Changes

This structure forms in the thoracic and lumbar regions and is important in embryonic life.  It has more tubules than the pronephros and the structure of these tubules is similar to that of the adult kidney. They are closed at one end and open at the other.  The open end drains into the pronephric duct which is now more appropriately called the mesonephric duct.  The closed end has a bundle of capillaries which form a filtration mechanism.  This organ is variable in size in relation to how efficient the placenta is at removing waste.  The worse the placenta the bigger the organ.  As the metanephros develops it supersedes this organ and it begins to regress as a result.  Parts of it do, however remain in the male and form part of the ductus deferens.

This structure forms in the thoracic and lumbar regions and is important in embryonic life.  It has more tubules than the pronephros and the structure of these tubules is similar to that of the adult kidney. They are closed at one end and open at the other.  The open end drains into the pronephric duct which is now more appropriately called the mesonephric duct.  The closed end has a bundle of capillaries which form a filtration mechanism.  This organ is variable in size in relation to how efficient the placenta is at removing waste.  The worse the placenta the bigger the organ.  As the metanephros develops it supersedes this organ and it begins to regress as a result.  Parts of it do, however remain in the male and form part of the ductus deferens.

===The Metanephros===

==The [[Developmental_Biology_-_Intermediate_Mesoderm_Development_-_Anatomy_%26_Physiology#Metanephros|Metanephros]]==

The metanephros forms from 2 primordia.  One is an out growth of the ureteric bud which grows from the lower part of mesonephric duct near the cloaca.  The bud grows up into the metanephros and divides.  The early divisions later go on to be reabsorbed to a variable degree accounting for the inter-species differences in the renal pelvis and calyces.  The later divisions form the collecting ducts. A mass of tissue is seen which is termed the metanephric mass.  The outer part of this mass goes on to form the renal capsule and interstitium.  The inner part goes on to form the nephrons via intermediates called cell cords.  Each cell cord joins with a collecting duct.  The other end invaginates around a tuft of capillaries arising from the aorta to form the glomerulus.

The metanephros forms from 2 primordia.  One is an out growth of the ureteric bud which grows from the lower part of mesonephric duct near the cloaca.  The bud grows up into the metanephros and divides.  The early divisions later go on to be reabsorbed to a variable degree accounting for the inter-species differences in the renal pelvis and calyces.  The later divisions form the collecting ducts. A mass of tissue is seen which is termed the metanephric mass.  The outer part of this mass goes on to form the renal capsule and interstitium.  The inner part goes on to form the nephrons via intermediates called cell cords.  Each cell cord joins with a collecting duct.  The other end invaginates around a tuft of capillaries arising from the aorta to form the glomerulus.