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During the fifth week of gestation, the mesonephric duct develops an outpouching, the ureteric bud, near its attachment to the cloaca. This bud, also called the metanephrogenic diverticulum, grows posteriorly and towards the head of the embryo. The elongated stalk of the ureteric bud, called the metanephric duct, later forms the ureter.
The metanephrogenic blastema or metanephric blastema (or metanephric mesenchyme, or metanephric mesoderm) is one of the two embryological structures that give rise to the kidney, the other being the ureteric bud. The metanephric blastema mostly develops into nephrons, but can also form parts of the collecting duct system.
By about 20 weeks, the ureteric bud has formed the ureters, the renal calyces, collecting ducts, and collecting tubules, while the metanephric blastema develops into the nephron itself, which includes the epithelial cells and the podocytes of Bowman’s capsule. In the third trimester and throughout infancy, the kidneys continue to grow and mature.
[17] [6] [18] Differences in kidney structure are the result of adaptations during evolution to variations in body mass and habitats (in particular, aridity) between species. [ 19 ] [ 20 ] [ 12 ] The cortex and medulla of the kidney contain nephrons , [ 21 ] each of which consists of a glomerulus and a complex tubular system. [ 22 ]
Ectopic ureter (or ureteral ectopia) is a medical condition where the ureter, rather than terminating at the urinary bladder, terminates at a different site. [1] [2] In males this site is usually the urethra, in females this is usually the urethra or vagina. [3]
The ureteric bud, also known as the metanephric diverticulum, [1]: 50 is a protrusion from the mesonephric duct during the development of the urinary and reproductive organs. [ 2 ] [ 3 ] It later develops into a conduit for urine drainage from the kidneys, which, in contrast, originate from the metanephric blastema .
A hydronephrotic kidney may present as a palpable abdominal mass in the newborn, and may suggest an ectopic ureter or ureterocele. In older children, ureteral duplication may present as: [citation needed] Urinary tract infection – most commonly due to vesicoureteral reflux (flow of urine from the bladder into the ureter, rather than vice versa).
During early development (approximately day 22 in humans), the pronephric duct forms from the intermediate mesoderm, ventral to the anterior somites. The cells of the pronephric duct migrate caudally whilst inducing adjacent mesenchyme to form the tubules of the initial kidney-like structure called the pronephros. [6]