Overview of the Urinary System

Overview of the Urinary System

  • Maintains composition, pH, and volume of body fluids.
  • Removes metabolic wastes and excess substances.
  • Key organs:
    • Kidneys: filter blood, form urine.
    • Ureters: transport urine to bladder.
    • Urinary Bladder: stores urine.
    • Urethra: conveys urine outside the body.

Structure of Kidneys

  • Bean-shaped organ, reddish-brown, enclosed in a fibrous capsule.
  • Retroperitoneal location; left kidney positioned higher than right.
  • Contains renal cortex (outer region), renal medulla (inner region), renal sinus, hilum, major/minor calyces.
  • Nephrons are the functional units of kidneys.

Renal Blood Supply

  • Afferent Arteriole: feeds blood into nephron.
  • Glomerulus: capillary cluster that filters blood.
  • Efferent Arteriole: carries unfiltered blood away.
  • Peritubular Capillaries: surround renal tubules for substance exchange.

Nephron Structure

  • Comprises a renal corpuscle (glomerulus + Bowman's capsule) and renal tubule.
  • Each kidney houses approximately 1 million nephrons.

Urine Formation Processes

  • Glomerular Filtration: filters water and small molecules.
  • Tubular Reabsorption: reclaims useful substances back into blood.
  • Tubular Secretion: adds wastes to urine from blood.

Urine Composition

  • Typically pH of 6.0; 95% water.
  • Contains metabolic wastes (urea, uric acid, creatinine).

Regulation of Urine Concentration

  • ADH regulates water reabsorption in kidneys, affecting urine concentration and volume.
  • Hormones influence solute concentrations.

Pathway of Urine Elimination

  • Urine follows the path: nephrons → renal papillae → minor calyces → major calyces → renal pelvis → ureters → urinary bladder → urethra.

Urinary Bladder

  • Hollow muscular organ; holds around 600 mL.
  • Internal urethral sphincter present.

Urethra

  • Female: ~4 cm; Male: ~19.5 cm; has three sections (prostatic, membranous, spongy).

Kidney Stones

  • Composed of uric acid or calcium, causing pain and urinary obstruction.

Aging & the Urinary System

  • Age-related changes in kidney function, structure, decreased filtration efficiency, increased risk of incontinence.