Which organ system is responsible for filtering blood and excreting waste through urine?

Urinary/renal system: kidneys (2), ureters (2), bladder, urethra. Functions: (1) Filter blood to remove metabolic wastes (urea, creatinine, excess salts and water); (2) Regulate fluid and electrolyte balance; (3) Maintain blood pH; (4) Regulate blood pressure (renin); (5) Produce erythropoietin (stimulates RBC production); (6) Activate vitamin D. Kidney function: each kidney contains ~1 million nephrons (functional units). Nephron stages: (1) Glomerulus — filters blood plasma; (2) Proximal tubule — reabsorbs water, glucose, ions; (3) Loop of Henle — concentrates urine; (4) Distal tubule — fine-tunes electrolytes; (5) Collecting duct — final water reabsorption based on ADH. Major body systems: (1) Skeletal — bones, joints; support, movement, blood cell production; (2) Muscular — skeletal/smooth/cardiac muscle; movement; (3) Cardiovascular — heart, blood, vessels; circulation; (4) Respiratory — lungs, airways; gas exchange; (5) Digestive — GI tract, accessory organs; nutrient absorption; (6) Urinary — kidneys, bladder; filtration; (7) Nervous — brain, nerves; control, sensation; (8) Endocrine — glands; hormone regulation; (9) Immune/Lymphatic — defense, fluid balance; (10) Integumentary — skin; barrier; (11) Reproductive — gonads; reproduction.