Changes

<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. The red and white pulp 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. The red and white pulp 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 - Anatomy & Physiology|macrophages]], [[B cell differentiation- Anatomy & Physiology#Plasma cells|plasma cells]], [[Lymphocytes - Anatomy & Physiology|lymphocytes]] and other mature blood cells e.g. [[Granulocyte - WikiBlood|granulocytes]] and [[Erythrocyte - Anatomy & Physiology|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 - Anatomy & Physiology|macrophages]], [[B cell differentiation- Anatomy & Physiology#Plasma cells|plasma cells]], [[Lymphocytes - Anatomy & Physiology|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>

===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 - Anatomy & Physiology#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 - Anatomy & Physiology#B cells|B cells]] and [[Macrophages - Anatomy & Physiology|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 basophilc 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 - Anatomy & Physiology#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 - Anatomy & Physiology#B cells|B cells]] and [[Macrophages - Anatomy & Physiology|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 basophilc in a H&E stain</p>

<p>The spleen has a number of functions:

<p>The spleen has a number of functions:

*It filters the blood removing ageing erythrocytes and antigens

*It filters the blood removing ageing erythrocytes and antigens

*It stores [[Erythrocyte - Anatomy & Physiology|erythrocytes]] and [[Thrombocytes - Anatomy & Physiology|platelets]]

*It stores [[Erythrocytes - WikiBlood|erythrocytes]] and [[Thrombocytes - Anatomy & Physiology|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 [[Erythrocyte - Anatomy & Physiology|erythrocyte]] producing organ during the hematopoietic 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 - WikiBlood|erythrocyte]] producing organ during the hematopoietic transitional phase.</p>

<p>In the developed animal the red pulp is involved in the removal of aged, damaged or abnormal erythrocytes (along with the liver and bone marrow). As [[Erythrocyte - Anatomy & Physiology|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 - Anatomy & Physiology|macrophages]]. If a splenectomy is performed the number of aged [[Erythrocyte - Anatomy & Physiology|erythrocytes]] in circulation increases.</p>

<p>In the developed animal the red pulp is involved in the removal of aged, damaged or abnormal erythrocytes (along with the liver and 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 - Anatomy & Physiology|macrophages]]. If a splenectomy is performed the number of aged [[Erythrocytes - WikiBlood|erythrocytes]] in circulation increases.</p>

<p> The red pulp also acts as a storage site for [[Erythrocyte - Anatomy & Physiology|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 [[Erythrocyte - Anatomy & Physiology|erythrocytes]]. In some species such as cats and rodents the red pulp acts as a storage site for [[Thrombocytes - Anatomy & Physiology|platelets]] and contains [[Thrombopoiesis - Anatomy & Physiology#Megakaryocyte|megakaryocytes]].</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 - Anatomy & Physiology|platelets]] and contains [[Thrombopoiesis - Anatomy & Physiology#Megakaryocyte|megakaryocytes]].</p>

===Lymphoid===

===Lymphoid===

<p>Blood flows through the marginal sinus meaning that most antigens present in the blood come into contact with the [[Lymphocytes - Anatomy & Physiology#B cells|B lymphocytes]] and dendritic cells in the spleen. Dendritic cells in the marginal sinus and red pulp take up antigens from the blood and transport them to the primary follicles in the white pulp. If the antigen activates the [[Lymphocytes - Anatomy & Physiology#B cells|B lymphocytes]] then a germinal centre will form in the primary follicle and this is called a splenic nodule. Antibody producing cells then migrate to the red pulp and marginal zone.</p>

<p>Blood flows through the marginal sinus meaning that most antigens present in the blood come into contact with the [[Lymphocytes - Anatomy & Physiology#B cells|B lymphocytes]] and dendritic cells in the spleen. Dendritic cells in the marginal sinus and red pulp take up antigens from the blood and transport them to the primary follicles in the white pulp. If the antigen activates the [[Lymphocytes - Anatomy & Physiology#B cells|B lymphocytes]] then a germinal centre will form in the primary follicle and this is called a splenic nodule. Antibody producing cells then migrate to the red pulp and marginal zone.</p>