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SPLEEN.pptx
- 2. SPLEEN • Large lymphoid organ in the body. • A soft and freely movable structure. • Location: upper quadrant of the abdominal cavity posterior to the upper part of the stomach. • Not a vital organ FUNCTION: • Important component of body’s immune defense system. • Filters blood (macrophages) • Removes and destroys damaged old RBC and platelets. • Storage area for blood.
- 3. HISTOLOGIC ORGANIZATION OF SPLEEN • Encased by a CAPSULE – dense irregular connective tissue • Significant number of smooth muscle cells and elastic fibers • HILUS – surface notch- blood enter and leaves • Capsule is enveloped by a PERITONEUM • Lined on external surface by MESOTHELIUM • CONNECTIVE TISSUE TRABECULAE – forming SEPTA – divides the substances of the spleen • Stroma consist of RETICULAR TISSUE
- 4. SPLEEN
- 5. PARENCHYMA OF THE SPLEEN • Composed of reddish-brown substance, scattered small masses of ovoid grayish-white structure • Red pulp and white pulp –forms the bulk of parenchyma
- 6. WHITE PULP • Consist of lymphoid nodules embedded in dense lymphoid tissue • Dense lymphoid tissue- form sleeves around the arteries of the spleen • Comprises lymphocyte population, uniquely associated with blood vessels. • Contains macrophages and dendritic cells RED PULP • Greater part of splenic parenchyma (80%) • Consist of large, blood-filled sinusoids separated by reticular tissue (SPLENIC CORDS – OF BILLROTH) • Blood accounts for the color of pulp
- 7. WHITE PULP
- 8. WHITE PULP
- 9. RED PULP
- 10. RED PULP
- 11. BLOOD VESSELS OF THE SPLEEN
- 12. BLOOD VESSELS OF THE SPLEEN • SPLENIC ARTERY –biggest branch of celiac artery (further divides) • The branches ramify to give off TRABECULAR ARTERIES • Trabecular artery give off branches – CENTRAL ARTERIES (arteries of white pulp) a small muscular artery • Central artery tunica adventitia is formed by PERIARTERIAL LYMPHOID SHEATH (PALS) consisting T-cells - eccentrically located in white pulp. - enveloped by PALS • FOLLICULAR ARTERIES supply lymphoid nodules and dense lymphoidal tissue of white pulp
- 13. BLOOD VESSELS OF THE SPLEEN • PENICILLAR ARTERY (arteries of red pulp) – terminates the central artery. - arteriole; cuboidal; gives off 2-3 sheathed arteries (ellipsoid) • ELLIPSOID is surrounded by macrophages; enveloped by SHEATH OF SCHWEIGGER SEIDEL. Filtering starts here. • Blood drains into SPLENIC SINUSOIDS (open circulation) - large regular lumens; very thin walls; no smooth muscle fibers; atypical endothelium- fusiform and capable of phagocytosis. • Numerous macrophages (PERISINUSOIDAL MACROPHAGES) – filters blood; help macrophages phagocytose materials. • Blood flows to collecting veins in red pulp, drain into TRABECULAR VEINS uniting to form SPLENIC VEINS.
- 14. LYMPH VESSELS OF THE SPLEEN • No afferent lymphatic vessels • Efferent vessels bind capillaries – unite to form bigger vessels following the course of veins
- 15. BLOOD FLOW IN SPLEEN
- 16. MALT-ASSOCIATED LYMPHOID TISSUE (MALT) •Enormous amount of lymphoid tissue - mucosa - submucosa - Gastrointestinal (GALT – Gut-associated lymphoid tissue) - Respiratory (Trachea and bronchi – BALT (Bronchus- associated lymphoid tissue))
- 17. MALT-ASSOCIATED LYMPHOID TISSUE (MALT) •Mucosal surfaces – loose/dense diffuse lymphoid tissue (occasional solitary lymph nodule) •Notable areas –colon, vermiform, appendix, ileum (PEYER’S PATCHES) •Entrance to lymphoid tissue – TONSILS •MALT consist of T-cell rich area (DIFFUSE LYMPHOID TISSUE) and B-cells-rich areas (LYMPHOID NODULES). •Numerous APC’s •Important: generating lymphocytes – immune response
- 19. SPLEEN RED & WHITE PULP
- 20. RED AND WHITE PULP OF SPLEEN
Editor's Notes
- The spleen contains the largest single accumulation of lymphoid tissue in the body and is the only lymphoid organ involved in filtration of blood, making it an important organ in defense against blood-borne antigens. It is also the main site of old erythrocyte destruction. As is true of other secondary lymphoid organs, the spleen is a production site of antibodies and activated lymphocytes, which here are delivered directly into the blood. located high in the left upper quadrant of the abdomen and typically about 12 × 7 × 3 cm in size, the spleen’s volume varies with its content of blood and tends to decrease very slowly after puberty.
