Flashcards in 1-6: Intro, Osmoregulation Deck (123):
What does surface tension do?
Keeps water out of where we don't want it
Eg. breathing tubes in insects
How much of an animal's body mass does water make up?
What fluid compartments is water divided into?
Intracellular fluid (ICF)
Extracellular fluid (ECF)
Is there more ECF or ICF in soft-bodied invertebrates?
What is ECF in vertebrates split into?
What is homeostasis?
The maintenance of a constant internal environment
What is the ICF high in?
K+, phosphates, proteins
What is the ECF high in?
How does the ICF make up for the lack of Na+?
3 types of carrier-mediated transport
Facilitated diffusion- uniport
Why are most animal cells more negative inside compared to outside?
Due to an asymmetric distribution of K+
How is K+ maintained?
The membrane is more permeable to K+ than other ions
What is the resting membrane potential?
How is water transported across cell membranes?
What are aquaporins?
6 membrane-spanning domain
Single polypeptide chains
13 types in mammals
What are aquaglyceroporins?
Also permeable to glycerol
What is osmosis?
The diffusion of water through a semi-permeable membrane from a region of lower total solute concentration to one of a higher total solute concentration
What is osmolarity?
The concentration of a solution expressed as the total number of solute particles per litre
What does the rate of osmosis depend on?
The osmotic permeability of the membrane
What is the total solute concentration?
The total of all the solute present
What is molarity?
The concentration in moles per litre (M)
What osmolarity do ICF and ECF have?
The same- equal osmolarity
What does isotonic mean?
What does hypertonic mean?
What does hypotonic mean?
ECF composition in marine vertebrates
ECF is similar to water
Lower Na+ and Cl- due to evolutionary origin in freshwater
ECF composition in freshwater/terrestrial
ECF is like diluted seawater
What are osmoconformers?
Marine organisms that maintain an internal environment that is osmotic to their external environment
Osmolarity of cell's is equal to osmolarity of surrounding environment
What are ionoconformers?
Same ion concentrations of ECF as the outer environment
What are osmoregulators?
ECF is kept different from environmental values
What is the best way to maintain constant ECF composition?
Seal off from the outside world
Unavoidable areas of uptake/loss of ions
2 distinct surfaces of a membrane
Apical (eg. facing gut lumen)
Basolateral (eg. ECF)
How are epithelia connected?
Examples of epithelia involved in osmoregulation
Nasal salt glands
Features of sea water
Rich in NaCl
Low in K
High in Mg and sulphate
Constant salinity at depth
Marine invertebrate ECF (compared to outside)
Some ionoregulation- high K+ in squid for nerve conduction, reduced SO42- in pelagic species for buoyancy
Marine invertebrate ICF
Isosmotic with sea water
Ionic balance is different
Marine vertebrate groups
1- ECF roughly isosmotic to sea water- eg. hagfish, elasmobranchs
2- ECF osmolarity roughly a third of sea water- eg. lampreys, teleosts
Na+ and Cl- concentration similar to seawater
More like marine invertebrates
Stenohaline (intolerant of brackish/dilute water)
Na+ and Cl- in ECF 1/3rd of seawater
Euryhaline- tolerate a range of osmolarity
Migrate into freshwater
How do elasmobranchs make up osmotic deficit?
Urea and TMAO
What is urea?
End product of protein metabolism
Actively reabsorbed in kidney
Kidney holds onto urea
What is TMAO?
Another protein metabolite
Balances destabilising effect of urea on proteins
Osmoregulation in elasmobranchs- parts of body
Digestive tract- salt uptake
Kidney- retains urea and TMAO
Gills- loss of urea and salts, water uptake
Urine- salt lost
Rectal gland- excretes excess salt
What is the elasmobranch rectal gland?
Cylindrical organ with central lumen, drains into rectum
How does the rectal gland work?
