Urinary system
The urinary system is a set of organs that ensure the formation, accumulation and excretion of urine. It plays a key role in maintaining homeostasis: it regulates the volume and composition of body fluids, removes metabolic end products, and participates in the control of blood pressure.
Organs of the urinary system
The system includes:
- Kidneys (2) - urine formation
- Ureters (2) - transport of urine
- Bladder (1) - accumulation of urine
- Urethra (urethra) (1) - excretion of urine
Ureters
The ureters are paired tubes 25–30 cm long and 4–7 mm in diameter that connect the renal pelvis to the bladder. Their wall contains three layers of smooth muscle that provide peristalsis - wave-like contractions that move urine.
The ureter has three physiological narrowings where stones most often get stuck:
- Ureteropelvic junction
- Place of intersection with the iliac vessels
- Place of entry into the bladder
The ureter enters the wall of the bladder obliquely, passing 1.5–2 cm in the thickness of the wall. This creates a valve mechanism: when the bladder fills, the wall compresses the mouth of the ureter, preventing backflow (reflux) of urine into the kidney.
Urethra
The urethra differs significantly between men and women:
- Female urethra - length 3–4 cm, straight, opens in front of the vagina. A short urethra is the cause of more frequent urinary tract infections in women.
- Male urethra - length 18–20 cm, passes through the prostate gland and penis. It is divided into prostatic, membranous and spongy parts.
Path of urine
The entire path from filtration to output:
- Blood enters the nephron glomeruli → filtration (180 l/day)
- Primary urine passes through the tubules → reabsorption (99% water and nutrients)
- The final urine (1.5–2 l/day) flows into the collecting ducts → calyces → pelvis
- Peristalsis of the ureters → bladder
- Accumulation up to 200–400 ml → urge
- Contraction of the detrusor + relaxation of the sphincters → urination
Composition of urine
Normal urine contains:
- Urea (the main product of protein metabolism)
- Creatinine (product of muscle metabolism)
- Uric acid, electrolytes (Na⁺, K⁺, Cl⁻)
- pH 5.0–7.0, specific gravity 1.010–1.025
The appearance of protein (proteinuria), glucose (glucosuria) or blood (hematuria) in the urine is a pathological sign that requires examination.
Urolithiasis
The formation of stones (calculi) in the urinary tract is a common pathology, affecting up to 10% of the population. Stones are formed from calcium salts, urates or oxalates. Understanding the anatomy of the ureteral narrowing helps the urologist predict whether the stone will pass on its own or require lithotripsy (crushing).
All organs of the urinary system - from the kidneys to the urethra - are presented in the 3D atlas Humio. Explore anatomy in an interactive format: rotate, zoom and highlight individual structures.