- The organ is surrounded by a capsule of dense connective tissue from which emerge trabeculae to penetrate the parenchyma or splenic pulp
- Spleen is encased by a CAPSULE, a connective tissue that sends TRABECULAE into the substance of the organ to divide into incomplete compartments. The parenchyma of the spleen is referred to as splenic pulp. It consist of island of lymphoid tissue collectively called WHITE PULP surrounded by RED PULP. The pulps are made up of sinusoids that are separated by reticular tissue.
- This is a higher magnification photomicrograph of th spleen showing the capsule. Trabeculae, white pulp, red pulp, cenral arteries, and follicular artery.
- Consist of lymphoid nodules embedded in dense lymphoid tissue Dense lymphoid tissue- form sleeves around the arteries of the spleen from the time thesevessels branch off from the trabecular arteries to shortly before they break up into capillaries. The lymphoid nodule on the other hand are interspersed along the course of these atrial sleeves Comprises lymphocyte population, uniquely associated with blood vessels. Contains macrophages and dendritic cells (splenic dendritic cells)
- The splenic white pulp consists of lymphoid tissue surrounding the central arterioles as the PALS (Periarteriolar lymphoid sheaths (or periarterial lymphatic sheaths, or PALS) are a portion of the white pulp of the spleen. They are populated largely by T cells and surround central arteries within the spleen) and the nodules of proliferating B cells in this sheath. (a) Longitudinal section of white pulp (W) in a PALS surrounding a central arteriole (arrowhead). Surrounding the PALS is much red pulp (R).
- A large nodule with a germinal center forms in the PALS and the central arteriole (arrowhead) is displaced to the nodule’s periphery. Small vascular sinuses can be seen at the margin between white (W) and red (R) pulp. Both X20. H&E.
- RED PULP, is made up of sinusoidal capillaries called splenic sinusoids that are separated by strands of reticular tissue referred as SPLENIC CORDS OF BILLROTH. The splenic red pulp is composed entirely of sinusoids (S) and splenic cords (C), both of which contain blood cells of all types. The cords, often called cords of Billroth, are reticular tissue rich in macrophages and lymphocytes.
- Higher magnification shows that the sinusoids (S) are lined by endothelial cells (arrows) with large nuclei bulging into the sinusoidal lumens. The unusual endothelial cells are called stave cells and have special properties that allow separation of healthy from effete(no longer capable of effective action) red blood cells in the splenic cords (C). X200. H&E.
- Blood vessels of the spleen
- The arterial supply of the spleen comes from the tortuous splenic artery, which reaches the spleen as it travels through the splenorenal ligament. This artery emerges from the celiac trunk, which is a branch of the abdominal aorta. The venous drainage of the spleen occurs via the splenic vein, which also receives blood from the inferior mesenteric vein. Posterior to the neck of the pancreas, the splenic vein unites with the superior mesenteric vein to form the hepatic portal vein.
- As expected of an organ where the blood is monitored immunologically, the splenic microvasculature contains unique regions shown schematically in Figure 14–22. Branching from the hilum, small trabecular arteries leave the trabecular connective tissue and enter the parenchyma as arterioles enveloped by the PALS, which consists primarily of T cells with some macrophages, DCs, and plasma cells as part of the white pulp. Surrounded by the PALS, these vessels are known as central arterioles (Figure 14–23). B cells located within the PALS may be activated by a trapped antigen from the blood and form a temporary lymphoid nodule like those of other secondary lymphoid organs (Figure 14–23b). In growing nodules the arteriole is pushed to an eccentric position but is still called the central arteriole. These arterioles send capillaries throughout the white pulp and to small sinuses in a peripheral marginal zone of developing B cells around each lymphoid nodule (Figure 14–22).Each central arteriole eventually leaves the white pulp and enters the red pulp, losing its sheath of lymphocytes and branching as several short straight penicillar arterioles that continue as capillaries (Figure 14–22). Some of these capillaries are sheathed with APCs for additional immune surveillance of blood. The red pulp is composed almost entirely of splenic cords (of Billroth) and splenic sinusoids and is the site where effete RBCs in blood are removed (Figure 14–24). The splenic cords contain a network of reticular cells and fibers filled with T and B lymphocytes, macrophages, other leukocytes, and red blood cells. The splenic cords are separated by the sinusoids (Figure 14–25). Unusual elongated endothelial cells called stave cells line these sinusoids, oriented parallel to the blood flow and sparsely wrapped in reticular fibers and highly discontinuous basal lamina (Figure 14–26). Blood flow through the splenic red pulp can take either of two routes (Figure 14–22): ■■ In the closed circulation, capillaries branching from the penicillar arterioles connect directly to the sinusoids and the blood is always enclosed by endothelium. ■■ In the open circulation, capillaries from about half of the penicillar arterioles are uniquely open-ended, dumping blood into the stroma of the splenic cords. In this route plasma and all the formed elements of blood must reenter the vasculature by passing through narrow slits between the stave cells into the sinusoids. These small openings present no obstacle to platelets, to the motile leukocytes, or to thin flexible erythrocytes. However stiff or effete, swollen RBCs at their normal life span of 120 days are blocked from passing between the stave cells and undergo selective removal by macrophages (Figure 14–24).
