Endocrine Functions Of The Kidney

In addition to its role in the regulation of solute and water excretion, the kidney has several endocrine functions, including the synthesis of erythropoietin, the release of angiotensin I and angiotensin II, the conversion of vitamin D3 to its final form, and the production of several autocrine and paracrine agents. Vitamin D3 from the diet and that produced by the skin must be hydroxylated to be fully active. Enzymes in the kidney are responsible for the final conversion of vitamin D3 to its most active form 1,25-dihydroxycholecalciferol [1,25(OH)2D3; see chapter 43].

Erythropoietin is interesting because it is a growth factor (or cytokine) that behaves like a hormone. Erythropoietin is a 34-kDa glycoprotein that is secreted by interstitial cells in the kidney, and its synthesis and release is increased by a low hematocrit or a fall in blood oxygen carriage. Erythropoietin acts on erythroid progenitor cells in bone marrow as a colony-stimulating factor and increases the production of red blood cells. As might be expected, renal failure is accompanied by anemia as one of its many side effects. However, the fall in erythropoietin production is not the only reason for the anemia. Disseminated tissue hemorrhaging and a decrease in hemoglobin and red blood cell production accompany uremia. Nevertheless, the anemia of renal failure can be reduced effectively by the administration of erythropoietin, which was one of the first human hormones to be produced industrially by recombinant DNA technology. Recombinant erythropoietin is also used extensively to boost red blood cell production in patients who wish to donate their own blood before surgery.

As discussed in more detail in the next chapter, juxtaglomerular cells in the afferent arterioles release renin, which results in the production of angiotensin I and angiotensin II. Both within the kidney and in the general circulation, angiotensin has broad effects as a pressor agent by increasing the total peripheral resistance of the circulation and by maintaining or increasing extracellular fluid volume. Several organs including the adrenal cortex, vascular smooth muscle, the brain, and the heart have receptors for circulating angiotensin II (see also Chapter 40).

The kidney produces several substances whose actions are limited to neighboring cells (paracrine agents) or on the cells that secrete them (autocrine agents). For example, prostaglandin E2 (PGE2) and prostacyclin (PGI2) are produced throughout the kidney, especially by medullary interstitial cells. They have various autocrine and paracrine functions within the kidney; however, these actions are usually manifest only when other stimuli such as circulating catechol-amines and sympathetic nerve input to the kidney are high. In this setting, prostaglandins help to maintain renal blood flow, glomerular filtration rate, and salt excretion. When the production of prostaglandins, especially PGE2, is high, they can also act as systemic vasodilators and tend to decrease blood pressure; however, they are rapidly converted to inactive metabolites.

Get Rid of Gallstones Naturally

Get Rid of Gallstones Naturally

One of the main home remedies that you need to follow to prevent gallstones is a healthy lifestyle. You need to maintain a healthy body weight to prevent gallstones. The following are the best home remedies that will help you to treat and prevent gallstones.

Get My Free Ebook


Post a comment