Osmotic Regulation and Excretion Chpt 44, all

4-12-06

Next lecture circulation Chpt 42, all

Environmental Extremes• Freshwater animals

– Show adaptations that reduce water uptake and conserve solutes

• Desert and marine animals face desiccating environments– With the potential to quickly deplete the body

water

Figure 44.1

Water, salt & metabolic wastes

• Osmoregulation (ions and water balance)– Regulates solute concentrations and balances the

gain and loss of water. Water cannot be actively transported—can only move from low osmotic concentration (low salt) across a semipermable membrane to a high osmotic concentration (high salt or other solute).

• Excretion– Gets rid of metabolic wastes (free amino groups-

NH2), the end product of metabolism of proteins and nucleic acids. Includes variable amounts of water to carry away the waste. Carbon dioxide route of excretion via the lungs.

• Osmoregulation balances the uptake and loss of water and solutes

• Osmoregulation is based largely on controlled movement of solutes– Between internal fluids and the external environment.– Most animals have blood that interfaces with the outside and

inside environments. Blood interfaces with the interstitial space (space between cells and capillaries). Interstitial space interfaces with cell membranes. Insects blood (hemolymph) directly bathes the cells

– IMPORTANT!– Animal cells must be in osmotic equilibrium

with their surrounding environments, because if they swell or shrink their membranes will rupture.

–Plants protected by a cellulose wall so can stand increased pressure

ATP

ADP + Pi

Na+/K+

ATPase(sodiumpump)

Na+ leak

K+ leak

2K+

3Na+

ExtracellularNa+ 145 mMK+ 4 mM Intracellular

Na+ 15 mMK+ 150 mM

Includes interstital space and blood space

Free amino acids?

Cl+110mM

Cl+ 20mM

Osmosis

• Cells require a balance– Between osmotic gain and loss of water

(thirst and heat stroke). Lose too much water from sweating and upset salt balance (K).

• Water uptake and loss– Are balanced by various mechanisms of

osmoregulation in different environments

Osmotic Challenges

• Osmoconformers, which are only marine animals– Are isoosmotic with their surroundings and do

not regulate their osmolarity (have the same osmotic pressure inside and outside). Wescor osmometer would show what???

• Osmoregulators expend energy to control water uptake and loss– In a hyperosmotic or hypoosmotic environment

Same reading!

Extreme Regulators• Most animals are said to be stenohaline

– And cannot tolerate substantial changes in external osmolarity

• Euryhaline animals– Can survive large fluctuations in external

osmolarity

Figure 44.2

Example: an African cichlid fish, Tilapia mossambica. Can tolerate fresh water and up to 200% seawater.100% seawater= 3.4g salt/100mls.Also killifish (minnow) with chloride cells on inside of opercular flap.

How do they do it??

Marine Animals• Most marine invertebrates are osmoconformers. The horseshoe

crab.• Those of you who have had the lab this week have found out that its

hemolymph osmolarity varies with that of the seawater. • Generalizations:• Most marine vertebrates and some invertebrates are

osmoregulators. • Ex:• The Fiddler crab however is an osmoregulator from 10% seawater

to about 90% seawater and then it conforms to its seawater concentration (However its osmolarity is about 100 milliosmoles less than the seawater it has been acclimated in.

• The Toad fish maintained a blood osmolarity of 300 in 100% seawater. (Good osmoregulator)

• What marine fish is a conformer? Clue –it lacks a back bone and a mouth!Hag Fish

Sharks!

Marine fish are hypoosmotic to Sea Water

• They lose water by osmosis and gain salt by diffusion across the thin gill epithelium. Gain salt from food if invertebrates. These fishes balance water loss by drinking seawater and excreting NaCl at the gills leaving behind the H2O.

Figure 44.3a

Gain of water andsalt ions from foodand by drinkingseawater

Osmotic water lossthrough gills and other partsof body surface if no scales

Excretion ofsalt ionsfrom gills

Excretion of divalent salt ionsand small amounts of water in scanty urine from kidneys

(a) Osmoregulation in a saltwater fish

NaCl and some water in ingested seawater absorbed by the intestine. Most divalent ions left behind.

Osmoregulation in Fresh H2O Fish

Water drawn in across the gill by osmosis. Some salt lost from the blood at gill. Water removed by excreting large amounts of very dilute urine. Salt replaced from ingested food and active uptake across the gills.

