urinary

• Urinary System

  Homeostasis<|>Excretion of metabolic waste products and excess water<|>Production of hormones & other biologically active substances
• Kidneys

  • Bean-shaped
  • Posterior abdominal wall
  • T12 - L3
  • 10-12cm long, 5-6cm wide, & 2.5-3cm thick
  • Convex laterally, concave medially; vertical fissure - hilus
• Kidney regions

  1. Cortex

  2. Medulla

  3. Cortico-medullary junction
• Renal pyramids

  • 10-15 per kidney
  • Longitudinal striations, conical
• Cortex


  • Pars convoluta (cortical labyrinth)
  • Renal pyramids
  • Renal columns of Bertin
• Lobes & Lobules

  • Lobe - renal pyramid, cortical tissue overlying the pyramid's base & surrounding its sides
  • Lobule - papillary duct, collecting tubules
• Blood vessels, lymphatics & nerves

  1. Right & Left renal arteries

  2. Interlobar arteries

  3. Arcuate arteries

  4. Interlobular arteries

  5. Afferent arterioles

  6. Glomerular capillaries

  7. Efferent arterioles

  8. Peritubular capillary network
• Uriniferous tubules


  Nephron & intrarenal ducts (collecting tubules & papillary ducts)<|>Distinction between urine producing nephrons & urine conducting tubes to the main excretory duct
• Nephrons


  • Basic functional unit of the kidney
  • 1 - 1.5M per kidney
• Renal Corpuscle (Malpighian Corpuscle)

  • Spherical
  • Proximal end of the nephron
  • 200 um diameter
  • In the cortex, granular
• Glomerulus


  • Ball-like structure
  • Mesangial matrix (mesangium)
  • Glomerular mesangial cells
• Bowman's Capsule

  • Parietal
  • Visceral (podocyte)
  • Bowman's space, capsular/subcapsular space, urinary space
  • Podocytes
  • Filtration slits
• Proximal Convoluted Tubule


  • Direct continuation of the Bowman's capsule
  • Longest segment, tortuous
  • Confined within the cortex (majority)
  • Simple cuboidal epithelium
• Loop of Henle

  Start in the cortex as continuation of the PCT, dip into the medulla where it makes a hairpin turn back to the cortex
• Thick Descending Limb of the Loop of Henle


  • Initial straight segment
  • Partly in the cortex and partly in the medulla
  • Histologic structure & function similar to PCT
• Thin Limb of the Loop of Henle

  • Continuation of the descending limb
  • Confined within the medulla
• Thick Ascending Limb of the Loop of Henle

  • Continuation of the thin limb
  • Starts from the medulla then heads up to the cortex to get in contact with the vascular pole of the renal corpuscle of its parent nephron
• Distal Convoluted Tubule


  • Last segment of the renal tubule
  • Entirely within the cortex
• Classification of Nephrons

  • Cortical
  • Juxtamedullary
• Juxtaglomerular Complex

  • JG cells
  • Macula densa
  • Extraglomerular mesangial cells
• JG Cells

  • Polyhedral cells that replace the smooth muscle cells in the tunica media of the afferent arteriole just before entering the renal corpuscle
  • Disappearance of the internal elastic lamina & thinned out tunica adventitia
• Macula Densa


  • Atypical epithelial cells on the wall of the DCT that abuts the afferent arteriole
  • Crowded, narrower, & rest on a very thin basal lamina
  • Intensely stained nuclei
• Extraglomerular Mesangial Cells


  • Form a conical mass between the macula densa & the afferent arteriole
  • Flat, light staining cells
• Intrarenal Ducts

  1. Collecting Tubules

  2. Papillary Ducts of Bellini
• Collecting Tubules

  • Continuation of the DCT
  • Start in the cortex as a short segment that curves then straightens to the medulla
  • Upon reaching the medulla, these tubules merge several times to form a much larger tube (100 -200um) - papillary duct
• Papillary Ducts

  • Main occupants of the renal pyramids
  • Portions of LoH, vasa recta, nerves, & minimal amount of connective tissues
  • A pyramid has about 25 papillary ducts whose ends form the renal papilla or apex of the pyramids which fits into a minor calyx
  • Area cribrosa
• Urinary Passages & Urinary Bladder

  • Mucosa - epithelium, lamina propria, ureter
  • Lamina Propria - thin in calyces & pelvis, thick in ureter & urinary bladder, LCT, elastic fibers
  • Adventitia/Serosa - blood vessels, lymphatic vessels, & nerves
• Urethra - Male

  • 20cm long
  • 3 segments: prostatic, membranous, spongy (penile, cavernous)
• Prostatic Urethra


  • Transitional epithelium
  • Poorly developed LP, many elastic fibers and veins
  • Few glands of Littre - small, branched mucous secreting tubulo-alveolar glands which empty into the lumen of the urethra
• Membranous Urethra

  • Stratified or pseudostratified columnar epithelium
  • Surrounded by skeletal muscle fibers belonging to the sphincter urethrae muscle
• Penile Urethra


  • Same type of epithelium as the membranous urethra
  • Except in certain areas and terminally with stratified non-keratinized squamous epithelium
• Urethra - Female

  • Shorter (4cm)
  • Opens in front of the vaginal opening on the vestibule
  • Transitional; stratified non-keratinizing squamous epithelium near the urethral orifice
  • Muscle layer - internal coat of longitudinal & obliquely arranged smooth muscle cells; outer coat of circularly arranged skeletal muscle fibers which makes up part of the sphincter urethrae muscle