Summary of Urinary System and Its Functions

Urinary System Learning Outcomes

  1. Identify urinary system organs and their functions.

  2. Describe kidney location and structure.

  3. Trace blood flow in and out of kidneys.

  4. Describe nephron structure and blood flow around nephrons.

  5. Explain ureters, bladder, and urethra functions.

  6. Discuss aging effects on the urinary system.

Major Functions of the Urinary System

  • Excretes organic wastes (e.g., urea).

  • Eliminates wastes externally.

  • Regulates blood volume and solute concentration.

Homeostatic Functions

  • Regulates blood volume and pressure.

  • Maintains plasma ion concentration (Na⁺, K⁺, Cl⁻, Ca²⁺).

  • Stabilizes blood pH.

  • Conserves nutrients (glucose, amino acids).

Organs of the Urinary System

  • Kidneys: Produce urine.

  • Ureters: Transport urine to the bladder.

  • Bladder: Stores urine.

  • Urethra: Conducts urine to the exterior.

  • Micturition: Process of urination.

Kidney Position and Structure

  • Kidneys are retroperitoneal (L1-L3 vertebrae).

  • Enclosed in a fibrous capsule and surrounded by adipose tissue.

Kidney Structure

  • Renal Cortex: Outer layer for blood filtration.

  • Renal Medulla: Inner layer with renal pyramids.

  • Nephrons: Functional units filtering blood to create urine.

  • Blood Supply: Receives 20–25% cardiac output (1200 mL/min).

Nephrons

  • Structure includes renal corpuscle, proximal & distal convoluted tubules, nephron loop.

  • Filtration Membrane: Glomerular capillaries filter blood to create filtrate.

  • Reabsorbs nutrients and water, and secretes wastes.

Ureters

  • Muscular tubes conducting urine from kidneys to bladder.

  • Wall consists of: transitional epithelium, smooth muscle, connective tissue.

Urinary Bladder

  • Hollow muscular organ storing urine (up to 1L).

  • Contains trigone area and detrusor muscle for expelling urine.

Urethra

  • Conducts urine from bladder to the exterior.

  • Contains voluntary sphincters; length varies between males (18-20 cm) and females (2.5-3 cm).

Age-Related Changes

  • Decrease in functional nephrons (30-40% by age 85).

  • Reduced GFR, sensitivity to hormones (ADH, aldosterone).

  • Weakened sphincters, prostate enlargement in males, and decreased total body water content.