- The spleen is surrounded by a dense connective tissue capsule (1) from which arise connective tissue trabeculae (3, 5, 11) that extend deep into the spleen’s interior. Th e main trabeculae enter the spleen at the hilus and extend throughout the organ. Located within the trabeculae (3, 5, 11) are trabecular arteries (5b) and trabecular veins (5a). Trabeculae that are cut in transverse section (11) appear round or nodular and may contain blood vessels. Th e spleen is characterized by numerous aggregations of lymphatic nodules (4, 6). Th ese nodules constitute the white pulp (4, 6) of the organ. Th e lymphatic nodules (4, 6) also contain germinal centers (8, 9) that decrease in number with age. Passing through each lymphatic nodule (4, 6) is a blood vessel called a central artery (2, 7, 10) that is located in the periphery of the lymphatic nodules (4, 6). Central arteries (2, 7, 10) are branches of trabecular arteries (5b) that become ensheathed with lymphatic tissue as they leave the connective tissue trabeculae (3, 5, 11). Th is periarterial lymphatic sheath also forms the lymphatic nodules (4, 6) that constitute the white pulp (4, 6) of the spleen. Surrounding the lymphatic nodules (4, 6) and intermeshed with the connective tissue trabeculae (3, 5, 11) is a diff use cellular meshwork that makes up the bulk of the organ. Th is meshwork collectively forms the red or splenic pulp (12, 13). In fresh preparations, red pulp is red because of its extensive vascular tissue. Th e red pulp (12, 13) also contains pulp arteries (14), venous sinuses (13), and splenic cords (of Billroth) (12). Th e splenic cords (12) appear as diff use strands of lymphatic tissue between the venous sinuses (13) and form a spongy meshwork of reticular connective tissue, usually obscured by the density of other tissue. Th e spleen does not exhibit a distinct cortex and a medulla, as seen in lymph nodes. However, lymphatic nodules (4, 6) are found throughout the spleen. In addition, the spleen contains venous sinuses (13), in contrast to lymphatic sinuses that are found in the lymph nodes. Th e spleen also does not exhibit subcapsular or trabecular sinuses. Th e capsule (1) and trabeculae (3, 5, 11) in the spleen are thicker than those around the lymph nodes and contain some smooth muscle cells.
- A higher magnifi cation of a section of the spleen illustrates the red and white pulp and associated connective tissue trabeculae, blood vessels, venous sinuses, and splenic cords. Th e large lymphatic nodule (3) represents the white pulp of the spleen. Each nodule normally exhibits a peripheral zone—the periarterial lymphatic sheath—with densely packed small lymphocytes. Th e central artery (4) in the lymphatic nodule (3) has a peripheral, or an eccentric, position. Because the artery occupies the center of the periarterial lymphatic sheath, it is called the central artery. Th e cells found in the periarterial lymphatic sheath are mainly T cells. A germinal center (5) may not always be present. In the more lightly stained germinal center (5) are found B cells, many medium-sized lymphocytes, some small lymphocytes, and lymphoblasts. Th e red pulp contains the splenic cords (of Billroth) (1, 8) and venous sinuses (2, 9) that course between the cords. Th e splenic cords (1, 8) are thin aggregations of lymphatic tissue containing small lymphocytes, associated cells, and various blood cells. Venous sinuses (2, 9) are dilated vessels lined with the modifi ed endothelium of elongated cells that appear cuboidal in transverse sections. Also present in the red pulp are the pulp arteries (10). Th ese represent the branches of the central artery (4) aft er it leaves the lymphatic nodule (3). Capillaries and pulp veins (venules) are also present. Connective tissue trabeculae with a trabecular artery (6) and trabecular vein (7) are evident. Th ese vessels have endothelial tunica intima and muscular tunica media. Th e tunica adventitia is not apparent, because the connective tissue of the trabeculae surrounds the tunica media.
- A low-magnifi cation photomicrograph illustrates a section of the spleen. A dense irregular connective tissue capsule (1) covers the organ. From the capsule (1), connective tissue trabeculae (3) with blood vessels extend into the interior of the organ. Th e spleen is composed of white pulp and red pulp. White pulp (2) consists of lymphocytes and aggregations of lymphatic nodules (2a). Within the lymphatic nodule (2a) are found the germinal center (2b) and a central artery (2c) that is located off -center. Surrounding the white pulp lymphatic nodules (2) is the red pulp (4). It is primarily composed of venous sinuses (4a) and splenic cords (4b).