Histology of Urinary System

• Urinary Histology


  • Schematic of Uriniferous Tubule
  • Renal Corpuscle
  • Proximal Convoluted Tubule
  • Distal Convoluted Tubule
  • Thick Descending Loop of Henle
  • Thick Ascending Loop of Henle
  • Thin Limb of Henle's Loop
  • Collecting Duct
  • Longitudinal Renal Section
• Nephron


  Functional unit (renal corpuscle, PCT, LoH and DCT) and collecting duct
• Renal Corpuscles


  • Malpigian corpuscles (110-150 µm)
  • Located in cortical renal parenchyma
  • Consist of: Glomerulus, Bowman's Capsule (parietal, visceral and Bowman's space), Intraglomerular mesangial cells, Vascular and urinary pole
• Glomerulus


  • Arises from the afferent arteriole (4-8 rami) with up to 50 anastomosing of capillary
  • Composed of: Endothelial cells, Basement membrane
• Endothelial cells


  Extremely thin fenestrated capillary endothelium without diaphragm, Anionic in nature, Produces endothelin for vasoconstriction
• Basement membrane


  Ultra-thin structure (0.1-0.2 µm) for attachment of endothelium and podocytes, Type-IV collagen fiber embedded sialic acids, Mainly produced by endothelial cells and partly by podocytes, 3 layers (lamina rara interna, middle lamina densa and lamina rara externa)
• Bowman's Capsule - Visceral Layer

  • Podocytes - flattened cells enwrap external surface of glomeruli, Primary process - actin-rich cytoplasm extension, Secondary process - branching from the primary process, Tertiary process - foot-pad expansion with close contact to the basement membrane, Slit diaphragm (25 nm) - interdigital space between tertiary processes (P-cadherin and nephrin)
• Bowman's Capsule - Parietal Layer & Bowman's Space


  • Parietal layer - External part of Bowman's capsule, Flattened, simple squamous epithelium, Covering from vascular pole to the urinary pole, Underneath has basal lamina and loose connective tissue
  • Bowman's space - Between visceral and parietal layer, To collect ultra-filtrate before leave renal corpuscle via urinary pole
• Intraglomerular Mesangial Cells


  • Location - in between glomeruli and vascular pole, Bizarre, spindle-like shape appearance with heterochromatic nucleus, Long cytoplasmic process and penetrating basement membrane and endothelial glomerulus, Mesangial matrix - scatted fibril bundle (to allow contraction), Expressing angiotensin II receptor
• Proximal Convoluted Tubule (PCT)


  • Location - cortical renal parenchyma, Histomorphology: Tall cuboidal and/or low columnar epithelium (acidophilic), Prominent apical brush border (microvilli), Apically abundant lysosomes, peroxisomes and resorption vacuoles, Numerous lipid droplet in the apical cytoplasm (feline and canine), Ruminant and equine lacking of apical lipid droplet, Infolding basal membrane with stacking of elongated mitochondria, Basal labyrinth connecting between the adjacent cells, Enwrapping by peri-tubular capillary network (vasa recta)
• Loop of Henle (LoH)

  • Location - mostly in the medullary renal parenchyma, Histomorphology: Hairpin-like bend, Thick and thin descending and ascending segment, Both have close proximity with vasa recta to establish counter-current system, Avian have lacking (absence or short) in this system, Thick and thin lining with cuboidal and squamous epithelium, respectively, Lack of border brush, Nuclei slightly protruding into the lumen
• Distal Convoluted Tubule (DCT)


  • Location - cortical renal parenchyma, Close contact with glomeruli to partly form juxtaglomerular apparatus, Histomorphology: Cuboidal epithelial cells (light acidophilic cytoplasm), Wider tubular lumen, Irregular, small microvilli apical membrane, Prominent basal labyrinth with numerous mitochondria, Epithelial highly hormonal regulated (aldosterone, ADH, calcitonin and parathyroid)

  
• Juxtaglomerular Apparatus (JGA)


  • Location - dorsal to the renal corpuscle (cortical renal parenchyma), Consist of: Macula Densa - Located adjacent to the vascular pole between afferent and efferent arteriole, Part of DCT with tall, narrow and pale modified columnar epithelial cells, Juxtaglomerular Cells - Modified smooth muscle cells in the tunica media of afferent and efferent arteriole, Extraglomerular Mesangial Cells - Between macula densa and arterioles (afferent and efferent), Continuous from intraglomerular mesangial cells
• Collecting Duct (CD)


