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Human Body Study

Bladder

A hollow, muscular organ that stores urine until it can be released.

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.

Structure

Section titled “Structure”

An expandable sac of smooth muscle; its wall stretches as it fills and contracts to empty. Two sphincters guard the outlet — one involuntary, one under conscious control.

What it does

Section titled “What it does”
  • Stores urine — typically until 300–400 ml has collected.
  • Signals the need to urinate via stretch receptors.
  • Contracts to expel urine when released.

Key idea

Section titled “Key idea”

The bladder makes urination a controllable event rather than a constant trickle — the voluntary outer sphincter is what allows it to be delayed.