Medullary Oxygen Tension and Perfusion of the Medulla

Oxygen tension in the medulla of the kidney is low, 10 to 25 mmHg. This is predicted to be a consequence of the countercurrent arrangement of vasa recta because oxygen in DVR blood diffuses to AVR to be shunted back to the cortex. Several hormonal systems play a role in the protection of the medulla from ischemic insult. Each shares the ability to enhance medullary blood flow and inhibit salt reabsorption by nephrons. Hypothetically this should have a dual effect to enhance the supply of oxygen and simultaneously reduce the demand for O2 consumption. One example is cyclooxygenase (COX) production of vasodilatory prostaglandins. Medullary perfusion is sensitive to COX inhibition, and renomedullary interstitial cells release prostaglandin E2 (PGE2) in response to Angll and bradykinin. Apparently, the cylooxygenase-2 isoform is responsible because Angll reduces medullary blood flow in COX2- but not COXl-deficient mice. In most vascular beds, ischemia favors generation of adenosine, a paracrine agent that enhances blood flow through local vasodilation. Within the renal medulla (but not the cortex) adenosine acts as a vasodilator and inhibits salt reabsorption by the medullary thick ascending limb of Henle (mTAL). It is reasonable to hypothesize that adenosine produced by the mTAL diffuses to and dilates DVR on the periphery of vascular bundles. Adenosine A1 and A2 receptor stimulation constricts and dilates DVR, respectively.

10 Ways To Fight Off Cancer

10 Ways To Fight Off Cancer

Learning About 10 Ways Fight Off Cancer Can Have Amazing Benefits For Your Life The Best Tips On How To Keep This Killer At Bay Discovering that you or a loved one has cancer can be utterly terrifying. All the same, once you comprehend the causes of cancer and learn how to reverse those causes, you or your loved one may have more than a fighting chance of beating out cancer.

Get My Free Ebook


Post a comment