Question

Why right kidney enlarges after left kidney lost?

Answer 1

The enlargement of right kidney after the left kidney is lost, mostly via nephrectomy is called compensatory hypertrophy. There is enlargement of the kidney nephrons due to increase in size of the epithelial cells. However, there is no change in the number of nephrons in the kidneys. Compensatory hypertrophy is initiated because of loss of the ideal mass of the Kidney tissue. The hypertrophy continues till the right kidney has the weight of both left + right kidney.

The kidneys respond by increasing the DNA content as well as mitotic activity. Synthesis of RNA and DNA occurs after 12 hours in right kidney post loss of the left kidney. This increased DNA and RNA synthesis is responsible for the cellular hypertrophy. Endogenous hormones are involved in the process. Insulin like growth factor 1 signaling has been implicated in the phenomenon. There is cell proliferation of the tubular cells, although number of nephrons does not increase.

Since the other kidney is non-functional or absent, there is increased blood flow (more than 30%) to the other kidney for filtration. The compensatory mechanism is required to increase the glomerular filtration rate. The increased GFR is a result of increased surface area available for filtration. Increased glomerular diameter and volume and increase in volume and diameter of proximal convoluted tubule and collecting duct will increase the filtration and reabsorption capacity of the right kidney. The increased load of protein in blood that needs to be filtered is also one of the reasons for compensatory hypertrophy. Renal hypertrophy is therefore a response initiated to increase the glomerular filtration, reabsorption and secretion capacity of the kidneys. It compensates for the lost functions of the other kidneys so that there is normal electrolyte balance maintained in the body.