Thermoregulation

Question 1

endotherm

Answer 1

an organism that generates heat to maintain its body temperature, typically above the temperature of its surroundings

Question 2

ectotherm

Answer 2

an organism that regulates its body temperature largely by exchanging heat with its surroundings (poikilotherm species)

Question 3

temporal heterothermy

Answer 3

observed in some endotherms: may be short term (torpor) or long term (hibernation) - can reduce metabolism such that body temperature drops to approximately the ambient temperature

Question 4

regional heterothermy

Answer 4

certain endotherms and ectothermic animals are able to maintain different temperature “zones” in different regions of the body

Question 5

fluctuations in body temperature occurs when:

Answer 5

the rate of heat gain is not balanced by the rate of heat loss

Question 6

metabolic rate

Answer 6

rate of energy expenditure (usually per hour), can be measured directly by direct calorimetric methods (using chamber) or indirectly by measuring oxygen consumption

Question 7

basal metabolic rate (BMR)

Answer 7

rate of energy expenditure in a post absorptive condition (has not eating for 12 hours), following a rest period at room temperature

Question 8

what is the relationship between body weight and mass-specific metabolic rate?

Answer 8

there is an inverse relationship

Question 9

what are some factors influencing BMR?

Answer 9

• surface area/mass ratio
• age
• gender
• muscle vs. fat content
• stress and hormones

Question 10

total metabolic rate

Answer 10

total rate of energy expenditure during ongoing involuntary and voluntary activities

Question 11

what mediates non-shivering thermogenesis?

Answer 11

hormones that mediate increases in total metabolic rate, this is particularly significant in brown fat

Question 12

chemical thermogenesis

Answer 12

increased sympathetic activity (short-term) via epinephrine and norepinephrine increases heat production

Question 13

mechanical thermogenesis

Answer 13

increased muscle activity such as shivering to increase heat production

Question 14

what is responsible for conductance of core temperature to the skin?

Answer 14

flow of blood to the skin (regulation of blood-flow to skin is an effective way of controlling body temperature)

Question 15

aldosterone

Answer 15

reduces secretion of sodium and chloride ions in the sweat (increases reabsorption)

Question 16

control of sweating

Answer 16

cholinergic sympathetic pathway in the subdermal region of sweat gland
-circulating epinephrine/adrenaline can also increase sweating (not related to cooling mechanisms)

Question 17

panting

Answer 17

an effective mechanism of heat loss, shallow breath, does not increase alveolar ventilation

Question 18

where is the temperature-regulatory centre located?

Answer 18

in the posterior hypothalamus, which receives nervous feedback signals from sensory thermoreceptors located peripherally and in the anterior hypothalamus

Question 19

what are the 4 types of sensory receptors?

Answer 19

1) cold pain receptors
2) cold receptors
3) warm receptors
4) heat pain receptors

Question 20

adaptation

Answer 20

peripheral temperature receptors are strongly stimulated when subjected to abrupt changes in temperature (i.e. extreme cold to extreme heat). the response fades away gradually, adaptation is not 100%

Question 21

spatial summation

Answer 21

thermal sensation is proportional to the number of thermoreceptors stimulated (small temp change over a large area has a greater effect than large temperature change over a small area)

Question 22

anterior hypothalamus

Answer 22

i.e. the preoptic area of the hypothalamus contains thermoreceptors and is a temperature sensitive area (contains more heat sensitive receptors than cold-sensitive receptors)

Question 23

critical temperature set-point

Answer 23

determined by the degree of activity of temperature receptors in the hypothalamus
-core temperatures above the set point initiates response to high temperature, and core temperatures below the set point initiates response to cold temperatures

Question 24

control of body temperature set-point

Answer 24

feedback from peripheral temperature receptors provides a physiological mechanism for altering the hypothalamic set point (increase in skin temperature results in a decrease in set point in anticipation of the warming trend; decrease in skin temperature results in an increase in set point in anticipation of cooling trend)

Question 25

specific response to heat:

Answer 25

- increased body temperature inhibits thermoregulatory centres in the posterior hypothalamus - increased sweating - vasodilation - decreased body heat production (decrease shivering and metabolism)

Question 26

specific response to cold

Answer 26

- decreased body temperature stimulates thermoregulatory centres in the posterior hypothalamus - vasoconstriction - piloerection (cholinergic sympathetic stimulation) - increased shivering - increased chemical thermogenesis (as a result of sympathetic stimulation by NE and E for short-term results or increased TH for long-term response)

Question 27

pyrexia

Answer 27

fever; a state of increased body temperature beyond the normal range, could result from infection/allergic reaction/CNS injuries/cancer

Question 28

what causes pyrexia?

