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Unit 4 Physiology > thermoregulation > Flashcards

thermoregulation Flashcards

1
Q

what are endotherms?

A

animals that generate their own body heat

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2
Q

what are homeotherms?

A

maintain their core body temperature within a narrow range despite large fluctuations in their environment (humans)

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3
Q

what is the average core temp and what method of taking temperature is most accurate?

A

37C and rectal readings are most accurate

oral readings are usually 1F below

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4
Q

although the core body temperature usually stays the same, what changes?

A

skin temperature

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5
Q

what are four conditions that change body temperature?

A

time of day (lower in the morning), stage of menstrual cycle (increases after ovulation), level activity and age (higher in children)

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6
Q

why is it so important to maintain body temperature within a narrow range?

A

enzymes, cells and organs function optimally in a narrow range of temperatures

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7
Q

when is hypothalamic regulation of temperature compromised and lost?

A

compromised at 94F and lost at 85F

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8
Q

how much is cellular heat production decreased for every 10F decrease in body temperature?

A

two fold

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9
Q

when is cardiac standstill a threat?

A

at low temperatures

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10
Q

what are the main threats at high temperatures?

A

heat stroke: multiple organ failure and brain lesions

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11
Q

what is the gain of body temperature maintenance?

A

very high (25-30)

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12
Q

at what temperatures can a naked person maintain their core body temperature for a few hours?

A

between 55-130F

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13
Q

what other factors influence the curve of body temp vs atmospheric temperature?

A

moisture and wind (water is a much better conductor)

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14
Q

where are the detectors of temperature?

A

the skin and hypothalamus (main)

also receptors in the core

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15
Q

what is radiation? how much of a person’s body heat is lost that way at rest indoors?

A

transfer of heat by electromagnetic waves (no contact). the rate is proportional to the temperature difference. lose 60% of heat this way

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16
Q

what is conduction and how much heat is lost this way from a person?

A

transfer between solid objects in contact. minimal in a person wearing shoes and clothing

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17
Q

what is convection and in what situation is most heat lost this way?

A

transfer of energy by air or water movement over the body. increased if the body is immersed in water

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18
Q

what is evaporation and where does it occur in the body?

A

heat lost by turning liquid water on the body into a vapor. happens most on the skin and in the respiratory tract

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19
Q

what makes evaporation more or less effective?

A

more: air circulation
less: high humidity

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20
Q

how is most heat produced by exercise dissipated?

A

evaporation

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21
Q

at what temperatures do heat exaustion and heat stroke occur?

A

39C is exhaustion and 41C is stroke

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22
Q

where is most body heat generated?

A

in deep organs like the liver, brain, heart, and skeletal muscle

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23
Q

what largely determines the rate of heat loss?

A

how rapidly heat is carried from the core to the skin and how quickly it is transferred to the surroundings

24
Q

what regulates blood flow to the skin and sweating?

A

the sympathetic nervous system

25
Q

what is passive or unregulated heat transfer?

A

when the rate of heat production from the core is matched by the flow of heat from the core to the skin and from the skin to the environment

26
Q

T or F. various homeostatic control systems not directly involved in temperature regulation can also affect heat flow.

A

true. ex: sweating with hypoglycemia, changes in blood flow in response to a fall in blood pressure and changes in metabolism in response to alterations in thyroid hormone

27
Q

what are two heat insulators and how do they work?

A

skin and subcutaneous fat. fat is a poor heat conductor

28
Q

how do arteries supply the skin venous plexus?

A

directly from small arteries in arteriovenous anastomosis

29
Q

how does dry clothing insulate the body from the environment?

A

by entrapping air next to the skin in the cloth reducing conduction and reducing convective air currents

30
Q

what is the difference in vasodilation in the constricted and dilated states?

A

an 8 full increase

31
Q

what happens to the skin venous plexus at low environmental temperatures?

A

arterioles and arteriovenous anastomoses constrict and reduce blood flow in the plexi

32
Q

what happens to the sympathetic nervous system supplying the skin vasculature when the body temperature rises?

A

it is inhibited (activated when it falls)

33
Q

when an unacclimatized person is exposed to heat, how much sweat do they produce? how does that change in acclimatization?

A

1L/hr. can increase up to 2-3L/hr in 1-6 weeks

34
Q

other than an increase in sweating, what else does acclimatization to hot weather induce?

A

aldosterone secretion that decreases the loss of NaCl from sweat

35
Q

what is the genetic inability to secrete sweat?

A

congenital anhidrosis

36
Q

what do lower animals do to dissipate heat?

A

panting

37
Q

what innervates sweat glands?

A

acetylcholine-secreting sympathetic nerve

38
Q

explain the sweat “distillate” and how it changes before it is excreted?

A

the primary secretion is like protein free plasma. most of the electrolytes are reabsorbed in the duct before secretion

39
Q

describe thermal sensors and how do they respond to changes in local temperature?

A

free nerve endings over the skin and in the hypothalamus. respond to changes by altering the frequency of firing action potentials

40
Q

do thermal sensors in the skin detect a change in core temperature?

A

no they anticipate a change in core temperature when the skin gets cold

41
Q

are the receptors for hot and cold the same? does the body more receive more hot or cold signals?

A

no they are different. there are many more cold receptors than hot on the skin and in deep sensors (prevent hypothermia)

42
Q

where is the temperature control system and how do temperature signals get there?

A

In the hypothalamus (integrator). nerve signals are transported in afferent nerves in the spinal cord

43
Q

at normal temperature is there more firing of hot or cold receptors?

A

they fire at the same amount

44
Q

at what skin temperature do the firing rate of warmth and cold receptor fibers increase?

A

warm: 44-46C
cold: below 37

45
Q

what type of temperature sensitive neurons are most abundant in the hypothalamus and where are they located?

A

heat sensitive neurons located in the preoptic area of the hypothalamus

46
Q

what parts of the heat regulation system produces anticipatory feedback and what parts produce negative feedback?

A

anticipatory- skin sensors

negative- core sensors

47
Q

through what mechanisms can thermogenesis be changed?

A

shivering, chemical excitation, and thyroid hormone production

48
Q

what is the chronological response to cold exposure?

A

body temp decreases, skin blood vessels constrict, you curl up to reduce surface area for heat loss, shivering to generate heat

49
Q

what are some ways that humans adapt to chronic cold exposure?

A

constriction of blood vessels in the skin, inhibition of sweat production and increase of BMR

50
Q

what is the most common cause of lethal hypothermia?

A

immersion in cold water for an extended period

51
Q

why does core temperature increase in the beginning of exercise and what is the response to it?

A

because the rate of production increases and exceeds the rate of dissipation. it is recognized by hypothalamic thermoreceptors and heat dissipation effectors are activated.

52
Q

how much does core body temperature rise during exercise?

A

about 1C (maintained until exercise is completed)

53
Q

how is fever regulated in the hypothalamus?

A

TNF crosses the blood brain barrier and cause the local release of prostoglandins. this increases the temperature set point (same mechanisms of temperature regulation-shivering)

54
Q

other than TNF production, what are other fever producing conditions?

A

degenerating body tissues, hypothalmic brain lesions, tumors that compress the hypothalamus and a thyroid storm

55
Q

how do aspirin and acetaminophen reduce fever?

A

they inhibit prostaglandin synthesis

56
Q

why can fever be beneficial?

A

because immune cells may operate optimally at higher temperatures

57
Q

how long does it take for the temperature to reach a fever set point and to return to the normal set point. how does it return?

A

takes several hours to become a fever

takes an hour to come back down- sweat and vasodilation

Unit 4 Physiology (31 decks)

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