Urine made in the kidney collects in the renal pelvis within the kidney, then flows down the ureter to the bladder where it is stored until voided. The kidney is composed of an outer layer, the cortex , and an inner core, the medulla . To the right is a diagram of an individual nephron. Each nephron has a closely associated blood supply. Blood comes in at the glomerulus and transfers water and solutes to the nephron at Bowman's capsule .
Capillaries wind around and exchange materials with the tubule.
From there, the urine flows down a collecting duct which gathers urine from several nephrons. As the collecting duct goes back through the medulla, more water is removed from the urine. The collecting ducts eventually end up at the renal pelvis which collects the urine from all of them. ADH promotes water retention by the kidneys, and its secretion is regulated by a negative feedback loop involving blood water and salt balances. ADH helps the kidney tubules reabsorb water to concentrate the urine.