Ch.28 Water and Salt Physiology of Animals in their Environments

Compare the blood of marine elasmobranchs to seawater.

(sharks) -hyperosmotic (more concentrated) than seawater, but hypoionic (less ions) than seawater -because organic solutes, mainly *urea*, keep the blood hyperosmotic

What's the difference between how xeric amphibians, reptiles, birds, and small mammals maintain water balance?

-*amphibians*: behaviorally; they are active only during favorable conditions, sometimes with seasonal dormancy (*aestivation*) -*reptiles*: behaviorally by *seeking shelter at hottest times of day*, physiologically by tolerating a wide range of blood plasma concentrations and producing *uric acid* -*birds*: behaviorally by *flying to water sources* and physiologically by producing *uric acid* -*small mammals*: behaviorally by eating air dried seeds underground that can absorb humidity from exhaled air, physiologically by *producing very concentrated urine* and restricting fecal water loss

How can evaporation via respiratory membranes be reduced in land animals?

-*by cooling the exhalant air via counter-current exchange* -increased air temp = increased water saturation -so, counter-current exchange cools air in distal passages from inhaled air. As exhaled air passes out, it's cooled from the previous inhalation and holds less water.

What's the difference between hyper-isosmotic regulation and hyper-hyposmotic regulation?

-*hyper-isosmotic*: freshwater animals that move into brackish water; can regulate at most values, but when they move into brackish water they must become conformers -*hyper-hyposmotic*: euryhaline fish; must regulate the whole time as water gets saltier (see graphs)

What are the different types of ways that animals maintain salinity homeostasis?

-*stenohalines*: narrow range of salinity (open ocean) -*euryhalines*: broad range of salinity (near coasts and brachish water) -*osmoconformers*: poikilosmotic -*osmoregulators*: homeosmotic

What's the difference between osmotic flux in freshwater fish and marine teleosts?

-Freshwater fish are hyperosmotic (more concentrated) to water, so they normally gain water and need to get rid of it. -Marine teleosts are hyposmotic (less concentrated) to water, so they normally lose water and need to gain it. -They have the same osmotic flux, but in opposite directions. -Marine teleosts are less permeable to water than freshwater fish.

What challenges do freshwater fish face in trying to maintain water and ion balance? How have they adapted to this challenge?

-Since water is constantly being gained via osmosis (blood hyperosmotic to water), the fish *increase their urine output.* -However, even *more ions are lost in the urine, and in the gills* (already losing ions to less concentrated environment). -To replenish these ions, *food and drinking water provide some input. The gills also actively uptake ions*, especially Na+ and Cl-.

How can animals reduce evaporative water loss? Give examples of each.

-behaviorally and physiologically -humidic animals limit activity to moist places and times (underground, at night) -xeric animals have low integumentary permeability from more lipids in the skin

How do terrestrial animals reduce the amount of dissolved matter excreted in the urine?

-birds and lizards have salt glands that help the kidneys -by choosing the appropriate kind of nitrogenous waste: -ammonia: least energy to make, but is very toxic so it requires the most water -urea: intermediate energy, toxicity, and amount of water -uric acid: takes the most energy to make, but its least toxic and requires the least amount of water

Compare freshwater animal blood to the environment.

-blood is more concentrated than freshwater -so, they tend to gain water by osmosis and lose major ions passively by diffusion

What does evaporative water loss (NOT rate) depend on?

-body size: small animals have high surface area to volume ratio (evaporate more via integument) -metabolic rate: endotherms have higher MR and breathe more (evaporate more via respiration) -phylogenetic group

What does excretory water loss depend on?

-concentrating ability of the excretory organs: high concentrating ability = less water loss -amount of solute that needs to be excreted: more solute = more water loss

anadromous fish

-fish that ascend rivers to breed -must be euryhaline hyper-hyposmotic regulators (going into less concentrated water)

catadromous fish

-fish that enter the ocean to breed -must be hyposmotic regulators (maintain low concentration inside)

Compare the blood of marine tetrapods to seawater. What is unique about their respiratory membrane compared to other marine animals?

-hyposmotic to sea water (less concentrated) -respiratory membrane is not exposed to water at all because they are air breathers

Compare the blood of most marine invertebrates to that of seawater.

-isomotic to seawater -so, they don't have any major problems with osmotic regulation. But ionic composition of blood is very different from the water.

What is the MWP/EWL ratio, and how does it affect kangaroo rats?

-metabolic water production / evaporative water loss ratio -as temperature drops, the ratio becomes much more favorable because less water is lost (decreased EWL)

Which is higher: integumentary water loss, or respiratory water loss? Why?

-respiratory water loss -because thick epithelia and lipids are characteristic of the skin, but it would be poor for gas exchange if it was in the respiratory epithelium (needs to be thin)

What does the rate of evaporation in land animals depend on?

-the difference in WVP between body fluids and air -integumentary permeability

What challenges do marine elasmobranchs face in trying to maintain water and ion balance? How have they adapted to this challenge?

-they can't remove salt by urine because they will also remove urea (they need to retain urea) -so, they remove salts via rectal salt glands

How do anadromous and catadromous fish adapt to changing water conditions when they migrate to breed?

-they reverse the direction of NaCl active transporters as needed -ex. when catadromous fish enter seawater, they increase drinking and decrease urine production. But, the urine is isosmotic instead of hyposmotic (more concentrated) to remove all the extra salt.

What challenges do marine teleosts face in trying to maintain water and ion balance? How have they adapted to this challenge?

-volume regulation worsens the problems of ionic regulation because water is taken up with NaCl (too much salt) -the kidneys can't get rid of the salt because then they'd be getting rid of the water just gained -so, the *gills are the main sites of osmotic regulation*: they actively excrete NaCl without water loss (*extrarenal salt excretion*)

In land animals, what are the 4 common themes of physiological specializations for maintaining water balance in arid-environment animals?

1. low skin permeability 2. low respiratory water loss 3. nitrogenous wastes in less or non-soluble form (uric acid) 4. ability to produced concentrated urine

In general, why is body fluid regulation important?

Passive forces would normally take water and ions to equilibrium, but body fluids are usually not supposed to be in equilibrium with the environment.

How do freshwater animals reduce the rates of passive water and ion exchange?

They have thick, low permeability integuments. However, this causes a tradeoff between permeability and the need to breathe.

How do most marine reptiles and birds regulate ions?

by extrarenal salt exretion via salt glands

Total evaporative water loss =

integumentary + respiratory water loss

List the terrestrial animals in increasing order of urinary concentrating ability.

lowest ability: amphibians (dilute urine) reptiles and birds large mammals small mammals

What is the major determinant of respiratory evaporative water loss?

metabolic rate

Order the integuments of marine tetrapods, freshwater fish, and marine teleosts from most permeable to least permeable.

most permeable: freshwater fish marine teleosts least permeable: marine tetrapods

Which animals cannot concentrate urine?

non avian reptiles

What type of salinity homeostasis does most marine invertebrates use?

stenohaline osmoconformers

When are kangaroo rats in water balance?

when the total water input is greater than or equal to the total minimal losses