chapter 28 questions

What are the challenges of osmotic, volume, and ionic regulation faced by freshwater animals?

Freshwater animals evolved this more dilute blood as an adaptation to its new environment. By lowering the blood osmotic pressure will decrease the osmotic gradient between body fluids and the environment. By lowering this gradient, will lower the rates of water gain and the rates of ion loss across the body via osmosis and diffusion. These are all animals that are going to required oxygen of course, and all of the adaptations that make the gills really good to take up oxygen, makes then really bad for water gain and ion losses. The large surface areas, their high permeability makes them also highly permeable for water and inorganic ions.

Why do energetic costs of freshwater animals increase with passive water and ion exchange?

Freshwater animals have integuments with low permeability to water and ions and will be really important to reduce the rate of passive exchange and this will reduce their energy cost of maintaining a relatively consistent osmotic pressure and ionic concentration on their body tissues. A problem for water exchange is across the gills.

Permeability in freshwater animals?

Freshwater animals have integuments with low permeability to water and ions and will be really important to reduce the rate of passive exchange and this will reduce their energy cost of maintaining a relatively consistent osmotic pressure and ionic concentration on their body tissues. A problem for water exchange is across the gills. These are all animals that are going to required oxygen of course, and all of the adaptations that make the gills really good to take up oxygen, makes then really bad for water gain and ion losses. The large surface areas, their high permeability makes them also highly permeable for water and inorganic ions. Most passive exchange occurs across the gills.

Describe osmotic and ionic gradients of freshwater animals.

Freshwater animals have lower osmotic pressures than marine counterparts. For example, most marine lobsters are essentially isosmotic to seawater (about 1000 mOsm), most freshwater decapods have blood osmotic pressures of 500 mOsm or less (e.g., ~440 mOsm in the crayfish). Freshwater animals evolved this more dilute blood as an adaptation to its new environment. By lowering the blood osmotic pressure will decrease the osmotic gradient between body fluids and the environment. By lowering this gradient, will lower the rates of water gain and the rates of ion loss across the body via osmosis and diffusion.

Describe the regulatory mechanisms of urine production by the kidneys in freshwater fish.

Freshwater animals void excess water gained by osmosis by producing large amounts of dilute urine (Hyposmotic to blood; U/P < 1) like a freshwater animal like a goldfish or a frog, the daily osmotic water influx is equal to one-third of its body weight and this will help remove a lot of that excess water that has been taken passively via osmosis. • The urine of freshwater animals, in addition to being produced in abundance, is typically markedly Hyposmotic to their blood plasma and contains much lower concentrations of Na+ and Cl- than the plasma. That is, the U/P ratios (urine: plasma ratios) for osmotic pressure, Na+, and Cl- are far less than 1 in these animals and when the osmotic U/P ratio is less than 1, urine production tends to raise the plasma osmotic pressure. Similarly, when the U/P ratio for an ion is less than 1, urine production tends to raise the plasma concentration of that ion. Typically, therefore, the kidneys of a freshwater animal not only solve the animal's volume-regulation problem by voiding the animal's excess volume of water, but also aid osmotic and ionic regulation by helping to maintain a high osmotic pressure and high ion concentrations in the blood. • Kidneys are regulatory organs and they characteristically adjust their function in ways that help to maintain stability of volume and composition in the body fluids. If an animal experiences an increase in the rate at which it takes in water by osmosis, its kidneys ordinarily increase their rate of urine production. • Kidneys limit [ion] in urine, but still a loss of ions • Any factor that increases an animal's rate of osmotic water influx tends to increase the animal's rate of ion loss. We see, therefore, that volume regulation and ionic regulation are basically at conflict with each other in freshwater animals.

What type of osmotic regulation is seen in freshwater animals?

Hyperosmotic regulation.

What type of osmotic regulation is seen in marine teleost fish?

Hyposmotic regulation

How do elasmobranch fish differ from teleosts in their plasma regulation? Describe osmotic regulation in elasmobranchs.

