Friday July 24, 2009 (pediatric pearl)
Kidney Blood Supply

Even though the kidney receives 25% of the cardiac output only 2% supplies the renal medulla. It is important so as to have sluggish flow and to be able to maintain high osmolarity in the interstitium for counter-current mechanism. However it predisposes the medulla to ischemia when there is arteriopathy (diabetes mellitus); abnormal blood cells (sickle cell disease); or with chronic use of analgesics (which impairs intra-renal auto-regulation and causes vasoconstriction). This can result in loss of concentrating capacity of the urine and causes the patient to have a fixed specific gravity (1.007 to 1.010).