Comparative Vertebrate Physiology Osmoregulation in non-mammalian vertebrates

Osmoregulation Strategies Osmoconformers (plasma > 290 mOsm) Osmoregulators (plasma ~ 290 mOsm)

Osmoregulation

Aquatic environment Euryhaline Estuarine, salt marshes Stenohaline Most other species

Aquatic environment Freshwater problems High amount of water intake Loss of body salts Problem Solution

Aquatic environment Saltwater problems Prone to losing water Build up of body salts Problem Solution

Terrestrial environment Problem is dehydration Solutions in lectures to come Nasal countercurrent exchange Water from food Metabolic water Salt glands Concentrate urine

Kidney/nephron structure

Renal processes Filtration What is filtered? Water and solutes What isn’t filtered? Protein Blood cells Basis for filtration Size and charge

Renal processes Reabsorption 99% of water & solutes Passive and active Proximal tubule (60-80%)

Renal processes Secretion Water and solutes (1%)

Vertebrates Functional unit is the nephron Components Glomerulus Proximal tubule Loop of Henle (birds, mammals) Distal tubule Collecting duct

Teleosts Freshwater Large glomeruli Dilute, copious ultrafiltrate Ions reabsorbed Dilute, copious urine

Teleosts Saltwater Small glomeruli “Concentrated”, little ultrafiltrate Ions secreted Isotonic, little urine

Amphibians Function resembles that of a FW teleost Nephron structure Dilute, copious ultrafiltrate ml/Kg/hr Ions reabsorbed (99%) Copious, dilute urine ml/Kg/hr

Amphibians Most solutes are reabsorbed distally

Reptiles Only have 1 kidney that is bi-lobed Kidney Caudal junction Vertebrae

Reptiles Nephron structure Lower GFR than amphibians ml/Kg/hr Ion reabsorption (99%) Isotonic, little urine

Birds Tri-lobed kidneys Comprised of lobules Has cortex and medulla Cortex Medulla

Birds Nephron structure Bird Mammalian - Type

Birds Little ultrafiltrate (1 - 4 ml/Kg/hr) Ion and water reabsorption (99%) Slightly hyperosmotic urine

Urine to plasma osmolarity