The document provides an overview of the renal system and its components and functions. It discusses how the kidneys, along with the ureters, urinary bladder, and urethra, work to maintain fluid balance and electrolyte levels in the body. The kidneys regulate fluid volume and composition through processes in the nephrons like glomerular filtration, tubular reabsorption and secretion. Hormones and systems like aldosterone, antidiuretic hormone, and the renin-angiotensin system also help control fluid balance and blood pressure. The kidneys activate vitamin D to promote calcium absorption and regulate other electrolytes.