Marine elasmobranch fish are hyperosmotic, but hypoionic to seawater. These are animals like sharks, skates and rays. They are unique in terms of the separation of the osmotic regulation and the ionic regulation. They maintain low blood concentrations of Na and Cl, lower than seawater, but they are still slightly hyperosmotic to water. They have high concentrations of urea and TMAO as a result of this decoupled of ionic concentrations and osmotic regulation. Urea is a nitrogenous waste product and is the major way that mammals release their waste, but these will produce ammonia instead to to the job of urea so urea will accumulate in the body fluids of these fish and this can be very damaging because it can alter protein structures. Urea in high concentrations can alter the structures of proteins, and the concentration of urea is kept low in most vertebrates (about 2-7 mM in human plasma). Plasma concentrations of urea in marine elasmobranchs—usually 300-400 mM—are "out of sight" by comparison. These higher concentrations of urea don't damage their body because they are counterbalanced by TMAO. TMAO serves as a counteracting solute. In the amounts present, TMAO offsets the effects of urea, evidently by opposing effects of urea on deleterious interactions of proteins with solvent water, interactions that if unopposed cause protein unfolding. In this fish osmotic regulation and ionic regulation are decoupled from each other. Excess salts are removed from the body fluids of elasmobranchs by the kidneys and, extrarenally, by rectal salt glands. Unlike teleost, therefore, elasmobranchs need not drink and need not incur an extra NaCl load to gain H2O from ingested seawater.

What are the challenges of osmotic, volume, and ionic regulation faced by marine teleost fish?

Marine teleost are decedents of freshwater ancestors so they are Hyposmotic to surroundings and because of this they tend to lose water passively via osmosis and take up ions passively via diffusion and to deal with these issues they do the following: 1. Ingest seawater where they build the gut to take up water from that seawater that is going through the gut. 2. Excrete those divalent ions that came with the seawater in urine 3. Excrete those monovalent ions across gills.

Describe the marine teleost strategy of regulation through: replacing water through drinking seawater, voiding ions in urine, and voiding ions across the gills. How do each of these processes work, and how are these processes related?

Replacement of water losses to replace water lost by osmosis, teleost fish actually drink seawater. 1. Ingestion of hyperosmotic seawater causes diffusion of body water into seawater in the gut. Water in the gut increases in volume and it comes more dilute. 2. In later parts of the gut: Na and Cl are actively transported out of gut and into blood and this requires ATP. It favors osmotic uptake of water into the blood. By the time ingested seawater is completely processed, about 50-85% of the H2O in the seawater is absorbed into the blood. Marine teleost fish will excrete excess divalent ions in the urine whereas excess monovalent ions are excreted by the gills. • Passive process, drinking seawater: ions are increased in the blood. • Divalent ions -> excreted in urine • Monovalent ions -> excreted by gills • Excreted urine is isosmotic to plasma (osmotic U/P = 1) • Ionic U/P ratios of monovalent ions < 1 • Ionic U/P ratios of divalent ions > 1like Mg and SO4 • The kidneys thereby void the major divalent ions preferentially in relation to water and keep plasma concentrations of those ions from increasing. • Ionic regulation via urine production conflicts with osmoregulation: teleost fish limit urine to what is necessary to excrete of solutes that are not excreted by other routes. • Nitrogenous wastes and the principal ions, Na+ and Cl-, are voided across the gills. Thus the role of the kidneys in marine teleosts is largely limited to excretion of divalent ions, and the rate of urine production can be low. The excretion of Chloride happens by secondary active transport and its carried out by special cells in the gills called mitochondria-rich cells so they have lots of mitochondria to generate lots of ATP to carried out these active processes. External NaCl excretion by gills: Na+, Cl-, nitrogenous wastes voided across gills. There is a Na-K pump creates electrochemical gradient favoring Na+ diffusion out of the cell. Na+ is diffused back into cell at NKCC (sodium, potassium, 2 chloride cotransporter) with K+, 2Cl-. So as sodium comes back into the cell, it takes with it one potassium and 2 chlorides with it. Cl- entry creates gradient favoring outward diffusion via Cl- channels in the apical membranes. Excretion of Na+ may be active or passive depending on the species. • The elimination of Cl- and Na+ by the gills of marine teleost fish provides our first example of extrarenal salt excretion: excretion of inorganic ions by structures other than the kidneys. • Fish that is able to excrete NaCl without also excreting water: gills are the sites in marine teleost fish where the primary site of osmotic regulation is accomplished.

What kinds of animals face changes in salinity?

Salmon, eels, animals that live near the margins of the continents, along coastlines, and brackish waters like estuaries, salt marshes and other settings. Oysters and mussels.

What aspect of the evolutionary history of freshwater animals particularly affects their water and salt physiology?

The animals living today in freshwater are descended from ocean-living ancestors: The major animal phyla originated in the oceans and later invaded all other habitats. Seawater was probably somewhat different in its total salinity and salt composition in the early eras of animal evolution than it is today. Nonetheless, when the animal phyla invaded freshwater from the oceans, there can be no doubt that they encountered a drastic reduction in the concentration of their surroundings. The osmotic pressure of freshwater is typically less than 1% as high as that of seawater today, and the major ions in freshwater are very dilute compared with their concentrations in seawater.

