Positional Changes of the Kidneys
Initially the kidneys lie in the pelvic region close to each other, at the vertebral level of S1 and S2. As the body along with lumbar and sacral region grows in size, the kidneys ascent to the abdomen and separate from each other and come to lie at T12- L3 vertebral level. During the relative ascent, the kidneys further rotate to 90 degree, thus causing the ventrally facing hilum initially, to finally face medially.
Rotation and ascent of the kidneys, available at: http://web.uni-plovdiv.bg/stu1104541018/docs/res/skandalakis%27%20surgical%20anatomy%20-%202004/Chapter%2023_%20Kidneys%20and%20Ureters.htm
Blood Supply of the Kidneys
At first the kidneys are supplied by renal arteries which are the branches of common iliac arteries. During the ascent of the kidneys, their blood supply progressively becomes higher until the definitive renal arteries develop at the level of L2. After the positional change, the initial caudal branches undergo involution and finally disappear.