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ZOOL463 > Thermoregulation > Flashcards

Thermoregulation Flashcards

1
Q

What is an endotherm?

A

An organism that generates heat to maintain body temp, typically above surroundings. Birds, mammals.

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2
Q

What is an ectotherm/poikilotherm?

A

An organism that regulates its body temp by exchanging heat with its surroundings. Reptiles and fish.

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3
Q

What is the difference between temporal and regional heterothermy?

A

In temporal heterothermy, at certain times the metabolic rate drops and the body temperature drops. In regional heterothermy, certain zones of the animal are maintained at different temps.

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4
Q

As a homeothermic endotherm, does your core or skin temperature remain constant?

A

Your skin temperature fluctuates with the environment but your core temperature remains constant.

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5
Q

What is metabolic rate?

A

The rate of energy expenditure (usually per hour)

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6
Q

What is your basal metabolic rate?

A

The metabolic rate in a post-absorptive condition (has not eaten ~12 hours) following rest period at room temp. Energy needed for most essential activities.

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7
Q

How is mass specific metabolic rate impacted by an increase in mass?

A

It decreases.

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8
Q

How is metabolic rate impacted by an increase in mass?

A

It increases.

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9
Q

What factors influence BMR?

A

SA/mass ratio, age, gender, muscle tone, stress and hormones

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10
Q

What is your total metabolic rate?

A

The rate of energy expenditure during ongoing involuntary and voluntary activities.

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11
Q

What affects TMR?

A

Exercise and hormones. Exercise can increase heat production briefly.
Hormones: Thyroid is long term thermoreg, catecholamines are short term thermoreg, sex hormones are gender diffs, growth hormones and growth factors.

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12
Q

What does a hormone-mediated increase in TMR do?

A

It contributes to non-shivering thermogenesis.

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13
Q

Why is brown fat important for thermogenesis?

A

Its metabolically active tissue with many mitochondria.

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14
Q

What factors are involved in heat production?

A

Byproducts of metabolism in the liver, muscle, heart, etc.
Increase in thyroid hormones for long term
Increase in sympathetic (catecholamine) activity for short term
Muscle activity like shivering

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15
Q

What factors are involved in heat loss?

A

Heat loss primarily through skin.
Increased or decreased rate of heat conductance from core to skin
Increased rate of heat transfer from skin to surroundings
Increased rate of sweating

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16
Q

How does skin insulation work?

A

Hair traps heat and reduces the temp gradient between the skin and environment.
Blubber/subcutaneous fat allows the body to limit conductance to the skin for anything but oxygen to survive, vasoconstriction, heat saves.

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17
Q

What body surfaces are most effective for conductance?

A

Your face, hands, and ears

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18
Q

What affects skin heat loss?

A

Radiation, conductance, evaporation (convection)

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19
Q

How does sweating work?

A

Its a heat loss mechanism, it gets carried to the skin by the sweat duct. When produced it is isotonic to plasma (minus the proteins) and most of the ions are reabsorbed during passage. Aldosterone reduces salt secretion in sweat. Acclimatization increases your ability to sweat (better reabsorption and tolerance for sweating lots)

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20
Q

How is sweating controlled?

A

By the cholinergic sympathetic pathway. Post-synaptic neuronal control. Normally, sympathetic are adrenergic and parasympathetic are cholinergic. This and piloerection are exceptions to the norm and its why both also occur during fear.

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21
Q

Do mammals with lots of fur sweat?

A

No. One method of cooling is panting which uses convection. Shallow breathing, no alveolar ventilation.

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22
Q

Where is the temperature regulatory centre?

A

The posterior hypothalamus

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23
Q

How does the temperature regulatory centre regulate temperature?

A

It receives signals from sensory thermoreceptors peripherally and from the anterior hypothalamus (the temp centre is in the posterior hypothalamus). Thermal signals relayed to the brain stem, thalamus, somatic sensory cortex, then to posterior hypothalamus which causes appropriate response.

