Structure and function of Spleen
- 2. Spleen • Lymphatic organ connected to blood vascular system • Part of mononuclear phagocyte system. • Wedge shaped
- 3. Spleen • situated principally in the left hypochondriac region, but its superior extremity extends into the epigastric region
- 4. • it lies between the fundus of the stomach and the diaphragm. • the largest of the ductless glands, and is of an oblong, flattened form, soft, of very friable consistence, highly vascular, and of a dark purplish color.
- 5. • 1" (2.5 cm) by 3“(7.5cm) by 5“(12.5cm) • 150 grams (5.3 oz) to 200 grams (7.1 oz) • lies between the 9th and 11th ribs on the left hand side.
- 7. Development • Appears about the fifth week • It arises in a series of hillocks, of the mesoderm in the dorsal mesogastrium above the tail of pancreas. • With the change in position of the stomach the spleen is carried to the left, and comes to lie behind the stomach and in contact with the left kidney. • The part of the dorsal mesogastrium between the spleen and the greater curvature of the stomach forms the gastrosplenic ligament.
- 8. • When the hillocks fail to unify • 20% of persons. • especially in the gastrolienal ligament and greater omentum, • vary in size from that of a pea to that of a plum.
- 9. Relations Diaphragmatic surface (external or phrenic surface) • convex, smooth • Relation -under surface of the diaphragm, which separates it from the ninth, tenth, and eleventh ribs of the left side, and the intervening costodiaphragmatic recess
- 10. Visceral surface divided by a ridge Gastric surface • broad and concave • is in contact with the posterior wall of the stomach; and below this with the tail of the pancreas. • It presents near its medial border a long fissure, termed the hilum. This is pierced by several irregular apertures, for the entrance and exit of vessels and nerves.
- 11. Renal surface • somewhat flattened, is considerably narrower than the gastric surface • upper part of the anterior surface of the left kidney and occasionally left suprarenal gland.
- 12. Colic surface • flat, triangular in shape, and rests upon the left flexure of the colon and the phrenicocolic ligament, and is generally in contact with the tail of the pancreas.
- 14. • anterior border -is free, sharp, and thin, and is often notched, especially below • posterior border- more rounded and blunter than the anterior, corresponds to the lower border of the eleventh rib and lies between the diaphragm and left kidney. • The intermediate margin is the ridge which separates the renal and gastric surfaces. • inferior border- rounded
- 15. Peritoneal relations • Gastrosplenic ligament : • from the hilum of the spleen to the greater curvature of the stomach; it contains short gastric vessels and associated lymphatics and sympathetic nerves. • Splenorenal ligament : from the hilum of the spleen to the anterior surface of the left kidney; it contains the tail of the pancreas and splenic vessels,ln • Phrenicocolic ligament :from the splenic flexure of the colon to the diaphragm along the midaxillary line
- 16. Structure External or serous coat (tunica serosa) • from the peritoneum • thin, smooth, and intimately adherent to the fibroelastic coat. It invests the entire organ, except at the hilum and along the lines of reflection of the phrenicolienal and gastrolienal ligaments. Fibroelastic coat (tunica albuginea) invests the organ, and at the hilum is reflected inward upon the vessels in the form of sheaths. From these sheaths, as well as from the inner surface of the fibroelastic coat, numerous small fibrous bands, trabeculae are given off in all directions
- 17. • The fibroelastic coat, the sheaths of the vessels, and the trabeculæ, are composed of white and yellow elastic fibrous tissues • spleen possesses a considerable amount of elasticity, which allows of the very great variations in size • small amount of non- striped muscular fiber The spleen consists of a number of small spaces, formed by the trabeculæ which contain the splenic pulp.
- 19. • The spleen is made of red pulp and white pulp, separated by the marginal zone; 76- 79% of a normal spleen is red pulp
- 20. red pulp • Red blood–filled sinusoids and reticuloendothelial cell– lined cords of Billroth (connective tissue ) • Splenic cords -reticular fibers, reticular cells, and associated macrophages Sinusoids • wide vessels that drain into trabecular veins. • Gaps in the endothelium lining the sinusoids mechanically filter blood cells as they enter the spleen.
- 21. Venous sinuses →a lining of endothelial cells that are positioned in parallel and connected by stress fibres to annular fibres, Contractility of the stress fibres allows the formation of slits between the endothelial cells, regulating the passage of blood Worn-out or abnormal red cells attempting to squeeze become damaged, and are devoured by macrophages
- 22. • Splenic cells-Large rounded cells, ameboid movement, often contain pigment and red-blood corpuscles in their interior. • Cells of the reticulum may contain pigment granules in their cytoplasm •B and T lymphocytes •Erythrocytes • granulocytes •plasma cells •hematopoietic cells •plasmablasts that migrate from the follicles and the outer PALS after antigen specific differentiation •macrophages
- 24. • white lymphoid follicles arrayed within the red pulp matrix • Contains lymphocytes and macrophages, dendritic cells, plasma cells, arterioles, and capillaries in reticular connective tissue meshwork Periarterial lymphatic sheaths (PALS)-Lymphatic tissue sheath that surrounds central artery • Most of the T cells are CD4+
- 26. Malpighian bodies, splenic lymphoid nodules: • hemispherical accumulations of B lymphocytes attached to the PALS at intervals. • 0.25 mm. to 1 mm. in diameter Secondary follicles •Follicles with a germinal centre •arise when antigen specific B- cell immune reactions occur in the spleen •existence is of limited duration. •attached to the smaller ramifications of the splenic artery.
