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Human Body Study

Urinary System

The body’s filtration and water-balance system — it cleans the blood and adjusts its composition.

The urinary tract Two kidneys at top with ureters descending to a single bladder and urethra exiting below; a separate inset shows a nephron, the kidney's microscopic functional unit. Each label links to the article for that part. Nephron Kidneys Ureters Bladder Urethra The urinary tract — kidneys, ureters, bladder, urethra; the nephron is the kidney's microscopic functional unit.

Main parts

Section titled “Main parts”
  • Kidneys — the paired organs that filter the blood.
  • Nephron — the kidney’s microscopic filtering unit.
  • Ureters — tubes carrying urine from the kidneys to the bladder.
  • Bladder — the muscular reservoir that stores urine.
  • Urethra — the tube through which urine leaves the body.

What it does

Section titled “What it does”
  • Filtration — removes waste products and excess substances from the blood.
  • Water and salt balance — fine-tunes how much water and which ions are kept or released.
  • Blood pressure and pH — helps regulate both, partly through the hormone system.
  • Hormone production — the kidneys release signals that drive red blood cell production and activate vitamin D.

Key idea

Section titled “Key idea”

The kidneys do not just remove waste — they decide the precise composition of the body’s internal fluid, reclaiming most of what they filter and discarding only what is in excess.