Urinary System

• Renal Cortex (Outer Region)


  • Stains darker than medulla
• Renal Medulla (Inner Region)


  • Contains 8-12 renal pyramids containing a renal lobe
• Renal Pelvis (Inner Collecting Tube)


  • Renal Pyramids
  • Apical end contains renal papilla and minor calyx that eventually become one of three major calyces
  • Renal pyramids are separated by structures called renal columns
• Renal Hilum

  • Where renal artery and vein are located
  • The ureter exits the kidney from here
• Renal Artery

  • Largest
  • Divides into 2 segmental arteries at hilum
  • Supplies oxygenated blood from the heart to the kidneys
• Interlobar Arteries


  • Branch from segmental arteries
  • Extend between renal pyramids towards corticomedullary junction
• Arcuate arteries


  • Branches from interlobar arteries
• Interlobular arteries


  • Branches from arcuate arteries
  • Extend all the way to renal cortex
• Blood flow


  1. From large blood vessels to smaller and smaller vessels

  2. Reaches nephrons

  3. Flows out through renal vein back to the heart
• Glomerulus


  Filters blood to form the initial filtrate
• Peritubular capillaries


  • Reabsorb important substances back into the bloodstream
• Vasa recta


  • Help to maintain the concentration gradient in the medulla for water reabsorption and urine concentration
• Vasa recta


  • Straight venules and arterioles in the medullary region
  • Provide oxygen and nutrients in the renal medulla
  • Surround Henle's loop
• Peritubular capillaries


  • Tiny blood vessels in the cortical region of the kidney
  • Provide oxygen and nutrients in the renal cortex
  • Lie to the distal and proximal convoluted tubules
• Urine formation


  1. Filtration

  2. Secretion

  3. Reabsorption
• Nephrons


  • Structural and functional unit of the kidney
  • Each kidney contains 1-4 million nephrons
• Major Divisions of Nephron

  • Renal Corpuscle
  • Nephron/Renal Tubules
  • Connecting Tubule and Collecting system
• Renal Corpuscle


  • Dilated part enclosing a tuft of capillary loops
  • Site of blood filtration
  • Contains Glomerulus, Glomerular capsule (Bowman's capsule), Podocytes
• Glomerulus

  • Fenestrated Capillary Endothelium
  • Glomerular Basement Membrane
  • Slit Pores
• Renal Tubules

  For reabsorption and secretion of substances
• Proximal Convoluted Tubule


  • Located at renal cortex
  • Simple cuboidal cells
  • Contains microvilli
  • Abundant mitochondria
  • Basolateral folds
  • Reabsorbs glucose, amino acids, electrolytes, water
• Loop of Henle


  • With Thin Ascending and Thin Descending parts
  • Contains simple SQUAMOUS epithelium
  • Also contains Thick Ascending Limb
  • Macula Densa
• Distal Convoluted Tubule


  • Where Electrolyte Levels are adjusted further
  • Simple cuboidal cells
  • Smaller and having no brush border and more empty lumens
  • Flatter than proximal tubule, more nuclei, fewer mitochondria
• Connecting Tubules


  • Join to form the cortical collecting ducts
  • Last part of each nephron
  • Carries the filtrate into a collecting system
• Principal Cell


  • Pale staining, few mitochondria
  • Contain cell membranes rich in aquaporins, for passive water reabsorption
• Intercalated Cell


  • With more abundant mitochondria and projecting apical folds
  • Help maintain acid-base balance by secreting H+ or HCO3-
• Urinary Bladder


  • Where urine temporarily is stored
  • Contains folded mucosa which unfold as bladder fills
  • Transitional epithelium gets thinner as bladder fills
• Ureter


  • Tubes that transport urine from the kidneys to the bladder
  • Lined by transitional epithelium
• Urethra

  • Drains the bladder in both genders
  • Lined initially by urothelium
  • In men, the two ducts for sperm transport during ejaculation join the urethra at the prostate gland
  • In women, transitions to nonkeratinized stratified squamous epithelium
• Male Urethra Regions

  • Prostatic Urethra
  • Membranous Urethra
  • Spongy Urethra
• The middle part of the urethra in both sexes is surrounded by the external striated muscle sphincter