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Renal Histology

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University of Windsor
Biological Sciences

Renal Histology--Dintzis GROSS ANATOMY - Kidney cortex: contains distinctive glomeruli, convoluted tubules, parts of collecting ducts - Kidney medulla: below the cortex, contains limbs of Henle & collecting ducts - Medullary ray: groups of collecting ducts that extend from cortex to medulla - Calyx: terminal expansions of ureter in the kidney, minor calyces meet up with papilla (papilla →minor calyx →major calyx →pelvis →ureter) - Papilla: termination of collecting duct into a minor calyx - Lobe: a medullary pyramid and the overlying cortex - Lobule: lateral borders marked by medullary rays - Arteries in order: abdominal aorta, renal artery, interlobar, arcuate, interlobular, intralobular, afferent arteriole, glomerulus, efferent arteriole, vasa recta RENAL CORPUSCLE - Renal corpuscle: glomerulus + Bowman’s capsule - Glomerulus: tufts of capillaries with fenestrated (“holey”) endothelium - Parietal Epithelium: squamous pariental epithelium of Bowman’s capsule that’s continuous w/ epithelium of proximal tubule - Visceral Epithelium: composed of podocytes - Podocytes: easily seen at border of glomerulus, obvious under EM, have filtration slits that act as filtration barrier; Fxn: manufacture basement membrane, provide filtration support - Mesangial cells: produce & breakdown basement membrane; uptake macromolecules; can respond to local injury; embedded in mesangial substance (stains bright purple/blue—PAS-positive) - Basement membrane: very thick (3500A), PAS-positive, trilaminar (lamina rara interna, lamina densa, lamina rara externa), primary glomerular filtration barrier o Contains type IV collagen, glycoproteins, & proteoglycans * Blood must pass through 1) endothelium, 2) basement membrane, 3) podocyte feet, before entering bowman’s space TUBULES Cortical nephrons—shorter loops, common Corticomedullary nephrons—less numerous, long loops, key in establishing gradient - Proximal convoluted tubule: longest thickest tubule, reabsorbs ~80% H2O & salts as well as all Glu, aa, & proteins; secretes organic cations/anions o Prominent brush border of microvilli for reabsorption (PAS+) o Tall columnar cells w/ interdigitation of cell surfaces o many mitochondria arranged perpendicular to basement membrane - Descending Thick Limb of Henle: sim. to proximal convoluted tubule - Thin limb of Henle: may be hard to distinguish from vasa recta (thin limb has thicker basement membrane than vasa recta), ascending (ATL) and descending (DTL) limbs cannot be distinguished 1 o Thick, PAS+ basal lamina o Low, cuboidal cells or squamous epithelium o DTL & ATL differ in permeability to H2O & salts - Thick ascending limb of Henle: active Na pumps => salt reabsorption but impermeable to H2O; o NO brush border; many mitochondria => striations o Eosinophilic cytoplasm - Distal convoluted tubule: sensitive to aldosterone (=> increased salt reabsorption) excretes K+; helps maintain acid-base balance o PAS stains heavier than collecting duct, cells smaller than collecting duct o Cuboidal cells w/ no brush border; abundant mitochondria - Collecting duct: columnar cells w/ sharp lateral border, no brush border, pale under PAS (paler than distal convoluted tubule), cells larger than distal convoluted tubule o Principal cells—remove H2O from filtrate; dependent on ADH for aquaporin placement in apical cell membranes o Intercalated cells—secrete & resorb protons - Macula densa: part of thick ascending limb that abuts vascular pole of
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