homeostasis osmoregulation, ph regulation, and nitrogen excretion
TRANSCRIPT
HomeostasisHomeostasis
Osmoregulation, pH regulation, Osmoregulation, pH regulation, and Nitrogen excretionand Nitrogen excretion
AnatomyAnatomy
Rectal GlandRectal Gland KidneyKidney GillsGills
Digitiform Rectal GlandDigitiform Rectal Gland Caudal region of Caudal region of
intestinal tractintestinal tract Atrophied and non-Atrophied and non-
functional in FW functional in FW elasmobranchselasmobranchs
Teleosts are lacking RGTeleosts are lacking RG Major site of NaCl Major site of NaCl
secretion (marine)secretion (marine) RG connected by rectal RG connected by rectal
duct to digestive tract, duct to digestive tract, secretions are expelledsecretions are expelled
KidneyKidney Paired organs on either side of vertebral columnPaired organs on either side of vertebral column Selachians: long and narrow; Batoids: short and Selachians: long and narrow; Batoids: short and
widewide Renal vascular anatomy…VERY intricate…what do Renal vascular anatomy…VERY intricate…what do
you need to know? Not much!you need to know? Not much! Elasmobranch nephron complexity rivals Elasmobranch nephron complexity rivals
mammalianmammalian
GillGill• 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 lamellaeshort 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)
OsmoregulationOsmoregulation
MarineMarine Plasma HyperosmoticPlasma Hyperosmotic Large osmotic uptake Large osmotic uptake
of water via gillsof water via gills Rectal gland secretes Rectal gland secretes
NaClNaCl Kidneys concentrate Kidneys concentrate
urea and reabsorb urea and reabsorb most watermost water
FreshwaterFreshwater Plasma HyperosmoticPlasma Hyperosmotic Large osmotic uptake Large osmotic uptake
of water via gillsof water via gills Rectal gland Rectal gland
nonfunctionalnonfunctional Large urinary Large urinary
excretionexcretion NaCl uptake via gills, NaCl uptake via gills,
reabsorbed by kidneysreabsorbed by kidneys
Osmoregulation
NaCl
MarineFreshwater
NaCl
NaCl
NaCl
pH RegulationpH Regulation
Gills primarily responsibleGills primarily responsible
MarineMarine Rapid pH bufferingRapid pH buffering Subsequent net acid-base excretionsSubsequent net acid-base excretions
FreshwaterFreshwater Rapid pH buffering & acid-base excretionRapid pH buffering & acid-base excretion Primary Ion absorptionPrimary Ion absorption
Aborbs NaAborbs Na++ with H with H++ secretion secretion Absorbs ClAbsorbs Cl-- with HCO with HCO33
-- secretion secretion
Nitrogenous Metabolite Nitrogenous Metabolite ExcretionExcretion
Mostly excreted as urea, but must be Mostly excreted as urea, but must be retained for osmoregulationretained for osmoregulation
Ammonia is secreted with acid-base Ammonia is secreted with acid-base excretionsexcretions
Evolution of Freshwater Evolution of Freshwater ElasmosElasmos
Stenohaline marine elasmosStenohaline marine elasmos Moderately euryhalineModerately euryhaline Fully euryhaline - no life cycles in fwFully euryhaline - no life cycles in fw Fully euryhaline - complete life cycle Fully euryhaline - complete life cycle
in fwin fw Stenohaline freshwater - irreversibleStenohaline freshwater - irreversible
Stenohaline MarineStenohaline Marine
Large rectal gland Large rectal gland Cannot regulate Cannot regulate
excretory function in excretory function in lower salinitylower salinity
Squalus acanthiasSqualus acanthias
Moderately EuryhalineModerately Euryhaline
Moderately-large Moderately-large rectal gland that can rectal gland that can
Some rectal gland Some rectal gland regulationregulation
Dasyatis sayDasyatis say
Carcharhinus limbatusCarcharhinus limbatus
Fully EuryhalineFully Euryhaline
Rectal gland Rectal gland decreases in size with decreases in size with reduced salininty – reduced salininty – can be “turned off” in can be “turned off” in fwfw
• Carcharhinus leucas• Pristis perotteti & Dasyatis sabina
(reproduce in fw)
Stenohaline - FreshwaterStenohaline - Freshwater
Rectal gland Rectal gland atrophied and non-atrophied and non-functionalfunctional
(IRREVERSIBLE!!!)(IRREVERSIBLE!!!) PotamotrygonidsPotamotrygonids
Future ResearchFuture Research
Has only been studied in a few speciesHas only been studied in a few species updated and expanded to other speciesupdated and expanded to other species
New molecular techniques are being New molecular techniques are being appliedapplied genes and proteins involved in genes and proteins involved in processesprocesses
Current research indicates homology of Current research indicates homology of cellular and molecular processes to cellular and molecular processes to mammalsmammals future genomic and future genomic and proteomic approaches to determine proteomic approaches to determine evolution of transport processes evolution of transport processes
Questions?Questions?