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24
Q

What are the four types of thermoreceptors?

A

Cold receptors, cold pain receptors, warm receptors, heat pain receptors. These led to the hypothesis of the set point (around 37 in humans b/c where cold and warm receptor activity is minimal)

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25
Q

Where are peripheral thermoreceptors? How about deep thermoreceptors?

A

Peripheral: skin region
Deep: spinal cords, abdominal viscera, great veins in upper abdomen and thorax

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26
Q

What stimulates pain receptors?

A

Extreme heat or cold

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27
Q

Are peripheral warmth and cold receptors present in more, less, or equal numbers relative to each other?

A

Peripheral cold receptors are present about 10x as much as peripheral warmth receptors.

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28
Q

Define adaptation as it relates to thermoregulation.

A

Your temperature receptors are strongly stimulated at first when introduced by a temperature change, but this response gradually fades. This is adaptation. It is not 100%

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29
Q

Define spatial summation as it relates to thermoregulation.

A

The thermal sensation you experience is proportional to the number of thermoreceptors stimulated (rather than the intensity of the stimulus). Ex: dipping your foot in versus jumping into a pool

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30
Q

What is the anterior hypothalamus’ role in thermoregulation?

A

It contains thermoreceptors and senses internal temperature changes.

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31
Q

In internal temperature sensors are there more, less, or equal numbers of cold and warmth receptors relative to each other?

A

There are 3x more heat receptors than cold receptors in the anterior hypothalamus

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32
Q

What is the set point?

A

Its the temperature your core tries to maintain. Your core’s temp fluctuates by a fraction of degrees. Its where your cold and warm response are at a minimum. Its determined by the activity of temp regulators in your hypothalamus. Note however that you are always producing some heat basally.

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33
Q

What is the relationship of skin temperature to set point?

A

Inverse. If your skin temperature increases your set point decreases in anticipation of a warming trend and vice versa for cold. It relies on your peripheral receptors.

34
Q

What is the relationship of body temperature in humans to environmental temperature changes?

A

A change of 1 degree internally for each 25-30 degrees externally.

35
Q

What happens when you are warm above your set point?

A

Your thermoregulatory centres in your posterior hypothalamus are inhibited. You sweat and experience vasodilation. Shivering and metabolism decrease.

36
Q

What happens when you are cold below your set point?

A

Your thermoregulatory centers in the posterior hypothalamus are stimulated. You experience vasoconstriction, piloerection (remember sweating? also an exception, sympathetic cholinergic), increased shivering (excitation in posterior hypothal, increased skeletal muscle tone, increased shivering), chemical thermogenesis (increased sympathetic (catecholamines) stimulation)

37
Q

Why is acclimatization more impactful in animals than in humans?

A

We lack brown fat.

38
Q

What does prolonged exposure to cold lead to?

A

Increased thyroid hormone production -> increased BMR. Can cause hyperplasia and hypertrophy of the thyroid. Very important for hibernating animals.

39
Q

How do behavioural aspects play into temperature regulation?

A

They complement the subconscious aspects because we move to remove discomfort. Ex going inside if its cold.

40
Q

Can the warming and cooling mechanisms be stimulated simultaneously?

A

No. they inhibit each other.

41
Q

What is pyrexia?

A

Fever. A state of increased body temp beyond a normal range.

42
Q

What are pyrogens and how does the body respond to them?

A

Fever-causing agents. Include Bacterial lipopolysaccharides toxins, viral polyribonucleotide pyrogen, and cytokines released from injured cells. Leukocytes release cytokines in response.

43
Q

How do pyrogens act?

A

They act on the Toll family of membrane receptors in the hypothalamus which initiates cellular immune responses, this leads to pyrexia. These receptors are evolutionarily conserved. This activates COX-11 enzyme which produces prostaglandins from arachidonic acid. Prostaglandins increase the set point and increase temperature. This is pathophysiological and not part of normal thermoregulation.

44
Q

How do medicines like aspirin work?

