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| + | <big><center>[[Developmental Biology - Anatomy & Physiology|'''BACK TO DEVELOPMENTAL BIOLOGY]]</center></big> |
| − | ==Introduction==
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| − | 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
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| − | :Mesonephros
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| − | :Metanephros
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| − | Mammals develop all three, and continue to use the metanephros in adult life. More primitive animals have only the first one or two.
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| − | ==Pronephros==
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| − | *''The earliest kidney. Develops in the anterior of the animal (adjacent to somites 1 - 10). Eliminated in later development''.
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| − | #At intervals along the intermediate mesoderm, dorsal evaginations occur.
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| − | #Evaginations extend caudally and eventually fuse with more caudal evaginations.
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| − | #*The caudal - most evagination fuses with the cloaca.
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| − | #Forms a continuous excretory tube to the cloaca.
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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.
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| − | #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''.
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| − | #The medial portion of the intermediate mesoderm forms a cup in the region of the capillaries.
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| − | #*This is an early Bowman's capsule and improves waste removal.
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| − | #The excretory channel pinches off from all surrounding tissue (lateral plate mesoderm) to become entirely closed.
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| − | #*Excretory duct now known as the '''Wolffian Duct'''.
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| − | *Amphibians and fish use the mesonephric kidney.
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| − | ==Metanephros==
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| − | *''Formation of the metanephros employs recipricol signalling''.
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| − | #At the level of the sacrum, a block of intermediate mesoderm breaks off from the Wolffian duct. It is called a '''metanephric blastema'''.
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| − | #The metanephric blastema signals to the Wolffian duct.
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| − | #*Wolffian duct is induced to grow, and a bud of Wolffian duct moves towards the metanephric blastema.
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| − | #*The bud is called the '''ureteric duct'''.
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| − | #The ureteric duct contacts the blastema, and divides into two branches.
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| − | #One of the branches induces adjacent mesenchyme to undergo a mesenchymal to epithelial transition.
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| − | #*It subsequently develops into a nephron.
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| − | #The remaining branch splits into two, and repeats the process.
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| − | #The primary branch forms the ureter; the remainder leads to the compact kidney of mammals.
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| − | {{OpenPages}}
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| − | [[Category:Developmental Biology]] | |
| − | [[Category:Urinary System - Anatomy & Physiology]]
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