The kidney plays an important endocrine role by secreting several hormones. The document discusses four key hormones secreted by the kidney: erythropoietin, calcitriol, thrombopoietin, and renin. Erythropoietin stimulates red blood cell production. Calcitriol helps absorb calcium. Thrombopoietin stimulates platelet production. Renin regulates blood pressure through the renin-angiotensin system. The kidneys secrete these hormones through specialized cells like the juxtaglomerular cells and extraglomerular mesangial cells to perform critical functions in the body.