How do freshwater fish regulate their ions?
- Freshwater fish are hyper-osmotic to their environment.
- Freshwater fish drink little water.
- Water enters the fish and ions exit the body by diffusion across thin membranes (gills/pharynx/skin/diet)
- Fish gain water and lose ions by diffusion
- Fish excrete large volumes of dilute water
- Ions are consumed through diet
- Monovalent ions (Na+, Cl-) are reabsorbed in nephron
- Active uptake of salts via gill epithelial (chloride cells and opercular epithelium)
How does the Chloride Cell work in freshwater teleost?
- active uptake of ions from environment
- Na+ from seawater into cell in exchange for H+ in chloride cell (H+/Na+ exchange pump) by active transport.
- Cl- from seawater is exchanged for HCO3- in chloride cell (Cl-/HCO3- exchange pump) by active transport.
- H+ and HCO3- are produces when CO2 from metabolism and H20 from body fluid combine.
- The Na+K+ATPase pump exchanges 3Na+ into extracellular for 2K+ into the chloride cell.
- The Cl- moves out through calcium channels on the basolateral membrane
How do chloride cells work in marine teleost?
- There is active transport of Na+ and Cl- out of the chloride cells.
- The NKCC co-transporter brings Na+, K+ and 2Cl- into the chloride cell from the extracellular fluid using the Na+ electrochemical gradient.
- The NKCC ions separate
The 2Cl- ions exit the chloride cell into seawater via chloride channels (down their concentration gradient) on the apical membrane. - K+ exits the cell back into the extracellular fluid through K+ channels (diffusion).
- Na+ exits the chloride cell via the Na+K+ATPase pump; 3NA+ into extracellular and 2K+ into chloride cell.
- High concentrations of Na+ in the extracellular cause Na+ to move from ECF to seawater via tight junctions - paracellular route.
How do marine teleost regulate their internal ion concentrations?
- Marine teleost are hypo-osmotic to their environment.
- Marine teleosts drink lots of seawater.
- Water moves out and ions move in by diffusion.
- Low volume of urine is produced.
- Urine mainly contains divalent ions (Mg2+, SO2-).
- Water is reabsorbed from the gut.
- There is active transport of monovalent ions out into seawater by chloride cells.
Why are chloride cells rich in mitochondria?
There is lots of active transport needed in a chloride cell and mitochondria produce ATP, which is needed.
Which bits of chloride cells are highly permeable and to which ions
The apical cleft is highly permeable to Cl- ions, and tight junctions are highly permeable to Na+
Give some features of Gills that make them perfect for ion exchange
- Short diffusion distance across epithelial
- Surface area of epithelial is large
- counter-current system for optimal exchange
- chloride cells and gas epithelial cells located on primary filament
- all cardiac output through gills
Where is the chloride cell located?
On the base of the secondary lamellae and operculum within the columnar cell (which spans the width of the epithelial membrane connecting the ECF to water)
What creates the ‘leaky junction system’?
Accessory cells
Which fluid is universal?
ICF is universal in ion composition but organic osmolytes vary.
