[The kidney, its anatomy and main functions]

The kidney performs several major functions: it eliminates toxins produced by cellular or xenobiotic metabolism, regulates the homeostasis of the internal environment and plays a hormonal role, producing erythropoietin, calcitriol and renin. Maintaining the body's homeostasis (hydric, ionic [sodium, potassium, calcium, phosphorus, etc.] or acid-base balance) requires the successive action of plasma filtration, followed by reabsorption/secretion mechanisms, which take place in the various portions of the kidney's functional unit known as the nephron. The initial part of the nephron, the glomerulus, is the site of filtration, while the tubule, which collects the glomerular filtrate, is the site of reabsorption/secretion, leading to the composition of the final urine. It's important to understand how these different structures work, before tackling the various disorders that can affect the kidney.