What is the relationship between body fluids and the environment for marine invertebrates?

Their body fluids are isosmotic to seawater, so they do not face problems of osmotic regulation because they do not gain or lose water by osmosis to aby great extent.

What are the three basic ways terrestrial animals lose water to the environment?

There are three basic ways that terrestrial animals will lose water to the environment via: 1. Evaporation across the integument 2. Evaporation during respiration 3. Excretion

What kind of osmoregulation is exhibited by migratory fish?

They can be hyperosmotic regulators in freshwater and hyposmotic regulators in seawater.

How does each achieve regulation of the blood plasma?

by voiding the animal's excess volume of water they solve the animal's volume regulation and also aid osmotic and ionic regulation by helping to maintain a high osmotic pressure and high ion concentrations in the blood. The kidneys are also regulatory organs that will adjust their function to help maintain stability of volume and composition in the body fluids.

What behavioral and physiological adaptations are exhibited by terrestrial animals to combat water loss in each of these three ways?

evaporation water loss, respiratory water loss and excretion water loss.

How do they minimize gradients?

freshwater animals's integuments have low permeability so that the rate of water exchange is minimized without the expenditure of energy.

Where does passive exchange occurs?

gills

What is water turnover?

it takes into account the water lost by urination and evaporation and the water gained per day by either metabolic water or preform water. A high rate of water turnover means that the animal losses a lot of water per day and then replaces that water. Life can be precarious for such an animal because if an imbalance develops, it can lead rapidly to a crisis.

For each group of marine animals discussed reptiles, birds, mammals, consider how the animal group's evolutionary history influences their water and salt physiology.

o All are descended from terrestrial ancestors, and their blood compositions are clearly carryovers from their ancestors. Many of the adaptations for terrestrial life in these groups also aid osmotic regulation or water loss that they have inherited in a marine habitat. For instance, all of these animals are air breathers and they don't have the problem of passive movements of water and ions across their respiratory exchange membranes which is not the case for fish. Another advantage of their terrestrial heritage is that they have inherited integuments that are adapted to limiting water losses in the dehydrating terrestrial environment, so they tend to exhibit low integumentary permeabilities. Despite these adaptations, they still have problems with water loss and salt loading from the environment.

What are some of the adaptations of lizards and small mammals for a terrestrial life?

o Chuckwalla have low metabolic rates and this reduces their water losses and also their food needs. They excrete nitrogenous wastes as uric acids, urates, which don't require much water for exclusion as oppose to urea. They use behavioral avoidance to avoid stresses by picking out shady places during the day. Some of these will use Salt glands for extrarenal salt excretion and they can survive high plasma composition. They are diurnal so they live during the day. o Round-tailed ground squirrels have higher metabolic rates so they will have higher respiratory water loss (but lower rates than non-desert relatives). They also use behavioral avoidance and they undergo daily torpor hibernation cycles when they are short on food or dehydrated.

What factors are part of an animal's water budget? What are the inputs of water and losses of water that contribute to an animal's overall water flux?

o Evaporative losses decrease with the increasing of humidity, so that first red line is the amount of water lost because of evaporation. As the humidity of the environment increases, we see that the water lost through evaporation decreases. Why? There is less of a gradient. o Urinary, fecal losses relatively constant despite changes of the humidity of environment. o The total water loss from evaporation, urine and fecal tends to decline with increase in humidity. o Metabolic water is constant and dependent on MR despite changes in humidity in the environment. o Total water intake increases with humidity (pre-formed water in air-dried grain food). o Kangaroo rats remain in water balance if total water inputs equal or exceed water losses. o Kangaroo rats can be in water balance if their total water inputs equal or exceed their total, minimum water losses. Based on the graph, therefore, the animals can be in water balance while eating air-dried grain and drinking nothing if the relative humidity is above about 10%. Most of their water input is metabolic water. This is not because they produce exceptional amounts of metabolic water. It is because they conserve water so well that metabolic water can meet most of their needs. o The animal is feed and it doesn't receive extra drinking water. The red lines are showing us all of the ways that water is lost and the blue lines show the water that is gain in this animal.

