Renal Endocrine Function

Introduction

The endocrine functions of the kidneys rely on their production of:

1. Renin
2. Erythropoietin
3. Calcitriol

Renin- Angiotensin-Aldosterone system

This system is used to regulate glomerular filtration and blood pressure. Renin is secreted by the renal juxtaglomerular apparatus depending on:

1) Afferent arteriole pressure

2) Sympathetic tone

3) Osmolality and chloride concentration in the DCT

4) Prostaglandin and Nitric oxide

Summary of the production pathway for angiotensin II and source of organs responsible for the various proteins.

Angiotensin II effects

1) Vasoconstriction

2) ↑ Na+ reabsorption

3)  Stimulates efferent more than afferent arteriolar constriction, increasing glomerular filtration rate but reducing renal blood flow

4) ↑ Aldosterone

5) ↑ Thirst and sodium appetite

Aldosterone effects

Acts on collecting duct to promote:

1) Sodium reabsorption

2) Potassium and H+ secretion

The above effects are partly achieved by upregulation of epithelial sodium channels (ENac) in the collecting ducts.

Erythropoietin

Erythropoietin is produced in the renal interstitium in response to hypoxia and functions to stimulate haemoglobin production.

Pathological changes can include:

1. Low erythropoietin: produces normochromic, normocytic anaemia. Caused by loss of renal substance
2. High erythropoietin: produces polycythaemia. Causes include polycystic kidney disease, renal carcinoma and renal cysts.

Calcitriol

Kidneys hydroxylate vitamin D to produce calcitriol. The effects of calcitriol are:

1. ↑ Gastrointestinal absorption of calcium
2. ↑ Osteoclast activity
3. ↑ Renal calcium reabsorption