24. Osmoregulation and the kidney Flashcards
What are the main functions of the excretory organs?
- Maintain osmotic concentrations
- Maintain proper concentrations of ions
- Remove metabolic end products
What is the definition of osmolarity?
The concentration of moles of active solutes per litre of solvent
What is osmotic pressure?
Force associated with the movement of water
What is the relationship between osmolarity and osmotic potential?
Low osmolarity = equals high osmotic potential
What is osmolality?
The concentration of solutes per kilogram of solvent
What is tonicity?
The concentration of non permeable solutes per litre of solvent
How do excretory organs control osmolarity and volume of extracellular fluids?
- By excreting water and solutes that are in excess
- By conserving water and solutes that are valuable or in short supply (eg glucose)
What are the three examples of nitrogenous waste?
- Ammonia (most water needed)
- Urea
- Uric acid (least toxic)
Where is urea synthesised?
in the liver
What are the challenges of marine animals?
They have to conserve water and excrete excess salts
What are the challenges of freshwater animals?
They have to excrete excess water and conserve salts
What are the challenges of terrestrial animals?
They have to conserve water and salts
What are osmoregulators?
Osmoconformers match their body osmolarity to their environment actively or passively
What are osmoconformers?
Osmoconformers are marine organisms that maintain an internal environment which is osmotic to their external environment
What are 3 measures marine teleost fish take to maintain the osmolarity of their body fluids (osmoregulator)?
- Drink seawater to replace the water lost to the environment
- Produce little urine (kidney has reduced role in ion and H2O excretion)
- Eliminate the salts ingested from salt water
What are chloride cells?
Cells in gills which actively transport salts from the blood into the environment
What is the main nitrogenous waste in aquatic invertebrates and bony fish?
Ammonia
How is ammonia excreted from aquatic invertebrates and bony fish?
Excreted by diffusion across the gill membranes directly into water
- Easily removed because it is very soluble in water
What is the behavioural stresses of desert animals to prevent water loss?
Avoid the daytime heat and emerge at night
What is aestivation?
Similar to hibernation, desert animals have low metabolic activity and low H2O turnover
What are physical and physiological strategies desert animals have to prevent water loss?
- They have a thick keratinised cuticle with a high lipid content
- Have efficient kidneys and excrete highly concentrated urine (long loops of Henle)
Who excretes uric acid?
Land animals, reptiles, birds and insects (uricotelic animals)
Who excretes urea?
Mammals, amphibians and cartilaginous fish (ureotelic animals)
Why is uric acid and urea preferred for terrestrial animals rather than ammonia?
They need less water to remove and thus conserve water in terrestrial animals