What challenges do marine reptiles, birds, and mammals face regarding water and salt physiology? What are some of the adaptations of these groups to a marine environment?

o Many of the adaptations for terrestrial life in these groups also aid osmotic regulation or water loss that they have inherited in a marine habitat. For instance, all of these animals are air breathers and they don't have the problem of passive movements of water and ions across their respiratory exchange membranes which is not the case for fish. Another advantage of their terrestrial heritage is that they have inherited integuments that are adapted to limiting water losses in the dehydrating terrestrial environment, so they tend to exhibit low integumentary permeabilities. Despite these adaptations, they still have problems with water loss and salt loading from the environment. o They lose water, for example, by pulmonary evaporation during breathing; they also lose water to some extent across their skin, not only when they are immersed in seawater, but also when they are exposed to the air. These animals often gain excess salts from the foods they eat; for example, when they prey on marine plants or invertebrates that are isosmotic to seawater, they ingest body fluids that have far higher salt concentrations than their own. In addition, they probably often take in quantities of seawater with the foods they eat, although, for the most part, they are thought not to drink seawater.

For each group of marine animals discussed marine teleost, consider how the animal group's evolutionary history influences their water and salt physiology.

o They are decedents of freshwater ancestors so they are Hyposmotic to surroundings and because of this they tend to lose water passively via osmosis and take up ions passively via diffusion and to deal with these issues they do the following: Ingest seawater where they build the gut to take up water from that seawater that is going through the gut. Excrete those divalent ions that came with the seawater in urine. Excrete those monovalent ions across gills.

What are some of the adaptations of xeric invertebrates for a terrestrial life?

o They have integuments that are highly resistant to water loss o Limitation of respiratory water loss o Excretion of waste nitrogen in poorly soluble forms o Production of concentrated urine o Desert ants exposed to heat of day while scavenging for their foods which are the bodies of such heat-killed insects and they get moisture from their prey. They have to go scavenging during the heat of the day. They have evolved adaptations like their long legs which will help them to increase their height from the surface, and it helps reduce their body temperature by 10 degrees Celsius. They have remarkable navigation system is another adaptation that they have evolved in which they make a straight line back to its nest no matter how much the twisted the way when they were looking for food, they can go straight back in a straight line. They could die if they don't find the food that they need and go back to where they have their humidity and nest. They can tolerate temperatures ~ 52-55 degrees Celsius.

What are some of the adaptations of amphibians for a terrestrial life?

o Water challenges: permeable integuments and urea is nitrogen waste product and they produce isosmotic urine. Moreover, although amphibians are notably adept at simply shutting off urine outflow when faced with dehydration, they are unable, when they do excrete urine, to produce a urine any more concentrated in total solutes than their blood plasma. o Hormonal control of anti-dehydration by ADH: its an endocrine system and its produced by the posterior pituitary gland released to the blood and then acts on the kidney and the bladder. Their functions are that they reduce rate of urine production and elevates the urine concentration and it does this by altering the number of aquaporins. It also stimulates bladder cells for the reuptake of water, so they take up water from the bladder and use it like a canteen. Also they do water uptake through ventral skin like frogs that sits on their pelvic patch (dark) against moist substrates to take up water across the skin. Desert amphibians exhibit behavioral adaptations to a xeric environment for example the spadefoot toads. They go at night when its cooler and then in the day they go underground and they also employ seasonal dormancy to simply "retire from the scene" and protect their water status during dry season. The Spadefoot toads, spend many months of each year in dormancy. Overall, these desert amphibians are reclusive animals, holed up in secluded places during much of their lives. For some, dormancy dominates their lives more than activity. Nonetheless, they are able to survive in deserts despite the high permeability of their skin and other vulnerabilities.

For each group of marine animals discussed hagfish, consider how the animal group's evolutionary history influences their water and salt physiology.

o they are an exclusively marine group of jawless primitive vertebrates, resemble the great majority of marine invertebrates in two key respects: (1) Their blood is approximately isosmotic with seawater, and (2) their blood solutes are principally Na+, Cl-, and other inorganic ions. The ionic regulatory processes of hagfish are similar to those of osmoconforming marine invertebrates. Hagfish appear to be the only modern vertebrates that trace a continuously marine ancestry.

For each group of marine animals discussed most marine invertebrates, consider how the animal group's evolutionary history influences their water and salt physiology.

o they are isosmotic, or nearly so, to seawater. Included are the marine mollusks—exemplified by the cuttlefish—and such other marine animals as sponges, coelenterates, annelids, echinoderms, and most arthropods. For the most part these animals are products of lines of evolution that never left the sea. Being essentially isosmotic to their environment, marine invertebrates do not tend to gain or lose water by osmosis to any great extent so they do not face problems of osmotic regulation.

How do they accomplish this?

when Migratory fish are in seawater, they produce very little concentrated urine to conserve the water that they have and they participate in extrarenal excreting of ions across the gills to rid themselves of extra ions and when they are in freshwater, they produce very dilute urine, but they show actively uptake of ions across the gills. So, in freshwater they are able to void excess water by making dilute urine. They are able to switch between these in respond to salinity changes.

