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| ==Introduction== | | ==Introduction== |
− | The spleen is a major lymphoid and blood filtration organ and is located in the left cranial abdomen. It is responsible for storing and removing [[Erythrocytes - WikiBlood|erythrocytes]] from the blood as well as antigen surveillance of the blood and antibody production. | + | The spleen is a major lymphoid and blood filtration organ and is located in the left cranial abdomen. It is responsible for storing and removing [[Erythrocytes|erythrocytes]] from the blood as well as antigen surveillance of the blood and antibody production. |
| ==Development== | | ==Development== |
| <p>The spleen develops in association with the digestive system in the dorsal mesogastrium, and as the [[Forestomach - Anatomy & Physiology|stomach]] rotates during development the spleen comes to occupy the left cranial abdomen. Haematopoietic cells in the spleen are derived from the AGM (aorta-gonad-mesonephros) and yolk sac and as the [[Primary Lymphoid Tissue - Anatomy & Physiology|primary lymphoid organs]] become established it becomes populated with [[Lymphocytes#Types|T and B lymphocytes]].</p> | | <p>The spleen develops in association with the digestive system in the dorsal mesogastrium, and as the [[Forestomach - Anatomy & Physiology|stomach]] rotates during development the spleen comes to occupy the left cranial abdomen. Haematopoietic cells in the spleen are derived from the AGM (aorta-gonad-mesonephros) and yolk sac and as the [[Primary Lymphoid Tissue - Anatomy & Physiology|primary lymphoid organs]] become established it becomes populated with [[Lymphocytes#Types|T and B lymphocytes]].</p> |
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| <p> The parenchyma is supported by a fine mesh of reticular fibres and is divided into two types of tissue, the red and the white pulp, which are separated by the marginal sinus.</p> | | <p> The parenchyma is supported by a fine mesh of reticular fibres and is divided into two types of tissue, the red and the white pulp, which are separated by the marginal sinus.</p> |
| ===Red Pulp=== | | ===Red Pulp=== |
− | <p>The red pulp makes up the majority of the spleen and is composed of a network of cell cords in series with vascular sinuses. The splenic cords contain [[Macrophages|macrophages]], [[B cell differentiation - WikiBlood#Plasma cells|plasma cells]], [[Lymphocytes|lymphocytes]] and other mature blood cells e.g. [[Granulocyte - WikiBlood|granulocytes]] and [[Erythrocytes - WikiBlood|erythrocytes]]. While the vascular sinuses are wide vascular channels lined with endothelial cells. Blood cells and fluid can pass into the splenic cords through fenestrations in the sinus walls. </p> | + | <p>The red pulp makes up the majority of the spleen and is composed of a network of cell cords in series with vascular sinuses. The splenic cords contain [[Macrophages|macrophages]], [[B cell differentiation - WikiBlood#Plasma cells|plasma cells]], [[Lymphocytes|lymphocytes]] and other mature blood cells e.g. [[Granulocyte - WikiBlood|granulocytes]] and [[Erythrocytes|erythrocytes]]. While the vascular sinuses are wide vascular channels lined with endothelial cells. Blood cells and fluid can pass into the splenic cords through fenestrations in the sinus walls. </p> |
| ===White Pulp=== | | ===White Pulp=== |
| <p>White pulp is organised in relation to the splenic arterioles and consists of discrete lymphoid tissue surrounding a central arteriole. There is a sheath of [[Lymphocytes#T cells|T cells]] directly around the arteriole, the periarteriolar lymphoid sheath (PALS), which is surrounded by a marginal sinus, and then a zone of [[Lymphocytes#B cells|B cells]] and [[Macrophages|macrophages]] (the marginal zone). B cell follicles are associated with the marginal zone and expand and develop germinal centres after antigen activation. The marginal sinuses are linked to the red pulp sinuses. </p><p>White pulp stains basophilic in a H&E stain</p> | | <p>White pulp is organised in relation to the splenic arterioles and consists of discrete lymphoid tissue surrounding a central arteriole. There is a sheath of [[Lymphocytes#T cells|T cells]] directly around the arteriole, the periarteriolar lymphoid sheath (PALS), which is surrounded by a marginal sinus, and then a zone of [[Lymphocytes#B cells|B cells]] and [[Macrophages|macrophages]] (the marginal zone). B cell follicles are associated with the marginal zone and expand and develop germinal centres after antigen activation. The marginal sinuses are linked to the red pulp sinuses. </p><p>White pulp stains basophilic in a H&E stain</p> |
