Renal 1 - Osmotic and Ionic Regulation

Origins of Life

• Began in a saltwater environment

• As organisms began to move, they encountered different environments

Aquatic Environments

• Can vary greatly in their salinity

  – Chesapeake Bay (is an estuary with mixing of salt + fresh water)

• Brackish Waters

• Estuaries

Concentrations of major ions in seawater and freshwater

Changing Environment

• Cells and organisms need to function in varied environments

• Strategies include:

  • Maintaining tight control of internal environment (regulators)

  • Maintain cellular function while matching the environment (conformers)

regulators

• Maintaining tight control of internal environment

• organisms that maintain that internal enviro regardless of what external enviro is like

• ex. maintain amount of solutes (Na, Cl) inside the organism despite what’s going on outside, need to ensure internal conc does’t change

conformers

• Maintain cellular function while matching the environment

• need to ensure cellular function continues even with internal enviro changing to match external

Regulation and Conformity

Under regulatory control -

• osmotic regulation → total dissolved solutes (ensure # doesn’t change)

• ionic regulation → regulate specific ions

• volume regulation → organisms like crabs and lobsters bring in excess salt to inflate body, since water follows salt, when molting (changing exoskeleton) thus allows them to control volume/size of body by shuttling salt and water around

osmotic regulators vs conformers

regulator vs conformer (examples)

• mussel = conformer

• shrimp = regulator

• green crab = regulator until extremes then conforms

Osmosis

diffusion of water

• Water will move to areas of higher concentration (tries to equilibriate)

• Water will move towards areas with LESS “free water” (water not bound up + surrounding solutes)

Osmolarity

Measurement of TOTAL dissolved solutes

regulators in freshwater

External Environment is Hypo-osmotic (hypo = less)

regulators in salt water

External Environment is Hyperosmotic (hyper = more)

isosmotic

having same/equal osmotic pressure

Challenges to Freshwater Regulators

• Constantly taking in water through osmosis

• Constantly LOSING ions

• (water is hyposmotic to organism)

Challenges to Marine (Salt Water) Regulators

• Constantly Losing water

• Constantly LOADING ions

• (hyperosmotic water)

Organs of Salt/Water Balance Gills

• this organ allows regulators to deal w challenges of maintaining balance

• folds increase SA of gills and is very permeable

Gills

• High permeability and large surface area

  • benefits to gas exchange (ensures lots of contact w water where O2 can be drawn out)

  • O2 is very low (low in water so need to acquire more O2 somehow)

• Counterproductive for water-salt balance

  • large SA increases osmosis of water

  • permeability allows for movement of ions

• Animals w high O2 demands (ex. salmon, fish that swim a lot) must deal w high water-salt exchange

gill anatomy

• Mitochondria Rich Cell (MRC)

• pavement cell

Cell Types Gills

• Pavement Cells

  – Occupy ~ 90% of gill epithelium

  – Principally responsible for O2 uptake

• Mitochondria-Rich Cells (MRCs)

  – Uptake of Cl-, Na+, and Ca2+ in freshwater

  – Excretion of Cl- and Na+ in salt water

  – Partially Under Hormonal Control

  – Density and TYPE can be changed in varying conditions

MRC cross section of gill

Reminder of the Challenges

• in freshwater (osmotic pressure in org > external enviro)

  • influx of H2O

  • loss of ions → [ion]in > [ion]out so wants to move down conc gradient

• in salt water

  • loss of H2O

  • influx of ions

Solution to challenges – Active Transport

• In Freshwater

  – Mitochondria-Rich Cells bring ions in (mitochondria are the power plants of cells, create ATP which powers transport)

  – Water loading countered by production of copious amounts of dilute urine

  • In Salt Water

  – Mitochondria-Rich Cells move ions out, (push to enviro where there is a high conc.)

  – Water loss countered by drinking

freshwater gills - membranes and cells 1

freshwater gills - V-type 2

freshwater gills - sodium potassium pump 3

freshwater gills - K+ leak channels 4

freshwater gills - electroneutral anion exchanger + CFTR 5

cystic fibrosis

• genetic mutation in CFTR

• reduces Cl- clearance

• maintains higher than normal electronegative potential in the cell

  • bc less negative leaving the cell so stronger electromotive force drawing cations into cells

• reduces extracellular removal of cations (Na+)

  • increased solute buildup, water follows solutes → waterlogged → makes it more prone to infection

• increase mucosal buildup → causes respiratory and digestive difficulties

freshwater gills - calcium co-transporter and calcium-ATPase 6

marine animals - summary

– Lose Water through osmosis

– Re-hydrate by drinking seawater

– Load up on ions that need to be removed

drinking seawater 1

• Water in the gut will be HYPEROSMOTIC to blood plasma

  • Will draw water out of the blood plasma by osmosis

  • Na and Cl will diffuse INTO blood plasma due to concentration difference

• Net result would be VERY concentrated blood plasma

• This is why we (mammals) can’t drink seawater to rehydrate

drinking seawater 2

• Later parts of the intestine, Na and Cl are ACTIVELY transported out of the gut

  • Creates a gradient that favours water retention

• 50 – 85% of water is absorbed into the blood

• 97% of Na and Cl MUST be absorbed!!

Ion Regulation

• Excess ions MUST be removed

• Occurs in the gills

• Also contain MRCs and pavement cells

  – As well as accessory cells

marine gills - membranes and cells 1

marine gills - NKCC cotransporter 2

marine gills - calcium co-transporter and calcium-ATPase 3

terrestrial organisms

No longer surrounded by water

• challenge, need to make sure that water is maintained inside organism

Marine Birds/Reptiles 1

• blood is hypo-osmotic to saltwater

• water loss

• salt loading

Marine Birds/Reptiles 2

• Less Permeable integument (skin surface)

  – Decreases water loss

• Water loss through respiration

• Hyperosmotic H2O ingested

  – Either directly, or through food source

• Must remove excess solutes (ex. Na, Cl)

Marine Birds - Strategies

• Gulls (Charadriiformes)

• Penguins (Sphenisciformes)

• Albatross (Procellariiformes)

• Pelicans (Pelecaniformes)

have ducts connecting salt glands to nostrils, excess NaCl excreted out through nostril

marine birds - how to get NaCl out of blood

salt glands

special cases

• Elasmobranchii

  – Sharks, Rays, Skates

• Marine Osmoconformers → matches internal enviro to external

  – Produce high concentrations of organic solutes

  – Urea (stable form of nitrogen, byproduct of metabolism converted to this)

  – TMAO (-counteracts toxic effects of urea)

Special Cases - Salmon

– Born in freshwater

– Migrate to seawater to grow

– Return to freshwater to reproduce

salmon - behavioural

• spend time in brackish waters → mixture of fresh and salt water

• increase or reduce the amount of water that is consumed (reduce: salt → fresh)

salmon - physiological

• Kidney function changes

  • High volume of dilute urine in freshwater saltwater

• Gills that take up ions in freshwater, remove them in sea water