Is the ability of the kidneys to maintain a relatively constant gfr despite changes in blood pressure without the input of nervous or hormonal control.

Renal autoregulation is the ability of the kidneys to maintain a relatively constant GFR or glomerulofiltration rate despite fluctuating blood pressure. Autoregulation is a remarkable property of multiunit smooth muscles of small arteries and arterioles to respond to changes in internal and external pressure. The blood vessels in the human body react by contracting whenever the blood pressure is elevated and by expanding when the blood pressure is reduced. On the other hand, if there is an elevation or reduction of the external interstitial pressure, it results in dilation and contraction, respectively. The lowest autoregulating pressure is about 60 mmHg. By a further reduction in perfusion pressure, RBF is sharply reduced.

Kidneys are the important organs of the excretory system involved in the removing of nitrogenous wastes from the body. Apart from this, they are involved in maintaining the acid-base balance, electrolytes and thus contibuting in homeostatis of the body.

The structural and functional unit of a kidney is called a nephron. Glomeruli of the nephrons are involved in the process of filtering the waste products and excess of fluids from the blood. This process is called the glomerular filtration. GFR or the glomerular filtration rate is the rate at which the fluids are filtered from the glomerulus of the nephron. A constant GFR is very essential for the healthy functioning of kidneys. Any change in the arterial pressure can injury the nephrons of the kidney. Hence a constant GFR despite of changes in the blood pressure is maintained by a process called the renal autoregulation.

Renal autoregulation together with the tubuloglomerular feedback help in maintaining a constant GFR inspite of changes in the sodium chloride levels in the urinary filtrate. An elevated level of sodium, results in constriction of the afferent arteriole, decreasing renin secretion and thus, lowering the GRF. Any decrease in sodium levels stimulates more renin production, constricts the efferent arteriole and increases the GRF.

Thus, renal autoregulation is the ability of the kidneys to maintain a constant GRF rate despite changes in the blood pressure.

that is wrong, its not thymus.