Osmoregulation Flashcards
lecture 9 & 10
define osmoregulation
The regulation of osmotic concentration (water content and solutes) in the body
define excretion
Is the elimination of waste products (potentially toxic products) from the body
What helps maintain homeostasis?
Excretion and osmoregulation
Deine osmosis
The spontaneous net movement of solvent molecules through a semi-permeable membrane into a region of higher solute concentration in the direction that tends to equalize the solute concentrations on the two sides
Define isotonic
The solution has an effective osmole concentration that is the same as the solute concentration of a cell
define hypertonic
Solution has a higher concentration of solutes outside the cell than inside the cell
define hypotonic
Solution has a lower concentration of solutes outside the cell than inside the cell
define osmoconformer
Are iso-osmotic (same osmole []) with their surroundings and do not regulate their osmolarity
define osmoregulator
Spend energy to control water loss and uptake in a hyperosmotic or hypo-osmotic environment
define stenohaline
Describes organisms (most animals) that cannot tolerate substantial changes in external osmolarity (salinities)
define euryhaline
Describes organisms that can survive large fluctuations in external osmolarity (salinities)
define excretion
It is the elimination of waste products from the body.
the movement of water and ions
Relative osmotic and ionic conditions exist between marine, freshwater, and terrestrial invertebrates and their environments
osmoregulation in fresh water
Constantly take-in water from their hypo-osmotic environment
Salts lost by diffusion are replaced by foods and water uptake across the gills
Some invertebrates living in temporary ponds, can lose almost all their body water when pond dries out and survive in a dormant state = anhydrobiosis
examples of anhydrobiotes
Tardigrades (‘water bears’) (Phylum Tardigrada)
Nematodes (Phylum Nematoda)
Rotifers (Phylum Rotifera)
Springtails (Phylum Arthropoda; Sub-class Collembola)
Midge larvae (Phylum Arthropoda; Class Insecta)
osmoregulation in marine environments
Most marine invertebrates are osmoconformers (e.g. starfish, anemones)
Therefore require little to no energy to maintain osmotic balance.
Organisms living in coastal environments must survive fluctuating conditions (fresh water, lack of water, desiccation, etc)
As a result, some coastal invertebrates are efficient osmoregulators – they maintain optimal salt concentrations regardless of changes in the environment.
example of osmoregulation in marine environments
Example: shore crab body fluids are hypertonic to brackish water (mixture of salt and fresh water) - gills remove salts from water and put into blood while excretory organs excrete excess water that diffuses in
osmoregulation on land
In terrestrial environments, lack of water is often a constraint. There are several ways arthropods can gather water
1. Drinking
2. Metabolic water
3. Water vapour absorption (oral & rectal uptake)
drinking arthropods on land
Drinking in arthropods is widespread, especially if they are dehydrated
Several species can take up capillary water from the soil against considerable water tension (termites)
Desert animals may drink condensation from vegetation and other surfaces
The Namib desert beetle Onymacris unguicularis climbs dunes in the early morning (fog-basking behaviour) and drinks water that condenses on its body, and trickles to its mouth
examples of drinking arthropods
Lepidochora beetle species dig trenches and fog condenses on the ridges
Beetles return later and close down the trenches, drinking the condensate
Metabolic water
Many species obtain water by processing food ingested (recall gas exchange lecture)
Carbohydrate= 0.033ml water / kJ
Lipid= 0.027ml water / kJ
Energy and water requirements have to be balanced
Increased O2 requirements or O2 limitation may mean that metabolising lipid has no advantage for particular organisms
Water vapour absorbtion
Several (> 50) species of arthropods can absorb water vapour from unsaturated air by using mouthparts or rectum:
Mouthparts: uptake of H2O in cockroaches, booklice (Psocoptera), lice, ticks, mites, and pleopods in isopods
Rectal uptake in a variety of insects (some beetle and lepidopteran larvae, silverfish (fish moths) and fleas) from air ventilated into the rectum
Association of Malpighian tubules and rectum to form a cryptonephridial complex
K+ (potassium) ions are actively pumped into Malpighian tubules by leptophragmata cells, water cannot follow owing to perinephric membrane
Water moves from the rectal lumen into the peri-rectal fluid at humidity’s above c. 88%
A water impermeable (periphrenic) membrane keeps the osmotic concentration of the peri-rectal fluid high
Water moves from the perirectal fluid to the tubule
A counter-current system may be important
what is filtration
the excretory tubule collects a filtrate from the blood. Water and solutes are forced by blood pressure accros the selectively permeable membranes of a cluster of capilaries and into the excretory tubules.
What is reabsorbtion?
the transport epithelium reclaims valuable substances from the filtrate and returns them to the body fluids.
