Changes

<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 erythrocytes and platelets

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

*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 haematopoiesis when it becomes the main erythrocyte producing organ during the hematopoietic transitional phase.</p>

<p>In the foetus the spleen also has a role in [[Haematopoiesis - Anatomy & Physiology|haematopoiesis]] when it becomes the main [[Erythrocyte - Anatomy & Physiology|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 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. If a splenectomy is performed the number of aged 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 [[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> The red pulp also acts as a storage site for 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. In some species such as cats and rodents the red pulp acts as a storage site for platelets and contains megakaryocytes.</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>

===Lymphoid===

===Lymphoid===

<p>Blood flows through the marginal sinus meaning that most antigens present in the blood come into contact with the B cells 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 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>

<p>Following splenectomy this doesn’t occur and animals are predisposed to septicaemia and infection with blood protozoa.</p>

<p>Following splenectomy this doesn’t occur and animals are predisposed to septicaemia and infection with blood [[Protozoa|protozoa]].</p>

 

==In pathology==

==In pathology==

[[Lymphoreticular/Haemotopoietic System - Spleen|See here]]

[[Lymphoreticular/Haemotopoietic System - Spleen|See here]]