Describe the regulatory mechanisms of active ion uptake in freshwater fish.

• Freshwater animals actively take up major ions into their blood directly from the water, while simultaneously removing metabolic wastes. • The site of active ion uptake is usually the gills or the general integument. In teleost (bony) fish and decapod crustaceans (e.g., crayfish), the site of uptake is the gill epithelium. In frogs, active ion uptake occurs across the gills when the animals are tadpoles but across the skin when they are adults.5 Active ion uptake also occurs across the general integument in leeches and aquatic oligochaete worms. • The active uptake of ions from the ambient water requires ATP. Thus active ion uptake places demands on an animal's energy resources. • The mechanisms that pump Na+ and Cl- from the ambient water into the blood are typically different and independent from each other. • The Cl- pump typically exchanges bicarbonate ions (HCO -) for Cl- ions, in this way remaining electro-neutral. • The Na+ pump typically exchanges protons (H+) for Na+ ions (or possibly exchanges ammonium ions, NH4+, for Na+ in some groups of animals), thereby remaining electro-neutral. • The HCO3- and H+ pumped from the blood into the ambient water by the Cl- and Na+ pumps are produced by aerobic catabolism, being formed by the reaction of metabolically produced CO2 with H2O. Thus the Na+ and Cl- pumps participate in removal of metabolic wastes. • Because HCO3- and H+ are principal players in acid-base regulation, the Na+ and Cl- pumps sometimes play critical roles in the acid-base physiology of freshwater animals.

Evaporation water loss across integument

• Humidic animals have highly permeable integuments to water and with this they can reduce water loss by choosing humid habitats which will decrease water pressure gradient between bodies and air. These animals often lose water through their integuments at rates that are 50-100% as great as rates of evaporation from open dishes of water of equivalent surface area! With such a high integumentary permeability, a humidic animal can restrict its integumentary rate of evaporation only by limiting the difference in water vapor pressure that exists across its integument. This explains why humidic animals are tied to humid habitats, where the air has a high water vapor pressure and this can reduce that gradient between the external environment and the tissues of the animal's body. • The xeric animals have integuments with a low permeability to water. Indeed, the evolution of a low integumentary permeability to water is one of the most important steps toward a xeric existence. In all the major xeric groups—vertebrate and invertebrate—microscopically thin layers of lipids are responsible for low integumentary water permeability. In mammals, birds, and nonavian reptiles, the lipid layers are structurally heterogeneous, lamellar complexes of lipids and keratin, less than 10 m thick, located in the stratum corneum, the outermost layer of the epidermis of the skin. The principal lipids present are ceramides, cholesterol, and free fatty acids. Mammals, birds, and nonavian reptiles differ in histological details of the lipid layers, and they evidently evolved their lipid layers independently. In insects and arachnids, the lipids responsible for low integumentary permeability—such as long-chain hydrocarbons and wax esters—are contained in the outermost layer of the exoskeleton (cuticle).

Excretion water loss

• There are two basic ways to reduce the amount of water lost in urine. One is to concentrate the urine, thereby decreasing the amount of water required to excrete a given amount of solute. The second is to reduce the amount of solute excreted in the urine. • One way to reduce the water demands of excretion is to incorporate the waste nitrogen into chemical compounds that are virtually insoluble—or poorly soluble—in water, thereby reducing the amount of material voided in solution which reduces the amount of water lost in urine.

Respiratory water loss

• When a mammal or bird inhales air into its lungs, the temperature of the air is raised to deep-body temperature, and the air becomes saturated with water vapor at the elevated temperature. That air is coming from the lungs so the water that is saturating that inhaled air is coming from the body. If the air were then exhaled without modification, it would carry all the added water away into the environment, so in other words huge water loss for that animal. • During the ensuing exhalation, air coming up from the lungs arrives at the interior ends of the nasal passages at a temperature of 37°C and saturated. However, as the air moves down through the nasal passages toward the nostrils, it encounters the increasingly cooler surfaces created by the previous inhalation. Thus the air being exhaled is cooled as it travels toward the nostrils. This cooling lowers the saturation water vapor pressure of the air, causing water to condense out of the air onto the nasal-passage walls. The overall process is considered a countercurrent process because it depends on flow of air in opposite directions and it's a major adaptation to reduce respiratory water losses. Humans don't really do this to a large extent, but small mammals are capable of doing this cooling and the cold nose of a dog is a great example.