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Kidney and Urinary Tract Development - Anatomy & Physiology (view source)
Revision as of 14:45, 21 August 2008
, 14:45, 21 August 2008no edit summary
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 differances 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 interstitum. 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 differances 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 interstitum. 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.
==Lower Urinary Tract==
The seperation between the termination of the digestive and urinary tracts on the outer surface of the body is not always the case. In fact the urinary tract comes from the horizontal division of the primitve hind gut in the cloacal region. This seperation is done by a wedge of mesoderm called the urorectal septum. This wedge is located between the hidgut and the allantoic bud. The wedge grows until it reaches the cloacal membrane and has thus then divided the original hindgut into dorsal(anal) and ventral (urogenital) parts. The divide is termed the pernieal body. The cloacal membrane covering the urogenital opening then breaks down forming the urogenital passage. This passage splits in cranial and caudal parts with the cranial part comprising the bladder and eventually the allantois and the caudal part comprising the urethra.
===The Bladder===
The widening of the cranial part of the urogenital passage forms the bladder. It is connected caudally the a closed urethra and cranially to a wide allantoic duct (urachus). This connects the bladder to the allantoic sac outside the embryo which collects urine during foetal life. At birth the urachus degenerates and closes however there is usually a scar on the wall of the bladder. The ends of the meso and metanephric ducts are attached to the urogenital passage. The metanephric ducts form the ureters and enter the bladder. The mesonephric ducts enter more caudally in the urogenital sinus. The mesoderm from the mesonephric ducts forms epithelium of the trigone of the bladder. The remaining epithelium comes from the the endothelium of the hindgut and the external layers are derived from local mesoderm.
===The Urethra===
As previously mentioned the caudal part of the urogenital passge forms the urethra. In females it forms the whole urethra however in males it is added to by the penile urethra which develops seperately as part of the genitals.