Urinary System Study Notes

Overview of the Urinary System

  • Basic Functions:
    • Remove waste products from body fluids (excretion).
    • Maintain volume and solute concentration of plasma (affects blood pressure and osmosis).
    • Eliminate waste products into the environment.

Major Organs of the Urinary System

  • Kidneys:
    • Produce urine.
    • Retroperitoneal position behind the peritoneum.
  • Ureters: Transport urine from kidneys to the urinary bladder.
  • Urinary Bladder: Stores urine prior to elimination.
  • Urethra: Conducts urine to the outside of the body (shared with reproductive system in males).

Kidney Structure

  • Location:
    • Positioned behind the last two ribs (floating ribs).
  • Supportive Structures:
    • Fibrous capsule (collagen fibers) surrounds kidneys.
    • Paranephric fat (fat layer around kidneys).
    • Renal fascia (connective tissue attaching kidneys).

Kidney Function

  • Blood Flow:
    • Kidneys receive 20-25% of cardiac output (approx. 1200 mL/min).
    • Blood enters via renal artery and exits through renal vein.

Nephron Structure

  • Functional Unit of the Kidney:
    • Approximately 1.25 million nephrons per kidney.
  • Components:
    • Renal corpuscle (filters plasma).
    • Renal tubule (consists of proximal convoluted tubule (PCT), nephron loop, distal convoluted tubule (DCT)).

Renal Corpuscle

  • Components:
    • Glomerular capsule (outer layer).
    • Glomerulus (capillary network).
  • Filtration Process:
    • Blood pressure pushes fluid from glomerulus into capsular space, then into renal tubule.

Renal Tubule Sections

  • Proximal Convoluted Tubule (PCT):
    • Simple cuboidal cells with microvilli (increase surface area).
  • Nephron Loop (Loop of Henle):
    • Composed of descending (thin) and ascending (thick) limbs.
  • Distal Convoluted Tubule (DCT):
    • Simple cuboidal cells with fewer microvilli.

Types of Nephrons

  • Cortical Nephrons:
    • 85% of nephrons, located primarily in the cortex.
  • Juxtamedullary Nephrons:
    • 15% of nephrons, extend into the medulla; utilize vasa recta instead of peritubular capillaries.