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PHYSIO > Temperature regulation: fundamental aspects > Flashcards

Temperature regulation: fundamental aspects Flashcards

1
Q

What is core body temperature?

A

The temperature of the body around the main organs (37 ºC).

Rather than a single core body temperature, healthy individuals show a range of normal temperatures.

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2
Q

How is core body temp maintained?

A

Within a narrow range, in contrast with skin temperature

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3
Q

What is the normal range of core body temp at rest?

A

36 - 37.5 ºC

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4
Q

What happens if the core body temp goes above and below 37 ºC?

A 
Above = hyperthermia
Below = hypothermia
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5
Q

What other processes is a range of temperature associated with?

A

1) Circadian rhythm - changes during 24 hr period; during daytime, Tc fluctuates but during sleep Tc decreases
2) Menstrual cycle - changes during days of month

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6
Q

How does Tc measured orally and rectally differ?

A

Temperature measured orally are about 0.5 ºC lower than rectally

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7
Q

What is the range of atmospheric pressure the Tc can remain stable in?

A

Between 20 and 30 ºC

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8
Q

How can Tc be measured?

A

1) Oral: simple, non-invasive, but can underestimate Tc
2) Aural: fast, can be uncomfortable and underestimate Tc
3) Rectal: continuous, slow, close to Tc
4) Oesophageal: continuous, slow, close to Tc (affected by food and drink)
5) GI tract: ‘temperature pill’ radio transmitter continuous, varies along tract. Has to be ‘retrieved’

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9
Q

What generates heat within the body?

A

Metabolism - energy is required to perform all the chemical reactions of the body at rest

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10
Q

What makes up the basal metabolic rate?

A

The sum of the sleeping metabolic and arousal

= 60% of daily energy usage

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11
Q

What does the % daily usage consist of?

A
  • Sleeping metabolic rate
  • Arousal
  • Basal metabolic rate (60%)
  • Thermic effect of food (7%)
  • Nonexercise activity (8%)
  • Purposeful physical activity (25%); can greatly affect DU
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12
Q

What is the basal metabolic rate?

A

This minimum level of energy required to live and generates heat

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13
Q

What is the MET?

A

Number of times your BMR is increased by e.g. increase BMR by 10 if running at 10 METs, but Tc doesn’t increase

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14
Q

During exercise, how is the majority of heat generated?

A

Skeletal muscle contraction

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15
Q

What’s the % of energy used for skeletal muscle contraction?

A

Up to about 25%* is converted to mechanical work (e.g. walking, swimming). The rest of the energy is lost as heat.

*varies between animals, amphibians, etc.

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16
Q

How is temp regulated to avoid increasing too much?

A

The body has active control of heat loss

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17
Q

Why does heat loss = heat production?

A

To maintain a steady temp

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18
Q

What are some modes of heat transfer?

A

1) Radiation (60%) - infrared wavelength; heat waves
2) Convection - air currents
3) Conduction; to air (15%), to objects (3%)
4) Evaporation (22%)

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19
Q

What is radiation?

A
  • Is in the infrared wavelength, longer than those of the visible spectrum
  • Meaured using infrared camera
  • Temp is very hot where red (closer to Tc) and very cold where dark
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20
Q

What is convection?

A
  • A gravitationally-induced heat transport, driven by the expansion of air or fluid on heating
  • The hot expanded air has lower density, so will rise to the top of colder, and therefore denser air
  • E.g. oven with heating source at the bottom and heat travels upwards
21
Q

What happens in forced convection?

A

A strong air (e.g. wind chill effect) or liquid flow can increase heat loss markedly.

22
Q

What is conduction?

A

Little heat is lost by conduction normally, as still air (in clothing) is a poor conductor - layer of clothing traps some air between clothes and body and air doesn’t conduct heat well

E.g. material to conduct heat (candle) which heats up metal stick; heat transfers from tip to hand of individual

23
Q

What is the thermal conductivity of water?

A

25x that of air

e.g. animal that lives in water - needs thick layer of fat instead of fur to isolate organs from cold
animal that live on land - thick layer of fur protects temp better

24
Q

What can happen in cold water immersion 10 ºC?

A

Can lead to death in 2 hours

25
Q

Summarise the first three modes of heat transfer

A

1) Convection = gravitational gradient effect - heat travels upwards
2) Conduction = need some material that conducts the heat from the heat source, away from the heat source
3) Radiation = occurs in any direction - heat that travels with waves

26
Q

What is evaporation?

A

Water evaporates insensibly from the skin and
lungs throughout the day; this heat loss cannot be
controlled for purposes of temperature regulation.

