Urinary System Anatomy and Physiology Notes

Functions of the Urinary System

  • Kidneys:

    • Filter blood to remove waste products.
    • Regulate blood volume and blood pressure.
    • Maintain acid-base (pH) homeostasis.

  • Urinary Tract (Ureters, Bladder, Urethra):

    • Transport urine from kidneys to bladder.
    • Store urine until excretion.
    • Facilitate the expulsion of urine from the body.

Renal Physiology

  • Renal Process Overview:
    • Filtration: Movement of fluid from blood into the nephron (lumen).
    • Initial step where blood is filtered to create filtrate.
    • Reabsorption: Transport of substances from the nephron back into the blood.
    • Allows recovery of necessary substances such as glucose and ions.
    • Secretion: Removal of specific substances from blood into the nephron.
    • Important for eliminating excess ions and waste products.
    • Excretion: Elimination of urine from the body.
    • The final product of processed filtrate.

Structure of the Kidney

  • External Structures:

    • Fibrous Capsule: Protective outer layer.
    • Renal Hilum: Indentation for the entrance of vessels and ureter.
    • Renal Sinus: Internal cavity housing the renal pelvis and calyces.
    • Renal Fat: Surrounds and cushions the kidney.

  • Internal Structures:

    • Cortex: Outer layer containing nephrons.
    • Medulla: Inner region organized into pyramids and columns.
    • Renal Pelvis: Collection point for urine before it moves to the ureters.
    • Calyces: Minor and major calyces collect urine from pyramids.

Nephron Structure

  • Renal Corpuscle:
    • Bowman's Capsule: Cup-shaped structure surrounding the glomerulus.
    • Glomerulus: Network of capillaries for filtration.
  • Renal Tubule:
    • Proximal Convoluted Tubule (PCT): Site for reabsorption.
    • Nephron Loop (Loop of Henle): Important for urine concentration.
    • Distal Convoluted Tubule (DCT): Additional reabsorption and secretion.
    • Collecting Duct: Final adjustment of urine composition.

Vascular Elements of the Nephron

  • Afferent Arteriole: Supplies blood to the glomerulus.
  • Efferent Arteriole: Carries blood away from the glomerulus.
  • Peritubular Capillaries: Surround nephron tubules for absorption and secretion.
  • Vasa Recta: Specialized capillary system serving the renal medulla.

Histological Differences

  • Cortex:
    • Contains round corpuscles and convoluted tubules.
  • Medulla:
    • Comprises renal pyramids with straight tubules.

Juxtaglomerular Apparatus

  • Located at the point where the afferent arterioles and DCT meet.
  • Contains:
    • Juxtaglomerular Cells: Regulate blood pressure via renin secretion.
    • Macula Densa: Senses sodium concentration, influencing glomerular filtration rate (GFR).

Gross Anatomy of Urinary Structures

  • Ureters: Conduct urine from kidneys to the bladder.
  • Urinary Bladder: Holds urine, composed of the detrusor muscle and transitional epithelium.
  • Urethra: Excretes urine from bladder; length varies in males and females.

Microscopic Anatomy of Urinary Structures

  • Ureters and Bladder:
    • Mucosa: Transitional epithelium allows stretching.
    • Muscularis: Inner longitudinal and outer circular muscle layers.
    • Adventitia: Outer connective tissue layer.
  • Urethra:
    • Proximally contains pseudostratified columnar epithelium; distally consists of stratified squamous epithelium.

Path of Urine

  • Filtrate Pathway: Begins at the renal corpuscle, proceeds through nephron, enters collecting duct, travels through renal pelvis, ureters, bladder, and finally out through the external urethral orifice.