A

They block prostaglandin production by inhibiting COX-11 and reduce the degree of fever

45
Q

Why do we feel cold when we are feverish?

A

Because of our elevated set-point. The body undergoes normal responses to cold even though we are burning up.

46
Q

Describe the onset and relief from fever.

A

Body set point elevates, pyresis. Feel cold, shiver, etc. Reach new set point, called crisis. Feel comfortable. Body set point drops, sweating, etc. Antipyresis, body has dealt with pyrogens. Fever often breaks and returns with these steps.

47
Q

What can sustained increased temperatures past our body’s upper limit cause?

A

Above 40 degrees, physiological damage is possible as well as death. Our thermoregulation process can be disrupted, this is rarely a problem in fever but can be.

48
Q

Why does fever happen?

A

Its a sign of disease that makes you aware and it seems like the increased temperatures increase your body’s defense response.

49
Q

What is hyperthermia?

A

Heat stroke. In endotherms, it occurs if the cooling mechanism is not efficient and they reach an upper limit. Beyond this upper limit, there’s a loss of ability to regulate temperature.

50
Q

What can sustained hyperthermia cause?

A

Damages to the cell membrane causing hemorrhages, degeneration of cells especially brain cells. Damage to liver kidney and brain cells usual cause of death with hyperthermia.

51
Q

What are causes of hyperthermia?

A

High humidity or excessive heat gain. Exercise can in some cases.

52
Q

What is an adaptation in some animals to allow sustained running and prevent heatstroke?

A

Ungulates and carnivores: sinous cavernosus. A net of arteries around a pool of venous blood. Cools blood on way to brain. They also keep their noses moist and wet to increase evaporative heat loss. Sustained running could still lead to heat stroke eventually. This isn’t present in rodents or primates.

53
Q

What is hypothermia?

A

Sustained exposure to extreme cold resulting in a decrease in body temperature towards a lower limit if heating ineffective. Most endos tolerate cold more than heat. Beyond lower limit lose ability to temperature regulate, this is where hypothermia symptoms develop.

54
Q

Why are your cheeks warm when the rest of you is cold?

A

Smooth muscles in your capillaries are paralyzed, meaning no vasoconstriction. Its a short term mechanism to prevent damage from frostbite.

55
Q

What are some adaptations to the cold in animals?

A

Marine mammals: blubber, countercurrent blood flow in extremities
Regional heterothermy in arctic animals allowed by more unsaturated fats in membranes in extremities. Fur thickness changes. Temporal heterothermy.

56
Q

What are the three types of temporal heterothermy?

A

Deep sleep, torpor (short-term change in body temp), hibernation (deep torpor)

57
Q

What tissue is required for torpor?

A

Brown fat. It allows the animals to rouse with increased metabolism because of the number of mitochondria.

58
Q

Why is dormancy advantageous in the animals who do it?

A

Since winters are periods of nonfeeding, it reduces energy loss and excessive catabolism.

59
Q

Why can’t all animals enter torpor or hibernation?

A

Very large and very small animals cannot. Large animals because of high SA:mass ratio leading to heat loss with no big reserves and a need for constant feeding and small animals because of their high metabolic rates. They can only go through deep sleep, not true torpor or hibernation. Like bears.

60
Q

What is the difference between winter sleep in larger animals and deep hibernation in smaller animals?

A

The body temperature falls only around 3-5 degrees rather than 25-35 degrees and they rouse easily.

61
Q

What causes torpor?

A

Photoperiod and a drop in temperature.

62
Q

What are characteristics of torpor?

A

Reduction of core temp by several degrees, decrease in metabolic rate, heart rate, breathing rate, and O2 consumption, low blood supply to limbs and mainly restricted to vital organs

63
Q

Which of hibernation and torpor sees a greater decrease in body temperatures?

A

Hibernation. Torpor is short term, hibernation is longer term.

64
Q

What animals can undergo hibernation?

A

Rodents and insectivores. Small (BUT NOT SUPER SMALL) mammals.

