Comparative Vertebrate Kidneys

Vertebrate Kidneys: Fish

Highest development in FW fish; degeneration in those species that migrated to SW (why?)No loop of Henle in FW teleostsproduce most monovalent-ion free urine in vertebratesAglomerular forms (e.g., toadfish)---proximal tubule subs for glomerus (highly vascularized) Antarctic fish that produce anti-freeze proteins also aglomerular (care to speculate why?)

Vertebrate Kidneys: AmphbiansAll parts of nephron except loopsCan produce isosmotic or hyposmotic urineAmt of glomerular filtrate voided (14-90%) much higher than mammals (1%)ADH plays important role depending upon hydration state

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Vertebrate Kidneys: Reptiles Similar to amphibians, but lack bladder Reabsorb water from cloaca; remaining urine converted to uric acid pellets GFR and reabsorption values much greater than for amphibians, but less than humans Marine species rely more on extra-renal pathways

Vertebrate Kidneys: BirdsKidney divided into 3 (non-functional) lobesLike mammals, can produce a hypertonic urine

Nephron more like reptiles than mammals; a few with long loopsNo bladder (exc. Ostrich)---ureters open directly into cloacaSalt glands (esp. marine species) important