Histology of the Urinary Tract

Lecture given:


List the main functions of the different segments of the nephron

  • nephron: production of ultrafiltrate from blood; conservation of water; removal of metabolic waste
Na/K/ATPase H2O Ions Glucose, AA, protein Uric acid, Creatinine, drugs Diuretic Histology Mutation
PCT yes reabs reabs reabs secrete CI 15mm; Dark cytosol, small lumen Fanconi's
Thin loop (D) little highly reabs little no no N/A 2-14mm; epithelial cells like sunny side up eggs
Thin loop (A) yes NO passive reabs no no N/A
TAL yes NO NaCl reabs, X2+ reabs no no Loop 12mm; Thicker cells, larger nucleus Bartter's
DCT yes no? Ca2+ reabs, Cl reabs no no Thiazide 5mm; lighter cytosol, larger lumen Gitelman's
CD (p) yes (aldo) yes (ADH + Aldo) reabs K or Cl no no K sparing 20mm; Cell divisions visible due to interdigitation
CD (α) yes no H secretion no no N/A

describe components, location and function of the juxtaglomerular apparatus

  • Located where the TAL/DCT touches the afferent arteriole
  • In TAL/DCT area (macula densa) - NaCl sensor
  • Juxtaglomerular cells (modified smooth muscle) senses BP through stretch receptors, and secrete renin
  • Extraglomerular mesangial cells
  • Renin release dependent on NaCl concentration and BP (stretch of the afferent arterial)

compare the epithelial lining of proximal tubule and distal tubule

Cytosol Darker (mitochondria) Lighter
Lumen Narrower (hard to see)* Wider
Length Longer Shorter

* due to brush border made of microvilli to faciliate reabsorption

describe the location and histology of the renal medulla

  • Made of loops of henle, descending and ascending tubules, collecting ducts and capillaries (vasa recta) arranged in parallel
  • Located deep to the cortex, but in-foldings of the cortex divides the medulla into renal pyramids
  • Coalesce of CDs into papillary ducts (columnar epithelium), and open at the tips of renal papillae

explain the structure and significance of transitional epithelium

  • Lines ureter and bladder
  • pseudostratified with all cells attached to one basement membrane (supported by lamina propria):
    • Not all cells reach the lumen, and nuclei are found at different levels. Short cells are often stem cells
    • Able to rearrange to accommodate pressure
  • Bladder: Protein plaques on apical plasma membrane anchored to cytoskeleton and can fold and expand as bladder fills

compare the features of ureter and urinary bladder

  • Ureter
    • lumen has stellate outline in transverse section due to longitudinal folds
    • Thick muscularis in two layers (outer circular, inner longitudinal)
    • Surrounded by adventitia
  • Bladder
    • thicker transitional epithelium, binucleate cells present
    • surface cells contain angular vesicles, representing a reservoir of surface membrane (protein plaques)
    • Mucosa normally folded in the relaxed state
    • Three layers in muscularis, prominent middle layer


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