E.g. breath in room air that gets heated up as it travels down the resp tract, breathe out = air comes out humidified (form of heat loss)

27
Q

How much energy does evaporation of 1 litre of water need?

A

2,400 kJ of energy

28
Q

What is the daily insensible water loss

A

About 800 ml, thus accounts for ~20 Watt

29
Q

What does sweating increase?

A

Heat loss to about 20 times basal metabolic rate (2,000 Watt) with loss of up to 3 litres of water per hour

30
Q

What is the basic closed loop: modern cruise control?

A

Analogy: car maintains speed with CC

  • Going uphill = actual speed initially declines
  • Sensors in car which measure reduction in speed (measure difference between actual and desired speed)
  • These inform the control centre (accelerator) to give more fuel to the engine
  • Engine develops a greater torque
  • This makes the wheels spin more rapidly so that the car maintains a speed close to the desired one
31
Q

What are some generic errors in the feedback loop?

A
  • Alterations in setpoint (includes too much gain)
  • Inaccurate sensitivity of receptors and effectors and can have limits which beyond, don’t work normally
  • Delays can occur in each step e.g. from receptor to control centre
32
Q

What are some components in normal negative feedback in thermoregulation?

A

1) Receptors (measures)
- Hypothalamus
- Skin
- Spinal cord
- Abdominal viscera
- Great veins

2) Control centre (compares)
- Hypothalamus

3) Effectors (responds)
- Skin blood vessels
- Muscles
- Hair
- Sweat glands
- Brown adipose tissue

33
Q

What is the negative feedback loop?

A

Restores to homeostasis

34
Q

What is the hypothalamus?

A

Lies in the walls of the 3rd ventricle just about the pituitary gland

35
Q

What are the preoptic and posterior areas of the hypothalamus?

A

Preoptic area = contains cells which respond to local change in temp (most respond to warming)

Posterior area = contains cells which respond to distant change in temp (e.g. skin). This looks like a central controller.

36
Q

What increases with exercise intensity?

A

Cardiac output - blood is reditributed, with skeletal muscle receiving a large portion

37
Q

What is the difference in cardiac output during rest and heavy exercise?

A 
Rest = ~6 L/min
Exercise = ~18 L/min

3x increase

38
Q

What is the difference in skin blood flow during rest and heavy exercise?

A 
Rest = 500 mL
Exercise = 1900 mL

4x increase

= can lose heat by warm blood travelling close to the skin surface, so that it can dissipate heat by the skin

Skin blood flow can also increase for thermoregulation.

39
Q

What is the thermaoneutral zone (TZ)?

A

Defined as the range of ambient temperatures in which humans employ vasomotor control alone to maintain a constant core body temp; no swearing or shivering occurs

40
Q

What is skin deep thermoregulation?

A

Skin = largest ‘specialised organ’ in the body (~8 kg)

  • arteriovenous anastomosis is present only in apical areas
  • blood flow in the skin can range from barely above 0 to more than 30% of CO
  • skin receptors can adapt markedly
41
Q

What is ateriovenous anastomosis?

A

????

42
Q

What is horripilation?

A

The erection of hairs on the skin due to cold, fear, or excitement

Fur and feathers thickness is important as an air-trapping mechanism in animals, but gives only goose-pimples in man

43
Q

What is the countercurrent exchange mechanism?

A
  • arteries transport warm blood deep in the arms and legs
  • deep veins are positioned alongside arteries

In the cold, blood returns through deep veins, heat transferring from the arteries to the veins and is conserved via a countercurrent exchange mechanism.

In situations where we want to lose heat, the deep veins vasoconstrict and more blood flows through the superficial veins.

44
Q

What is the role of sweat glands?

A

A primary protein-free secretion is formed by the glandular portion

Water and salt are reabsorbed while passing grouch the duct, depending on the rate of sweating

45
Q

How do sweat glands function at low and high sweating rates?

A

Low:
Much of the salt and water are reabsorbed
Sweat is rich in urea, lactate and potassium

High:
More salt than water is reabsorbed

46
Q

What can alter the set point (or range) of temperature?

A

Skin temperature alters the set point and can anticipate the change in core temp

47
Q

What happens when skin temperature increases and decreases?

A

Increases:
Sweating starts at a lower hypothalamic temp (sweat point is reduced)

Decreases:
Sweating starts at a higher hypothalamic temperature (set point is raised)

48
Q

What happens when the skin is warm and cold?

A

Warm:
Shivering stats at a lower core temp (set point is reduced)

Cold:
Shivering starts at a higher core temp (set point is raised)

PHYSIO (12 decks)

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