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<p>The spleen lies vertically on the left side of the cranial abdomen. It is attached to the greater curvature of the stomach by the greater omentum. The spleen is covered in a enclosed in a capsule of fibrous and elastic tissue that extends into the parenchyma as trabeculae.  </p>

<p>The spleen lies vertically on the left side of the cranial abdomen. It is attached to the greater curvature of the [[Alimentary - Anatomy & Physiology#Stomach|stomach]] by the gastrosplenic ligament. The spleen is covered in a enclosed in a capsule of fibrous and elastic tissue that extends into the parenchyma as trabeculae.  </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>

<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, plasma cells, lymphocytes and other mature blood cells e.g. granulocytes and 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 - Anatomy & Physiology|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>

===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>

**Is flat and oblong shaped

**Is flat and oblong shaped

*Horses

*Horses

**Lies under the last three ribs. Dorsally it is broad but narrows as it extends cranially and ventrally

**Lies under the last three [[Ribs and Sternum: Anatomy and Physiology|ribs]]. Dorsally it is broad but narrows as it extends cranially and ventrally

**On rectal palpation it is loacted against the body wall and feels smooth with a sharp border

**On rectal palpation it is loacted against the body wall and feels smooth with a sharp border

*Pigs

*Pigs

**Elongated and strap like under the last few ribs

**Elongated and strap like under the last few [[Ribs and Sternum: Anatomy and Physiology|ribs]]

*Birds

*Birds

**Lies alongside, to the right, of the [[The Proventriculus - Anatomy & Physiology|proventriculus]] and is found caudaodorsally to the liver

**Lies alongside, to the right, of the [[The Proventriculus - Anatomy & Physiology|proventriculus]] and is found caudaodorsally to the [[Avian Liver - Anatomy & Physiology|liver]]

**Spherical in chickens, triangular in ducks & oval in pigeons

**Spherical in chickens, triangular in ducks & oval in pigeons