Changes

==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 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 - WikiBlood|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 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 organs become established it becomes populated with 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 - WikiBlood#Types|T and B lymphocytes]].</p>

==Structure==

==Structure==

{|align="right"

{|align="right"

*Terminate with open ends in the splenic cords

*Terminate with open ends in the splenic cords

Blood released into the splenic cords, either from the sinuses or capillaries eventually filters back into the sinus network. The sinuses converge and empty into trabecular veins, which then merge into a single splenic vein which then empties into the portal vein.</p>

Blood released into the splenic cords, either from the sinuses or capillaries eventually filters back into the sinus network. The sinuses converge and empty into trabecular veins, which then merge into a single splenic vein which then empties into the portal vein.</p>

<p>Lymphocytes in the arterial blood migrate from the red pulp sinuses, through the splenic cords and through the white pulp. T cells specifically migrate through the PALS and B cells specifically migrate through the follicles. Antigen in the blood is filtered by the large numbers of macrophages in the splenic cords and white pulp.</p>

<p>[[Lymphocytes - WikiBlood|Lymphocytes]] in the arterial blood migrate from the red pulp sinuses, through the splenic cords and through the white pulp. [[Lymphocytes - WikiBlood#T cells|T cells]] specifically migrate through the PALS and [[Lymphocytes - WikiBlood#B cells|B cells]] specifically migrate through the follicles. Antigen in the blood is filtered by the large numbers of [[Macrophages - WikiBlood|macrophages]] in the splenic cords and white pulp.</p>

====Species Differences====

====Species Differences====

<p>The splenic artery:

<p>The splenic artery:

==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 and antigens

*It filters the blood removing ageing [[Erythrocytes - WikiBlood|erythrocytes]] and antigens

*It stores [[Erythrocytes - WikiBlood|erythrocytes]] and [[Thrombocytes - WikiBlood|platelets]]

*It stores [[Erythrocytes - WikiBlood|erythrocytes]] and [[Thrombocytes - WikiBlood|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 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 [[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 - WikiBlood|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 - 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 - WikiBlood|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 [[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 - WikiBlood|platelets]] and contains [[Thrombopoiesis - WikiBlood#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 - WikiBlood|platelets]] and contains [[Thrombopoiesis - WikiBlood#Megakaryocyte|megakaryocytes]].</p>

===Lymphoid===

===Lymphoid===