Osmoregulation and Excretion Flashcards
Lecture 12
Why must animals regulate the composition of their internal fluids?
is the control of the levels of water and mineral salts in the blood.
Define osmoregulation, osmolarity, osmosis, iso-osmotic, hyper-osmotic, hypo-osmotic
Osmoregulation - is the process by which an animal regulates the concentration of solutes (ions, salts, nutrients) and balances the gain and loss of water
Osmosis - is the movement of water across a membrane; this is how water enters and leaves cells in the body
Iso-osmotic - both solutions have the same osmolarity; no net movement of water
Hyper-osmotic - solution which has greater concentration of solutes (less water); water will move into this solution
Hypo-osmotic - solution which has lower concentration of solutes (more water); water will move away from this solution
What is an osmoconformer? Where do they live?
Do not adjust their internal osmolarity; their body fluids are iso-osmotic to the environment. This is possible only in the marine environment
What is an osmoregulator? Why does osmoregulation carry an energy cost?
Do not adjust their internal osmolarity; their body fluids are iso-osmotic to the environment. This is possible only in the marine environment
If body fluids are kept at a different osmolarity to the environment, osmoregulators must use energy to counter this tendency for solutes to equilibrate
Why do freshwater species often have lower solute concentrations in their body fluids than
their marine relatives?
Osmocon - body fluids have the same osmolarity as sea water, they do not gain or lose water from/to the environment.
Osmoreg - must take in water to offset loss as water tends to flow out of body
Define stenohaline, euryhaline
Stenohaline - can’t tolerate much change in external osmolarity; this group includes most animals
Euryhaline - can survive larger fluctuation in external osmolarity; this group includes some osmoconformers and some osmoregulators
What is the problem associated with living in a marine environment? How do marine bony
fish deal with this problem?
Sea water is dehydrating because it is saltier (hyper-osmotic) than body fluids and water tends to flow out by osmosis
Balance this water loss by drinking lots of sea water. The gills and skin are used to get rid of excess salt (NaCl). The kidneys excrete little water
What is the problem associated with living in freshwater environment? How do freshwater
bony fish deal with this problem?
Salts lost by diffusion and in urine are gained from food and by uptake in the gills = opposite function than in marine fish. Body fluids of freshwater species tend to have lower salt concentrations than their marine relatives.
What is the main problem associated with living on land? Name three adaptations for
dealing with this problem.
the primary problem is desiccation. Considerable water loss occurs from moist body surfaces (e.g. respiratory membranes), across skin and in urine and faeces.
Three adaptation include
- Impervious body coverings e.g. waxy cuticle of insect exoskeleton, shell of land snails, layers of keratinized skin in terrestrial vertebrates
- Lifestyle/behaviour – nocturnal activity reduces evaporative water loss
- Fur
Why is transport epithelium important in osmoregulation and waste disposal?
They allow movement of specific solutes in controlled amounts in specific directions (selectively permeable)
What are the three forms of nitrogenous waste? What is the advantage of excreting urea
and which groups use this form?
Ammonia
Urea
Uric acid
Advantage of excreting urea is much less toxic than ammonia and can be stored.
Mammals, sharks, some marine fish, turtles and most adult amphibians excrete mainly urea
What are the two main functions of the excretory system?
Filtration
Selective reabsorption
Selective secretion
Excretion
Describe the four steps of urine production
glomerulus, the filtrate passes through 4 segments of the nephron: Proximal convoluted tubule: reabsorption of nutrients and substances that the body needs. Loop of henle: thin-lobed structure that controls the concentration of the urine
How are sharks able to expend proportionately less energy for osmoregulation compared
to marine bony fish?
They maintain high concentrations of urea (nitrogenous waste) in their body fluids. This means that the total solute concentration in their body fluids is slightly higher than the osmolarity of sea water (slightly hyper-osmotic). So water slowly enters the body by osmosis (this small influx is excreted by kidneys
Dragonfly larvae, which are aquatic, excrete ammonia, whereas adult dragonflies, which are terrestrial, excrete uric acid. Explain.
Because uric acid is largely insoluable in water, it can be secreted as a semisolid paste, thereby reducing an animals water loss Excretory Systems
