kidney – ectopic

description

the three embryonic kidneys are the pronephros, mesonephros and metanephros. the first two are important in inducing the development of the third. the ureteral bud grows toward the metanephros and induces differentiation of the nephrogenic blastema into the renal parenchyma. the ampulla (growing ureteral bud) undergoes multiple divisions to induce the nephron development to establish a communication. this process continues until the 32-36 week of gestation. the ureteral bud gives rise to the renal pelvis, calyces, papillae, and collecting tubules, but the metanephric blastema gives rise to the nephron. the differentiation, elongation and maturation of the nephron continues even after birth. during the 7th week the kidneys move over the ridges formed by the umbilical arteries and by the ninth week they rise above the aortic bifurcation. a rotation occurs during the ascent so that the renal pelves which have been forward become directed toward the midline. this occurs by the 10th week. if the migration or rotation of the kidney are disturbed, the embryonic anteroposterior rotation is maintained. the metanephros are originally located in the fetal pelvis. the rapid growth of the embryo results in kidney displacement until they reach their normal position in the lumbar fossae. abnormalities in this process of ascent result in ectopic kidneys. a pelvic kidney is one that has failed to ascend out of the pelvis. the lower the kidney, the less it will have rotated. in a crossed renal ectopic it has been proposed that one kidney is located on the contralateral side and the ureter crosses the median plane. frequently the ectopic and normal kidney are united. rarely, the kidneys are displaced into the thorax. the length of the ureter depends upon the kidney placement.