- 27. Germinal centre • Antigen specific larger B cells • pale-staining nuclei and abundant cytoplasm Mantle zone or corona. • The expanding germinal centre displaces the small, dark recirculating B lymphocytes to the periphery of the follicle Marginal Zone • broad region primarily occupied by relatively large memory B cells. • light impression after routine staining • delimited from the PALS and the follicles by a very irregular capillary blood vessel called the marginal sinus.
- 28. • white pulp of the spleen is seen in a lymphoid follicle, outlined by the dashed line found. The lymphoid follicle has a pale-staining germinal center (GC) in which B cells are proliferating. mantle zone (ManZ) contains small lymphocytes and an outer marginal zone that contains larger lymphocytes that are less densely packed than cells in the mantle zone.
- 30. Blood supply Blood flow is about 150 mL/min Splenic A. • large size in proportion to the size of the organ • tortuous course
- 31. •Passes through leinorenal ligament to reach the hilum where it divides into six or more branches •receive sheaths the external fibrous tissue •branches into numerous arterioles
- 32. • When arterioles acquire a coating of T cells, they are called central arteries and the surrounding lymphoid tissue is called the PALS, i.e., the periarteriolar lymphoid sheath.
- 34. • The arterioles end by opening freely into the splenic pulp; their walls become much attenuated, they lose their tubular character, and the endothelial cells become altered, presenting a branched appearance, and acquiring processes which are directly connected with the processes of the reticular cells of the pulp •
- 37. The spleen comprises many units of red and white pulp centered around small branches of the splenic artery, called central arteries. White pulp is lymphoid in nature and contains B cell follicles, a marginal zone around the follicles, and T cell–rich areas sheathing arterioles. The red pulp areas include pulp sinuses and pulp cords. The cords are dead ends. In order to regain access to the circulation, red blood cells must traverse tiny openings in the sinusoidal lining. Stiff, damaged, or old red cells cannot enter the sinuses.
- 38. Pitting Red cell–inclusion bodies such as parasites ,nuclear residua (Howell-Jolly bodies), or denatured hemoglobin (Heinz bodies) are pinched off in the process of passing through the slits The culling of dead and damaged cells and the pitting of cells with inclusions appear to occur without significant delay because the blood transit time through the spleen is only slightly slower than in other organs
- 40. Splenic vein and tributaries
- 41. Open circulation
- 43. Nerve supply • Sympathetic fibres derived from the celiac plexus • They are distributed to the blood vessels and to the smooth muscle of the capsule and trabeculae.
- 44. Lymphatic vessels • Splenic tissue proper has no lymphatics • Lymphatics from connective tissue drain into pancreaticosplenic lymph nodes along splenic artery
- 45. • Red pulp- Mechanical filtration of red blood cells. • white pulp -Active immune response through humoral and cell-mediated pathways. • Production of opsonins, properdin, and tuftsin.
- 47. Storage • contains approximately one-third of the total body platelets and a significant number of marginated neutrophils. • sequestered cells are available when needed to respond to bleeding or infection. • the normal human spleen does not sequester or store red blood cells
- 48. Removal of Red Blood Cells • Removes senescent and defective red blood cells • through a unique organization of its parenchyma and vasculature • After normal lifespan RBC will be broken down and some parts recycled. •Removes all abnormal red blood cells.
- 49. • The removal of antibody-coated bacteria and antibody-coated blood cells from the circulation. Phagocytes: 1. Reticular cells and free macrophages of red pulp 2. Modified reticular cells of ellipsoid 3. Free macrophages and endothelial cells of venous sinusoids 4. Surface reticular cells of lymphatic follicle
- 50. • (1) clearance of bacteria and particulates from the blood • (2) the generation of immune responses to certain pathogens • (3) the generation of cellular components of the blood under circumstances in which the marrow is unable to meet the needs (i.e., extramedullary hematopoiesis).
