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− | <big><center>[[Developmental Biology - Anatomy & Physiology|'''BACK TO DEVELOPMENTAL BIOLOGY]]</center></big>
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| ==Introduction== | | ==Introduction== |
| The intermediate mesoderm exists as a strip of tissue between the lateral plate mesoderm and somites. It gives rise to the urinary system and some parts of the reproductive system. Kidney development includes three forms: | | The intermediate mesoderm exists as a strip of tissue between the lateral plate mesoderm and somites. It gives rise to the urinary system and some parts of the reproductive system. Kidney development includes three forms: |
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| ==Pronephros== | | ==Pronephros== |
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− | *''The earliest kidney. Develops in the anterior of the animal (adjacent to somites 7 - 10). Eliminated in later development''. | + | *''The earliest kidney. Develops in the anterior of the animal (adjacent to somites 1 - 10). Eliminated in later development''. |
| #At intervals along the intermediate mesoderm, dorsal evaginations occur. | | #At intervals along the intermediate mesoderm, dorsal evaginations occur. |
| #Evaginations extend caudally and eventually fuse with more caudal evaginations. | | #Evaginations extend caudally and eventually fuse with more caudal evaginations. |
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| #Capillaries develop at the medial aspect of the intermediate mesoderm so that waste can diffuse from the blood to the excretory channel. | | #Capillaries develop at the medial aspect of the intermediate mesoderm so that waste can diffuse from the blood to the excretory channel. |
| #Connections between the intermediate mesoderm and somites as well between the intermediate mesoderm and lateral plate mesoderm break down. | | #Connections between the intermediate mesoderm and somites as well between the intermediate mesoderm and lateral plate mesoderm break down. |
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| + | ==Mesonephros== |
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| + | *''Development occurs in an anterior to posterior direction; the mesonephros kidney is found at the thoracic to lumbar level''. |
| + | #The medial portion of the intermediate mesoderm forms a cup in the region of the capillaries. |
| + | #*This is an early Bowman's capsule and improves waste removal. |
| + | #The excretory channel pinches off from all surrounding tissue (lateral plate mesoderm) to become entirely closed. |
| + | #*Excretory duct now known as the '''Wolffian Duct'''. |
| + | *Amphibians and fish use the mesonephric kidney. |
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| + | ==Metanephros== |
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| + | *''Formation of the metanephros employs recipricol signalling''. |
| + | #At the level of the sacrum, a block of intermediate mesoderm breaks off from the Wolffian duct. It is called a '''metanephric blastema'''. |
| + | #The metanephric blastema signals to the Wolffian duct. |
| + | #*Wolffian duct is induced to grow, and a bud of Wolffian duct moves towards the metanephric blastema. |
| + | #*The bud is called the '''ureteric duct'''. |
| + | #The ureteric duct contacts the blastema, and divides into two branches. |
| + | #One of the branches induces adjacent mesenchyme to undergo a mesenchymal to epithelial transition. |
| + | #*It subsequently develops into a nephron. |
| + | #The remaining branch splits into two, and repeats the process. |
| + | #The primary branch forms the ureter; the remainder leads to the compact kidney of mammals. |
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| + | {{OpenPages}} |
| + | [[Category:Developmental Biology]] |
| + | [[Category:Urinary System - Anatomy & Physiology]] |