  • Location - cortical and medullary renal parenchyma, Short, arched collecting tubules merge to the CD, One CD drained from 10 nephrons, Grouped in parallel straight to the medulla to form medullary rays, CD merge to the papillary ducts and empty into renal papilla (area cribrosa), Gradually modified from cuboidal in the cortex to columnar in the medulla, Centrally located nucleus and pale cytoplasm, Lipid droplets in older animals and Goblet cells in equine, Expressing epithelial ADH receptors
• Ureter


  • Tunica mucosa - transitional epithelium, Empty ureter form longitudinal fold with stellate lumen, Loose lamina propria (equine - mucoid glands in the lamina propria), Tunica muscularis - inner and outer longitudinal smooth muscle layer with middle circular smooth muscle layer, Cat - inner circular and outer longitudinal smooth muscle layer, Each muscle layers joined obliquely, Tunica externa - tunica adventitia (fat) or tunica serosa (epithelial)
• Urinary Bladder


  • Tunica mucosa - transitional epithelium (to protect from hypertonic urine) - urothelium, Possess subplasmalemmal filament bundles and membrane vesicles, Lamina propria - delicate elastic fibers and highly mobilized, Present lymphoid follicles or lymphoid aggregation, Subepithelial highly vascularized (capillaries) - especially in ruminant, Tunica muscularis (detrusor muscle) - similar arrangement in ureter, Porcine and equine - inner longitudinal and outer circular smooth muscle, Intramural autonomic ganglia plexus (sympathetic and parasympathetic), Tunica externa - serosal layer
• Nephron


  Functional unit (renal corpuscle, PCT, LoH and DCT) and collecting duct
• Renal Corpuscles


  • Malpigian corpuscles (110-150 µm)
  • Located in cortical renal parenchyma
  • Consist of: Glomerulus, Bowman's Capsule (parietal, visceral and Bowman's space), Intraglomerular mesangial cells, Vascular and urinary pole
• Glomerulus


  • Arises from the afferent arteriole (4-8 rami) with up to 50 anastomosing of capillary
  • Composed of: Endothelial cells, Basement membrane
• Endothelial cells


  Extremely thin fenestrated capillary endothelium without diaphragm, Anionic in nature, Produces endothelin for vasoconstriction
• Basement membrane


  Ultra-thin structure (0.1-0.2 µm) for attachment of endothelium and podocytes, Type-IV collagen fiber embedded sialic acids, Mainly produced by endothelial cells and partly by podocytes, 3 layers (lamina rara interna, middle lamina densa and lamina rara externa)
• Bowman's Capsule - Visceral Layer

  • Podocytes - flattened cells enwrap external surface of glomeruli, Primary process - actin-rich cytoplasm extension, Secondary process - branching from the primary process, Tertiary process - foot-pad expansion with close contact to the basement membrane, Slit diaphragm (25 nm) - interdigital space between tertiary processes (P-cadherin and nephrin)
• Bowman's Capsule - Parietal Layer & Bowman's Space


  • Parietal layer - External part of Bowman's capsule, Flattened, simple squamous epithelium, Covering from vascular pole to the urinary pole, Underneath has basal lamina and loose connective tissue
  • Bowman's space - Between visceral and parietal layer, To collect ultra-filtrate before leave renal corpuscle via urinary pole
• Intraglomerular Mesangial Cells


  • Location - in between glomeruli and vascular pole, Bizarre, spindle-like shape appearance with heterochromatic nucleus, Long cytoplasmic process and penetrating basement membrane and endothelial glomerulus, Mesangial matrix - scatted fibril bundle (to allow contraction), Expressing angiotensin II receptor
• Proximal Convoluted Tubule (PCT)


  • Location - cortical renal parenchyma, Histomorphology: Tall cuboidal and/or low columnar epithelium (acidophilic), Prominent apical brush border (microvilli), Apically abundant lysosomes, peroxisomes and resorption vacuoles, Numerous lipid droplet in the apical cytoplasm (feline and canine), Ruminant and equine lacking of apical lipid droplet, Infolding basal membrane with stacking of elongated mitochondria, Basal labyrinth connecting between the adjacent cells, Enwrapping by peri-tubular capillary network (vasa recta)
• Loop of Henle (LoH)


  • Location - mostly in the medullary renal parenchyma, Histomorphology: Hairpin-like bend, Thick and thin descending and ascending segment, Both have close proximity with vasa recta to establish counter-current system, Avian have lacking (absence or short) in this system, Thick and thin lining with cuboidal and squamous epithelium, respectively, Lack of border brush, Nuclei slightly protruding into the lumen
• Distal Convoluted Tubule (DCT)


