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<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 T-cells directly around the arteriole, the periarteriolar lymphoid sheath (PALS), which is surrounded by a marginal sinus, and then a zone of B-cells and 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 is organised in relation to the splenic arterioles and consists of discrete lymphoid tissue surrounding a central arteriole. There is a sheath of T-cells directly around the arteriole, the periarteriolar lymphoid sheath (PALS), which is surrounded by a marginal sinus, and then a zone of B-cells and 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>
====Species Differences====
====Species Differences====
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<p>The capsule and trabeculae are much more muscular in carnivores than ruminants</p>
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<p>The capsule and trabeculae are much more muscular in carnivores and horses than ruminants</p>
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*Carnivores
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**Is elongated and dumb bell shaped (larger ventrally)
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*Ruminants
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**Is flat and oblong shaped
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*Horses
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**Lies under the last three ribs. Dorsally it is broad but narrows as it extends cranially and ventrally
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*Pigs
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**Elongated and strap like under the last few ribs
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*Birds
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**Lies alongside, to the right, of the proventriculus and is found caudaodorsally to the liver
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**Spherical in chickens, triangular in ducks & oval in pigeons
===Vasculature===
===Vasculature===