Figure 44.3b

Uptake ofwater and someions in food

Osmotic water gainthrough gills and other partsof body surface

Uptake ofsalt ions by gills

Excretion oflarge amounts ofwater in dilute urine from kidneys. 3% of body weight/hr

(b) Osmoregulation in a freshwater fish

Animals That Live in Temporary Waters• Some aquatic invertebrates living in

temporary ponds– Can lose almost all their body water and

survive in a dormant state

• This adaptation is called anhydrobiosis

Figure 44.4a, b (a) Hydrated tardigrade (b) Dehydrated tardigrade

100 µm

100 µm

Land Animals• Land animals manage their water budgets

– By drinking and eating moist foods and by using metabolic water

Figure 44.5

Waterbalance in a human

(2,500 mL/day= 100%)

Waterbalance in akangaroo rat

(2 mL/day= 100%)

Ingested in food (0.2)

Ingested in food (750)

Ingested in liquid(1,500)

Derived from metabolism (250)

Derived from metabolism (1.8)

Water gain

Feces (0.9)

Urine(0.45)

Evaporation (1.46)

Feces (100)

Urine(1,500)

Evaporation (900)

Water loss

Transport Epithelia

• Transport epithelia (thin pavement cells with tight junctions). No solutes move between cells.– Are specialized cells that regulate solute movement

(by actively transporting solutes across their cell membranes). Their membranes are permeable to selected solutes and may or may not be permeable to water.

– Generally arranged into complex tubular networks, like salt glands and kidney tubules, but can be arranged in sheets like in the intestine and killifish opercular flap.

Salt Gland in a Sea Gull• An example of transport epithelia is found in the salt glands of

marine birds

– Which remove excess sodium chloride from the blood

Figure 44.7a, b

Nasal salt gland

Nostrilwith saltsecretions

Lumen ofsecretory tubule

NaCl

Bloodflow

Secretory cellof transportepithelium

Centralduct

Directionof saltmovement

Transportepithelium

Secretorytubule

Capillary

Vein

Artery

(a) An albatross’s salt glands empty via a duct into thenostrils, and the salty solution either drips off the tip of the beak or is exhaled in a fine mist.

(b) One of several thousand secretory tubules in a salt-excreting gland. Each tubule is lined by a transportepithelium surrounded by capillaries, and drains intoa central duct.

(c) The secretory cells actively transport salt from theblood into the tubules. Blood flows counter to the flow of salt secretion. By maintaining a concentrationgradient of salt in the tubule (aqua), this countercurrentsystem enhances salt transfer from the blood to the lumen of the tubule.

Countercurrent flow ensures that maximum salt is extracted from

the blood.

Proteins Nucleic acids

Amino acids Nitrogenous bases

–NH2

Amino groups

Most aquaticanimals, includingmost bony fishes

Mammals, mostamphibians, sharks,some bony fishes

Many reptiles(includingbirds), insects,land snails

Ammonia Urea Uric acid

NH3 NH2

NH2

O C

C

CN

CO N

H H

C ONC

HN

OH

Nitrogen Excretion (NH3)• Among the most important wastes

– Are the nitrogenous breakdown products of proteins and nucleic acids

Figure 44.8

An animal’s nitrogenous wastes reflect its phylogeny and habitat. The type and quantity of an animal’s waste products has a large impact on its water balance.

Forms of Nitrogenous Wastes

• Different animals– Excrete nitrogenous wastes in different forms

• Overview: A balancing act

• The physiological systems of animals– Operate in a fluid environment

• The relative concentrations of water and solutes in this environment– Must be maintained within fairly narrow limits

Ammonia

• Animals that excrete nitrogenous wastes as ammonia (very toxic but very water soluble).

• Fishes and tadpoles living in waterRelease it across the whole body surface or

through the gills (fishes and frog tadpoles)

Urea

• The liver of mammals and most adult amphibians– Converts ammonia to less toxic urea

• Urea is carried to the kidneys, concentrated and excreted with a minimal loss of water. Desert rodents especially efficient at concentrating urea.

• Estivating lung fish converts amino nitrogen to urea when in the mud cocoon and when rain reappears it converts urea to ammonia and excretes it via the gills. Can do this because urea less toxic.

Uric Acid-nontoxic and poorly soluble

• Insects, land snails, and many reptiles, including birds

• Excrete uric acid as their major nitrogenous waste (white pasty cap on bird feces)

• Uric acid is largely insoluble in water– And can be secreted as a paste with little

water loss. Water reabsorbed in cloaca of birds and reptiles

Evolution and Environment influence type of Nitrogenous Waste Excreted

• The kinds of nitrogenous wastes excreted– Depend on an animal’s evolutionary history

and habitat

• The amount of nitrogenous waste produced– Is coupled to the animal’s energy budget