Cl- accumulated in cell
Cl- efflux into the tubule lumen by secondary active transport
Secretion of isotonic NaCl
Na+ flux through tight junctions into tubule lumen
Other examples of ureo-osmoconformers
Hypoosmotic- 1/3 of sea water
No urea or other ECF osmolyte to make up the difference
Problems with teleost ECF
Loss of water by osmosis (by gills)
Gain of salt (by digestive tract)
To solve teleost ECF problems
Drink sea water to replace lost water
Produce minimal urine
Excrete excess salt via gills
Teleost parts of body
Gills- actively excrete salt, lose water
Mouth- gain water and salt from drinking sea water
Urine- small volume of isosmotic urine produced
Teleost kidney features
No loop of Henle
Can't concentrate urine
Rich in divalent ions
Chloride cells in teleosts
Large epithelial cells at the base of secondary lamellae
Packed with mitochondria
Lots of folding of basolateral membrane
For salt transport- same mechanism as elasmobranch rectal glands
Secondary active transport of Cl- across basolateral membrane
Paracellular diffusion of Na+ driven by electric potential gradient
What volume of all water on earth is freshwater?
What can freshwater be composed of?
Salts from rainwater, picked up from dust as it falls
Minerals picked up from rocks- few from granite, lots from limestone
What is the normal freshwater salt concentration?
What type of water contains more ions?
Fresh water ICF
All maintain above the fresh water value
Some higher than others
What do you not find in freshwater?
Freshwater ECF composition
Na+ and Cl- dominate
Some K+ and divalent ions
Gain water by osmosis
Lose solutes by diffusion and excretion
Minimise permeable surfaces- but need for gas exchange
Produce hyposmotic urine- lose lots of water, little salts
Actively take up salts from environment- via gills and skin
How do freshwater animals lower water permeability of external surfaces?
Have hard surfaces
What are flame cells?
In freshwater flatworms, rotifers and nemerteans
Produce primitive urine
Found all over body
How do flame cells work?
Have a flagellum that propels fluid down the duct
Cilia draws ECF through gaps between cells
Negative hydrostatic pressure sucks water in
Reabsorption of ions by tubule cell
What are flame cells grouped as?
What are metanephridia?
Excretory glands found in many types of invertebrates
Eg. annelids, arthropods, mollusca
What are coelomoducts?
Excretory gland and genital ducts
Wide and ciliated lumen opening into a coelom
Terminate externally by a small pore in the body wall
What is the crayfish antennal gland?
The 'green gland'
Ultrafiltrates haemolymph into a coelomosac
Reabsorption of ions in the labyrinth and canal
Minimal water reabsorption
Basic principles of urine production
Energetically expensive due to reabsorption
But safe for excreting toxins
Excrete everything, reabsorb what you want to keep
Fresh water elasmobranch features
A few marine species enter rivers successfully, some are exclusively fresh-water
Eg. Amazon stingray, Lake Nicaragua shark (bulls)
ECF similar to humans, very different from marine sharks
ECF doesn't contain urea or TMAO
Freshwater teleost features
ECF around 300mOsm
Gain salt and water from feeding
Gain water from gills and body surface
Actively uptake salt via the gills
Excrete large amounts of hyposmotic urine- loss of salt
Freshwater teleost kidneys
Higher filtration rate than sea water species
Similar proximal tubule function to sea water- reabsorption of vital solutes
Different distal tubule and collecting duct- NaCl reabsorption, low water permeability
Freshwater teleost gills
NaCl uptake is coupled with CO2 excretion
Want to absorb as much salt as possible
Use 2 pumps- NaCl pump and proton pump at apical side
What are catadromous fish?
Spawn in the sea
Young migrate up rivers for most of their life
Return to sea to spawn
Eg. freshwater eels
What are anadromous fish?
Spawn in rivers
Young migrate to sea to grow
Return to rivers to spawn
Eg. atlantic salmon
How do fish go from freshwater to seawater?
H+ATPase is downregulated
NaCl uptake is supressed
Increased plasma Na+ = hormone secretion
Hormones stimulate chloride cell proliferation
Increase in Na+K+ATPase activity, secretion of NaCl
Plasma Na+ levels are restored
How do fish go from seawater to freshwater?
Low Na+ closes tight junctions
NaCl excretion stops
Plasma prolactin levels rise, which reduce no. of chloride cells
Na+K+ATPase activity falls
Up-regulation of H+ATPase
NaCl uptake restored
2 evolutionary routes onto land
From sea water via the littoral zone- tolerate desiccation and osmotic variations
From fresh water via swamps and bogs- produce hyposmotic urine
What are the most successful phyla and what routes did they take?
