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Principles 2018 > Feedback control: Temperature and other vital signs > Flashcards

Feedback control: Temperature and other vital signs Flashcards

1
Q

What are the commonly assessed vital signs?

A

Pulse HR (60-100)

BP

Temp

RR (12-20)

CRT <2 sec

Oxygen saturation >95%

Consciousness AVPU

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2
Q

What is the outer shell of the human body?

A

Skin and subcutaneous tissue

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3
Q

What it the core body temp?

A

37.8

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4
Q

What is normothermia?

A

Core body temperature that is optimal for cellular metabolism and function

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5
Q

what does increased core body temperature do?

A

Speeds up cellular metabolism

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6
Q

What does overheating cause?

A

Protein denaturation
Nerve malfunction
Convulsions
Death

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7
Q

What does decreased body temperature do?

A

Slows down cellular response

Fatally slow down the metabolism

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8
Q

List the sites for body temperature monitoring?

A 
Ear drum (tympanic)
-35.5-37.5

Rectal
-36.7-37.5

Oral

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9
Q

How does normal body temperature vary?

A

> Differ slightly in different individuals

> Varies slightly during the day (lowest temperature in early morning) - diurnal variation in body temperature

> May be altered by activity, emotions, exercise, or exposure to extremes of temperature

> Varies slightly during menstrual cycle in menstruating females (higher during the 2nd half of cycle from the time of ovulation)

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10
Q

How can heat gain happen?

A

From internal environment
>metabolic heat

From external environment
>radiation
>convection
>conduction

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11
Q

How can heat loss happen?

A 
To external environment
>convection
>conduction
>radiation
>evaporation
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12
Q

What is metabolic heat?

A

Oxidation of metabolic fuel derived from food in body

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13
Q

What is BMR?

A

Basal Metabolic Rate - BMR (minimum amount of energy required to sustain vital body functions) leads to basic level of Heat Production

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14
Q

What increases BMR?

A

hormones such as adrenaline, noradrenaline, and thyroxine

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15
Q

How can metabolic heat be increased?

A

> Muscle Activity and hence metabolic heat production can be increased enormously

> Shivering increases heat production by increasing Muscle Activity

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16
Q

Where is nonshiverisg thermogenesis?

A

Brown fat

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17
Q

Describe radiation?

A

Emission of heat energy in the form of electromagnetic waves from a surface

Electromagnetic waves travel through the space and transformed into heat on striking another surface

The human body both emits and absorbs radiant heat

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18
Q

What does net heat transfer depend upon?

A

relative temperature of body and surrounding objects (including the sun)

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19
Q

How important is radiation in humans?

A

half the body’s heat loss is through radiation

20
Q

Describe conduction?

A

Transfer of heat between objects in contact

Heat moves from warmer to cooler object

21
Q

What does heat conduction depend upon?

A

temperature gradient and thermal conductivity (e.g. water is a better thermal conductor than air)

22
Q

How important is conduction in humans?

A

a small percentage of total heat exchange takes place through conduction alone

23
Q

Describe convection?

A

Transfer of heat energy by air (or water) currents that help to carry the heat away from the body

Combines with conduction to dissipate heat from the body

Air next to the skin warmed by conduction, warmed air becomes less dense and rises while cooler air moves in next to the skin

Forced air movement across the body surface (caused by e.g. wind or a fan) increases the combined effect of conduction-convection

Forced air movement allow a greater total amount of heat to be carried away from the body in a given period of time - the wind chill factor

Air trapping clothing reduces convection

24
Q

Describe evaporation

A

Energy is required to convert water in the skin surface and the lining of the respiratory airways into vapour

This energy comes from the body resulting in evaporative heat loss and hence cooling of the body

25
Q

Where does passive evaporative heat loss occur?

A

water molecules continuously passively diffuse from the surface of the skin and the linings of the respiratory airways

26
Q

How is Passive evaporative heat loss from skin & respiratory controlled?

A

Not under physiologic control

27
Q

How is sweating controlled?

A

sympathetic nervous system

28
Q

What effects the extent of evaporation?

A

relative humidity of the atmosphere affects the extent of evaporation and hence evaporative heat loss

29
Q

How does the body maintain core temperature at a set point?

A

homeostatic mechanisms involving a negative feedback control system

30
Q

What are the sensors in the temperature control system?

A 
Central thermoreceptors 
(in hypothalmus, abdominal organs, elsewhere)

Peripheral thermoreceptors (in skin)

31
Q

Where is the control centre in the temperature control system?

A

Hypothalamus

32
Q

Where are the effectors in the temperature control system?

A

Skeletal muscle
Skin arterioles
Sweat glands

33
Q

The posterior hypothalamus is activated by…

A

Cold

34
Q

The anterior hypothalamus is activated by…

A

Heat

35
Q

How does the hypothalamus cause a response?

A

neural connections with e.g. the limbic system & cerebral cortex, the motor neurons which controls skeletal muscles, and the sympathetic nervous system

36
Q

What is the response to cold in the skin arterioles?

A

Vasoconstriction

blood flow to the skin surface is reduced - heat conservation (Decreased heat loss)

37
Q

What is the response to cold in the skeletal muscles?

A

Increased muscle tone

Shivering

Increased voluntary movement

38
Q

What other behavioural adaptations occur as a response to cold?

A

> Postural changes
(reduce exposed surface area)

> Warm clothing

39
Q

What is the response of the skin arterioles to heat?

A

Vasodilatation (relaxation of the arterioles smooth muscles) - blood flow to the skin surface is increased (Increased heat loss)

40
Q

What is the response of the sweat glands to heat?

A

Sweating – Evaporation of sweat

41
Q

What is the response of the skeletal muscle to heat?

A

Decreased muscle tone

Decreased voluntary movement

42
Q

How is the hypothalamic temperature set pint raised in fever?

A

Chemicals released from macrophages (certain type of phagocytic white blood cells) in response to infection or inflammation act as an endogenous pyrogen

Endogenous pyrogen (e.g. interleukins) stimulate the release of prostaglandins in the hypothalamus

The prostaglandins act on the hypothalamic thermo-regulatory centre to “reset” the thermostat at a higher temperature

The hypothalamus initiate mechanisms to heat the body “cold response” (e.g. shivering and skin vasoconstriction) to raise the body temperature to the new set point

The body temperature increases to reach the new set point resulting in “fever”

43
Q

When is the hypothalamic set point restored post fever?

A

if the pyrogen release is reduced/stopped or the prostaglandins synthesis is decreased/ceased

44
Q

What will the hypothalamus do to cool the body after fever?

A

initiate mechanisms to cool the body “hot response” (e.g. sweating and skin vasodilatation) to reduce the body temperature to the normal hypothalamic set point

45
Q

What is the new level of temperature during fever?

A

38-40

46
Q

What is hyperthermia?

A

Extreme uncontrolled increase in body temperature (elevation of body temperature beyond accepted range due to failure of heat regulating mechanisms) is known as “hyperthermia” Temperature above 40oC

47
Q

What is hypothermia?

A

Drop in body temperature below that required for cellular metabolism and function is known as “hypothermia” Temperature at or below 35oC

Principles 2018 (34 decks)

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