Lecture Notes: The Urinary System

Overview

• Focus on the urinary system, beginning with the kidneys.
• Kidneys are responsible for initiating urination.

Anatomy of the Kidneys

• Position and Structure:
  • Right kidney sits lower than the left due to the liver.
  • Shape: Kidney bean-like.
  • Frontal cross-section: right and left look different due to structure accommodation.
• Blood Supply:
  • Inferior vena cava (IVC) and renal veins bring blood from kidneys.
  • Aorta and renal arteries bring blood to kidneys.
• Kidney Structure:
  • Outer Layer: Renal capsule, snug fit like a hotdog casing.
  • Two Main Parts:
    • Renal cortex (outer part)
    • Renal medulla (middle part)
      • Renal pyramids (6-8 pyramids per kidney)
• Internal Structures:
  • Renal papilla: End of pyramids, leads to minor calyx.
  • Minor & major calyx, renal pelvis, and ureter connection.
  • Renal Hilum: Entry/exit zone for veins, arteries, lymphatics, nerves, and ureter.
• Functional Unit: Nephron, filters plasma.

Kidney Location

• Situated in the retroperitoneal space.
• Retroperitoneal vs. Peritoneal cavity: Kidneys are retroperitoneal.

Urinary Pathway

• Starts at renal pyramids, through papillas, minor/major calyx, renal pelvis, ureter.

Bladder Anatomy

• Function: Stores urine.
• Structure:
  • Ureters enter bladder posteriorly.
  • Triangular area (trigone) where ureters enter.
  • Detrusor muscle: Surrounds bladder, contracts during urination.
• Urination Process:
  • Micturition (clinical term for urination)
  • Steps: Stretch receptors activate, detrusor muscle contracts, internal urethral sphincter (smooth muscle) relaxes, urine enters urethra.
  • External Urethral Sphincter: Voluntary skeletal muscle for urine control.

Urethra and Gender Differences

• Female Urethra:
  • Length: ~4 cm.
  • Ends at urethral orifice.
• Male Urethra:
  • Length: ~20 cm.
  • Passes through prostate and penis.
  • Three parts: Prostatic, membranous, penile/spongy urethra.
  • Ends at urethral orifice.

Additional Insights

• Importance of transitional epithelium in bladder and ureters for stretch.
• Clinical observations on muscle-related bladder issues.

Conclusion

• Review of the pathway from kidney to urethral orifice.
• Differences in male and female urinary systems and significance of various structures.