THERMOREGULATION AND OSMOREGULATION

Homeostasis Strand

THERMOREGULATION

- maintenance of body temperature within a range that enables cells to function efficiently

- metabolism is very sensitive to changes in the temperature of an animal’s internal environment

- intense heat denatures enzymes

- properties of membranes change with temperature

- each animal has an optimal temperature range

- heat transfer between organisms and their surroundings occurs in four physical processes :

1. conduction - direct heat transfer between molecules of the environment and those of the body surface

2. convection - transfer of heat by moving air or liquid past a surface of the body

3. radiation - emission of electromagnetic waves produced by all objects; contact not needed

4. evaporation - loss of heat from a liquid’s surface

- mammals and birds are endotherms • derives most or all of its body heat from its own

metabolism • relatively constant body temperature regardless

of environment - everything else is ectothermic • warms its body mainly by absorbing surrounding

heat • amount of heat derived from metabolism is

negligible • air temperature regulates metabolic rates

- the terms cold-blooded and warm-blooded are misleading

- the terms ectotherm and endotherm are not based on body temperature but rather the main source of body heat

- both endothermic and ectothermic animals thermoregulate using some combination of up to four general categories of adaptations

1. Adjusting the rate of heat exchange between the animal and its surroundings.

- body insulation (hair, feathers, fat) - vasodilation / vasoconstriction - countercurrent heat exchanger (esp. marine mammals / birds) 2. Cooling by evaporative heat loss. - panting, sweating 3. Behavioural responses. - basking in the sun or on warm rocks in winter - find cool, damp areas or burrow in summer - migration 4. Changing the rate of metabolic heat production. - endotherms only - double or triple metabolic heat production when exposed to cold

Thermoregulation in animals

• Invertebrates - desert locust orients itself in the direction of sunlight - bees and large moths synchronize their flight muscles to

“warm up” before taking off - honeybees huddle (and circle) to retain heat - honeybees fan water in their hive with their wings, cooling it • Amphibians and Reptiles - bullfrogs vary amount of mucus they secrete from their

surface - lizards may sit alternately in the sun and the shade - iguanas vasoconstrict while swimming - female pythons shiver while incubating eggs

• Fishes - swimming muscles provide metabolic heat - large arteries • Mammals and Birds - increased contraction of muscles - action of hormones that increase metabolic rate and the

production of heat instead of ATP - brown fat : rapid heat production - vasodilation / vasoconstriction - fur / feathers / fat / blubber / goose bumps / panting /

sweating - some kangaroos spread saliva on body surfaces and some

bats use both saliva and urine to enhance evaporative cooling

OSMOREGULATION

• osmoregulation - a complex process utilized by living organisms to ensure that their water levels remains stable

- there are a number of different types of osmoregulation, and a wide variety of techniques can be used to regulate osmotic pressure in everything from plants to whales

- in all cases, the goal is to keep the consistency and level of body fluids constant

• osmoconformers – match their body osmolarity to their environment

(ex. most marine invertebrates and sharks)

• osmoregulators – tightly regulate their body osmolarity, which always stays constant

(ex. more common in the animal kingdom)

FRESHWATER FISH

SALTWATER FISH

• osmoregulation in plants

- stomata (evapotranspiration)

- vacuoles

• osmoregulation in protists

- contractile vacuoles

• osmoregulation in animals

- excretory system (kidneys)