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| ==Functions== | | ==Functions== |
| <p>The spleen has a number of functions: | | <p>The spleen has a number of functions: |
− | *It filters the blood removing ageing [[Erythrocytes - WikiBlood|erythrocytes]] and antigens | + | *It filters the blood removing ageing [[Erythrocytes|erythrocytes]] and antigens |
− | *It stores [[Erythrocytes - WikiBlood|erythrocytes]] and [[Thrombocytes|platelets]] | + | *It stores [[Erythrocytes|erythrocytes]] and [[Thrombocytes|platelets]] |
| *[[Secondary Lymphoid Tissue - Anatomy & Physiology|Secondary lymphoid organ]]</p> | | *[[Secondary Lymphoid Tissue - Anatomy & Physiology|Secondary lymphoid organ]]</p> |
| ===Erythrocytes & Platelets=== | | ===Erythrocytes & Platelets=== |
− | <p>In the foetus the spleen also has a role in [[Overview of Haematopoiesis - WikiBlood|haematopoiesis]] when it becomes the main [[Erythrocytes - WikiBlood|erythrocyte]] producing organ during the haematopoietic transitional phase.</p> | + | <p>In the foetus the spleen also has a role in [[Overview of Haematopoiesis - WikiBlood|haematopoiesis]] when it becomes the main [[Erythrocytes|erythrocyte]] producing organ during the haematopoietic transitional phase.</p> |
− | <p>In the developed animal the red pulp is involved in the removal of aged, damaged or abnormal [[Erythrocytes - WikiBlood|erythrocytes]] (along with the [[Liver - Anatomy & Physiology|liver]] and [[Bone Marrow - Anatomy & Physiology|bone marrow]]). As [[Erythrocytes - WikiBlood|erythrocytes]] age they become less supple and this causes them to become damaged when they pass through the very narrow capillaries of the spleen, after which they are phagocytised by splenic [[Macrophages|macrophages]]. If a splenectomy is performed the number of aged [[Erythrocytes - WikiBlood|erythrocytes]] in circulation increases.</p> | + | <p>In the developed animal the red pulp is involved in the removal of aged, damaged or abnormal [[Erythrocytes|erythrocytes]] (along with the [[Liver - Anatomy & Physiology|liver]] and [[Bone Marrow - Anatomy & Physiology|bone marrow]]). As [[Erythrocytes|erythrocytes]] age they become less supple and this causes them to become damaged when they pass through the very narrow capillaries of the spleen, after which they are phagocytised by splenic [[Macrophages|macrophages]]. If a splenectomy is performed the number of aged [[Erythrocytes|erythrocytes]] in circulation increases.</p> |
− | <p> The red pulp also acts as a storage site for [[Erythrocytes - WikiBlood|erythrocytes]]. The degree of storage is variable between species but is particularly notable in horses which, during exercise under sympathetic activity, can contract their spleen to increase the concentration of circulating [[Erythrocytes - WikiBlood|erythrocytes]]. In some species such as cats and rodents the red pulp acts as a storage site for [[Thrombocytes|platelets]] and contains [[Thrombopoiesis - WikiBlood#Megakaryocyte|megakaryocytes]].</p> | + | <p> The red pulp also acts as a storage site for [[Erythrocytes|erythrocytes]]. The degree of storage is variable between species but is particularly notable in horses which, during exercise under sympathetic activity, can contract their spleen to increase the concentration of circulating [[Erythrocytes|erythrocytes]]. In some species such as cats and rodents the red pulp acts as a storage site for [[Thrombocytes|platelets]] and contains [[Thrombopoiesis - WikiBlood#Megakaryocyte|megakaryocytes]].</p> |
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| ===Lymphoid=== | | ===Lymphoid=== |