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System

Urinary system

Not medically reviewed · Content last updated · 1 min read ·

This is the date the draft was written, not a medical review date.

The urinary system filters blood, forms urine and conveys it out of the body. It regulates fluid, electrolyte and acid-base balance, excretes metabolic waste and has endocrine functions.

Terminologia Anatomica (Latin): Systema urinarium

Components

It consists of two kidneys, two ureters, the urinary bladder and the urethra. The kidney is organised into cortex and medulla, with the nephron (glomerulus and tubule) as its functional unit, and urine drains through calyces and the renal pelvis into the ureter.

Function

Glomerular filtration, tubular reabsorption and secretion determine the composition and volume of urine and so control plasma volume, osmolality and pH. The kidney also secretes erythropoietin and renin and activates vitamin D, and the bladder stores urine until voiding.

Clinical correlations

Acute kidney injury, chronic kidney disease, urinary tract infection, nephrolithiasis, glomerular disease and urinary obstruction are common. Renal function is assessed by creatinine-based estimated GFR and urinalysis, and reference values and equations vary by laboratory and region.

Common exam points

  • Kidneys are retroperitoneal at about T12 to L3, the right slightly lower than the left.
  • Renal coverings from deep to superficial: fibrous capsule, perirenal fat, renal fascia, pararenal fat.
  • Three sites of ureteric narrowing: pelviureteric junction, pelvic brim, vesicoureteric junction.
  • Nephron segments and the countercurrent mechanism that concentrates urine.
  • Micturition involves parasympathetic (S2 to S4) detrusor contraction and somatic control of the external sphincter.

References

  1. Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. Elsevier — Tier 3 (textbook)
  2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. Wolters Kluwer, 8th edition (2018) — Tier 3 (textbook)
  3. Hall JE, Hall ME. Guyton and Hall Textbook of Medical Physiology. Elsevier, 14th edition (2020) — Tier 3 (textbook)
  4. Brenner and Rector's The Kidney. Elsevier, 11th edition (2019) — Tier 3 (textbook)

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