Osmoregulation, pH regulation, and Nitrogen excretion Homeostasis Osmoregulation, pH regulation, and Nitrogen excretion

Anatomy Rectal Gland Kidney Gills

Digitiform Rectal Gland Caudal region of intestinal tract Atrophied and non-functional in FW elasmobranchs Teleosts are lacking RG Major site of NaCl secretion (marine) RG connected by rectal duct to digestive tract, secretions are expelled

Kidney Paired organs on either side of vertebral column Selachians: long and narrow; Batoids: short and wide Renal vascular anatomy…VERY intricate…what do you need to know? Not much! Elasmobranch nephron complexity rivals mammalian

Gill 10 cartilaginous gill arches; 5 on each side of pharynx 5 to 7 gills slits on either side of head Filaments: functional unit of gills; thin lamellaeshort diffusion distance for gas exchange between blood and environment thus increasing SA Countercurrent exchange between afferent and efferent arterioles increases gas exchange efficiency (of lamellae)

Osmoregulation Marine Plasma Hyperosmotic Freshwater Large osmotic uptake of water via gills Rectal gland secretes NaCl Kidneys concentrate urea and reabsorb most water Freshwater Plasma Hyperosmotic Large osmotic uptake of water via gills Rectal gland nonfunctional Large urinary excretion NaCl uptake via gills, reabsorbed by kidneys

Freshwater Marine Osmoregulation NaCl NaCl NaCl NaCl

pH Regulation Gills primarily responsible Marine Freshwater Rapid pH buffering Subsequent net acid-base excretions Freshwater Rapid pH buffering & acid-base excretion Primary Ion absorption Aborbs Na+ with H+ secretion Absorbs Cl- with HCO3- secretion

Nitrogenous Metabolite Excretion Mostly excreted as urea, but must be retained for osmoregulation Ammonia is secreted with acid-base excretions

Evolution of Freshwater Elasmos Stenohaline marine elasmos Moderately euryhaline Fully euryhaline - no life cycles in fw Fully euryhaline - complete life cycle in fw Stenohaline freshwater - irreversible

Stenohaline Marine Large rectal gland Cannot regulate excretory function in lower salinity Squalus acanthias

Moderately Euryhaline Moderately-large rectal gland that can Some rectal gland regulation Dasyatis say Carcharhinus limbatus

Fully Euryhaline Rectal gland decreases in size with reduced salininty – can be “turned off” in fw Carcharhinus leucas Pristis perotteti & Dasyatis sabina (reproduce in fw)

Stenohaline - Freshwater Rectal gland atrophied and non-functional (IRREVERSIBLE!!!) Potamotrygonids

Future Research Has only been studied in a few species updated and expanded to other species New molecular techniques are being applied genes and proteins involved in processes Current research indicates homology of cellular and molecular processes to mammals future genomic and proteomic approaches to determine evolution of transport processes

Questions?