Lecture on the Urinary System

Overview

• Professor Dave introduces the urinary system following a discussion on the digestive system.
• Focus: filtration and expulsion of metabolic waste from the bloodstream.
• Main components: Kidneys, ureters, urinary bladder, urethra.

Key Components of the Urinary System

Kidneys

• Primary Organ: Perform numerous tasks including:
  • Regulating water volume and solute concentration.
  • Blood pH regulation.
  • Production of erythropoietin.
  • Key Function: Filter bloodstream, remove toxins/waste, return necessary components to blood.
• Structure:
  • Two bean-shaped organs in the lumbar region.
  • Protected partially by the ribcage.
  • Each has a renal hilum leading to a renal sinus.
  • Associated with adrenal glands on top (not directly related to urinary function).
• Supportive Tissues:
  • Renal fascia: Outer dense fibrous connective tissue.
  • Perirenal fat capsule: Cushions kidneys.
  • Fibrous capsule: Prevents infection spread.
• Internal Structure:
  • Renal cortex and medulla (contains renal pyramids and columns).
  • Renal pelvis, connected to ureter, has calyces for urine collection.

Blood Supply and Filtration

• Arteries: Renal arteries → Segmental → Interlobar → Arcuate → Cortical radiate arteries.
• Veins: Cortical radiate veins → Arcuate → Interlobar → Renal veins → Vena cava.
• Nephrons: Basic filtration units.
  • Consist of glomerulus in the renal corpuscle and renal tubule.
  • Renal tubule has proximal convoluted tubule, nephron loop, distal convoluted tubule.

Urine Production

• Three-step process:
  1. Glomerular Filtration:
     • Occurs in renal corpuscle.
     • Blood forced through filtration membrane into glomerular capsule.
  2. Tubular Reabsorption:
     • Most filtrate (water, glucose, amino acids) reabsorbed into blood.
     • Remaining becomes urine.
  3. Tubular Secretion:
     • Substances from blood (e.g., drugs, excess potassium) secreted into filtrate.
• Urine Composition:
  • Mostly water.
  • Contains urea, uric acid, creatinine, ionic solutes (sodium, potassium, phosphate).

Urine Transport and Expulsion

• Ureters:
  • Transport urine from kidneys to bladder.
  • Walls have three layers: mucosa, muscularis, adventitia.
• Urinary Bladder:
  • Flexible muscular sac with a region called trigone.
  • Connects to urethra.
• Urethra:
  • Muscular tube conveying urine out of the body.

Conclusion

• Appreciation for Kidneys: Often overlooked despite their critical functions.
• Urethra's Dual Role: Part of both urinary and reproductive systems.