  • Location - cortical renal parenchyma, Close contact with glomeruli to partly form juxtaglomerular apparatus, Histomorphology: Cuboidal epithelial cells (light acidophilic cytoplasm), Wider tubular lumen, Irregular, small microvilli apical membrane, Prominent basal labyrinth with numerous mitochondria, Epithelial highly hormonal regulated (aldosterone, ADH, calcitonin and parathyroid)
• Juxtaglomerular Apparatus (JGA)


  • Location - dorsal to the renal corpuscle (cortical renal parenchyma), Consist of: Macula Densa - Located adjacent to the vascular pole between afferent and efferent arteriole, Part of DCT with tall, narrow and pale modified columnar epithelial cells, Serves as a chemoreceptor (Na+)
  • Juxtaglomerular Cells - Granular cells, Modified smooth muscle cells in the tunica media of afferent and efferent arteriole, Highly innervated by sympathetic nerve fibers
  • Extraglomerular Mesangial Cells - Polkissen cells and lacis cells, Between macula densa and arterioles (afferent and efferent), Continuous from intraglomerular mesangial cells, Proposed to serve as reserve cells for juxtaglomerular cells
• Collecting Duct (CD)


  • Location - cortical and medullary renal parenchyma, Short, arched collecting tubules merge to the CD, One CD drained from 10 nephrons, Grouped in parallel straight to the medulla to form medullary rays, CD merge to the papillary ducts and empty into renal papilla (area cribrosa), Gradually modified from cuboidal in the cortex to columnar in the medulla, Centrally located nucleus and pale cytoplasm, Lipid droplets in older animals and Goblet cells in equine, Expressing epithelial ADH receptors
• Ureter


  • Tunica mucosa - transitional epithelium, Empty ureter form longitudinal fold with stellate lumen, Loose lamina propria (equine - mucoid glands in the lamina propria)
  • Tunica muscularis - inner and outer longitudinal smooth muscle layer with middle circular smooth muscle layer, Cat - inner circular and outer longitudinal smooth muscle layer, Each muscle layers joined obliquely
  • Tunica externa - tunica adventitia (fat) or tunica serosa (epithelial)
• Urinary Bladder


  • Tunica mucosa - transitional epithelium (to protect from hypertonic urine) - urothelium, Possess subplasmalemmal filament bundles and membrane vesicles, Lamina propria - delicate elastic fibers and highly mobilized, Present lymphoid follicles or lymphoid aggregation, Subepithelial highly vascularized (capillaries) - especially in ruminant
  • Tunica muscularis (detrusor muscle) - similar arrangement in ureter, Porcine and equine - inner longitudinal and outer circular smooth muscle, Intramural autonomic ganglia plexus (sympathetic and parasympathetic)
  • Tunica externa - serosal layer
• Distal Convoluted Tubule (DCT)


  Located in the cortical renal parenchyma, close to glomeruli and forms part of the juxtaglomerular apparatus. Epithelial cells are cuboidal with light acidophilic cytoplasm, and have a wider tubular lumen with irregular, small microvilli on the apical membrane. The basal membrane has a prominent basal labyrinth with numerous mitochondria. Highly hormonally regulated by aldosterone, ADH, calcitonin, and parathyroid hormone.
• DCT Location


  Found in the cortical renal parenchyma, in close contact with glomeruli and forms part of the juxtaglomerular apparatus.
• DCT Epithelial Cells


  Cuboidal in shape with light acidophilic cytoplasm, wider tubular lumen, irregular, small microvilli on the apical membrane, and a prominent basal labyrinth with numerous mitochondria on the basal membrane.
• DCT Hormonal Regulation


  Highly regulated by aldosterone, ADH, calcitonin, and parathyroid hormone.
• Distal Convoluted Tubule (DCT)

  Located in the cortical renal parenchyma, close to glomeruli, and forms part of the juxtaglomerular apparatus.
• Cuboidal Epithelial Cells


  Line the DCT and have light acidophilic cytoplasm.
• Tubular Lumen


  Wider in the DCT with irregular, small microvilli on the apical membrane.
• Basal Membrane


  Holds a prominent basal labyrinth with numerous mitochondria.
• Hormonal Regulation


  Regulated by aldosterone, ADH, calcitonin, and parathyroid hormone.