Editor's Notes
- #7: Obliquely along 10 rib, directed downwards, forwards and lat 45 with horizntl plane Medial end 4-5 cm from midline and lat at midax line
- #8: The mesenchymal cells differentiate into the parenchymal cells, connective tissue and the surface capsule. The spleen functions as a hematopoietic center until late fetal life. 1. Liver 2. Stomach 3. Spleen 4. Pancreas 5. Adrenal gland 6. Aorta 7. Dorsal mesogastrium 8. Omental bursa 9. Falciform ligament 10. Lesser omentum 1. Liver 2. Stomach 3. Spleen 4. Pancreas 5. Adrenal gland 6. Aorta 7. Lesser omentum 8. Lienorenal ligament 9. Gastrolienal ligament 10. Falciform ligament 11. Parietal peritoneum
- #9: lien accessorius/supernumerary Broad lig, spermatic cord
- #10: , and is directed upward, backward, and to the left, except at its upper end, where it is directed slightly medially.
- #11: directed forward, upward, and medially
- #12: directed medialward and downward
- #13: superior extremity directed toward the vertebral column, where it lies on a level with the eleventh thoracic vertebra.
- #15: Sup, inf, intermed bor, post ant ends; it separates the diaphragmatic from the gastric surface. separates the renal from the diaphragmatic surface; separates the diaphragmatic from the colic surface.
- #18: or areolae More yellow
- #21: The spleen is in the portal circulation. The reason for this is unknown but may relate to the fact that lower blood pressure allows less rapid flow and minimizes damage to normal erythrocytes The reticular cells are considered to be myofibroblasts and may play a role in splenic contraction Cords-consisting of fibrils and connective tissue cells with a large population of monocytes and macrophages
- #22: Schema of a venous sinus located in the cords of the red pulp. Blood from the cords collects in the sinuses (shown by arrows). The venous sinuses consist of a lining of endothelial cells that are positioned in parallel and connected by stress fibres to annular fibres, which are composed of extracellular-matrix components. The stress fibres run along the long axis of the endothelial cells and are most prominent where the endothelial cells are in contact. Contractility of the stress fibres allows the formation of slits between the endothelial cells, thereby regulating the passage of blood and blood cells from the red-pulp cords into the sinuses and back into the venous system. Because the red-pulp cords contain a large number of macrophages, ageing erythrocytes that are no longer able to pass through the slits are phagocytosed.
- #23: Cells of reticulum do not stain deeply with carmine, and in this respect differ from the cells of the Malpighian corpuscles.
- #28: Germinal centre Bcells are surface IgD2, while mantle zone B cells coexpress IgM and IgD.
- #31: 1,200 to 1,400 mL/min (~ in liver
- #33: The splenic artery enters the spleen at the hilus, then that run through the parenchyma or pulp of the spleen.
- #36: Superi or and inferior vascular segments sep by avascular plane Ellip-localised thickening, marcophagal lymphoid sheaths
- #38: RE, reticuloendthelial. Smaller penicillary arteries branch off of the central arteries and end in sheathed capillaries that are special capillaries which actually have no endothelial cells and end blindly. These unique capillaries are surrounded by macrophages which serve to filter materials from the blood. After the blood flows through these sheathed capillaries, it flows into a complicated system of sinuses that drain into larger and larger sinuses which eventually drain into the splenic vein
- #39: liver—about 1.4 l (about 3 pt) every minute
- #41: Formed at hilum, straight course behind pancreas Joins sup mes v to form portal v
- #42: Trabecular veins Trabecular arteries Pulp veins Penicillar arterioles Follicle with follicle capillaries Artery with periarterial lymphatic sheath (PALS) 7 8 9 10 Splenic sinus Reticular fibrous framework Open capillaries Closed capillaries
- #44: chiefly non-medullated.
- #45: All the efferents pass into the intestinal lymph trunks, which then enter the cisterna chyli or the abdominal confluence of lymph trunks.
- #46: Tuftsin binds to specific receptors on the surface of macrophages and polymorphonuclear leukocytes, stimulating their migration, phagocytic, bactericidal, and tumoricidal activity. It also influences antibody formation. Opsonin-molecules that act as a binding enhancer for the process of phagocytosis, especially antibodies, which coat the negatively-charged molecules on the membrane. Molecules that activate the complement system are also considered opsonins. Properdin-It plays a part in tissue inflammation as well as the engulfing of pathogens by phagocytes. In addition it is known to help to neutralize some viruses. As a component of the alternative pathway for complement activation (otherwise known as the "properdin pathway"), it complexes with another protein, C3b, to stabilize the alternative C3 convertase (C3bBb) that then cleaves more C3.
- #48: The red blood cells can be released when needed. In humans, up to a cup (236.5 ml) of red blood cells can be held in the spleen and released in cases of hypovolemia. It can store platelets in case of an emergency. Up to a quarter of lymphocytes can be stored in the spleen at any one time In some animals, the spleen also serves a role in the vascular adaptation to stress because it stores red blood cells (often hemoconcentrated to higher hematocrits than normal) under normal circumstances and contracts under the influence of -adrenergic stimulation to provide the animal with an autotransfusion and improved oxygen-carrying capacity.
- #52: Nixon,castell,traube, middleton