Ch28 water and salt physiology

Freshwater osmotic pressure

10 mOsmol/kg

Freshwater animals

Blood has high salt conc compared to freshwater; osmosis: water flows inward, gain water and lose salts

Freshwater crayfish adaptations

Gills: water in by osmosis, salts out by diffusion; ion pumps move salt in

Antennal Glands: produce copious dilute urine (water moves out)

Cuticle/Shell: low permeability to salts and water

Blood concentration: dilute, about 50% less conc than seawater

Freshwater teleost fish osmoregulation

Gills: water in by osmosis, salts out by diffusion; ion pumps move salt in (active Na and Cl transport across gill); mitochondria rich cells surrounded by pavement cells in gill epithelium

Amphibians osmoregulation

Ion pumps move sodium across frog skin from water into blood; measure ion movements across frog skin using Ussing Chamber

Seawater

1 liter has about 35 g dissolved salts (35g/L): Na and Cl

Salinity 35 ppt= 35 g/L = 3.5% = 599 mM

Molarity: 599 mM/L

Osmotic pressure about 1000 mOsmol/kg

Marine invertebrates and hagfish

Blood salts 100% seawater; isosmotic to sw; narrow tolerance for dilute sw (stenohaline) osmoconformers (do not osmoregulate)

Marine teleost fish

Osmoregulators; blood salts dilute; only 33% sw

Problematic gradients: osmosis-constant water gain, diffusion-constant salt gain

Gills: mitochondria rich cells pump salts out, fish drink sw

Marine reptiles

Have salt glands to get rid of high salt load from ingesting sw

Salt glands

Pump salts out of body; kidneys cannot excrete a lot of salt

Marine iguanas

Salt glands in nasal cavity; sneezes out a spray of salt solution from nostrils

Marine turtles

Salt glands in orbit; salt solution secreted as tears

Sea snakes

Salt glands in oral cavity; salt solution secreted into mouth

Saltwater crocodiles

Salt glands under tongue (lingual), salt solution secreted into mouth

Marine birds

Salt glands in head to pump salts out of body; produce hypertonic solution of NaCl several times as high as the maximum urine conc

Fish, reptiles, birds

All have kidneys, but marine species all have either salt-secreting cells in gills of salt-secreting glands in head region

Marine sharks, skates, and rays

Salt-secreting rectal glands

Urea

Nitrogenous waste product of sharks, skates, rays (elasmobranchs), coelocanth, crab-eating frog

Marine elasmobranchs

Osmoregulatory organs: rectal glands and kidneys

Blood OP about 1018 mOsmol/kg (slightly above SW)

Water in across gills slowly by osmosis, do not need to drink SW (avoids the extra NaCl load)

Elasmobranchs

High blood OP result of blood salts only about 50% SW, raise OP to 100% by retaining urea in blood (w/ TMAO)

Osmoregulatory organs: kidneys, rectal gland (role of gills uncertain)

Freshwater elasmobranch

Amazon sting ray

Blood OP low (308 mOsm), does not retain urea, no TMAO in blood, OP of FW 10 mOsm (water in by osmosis, salts out by diffusion)

Coelocanth

Osmoregulatory organs: gills and kidneys

Blood salts only 42% SW

OP raised to same as SW by retaining urea and TMAO

Marine Crab-eating Frog

Blood salts only 54% SW

OP raised to same as SW by retaining urea and TMAO

Stenohaline fish

Tolerate only a narrow range of salinities (osmoconformers)

Euryhaline fish

Tolerate wide range of salinities (osmoregulators)

Catadromous fish (eels)

Born in SW, juveniles migrate into FW and adults grow in FW, adults migrate down-river back to SW to spawn

Anadromous fish (salmon)

Born in FW, juveniles migrate into SW and adults grow in SW, adults migrate down-river back to FW to spawn

Bony fish

Osmoconformers and osmoregulators: Eel (catadromous) lives in FW, breeds in SW, OP blood in SW 371 mOsm, in FW 323 mOsm

Atlantic salmon (anadromous)

Lives in SW, breeds in FW, OP blood in SW 400 mOsm, OP blood in FW 340 mOsm

When fish move from SW to FW

Reverse direction of NaCl transport across gills (out in SW, inward in FW)

In FW, stop drinking or decrease drinking rate

In FW, increase rate of urine production

In FW, switch urine from isosmotic to copious hyposmotic urine