdominal laparotomy  Laparoscopic surgery. SPLENECTOMY CONT’D Following splenectomy, The platelet count may rise dramatically in the early postoperative period, up to 1000 × 109/L It peaks at 1–2 weeks. Thrombotic complications are seen in some patients Prophylactic aspirin or heparin is often required Long-term alterations may include Persistent thrombocytosis, lymphocytosis or monocytosis. PREVENTION OF INFECTION IN HYPOSLENIC PATIENTS Hyposplenic patients are at lifelong increased risk of infection from a variety of organisms. Seen in children under the age of 5 years and those with sickle cell anaemia. Susceptibility is mainly to encapsulated bacteriae Streptococcus pneumoniae Haemophilus influenzae type B Neisseria meningitidis. PREVENTION OF INFECTION IN HYPOSLENIC PATIENTS Streptococcus pneumoniae is a concern. It can cause a rapid and fulminant disease. Malaria and infection caused by animal bites tend to be more severe in splenectomized individuals PREVENTION OF INFECTION IN HYPOSLENIC PATIENTS Measures to reduce the risk of serious infection 1) Inform Patients about their increased susceptibility to infection and advised to carry a card about their condition. Counselled about the increased risk of infection on foreign travel from malaria, tick and animal bites. PREVENTION OF INFECTION IN HYPOSLENIC PATIENTS 2) Prophylactic oral penicillin is recommended, usually for life. High-risk groups includes Less than 16 years and greater than 50 years, Splenectomised patients for haematological malignancy Previous invasive pneumococcal disease PREVENTION OF INFECTION IN HYPOSLENIC PATIENTS Erythromycin may be prescribed for patients allergic to penicillin. Antibiotics should be given the patients with fever before medical care is available. 3) Vaccination against pneumococcus, haemophilus, meningococcus and influenza infection is recommended. PREVENTION OF INFECTION IN HYPOSLENIC PATIENTS All types of vaccine, including live vaccines, can be given safely to hyposplenic individuals, although the immune response to vaccination may be impaired TROPICAL SPLENOMEGALY SYNDROME(TSS) A syndrome of massive splenomegaly of uncertain aetiology Found mostly in malarious zones of the tropics eg Uganda, Nigeria, New Guinea and the Congo. Some cases are seen in Southern Arabia, Sudan and Zambia. Old terminology include ‘big spleen disease’, ‘cryptogenic splenomegaly’and ‘African macroglobulinaemia’. TROPICAL SPLENOMEGALY SYNDROME(TSS) CONT’D While it seems probable that malaria is the fundamental cause of TSS It is not the result of active malarial infection Parasitaemia is usually scanty and malarial pigment is not found in biopsy material from the liver and spleen. TROPICAL SPLENOMEGALY SYNDROME(TSS) CONT’D TSS results from an abnormal host response to the continual presence of malarial antigen Resulting in a reactive and relatively benign lymphoproliferative disorder that predominantly affects the liver and spleen TROPICAL SPLENOMEGALY SYNDROME(TSS) CONT’D  Features Hepatosplenomegaly with massive spleen. Portal hypertension. Severe anaemia Leucopenia Thrombocytopaenia Lymphocytosis in some patients High Serum immunoglobulin (Ig) M High titres of malarial antibody. TROPICAL SPLENOMEGALY SYNDROME(TSS) CONT’D Splenectomy corrects the pancytopenia Risk of fulminant malarial infection following splenectomy. Antimalarial therapy has proved successful in the management of TSS.e.g use of proguanil THANK YOU FOR LISTENING