65
Q

Do animals still thermoregulate while hibernating?

A

Yes, their set point is just changed.

66
Q

Why do animals periodically arouse from hibernation?

A

To remove wastes, to drink, to feed

67
Q

How long can hibernation periods last?

A

Weeks or months.

68
Q

How is blood flow restricted to vital organs in hibernation?

A

Selective vasoconstriction hormones.

69
Q

In deep hibernation, what happens to brain activity, respiration rate, heart rate, cellular division, and protein synthesis?

A

Low brain activity, lowered resp rate, lowered heart rate, no cellular division, no protein synthesis.

70
Q

What is estivation?

A

Ectotherm/poikilotherm dormancy in winter, like hibernation and temporal heterothermy in mammals and birds.

71
Q

Why is poikilothermy so energy efficient?

A

No need to maintain a constant body temperature.

72
Q

How do poikilotherms regulate temps?

A

Metabolism depends on enviro temps, developmental stage, species. Heterothermy in some.

Control of temperature conductance, increase heart rate and vasodilation when warming, lower heart rate and vascoconstrict when in cold. Slow heart rate to maintain heat.

73
Q

How do poikilotherms deal with low temperatures?

A

Biochemical adaptation (increase in unsaturated fatty acids in membranes)

74
Q

What does high temperature do to poikilotherms?

A

Affinity of hemoglobin for O2 lowered, use physio, anatomy, and behavioural to cope. They have upper critical temperature at which point physio breaks down.

75
Q

How do poikilotherms tolerate heat?

A

Behavior is a part. Ex: honeybee swarming.

76
Q

Describe some examples of regional heterothermy in poikilotherms

A

Flying insects have increased thorax tempratures to fly (ATP needs) and circulation in the abdomen to cool during flight (mechanical thermogenesis of flying makes heat, could overheat).
Snakes shiver while brooding eggs. Heat generation greated while ambient lower.
Tuna have darker (more mitochondria) muscle tissue for faster and more powerful swimming. The gills don’t lose heat because the dorsal aorta is outside and it warms blood as it returns to the body from the outside and cools blood as it goes to the skin, thus reducing the temp gradient between the outside of the animal and the environment.

This conserves temperature compared to complete ectotherms like trout.

77
Q

How do poikilotherms deal with extreme cold?

A

Freeze avoidance by super cooling or antifreeze
Partial freeze tolerance by freezing ECF or generating cryoprotectants

78
Q

How does supercooling avoid freezing in poikilotherms?

A

Body fluids below freezing but unfrozen because avoid ice nucleating. Like can of pop in freezer.

79
Q

How does antifreeze production work in poikilotherms?

A

Some fish and insects make antifreeze molecules that lower the freezing point by adhering to growing ice crystal lattices and preventing them from growing large enough to do damage. Examples are glycoprotein antifreeze protein in fish which lowers freezing points and the more effective sorbitol and glycerol in insects which raises osmotic pressure and lowers freezing point. Glycerol used in cryopreservation.

80
Q

How does the freezing of the ECF work in poikilotherms?

A

Only in insects because they have hemolymph. Some beetles have nucleating proteins that accelerate freezing outside of cells which increases the osmotic pressure in the ECF annd dehydrates the cells, lowering the freezing point and increasing the intracellular concentration of the cells and thus preventing freezing

81
Q

How does freeze tolerance work in poikilotherms?

A

Mostly in invertebrates. Allows partial freezing and can survive for weeks. Cryoprotectants like trehalose and proline are created in insects which forms a gel phase as cells dehydrate and prevents disruption of internal cell organelles by stabilizing the membrane. Rare in vertebrates but some amphibians and reptiles have it. Like the wood frog!

82
Q

How are antifreezes and cryoprotectants synthesizes?

A

Through normal pathways! Ex: sorbitol and glycerol (antifreeze) and trehalose (cryoprotectant) can be synthesized by products of the glycogenolysis pathway.

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