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- Cortex shows glomeruli plus proximal/distal tubules; medulla has loops of Henle and collecting ducts.
- Glomerular architecture: capillary loops with podocytes, mesangium, and parietal epithelium on Bowman capsule.
- Collecting system transitions to urothelium (renal pelvis → ureter → bladder) with smooth muscle in the wall.
- Vessels follow lobular pattern: interlobular → arcuate → interlobar with accompanying veins.
- Glomeruli: open capillary loops, thin basement membranes; mesangial areas delicate; parietal layer simple squamous.
- Proximal tubules: eosinophilic, brush border, larger cells; reabsorption workhorses.
- Distal tubules: paler cytoplasm, no brush border; tighter lumens.
- Collecting ducts (cortical): cuboidal to low columnar, clear cytoplasm, distinct borders.
- Thin loops of Henle (simple squamous), thick ascending limb (cuboidal, no brush border), vasa recta capillaries.
- Medullary collecting ducts columnar in inner medulla; interstitium sparse but can have scattered lymphocytes/medullary fibroblasts normally.
- Stratified epithelium with umbrella cells on top; thickness varies with distension.
- Lamina propria collagenous; muscularis with inner longitudinal + outer circular (opposite of GI) in ureter.
- Adventitia/serosa depending on segment; nerves and vessels in adventitia are normal.
- Glomerular/podocyte: WT1, podocalyxin, synaptopodin.
- Tubules: PAX8+, E-cadherin in distal nephron, CD10/LRP2 in proximal.
- Collecting duct: CK7+, EMA+, aquaporin-2.
- Urothelium: GATA3, uroplakin, CK7/CK20 pattern (surface CK20), p63 in basal cells.
