Difference between revisions of "Spleen - Anatomy & Physiology"
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| − | + | {{toplink | |
| − | { | + | |backcolour = f5fffa |
| − | + | |linkpage =Lymphoreticular & Haematopoietic System - Anatomy & Physiology | |
| − | { | + | |linktext =LYMPHORETICULAR & HAEMATOPOIETIC SYSTEM (Ant & Phys) |
| − | | | + | |tablelink = Lymphoreticular & Haematopoietic System (Table)- Anatomy & Physiology |
| − | + | |conceptlink = Lymphoreticular & Haematopoietic System (Concept Map)- Anatomy & Physiology | |
| − | | | + | |sublink1 =Secondary Lymphoid Tissue - Anatomy & Physiology |
| − | + | |subtext1 =SECONDARY LYMPHOID TISSUE (Ant & Phys) | |
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==Development== | ==Development== | ||
| − | <p>The spleen develops in association with the digestive system in the dorsal mesogastrium, and as the | + | <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> |
==Structure== | ==Structure== | ||
| − | + | <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 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> | |
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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 | ||
| − | <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 | ||
===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 | + | <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> |
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===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 | + | <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 and horses than ruminants</p> | <p>The capsule and trabeculae are much more muscular in carnivores and horses than ruminants</p> | ||
*Carnivores | *Carnivores | ||
| − | **Is elongated and dumb | + | **Is elongated and dumb bell shaped (larger ventrally) |
*Ruminants | *Ruminants | ||
**Is flat and oblong shaped | **Is flat and oblong shaped | ||
*Horses | *Horses | ||
| − | **Lies under the last three | + | **Lies under the last three ribs. Dorsally it is broad but narrows as it extends cranially and ventrally |
| − | **On rectal palpation it is | + | **On rectal palpation it is loacted against the body wall and feels smooth with a sharp border |
*Pigs | *Pigs | ||
| − | **Elongated and strap | + | **Elongated and strap like under the last few ribs |
| − | *Birds | + | *Birds |
| − | **Lies alongside, to the right, of the | + | **Lies alongside, to the right, of the proventriculus and is found caudaodorsally to the liver |
**Spherical in chickens, triangular in ducks & oval in pigeons | **Spherical in chickens, triangular in ducks & oval in pigeons | ||
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*Connect with the venous sinuses, or | *Connect with the venous sinuses, or | ||
*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 | + | 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> | + | <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> |
====Species Differences==== | ====Species Differences==== | ||
<p>The splenic artery: | <p>The splenic artery: | ||
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*Branches regularly as it passes through the spleen in horses and pigs | *Branches regularly as it passes through the spleen in horses and pigs | ||
*Branches before it reaches the spleen in dogs and cats</p> | *Branches before it reaches the spleen in dogs and cats</p> | ||
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===Innervation=== | ===Innervation=== | ||
| − | Innervation is purely sympathetic< | + | Innervation is purely sympathetic[[LH References - Anatomy & Physiology#Nance|<sup>Ref:Nance</sup>]] and nerve fibres travel with the artery into the spleen. |
| + | ===Lymphatics=== | ||
===Histology=== | ===Histology=== | ||
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| + | ==Function== | ||
==In pathology== | ==In pathology== | ||
| − | + | [[Lymphoreticular/Haemotopoietic System - Spleen|See here]] | |
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Revision as of 14:44, 17 July 2008
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Development
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.
Structure
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.
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.
Red Pulp
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.
White Pulp
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.
Species Differences
The capsule and trabeculae are much more muscular in carnivores and horses than ruminants
- Carnivores
- Is elongated and dumb bell shaped (larger ventrally)
- Ruminants
- Is flat and oblong shaped
- Horses
- Lies under the last three 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
- Pigs
- Elongated and strap like under the last few ribs
- Birds
- Lies alongside, to the right, of the proventriculus and is found caudaodorsally to the liver
- Spherical in chickens, triangular in ducks & oval in pigeons
Vasculature
The splenic artery, a branch of the celiac artery, supplies the spleen. The artery branches into arterioles and capillaries, which may either:
- Connect with the venous sinuses, or
- 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.
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.
Species Differences
The splenic artery:
- Passes through the spleen without dividing in ruminants
- Branches regularly as it passes through the spleen in horses and pigs
- Branches before it reaches the spleen in dogs and cats
Innervation
Innervation is purely sympatheticRef:Nance and nerve fibres travel with the artery into the spleen.