Answer 28

pyrogens, which are released by macrophages and neutrophils - bacterial lipopolysaccharides toxins (LPS) - viral polyribonucleotide pyrogen (Poly I:Poly C) - cytokines released from injured cells

Question 29

what is the mechanism by which pyrogens act?

Answer 29

binds and activates Toll family of membrane receptors which initiates cellular innate immune responses - ascyotkines (interleukins, TNF) act through specific hypothalamic membrane receptors resulting in activation of COX-II enzyme which results in production of prostaglandins, prostaglandins increase the hypothalamic set-point which increases body temperature (activates responses to cold)

Question 30

how does aspirin reduce the degree of fever?

Answer 30

blocks prostaglandin production from arachidonic acid (inhibits COX-II enzyme)

Question 31

antipyresis

Answer 31

response to reduce body temperature when the factor causing fever is removed, which causes set-point to be reduced to lower level

Question 32

hyperthermia

Answer 32

beyond the upper limit, loss of ability to regulate temperature -further increases body temperature and causes development of symptoms of heat stroke

Question 33

counter-current heat exchanger

Answer 33

- anatomical adaptation to prevent overheating of the brain - head carotid artery passes through a venous blood sinus (sinus cavernosus) which contains cool blood returning from nasal cavity

Question 34

hypothermia

Answer 34

sustained exposure to extreme cold will result in decreased body temperature, may reach a lower limit if heating mechanisms are not sufficient. - leads to loss of ability to regulate temperature - results in further decline in body temperature and development of initial symptoms of hypothermia

Question 35

frostbite

Answer 35

ice crystal formation (if ice crystals come into contact with cell membranes, cell will die)

Question 36

regional heterothermy

Answer 36

- part of the body such as extremities are maintained at lower temperatures (physiological adaptation) - cold-acclimatization results in a change in the lipids by becoming less saturated in the extremities - more oily and viscous to allow adequate functioning of cell membranes (biochemical adaptation) - changes in fur thickness (anatomical adaptation)

Question 37

deep sleep

Answer 37

temporal heterothermy; adaptation to cope with extreme cold | -body temperature decreases by several degrees

Question 38

torpor

Answer 38

temporal heterothermy; adaptation to cope with extreme cold (e.g. bats, small birds/hummingbirds) - short-term changes in body temperature for a few hours to help animals survive in cold climate - reduction in core temperature - decrease in metabolic rate, heart rate, breathing rate, and oxygen consumption - low blood supply to limbs, blood is mainly restricted to the vital organs

Question 39

hibernation

Answer 39

temporal heterothermy; adaptation to cope with extreme cold - a period of deep torpor with a significant drop in body temperature - hypothalamic thermostat is reset to very low level (but thermoregulation is not suspended) - change in hibernating metabolic rate is smaller in animals with larger masses

Question 40

which animals can go through hibernation

Answer 40

animals with medium masses/metabolic rates

Question 41

is hibernation and temporal heterothermy only observed in endotherms?

Answer 41

no, a number of ectotherm vertebrates also remain dormant and inactive in winter (e.g. snakes and frogs)

Question 42

poikilotherms

Answer 42

- does not need to maintain a constant body temperature (energy efficient) - requires thermoregulation and physiological/anatomical adaptations to deal with extreme temperatures - regional heterothermy is present in some species (e.g. bumblebees, female python, tuna)

Question 43

rate of metabolism in poikilotherms depends on:

Answer 43

environmental temperature, developmental stages, and species

Question 44

Q10 effect

Answer 44

rate of enzyme activity doubles for every 10 degree increase

Question 45

all ectotherms have an:

Answer 45

upper critical temperature (UCT) beyond which there is a breakdown in physiological processes

Question 46

how do poikilotherms survive cold temperatures?

Answer 46

1) freeze avoidance (super cooling - body fluids are cooled below their freezing temperatures but prevent the formation of ice nucleating centres, production of antifreeze-proteins that lower the freezing point) 2) partial freeze tolerance (freezing of extracellular fluid compartment-increases ECF osmotic pressure and results in dehydration of cells which increases intracellular concentration and lowers freezing point, production of cryoprotectants)

Question 47

examples of animals that produce antifreeze

Answer 47

1) flounder and arctic cod contain specific glycoprotein antifreeze protein that lowers freezing point by several degrees 2) certain insects increase the concentration of sorbitol and glycerol in their body fluid, this raises the osmotic pressure and lowers the freezing point

Question 48

cryoprotectants

Answer 48

trehalose (sugar) and proline in insects forms a gel phase as cells dehydrate, this prevents disruption of internal cell organelles by stabilizing the membrane