Urinary System Summary

Functions of the Urinary System

  • Filtration of Plasma: Removes metabolic wastes (e.g., urea)
  • Regulation of Acid-base Balance: Maintains H+ and HCO3- levels
  • Regulation of Fluid and Electrolytes: Controls Na+, K+, Ca++
  • Regulation of Blood Pressure: Through renin secretion
  • Regulation of Erythropoiesis: Erythropoietin production
  • Contributes to Calcium Homeostasis
  • Supports Blood Glucose Levels During Starvation

Anatomy of Kidneys

  • Location: Retroperitoneal, T12 to L3, right kidney lower than left.
  • Capped by Adrenal Glands
  • Protection:
    • Renal fascia (dense irregular CT)
    • Perirenal fat capsule
    • Fibrous capsule

Kidney Structure

  • Renal Layers:
    • Renal Capsule
    • Renal Cortex (90-95% of blood vessels)
    • Renal Medulla (contains renal pyramids)

Blood Circulation in Kidneys

  • Key Arteries and Veins:
    • Renal artery and vein
    • Cortical radiate arteries and veins
    • Afferent and Efferent arterioles
    • Peritubular capillaries

Nephron Structure

  • Functional Unit:
    • Comprised of renal corpuscle and renal tubules
    • Key Components: Glomerulus, Glomerular (Bowman's) capsule, PCT, DCT
    • Types of Nephrons: Cortical (85%) and Juxtamedullary (15%)

Urine Formation

  • Processes:
    1. Filtration: Movement of fluid into nephron
    2. Reabsorption: Returns 99% of fluid to blood
    3. Secretion: Moves substances into tubular lumen
    4. Water Conservation: Removes water, concentrating wastes

Collecting System

  • Components: Connecting tubules -> collecting duct -> papillary duct
  • ADH's Role: Alters permeability; water recovery influenced by aquaporins

Ureters and Bladder Structure

  • Ureters: 25 cm long, transitional epithelium
  • Bladder: Posterior to symphysis pubis, transitional epithelium, rugae, 3 layers of muscle

Urethra Structure

  • Components: Protective mucous membrane, internal (smooth) and external (skeletal) urethral sphincters
  • Differences:
    • Female: 3-5 cm, anterior to vagina
    • Male: 18-20 cm, with 3 segments (prostatic, membranous, spongy)