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

2. Anatomy
Rectal Gland
Kidney
Gills

3. 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

4. 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

5. 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)

6. 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

7. Freshwater
Marine
Osmoregulation
NaCl
NaCl
NaCl
NaCl

8. 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

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

10. 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

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

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

13. 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)

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

15. 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

16. Questions?