Arthropods- both routes
Vertebrates- mainly freshwater
What are interstitial fauna?
Small soil organisms surrounded by water film
Eg. rotifers, nematodes
What are cryptozoic fauna?
Hiding animals- larger soil organisms
Eg. worms, centipedes
What are hygrophilic fauna?
Limited tolerance of desiccation
Eg. slugs, snails, amphibians
What are xerophilic fauna?
Free-living above ground
Eg. insects, mammals, birds
ECF composition of land animals
Lower in ex-fresh than ex-marine
Dominance of Na+ and Cl-
High Ca2+ in some inverts
Vertebrates have ECF osmolarity of around 300, similar to freshwater fish
What is the main form of water loss?
Called evaporative water loss (EWL)
2 ways that water can be lost
Cutaneous- by skin
Respiratory- by the linings of airways, alveoli
How is water loss increased?
Low humidity and airflow
Behavioural adaptations to prevent water loss
Seek dark, damp, cool places
How is cutaneous water permeablility reduced?
Dense cuticles (arthropods)
Keratinised layers of dead skin cells (tetrapods)
How is water aquired?
Diet- wet or hygroscopic foods, eg. seeds
Osmosis via other organs- abdominal skin in amphibia
Dew capture- dawn frogs in coastal deserts, condensation drains to the head
Metabolic water- from oxidative metabolism
How is drinking controlled?
Increased ECF osmolarity detected by osmoreceptors, goes to hypothalamic thirst centre
Decreased ECF volume detected by volume receptors, activates renin-angiotensin system, goes to hypothalamic thirst centre
What are kidneys/variations of kidneys for?
The excretion of waste products
Require a modest output of water
Main site for regulating water content and ion balance
Nephridia in flatworms and nemerteans
Flame cells organised into protonephridia
Slighly hyposmotic urine
Nephridia in annelid worms
Each segment has its own 'kidney'
Nephridia in slugs and snails
Ultrafiltration from the pericardium
Hyposmotic urine with water is plentiful
Solid paste when water is short
Can't produce hyperosmotic urine
Malpighian tubes in xerophilic arthropods
Produce isosmotic fluid by active secretion from haemolymph
Drains into midgut
Active reabsorption of hyposmotic fluid in rectum
What are malphighian tubules?
Have cation pumps at the apical membrane
Cation is K+ in herbivores, Na+ in blood feeders
Cl- moves passively via stellate cells
High water permeability
What is the cryptonephridial system?
In some beetles and lepidopteran larvae
Malpighian tubes lie close to rectum
Have an impermeable perinephric membrane
Also counter current system
Produce hyperosmotic excreta (up to 5000mOsm)
Salt uptake via skin
Salt excretion via salt glands
Normally hyposmotic urine
Some have salt glands
Some have loop of Henle
Most have loop of Henle
Hypo or hyperosmotic according to need
What are salt glands?
Important in birds/reptiles living close to sea
Secrete hypertonic NaCl
Can be in eye sockets, nasal cavity, mouth, top of skull
Similar mechanism to rectal glands and chloride cells
Main principle of the mammalian kidney
What does too little sodium cause?
Collapse in the circulatory system
How is the kidney able to produce hyperosmotic urine?
Due to the loop of Henle
What cannot pass through into the filtrate?
What is the filter in the glomerulus
Basement membrane of the capillary endothelium
What happens in the proximal convoluted tubule?
Isosmotic reabsorption of 75% of NaCl and water
Concentration of waste products eg. urea
What happens in the descending limb of the loop of Henle?
Passive reabsorption of water
What happens in the thick ascending limb of the loop of Henle?
Active reabsorption of NaCl
What happens in the distal convoluted tubule?
Aldosterone-regulated reabsorption of Na+
What happens in the collecting duct?
ADH-regulated reabsorption of water
How does the loop of Henle create a hyperosmotic ECF in the inner medulla?
Osmotic water efflux from descending limb
Passive salt efflux from thin ascending limb
Active salt transport out of thick ascending limb
What does ADH do?
Causes an organism to retain water
Kangaroo rat water
Survive without drinking
Produce small volumes of very hyperosmotic urine
Water gained from metabolism
Unavoidable loss by evaporation