Lecture 7: Urine Storage, Transportation, and Elimination

Key Processes of Urine Transport

• Pathway of Urine:
  • Produced in kidneys
  • Drains through papillary ducts > minor calyces
  • Minor calyces fuse to form major calyces
  • Major calyces unite to form the renal pelvis
  • Urine drains into ureters > urinary bladder > urethra

Anatomy and Function of Ureters

• Description:

  • Two ureters, retroperitoneal
  • Transport urine from renal pelvis to urinary bladder
  • Length: 10-12 inches, Diameter: 1-10 mm

• Transport Mechanism:

  • Primary: Peristalsis
  • Secondary: Hydrostatic pressure, Gravity

• Structure:

  • Composed of mucosa, muscularis, adventitia
  • Transitional epithelium allows for stretching

Historical Anecdote: Urination in Space

• Zero gravity affects urinary bladder sensation
• Initial issues with astronauts not feeling bladder fullness
• Adaptations needed for altered physiology in space

Anatomy and Function of the Urinary Bladder

• Location:

  • Hollow, smooth muscle organ
  • Situated in pelvic cavity, behind pubic symphysis

• Components:

  • Trigone: Small smooth triangular area
  • Muscularis: Detrusor muscle (longitudinal, circular, additional longitudinal layer in distal third)
  • Mucosa: Transitional epithelium, mucus for protection against acidic urine

• Urinary Bladder in Women:

  • Located below the uterus
  • Pregnancy increases urinary frequency due to pressure on bladder

• Capacity:

  • 700-800 milliliters

Health Implications

• Carcinogens from cigarette smoke can affect urinary bladder cells
• Smokers may develop bladder cancer prior to lung cancer

Anatomy of the Urethra

• Female Urethra:

  • Length: ~1.5 inches
  • Located between the clitoris and vagina
  • Epithelium: Transitional changing to stratified squamous

• Male Urethra:

  • Longer, passes through prostate, urogenital diaphragm, and penis
  • Regions: Prostatic, membranous, spongy urethra

Micturition (Urination) Reflex

• Reflex Trigger:

  • Activated by stretch receptors in bladder (200-400 mL)
  • Signals sent to spinal cord and brain

• Mechanism:

  • Parasympathetic activation: Contraction of detrusor muscle, relaxation of sphincters
  • Internal sphincter: Involuntary
  • External sphincter: Voluntary control

• Infant Development:

  • Lack of micturition control until nervous system matures

Other Body Waste Management Systems

• Buffers, liver, lungs, sweat glands, and GI tract play roles in excreting different waste products

Goals of the Lecture

• Describe anatomy and histology of ureters, urinary bladder, and urethra
• Explain why women have more urinary tract infections than men
• Understand the initiation of the micturition reflex
• Identify other body systems involved in waste management