Ion and Water Balance 3 Flashcards
what animals possess salt glands (2)
- reptiles
- birds
salt gland location (2)
- near the eye
- drain into ducts that empty near the nostril
what do salt glands do
- excrete hyperosmotic solutions of Na+ and Cl- (large amounts of salt in small volume of water)
how do salt glands produce hyperosmotic solutions (2)
- ion pumps
- countercurrent multipliers
how do the ion pumps of salt glands work (2)
- several ion pumps take ions from the blood and pump them into the lumen of the secretory tubule
- water cannot passively follow the ions due to the high cholesterol content of the membrane, making it impermeable
how does the countercurrent flow of salt glands work
- fluids flow down the secretory tubule in the opposing direction of blood flow
what organisms have a rectal gland
- elasmobranchs
where is the rectal gland located
- empties into the digestive tract
function of rectal gland
- accessory excretory organ that transports Na+ and Cl- from the blood into lumen of the gland
rectal gland ion movement
- ion transport similar to ionocytes and salt glands
rectal gland: rate of salt excretion (2)
- regulated by hormones
- specifically, vasoactive intestinal peptide (VIP)
terrestrial animals: water loss (2)
- across skin and respiratory surface
- in urine
terrestrial animals: water gain (3)
- metabolic water
- drinking
- food
what is the rate of water loss associated with (2)
- surface area to volume ratio
- there is more water loss in smaller animals that have a larger SA:V ratio
mechanism of water conservation: breathing
- nasal countercurrent heat exchanger operates to recycle and conserve water
nasal countercurrent heat exchanger: inspiration (2)
- incoming air is warmed and humidified in nasal cavity before entering warm lung environment
- nose is cooled as water evaporates into the air
nasal countercurrent heat exchanger: expiration (2)
- outgoing air is cooled and loses water before exiting
- nose is wetted from water condensing out of the air
what are mammal adaptations to desert life: water intake (2)
- metabolic water derived from dry seeds
- free water is consumed from seeds
what are mammal adaptations to desert life: water conservation (4)
- animals remain in cool burrows during daytime
- longer nose helps condense respiratory moisture in nasal passages
- feces are dehydrated prior to defecation
- urine concentrated by countercurrent exchange in extralong loop of Henle
what epithelia are typically involved in excretion of nitrogenous wastes
- the epithelia that are involved in ion and water balance (gills, kidneys, etc)
why is nitrogen excretion (2)
- ammonium produced during amino acid breakdown is toxic and must be excreted
- ammonic is produced from consumed proteins
what forms are ammonia nitrogen excreted as (3)
- ammonium
- uric acid
- urea
what is the term for the animals that excrete nitrogen in the form of ammonia
- ammonioteles
what is the term for the animals that excrete nitrogen in the form of uric acid
- uricoteles
what is the term for the animals that excrete nitrogen in the form of urea
- ureoteles
what animals are typically ammonioteles (2)
- most aquatic animals, including most bony fishes
- simple invertebrates
what animals are typically ureoteles (4)
- all mammals
- most amphibians
- sharks
- some bony fishes
what animals are typically uricoteles (3)
- many reptiles, including birds
- insects
- land snails
what are the “special” animals in the ureotele group (2)
- some larval bony fish
- estivating lungfish
ureotele larval bony fish (2)
- produce urea because ammonium cannot leave amniotic sac
- built up ammonium would be toxic
ureotele estivating lungfish (2)
- lungfish go into hibernation during drought, lasting multiple years
- produce urea to decrease toxicity levels during this phase
aquatic animal nitrogen excretion
- typically excrete ammonium
terrestrial animal nitrogen excretion
- typically excrete uric acid or urea
how can animals respond to water availability in relation to nitrogen excretion
- change mode of nitrogen excretion to match the availability of water
ammonium excretion: advantages (2)
- ammonium released by deamination of amino acids, requiring little energy to produce
- more energy efficient in aquatic animals where water is abundant
ammonium excretion: disadvantages (2)
- highly toxic
- requires large volumes of water to store and excrete (500mL H2O per gram)
ammonia (2)
- NH3
- gas that moves rapidly across membranes down its partial pressure gradient
ammonium (3)
- NH4+
- more toxic form of NH3 with similar composition to K+
- can substitute for K+ in nervous tissue, resulting in convulsions at high levels
what is the reaction between ammonia and ammonium
NH3 + H+ <–> NH4+
what is the pK of the reaction between ammonia and ammonium
- pK = 9
at pH7, how much ammonia vs ammonium will exist
- 99% ammonium, 1% ammonia
at pH7, how much ammonia vs ammonium will exist
- 50% ammonium, 50% ammonia
fish: acid trapping (2)
- H+ combines with NH3 to form NH4+ in the external environment
- partial pressure of NH3 outside remains low, which encourages NH3 to continue diffusing out of the plasma and into the environment
fish: how does NH3 leave the plasma
- it travels transcellularly and paracellularly into the environment and down its partial pressure gradient
fish: how does NH4+ leave the plasma (2)
- it cannot leave the plasma in its form
- must be converted into NH3 as NH3 is removed down its partial pressure gradient
fish: where does the protons that combine with NH3 come from (2)
- from CO2 after it is converted to bicarbonate and H+ by carbonic anhydrase
- H+ ATPase transports it outside of the cell
how will low pH water affect excretion of nitrogen in fish (2)
- it will elevate nitrogen excretion
- it will encourage NH3 to be converted into NH4+, which will continue to drive more NH3 out of the cell
how will high pH affect excretion of nitrogen in fish (2)
- it will slow nitrogen excretion
- it will discourage NH3 to be converted into NH4+, which will halt the driving of NH3 out of the cell
uric acid excretion: advantages (2)
- few toxic effects
- can be excreted in small volume of water (10mL per gram)
uric acid excretion: disadvantages
- ATP expensive to produce
how is uric acid excreted
- as anhydrous white crystals
why did uric acid excretion evolve
- to combat water loss in terrestrial environments
urea excretion: advantages (3)
- only slightly toxic
- relatively inexpensive to produce
- requires relatively less water (50mL per gram)
urea excretion: disadvantages (2)
- urea is a pertubing solute, it can cause issues with macromolecule folding in high concentrations
- buildup of urea can result in gout, the crystallization of urea in joints
where is urea synthesized and transported (2)
- synthesized in the liver
- transported by the blood to the kidney
how do elasmobranchs use ureas (2)
- as an osmolyte to increase plasma osmolarity to be similar to seawater while keeping ion concentrations low
- helps to prevent water loss in marine environment
how are ureas perturbing effects counteracted in elasmobranchs
- counteracted by TMAO
