Chapter 44

Regulating the Internal

Environment

• Thermoregulation• Osmoregulation• Excretion

Homeostasis

All organisms must maintain a constant internal environment to function properly• Temperature

• pH

• ion levels

• hormones

HomeostasisHomeostasis

Body Temperature RegulationNegative Feedback

Coping with Environmental Fluctuations

Regulating:Endotherms are thermoregulatorsFundulus-osmoregulator

Conforming:EctothermsMany inverts- nonregulator

                                                                                                                                        

                 

Regulators & Conformers

Spider crab Libinia

Anadromous Salmon

Heat exchange by:• Conduction- transfer of heat between objects in

direct contact with each other• Convection- heat is conducted away from an

object of high temp to low temp

- Rate varies with different materials• Radiation- transfers heat between objects not in

direct contact

- sun energy• Evaporation- change of liquid to vapor

- cooling

Four physical processes account for heat gain or loss

Heat exchange between an organism and its environment

Ectotherm vs Endotherm

Advantages of Endothermy :

• Maintains stable body temp– Cooling & heating the body

cooling and heating the body• high levels of aerobic metabolism• sustains vigorous activity for much longer than

ectotherms– Long distance running– Flight

Disadvantages of Endothermy :

Greater food consumption to meet metabolic needs

• Human metabolic mate at 200C & at rest 1,300 to 1,800 kcal per day.

• American alligator metabolic rate at 200C & at rest 60 kcal per day at 200C.

Mechanisms for thermoregulation• Insulation

- Fur- Hair- Feathers- Fat- Blubber

• Evaporative cooling- sweating, panting, bathing

• Shivering• Nonshivering thermogenesis & brown fat• Circulation adaptations

- Countercurrent exchange- Vasodilatation (cooling)- Vasoconstriction (heat conservation)

• Behavioral responses

Countercurrent heat exchangers

Goose leg Dolphin flipper

Evaporative Cooling

Hippos bathing

Brown fat- generates heat • important in neonates, small mammals in

cold environments, and animals that hibernate

• Located in neck and in inner scapula area

Non-shivering Thermogenesis• Larges amts of heat produced by oxidizing

fatty acids in the mitochondria

Brown Fat & Non-shivering Thermogenesis

Regulating Body Temp in Humans

Acclimatization to New Env. Temps.

• Endotherms (birds and mammals): grow a thicker fur coat in the winter and shedding it in the summer - and sometimes by varying the capacity for metabolic heat production seasonally.

• Ectotherms compensate for changes in body temperature through adjustments in physiology and temperature tolerance.

• For example, winter-acclimated catfish can only survive temperatures at high as 28oC, but summer-acclimated fish can survive temperatures to 36oC.

• Some ectotherms that experience subzero body temperatures protect themselves by producing “antifreeze” compounds (cryoprotectants) that prevent ice formation in the cells.– In cold climates, cryoprotectants in the body

fluids let overwintering ectotherms, such as some frogs and many arthropods and their eggs, withstand body temperatures considerably below zero.

– Cyroprotectants are also found in some Arctic and Antarctic fishes, where temperatures can drop below the freezing point of unprotected body fluids (about -0.7oC).

• Cells can often make rapid adjustments to temperature changes.– For example, marked increases in temperature

or other sources of stress induce cells grown in culture to produce stress-induced proteins, including heat-shock proteins, within minutes.

– These molecules help maintain the integrity of other proteins that would be denatured by severe heat.

– These proteins are also produced in bacteria, yeast, and plants cells, as well as other animals.

– These help prevent cell death when an organism is challenged by severe changes in the cellular environment.

• Torpor in Ground Squirrels– Body temperature: 37oC – Metabolic rate: 85 kcal per day.– During the eight months the squirrel is in

hibernation, its body temperature is only a few degrees above burrow temperature and its metabolic rate is very low.

Hibernation: long-term torpor as an adaptation to long-term winter cold and food shortage

Body Temperature and metabolism during hibernation of Belding’s ground squirrel

Osmoregulation- the control of the concentration of body fluids.

Diffusion- movement of substance from an area of greater concentration to an area of lower concentration

Osmosis- diffusion of water through a semipermeable membrane

Adaptation to Marine EnvironmentReducing salt

• Seabird and marine iguana- nasal salt secreting gland

• Sea snake- sublingual gland• Crocodile- lacrimal gland• Fish gills- chloride cells• Shark- rectal gland

Salt Excretion in Birds

Nitrogenous Waste Excretion

• Ammonia- toxic- Excrete directly into water- jellies- Detoxifyurea

• Urea- need lots of water to get rid of• Uric Acid- birds & reptiles

- more costly to produce than urea, but needs less water to be removed

Strategies to remove Nitrogenous Waste

• Osmoconformer: isoosmotic

• Osmoregulator: hyper-, hypo-,

ureoosmotic

• Euryhaline: wide tolerance range

• Stenohaline: narrow tolerance range

Balancing NaCl in Blood

Osmols- total solute concentration in moles of solute/liter of solution

Osmols- total solute concentration in moles of solute/liter of solution

Marine Fish: hypoosmotic

H2O continually leaves body

continually drinks seawater

excretes salt through gills produces small

amts of dilute urine

Less salt than external

environment

Freshwater Fish: hyperosmotic

H2O continually enters body

does not drinks water

produces large amts of dilute urine

More salt than external

environment

Shark and Coelacanth: ureoosmotic

Maintains high levels of urea and TMAO in blood

excretes salt through rectal gland

coelacanth Rana cancrivora

Hagfish: ionosmotic

nonregulator

Seawater concentration = internal concentration

Osmolarity- measure of total solutes(dissolved particles)

Ions FW m osmol/l SW m osmol/lNa+ 1 470 Cl- 1 550Ca++ variable 10 Total 10 1000

Osmolarity in Freshwater and Saltwater

  Habitat Na+ Cl- Urea

seawater sw 478 558  

hagfish (Myxine) sw 537 542  

lamprey fw 120 96  

Goldfish (Carassius) fw 115 107  

Toadfish (Opsanus) sw 160    

Crab-eating frog (Rana) sw 252 227 350

Dogfish sw 287 240 354

freshwater ray fw 150 149 <1

coelacanth sw 197 199 350

Adaptations to Dry Environment

• Many desert animals don’t drink water

• Kangaroo rats lose so little water that they can recover 90% of the loss from metabolic water and gain the remaining 10% in their diet of seeds.

• Also have long loop of Henle

• Most excretory systems produce a filtrate by pressure-filtering body fluids into tubules.

• Flatworms have an excretory system called protonephridia, consisting of a branching network of dead-end tubules.– The flame bulb draws water

and solutes from the interstitial fluid, through the flame bulb, and into the tubule system.

Diverse excretory systems are variations on a tubular theme

• Metanephridia consist of internal openings that collect body fluids from the coelom through a ciliated funnel, the nephrostome, and release the fluid through the nephridiopore.– Found in most annelids, each segment of a

worm has a pair of metanephridia.

• Insects and other terrestrial arthropods have organs called Malpighian tubules that remove nitrogenous wastes and also function in osmoregulation.– These open into the

digestive system and dead-end at tips that are immersed in the hemolymph.

Nephron

Hormonal Control via Negative Feedback

Hormonal Control