Feedback Control: Temperature and other vital signs

Question 1

What is pulse?

Answer 1

Pulse is the heart rate

Question 2

What is the range of a normal resting heart rate?

Answer 2

60-100 beats/min

Question 3

What is the range of a normal resting respiratory rate?

Answer 3

A normal resting respiratory rate is between 12-20 breaths/min

Question 4

What is considered a normal capillary refill time?

Answer 4

normal is<2 seconds

Question 5

What is considered a normal oxygen saturation?

Answer 5

normal is >95%

Question 6

How is Consciousness measured?

Answer 6

AVPU
Alert
Verbal
Pain
Unconscious

Question 7

What is the definition of core body temperature?

Answer 7

The temperature of structures deep within the body.

Question 8

What is the normal core temperature?

Answer 8

The core body temperature is homeostatically maintained in the structures deep within the body at about 37.8°C.
The core body temperature is kept within a narrow range despite changes in the environment.

Question 9

Why is the skin not a good site for monitoring body temperature?

Answer 9

Skin temperature varies more widely

Question 10

Why is the core body temperature kept within a narrow range?

Answer 10

The normal core body temperature (normothermia) is optimum for cellular metabolism and function.

Question 11

How does increasing the body temperature affect cellular metabolism?

Answer 11

It increase cellular metabolism.

Question 12

What does overheating cause?

Answer 12

Overheating causes protein denaturation, nerve malfunction, convulsions and death.

Question 13

How does decreasing body temperature affect cellular metabolism?

Answer 13

It slows down cellular reaction and may fatally slow down metabolism.

Question 14

What are the 3 sites for measuring body temperature?

Answer 14

ear drum (tympanic)
Rectal
Oral

Question 15

What is the normal temperature range for tympanic temperature monitoring and is this method commonly used?

Answer 15

The normal range is 35.5-37.5 Tympanic thermometers are commonly used in clinical practice.

Question 16

What is the normal rectal temperature rang and is this method of taking temperature commonly used?

Answer 16

The normal rectal temperature range is 36.7-37.5

This temperate may become important at extremes of body temperature e.g. very low body temperature (hypothermia)

Question 17

Why is oral temperature not a good indication of temperature?

Answer 17

It is affected by the consumption of food and drinks

Question 18

In what 4 ways can normal body temperature fluctuate?

Answer 18

It differs slightly in different individuals.
It varies slightly during the day (lowest temperature in early morning) - diurnal variation in body temperature.
May be altered by physical activity, emotions, exercise or exposure to extremes of temperature.
It varies slightly during the menstrual cycle in menstruating females (higher during the 2nd half of the cycle from the time of ovulation).

Question 19

How is the core body temperature maintained?

Answer 19

The heat gain and heat loss must be in balance.
If core temperature decreases heat gain is increased and heat loss is decreased.
If core temperature is increased heat loss is increased and heat gain is decreased.

Question 20

How can heat be gained from the internal and external environment?

Answer 20

Internal - Metabolic heat
External - Radiation
- Convection
- Conduction

Question 21

How is heat lost to the internal and external environment?

Answer 21

Heat is not lost in the internal environment.
External - Convection
- Conduction
- Radiation
- Evaporation

Question 22

What is metabolic heat?

Answer 22

Metabolic heat is the oxidation of metabolic fuel derived from food in the body

Question 23

What is the definition of basal metabolic rate (BMR)?

Answer 23

BMR is the minimum amount of energy required to sustain vital body functions) leads to basic level of heat production.

Question 24

How can BMR be increased?

Answer 24

By hormones such as adrenaline, nonadrenaline and thyroxine.
Muscle activity and hence metaboic heat production can be increased enormously.
Shivering increases heat production by increasing muscle activity.

Question 25

What are methods of nonshivering thermogenesis?

Answer 25

Brown fat, although the role is uncertain in adults

Question 26

What are the 4 methods by which heat is exchanged with the external environment?

Answer 26

Radiation
Conduction
Convection
Evaporation

Question 27

What is the definition of radiation?

Answer 27

Radiation is the emission of heat energy in the form of electromagnetic waves from a surface.

Question 28

What is the method by which radiation is carried out?

Answer 28

Electromagnetic waves travel through the space and are transformed into heat on striking another surface.
The human body both emits and absorbs radiant heat.

Question 29

What does net heat transfer depend on?

Answer 29

It depends upon the relative temperature of the body and surrounding objects (including the sun).

Question 30

In humans about how much of the body’s heat loss is through radiation?

Answer 30

half

Question 31

What is the definition of conduction?

Answer 31

Conduction is the transfer of heat between objects in contact.

Question 32

What is the method by which conduction is carried out?

Answer 32

Heat conduction depends on temperature gradient (as heat moves from a warmer to cooler object) and thermal conductivity (e.g. water is a better thermal conductor than air).

Question 33

How much of a human’s total heat exchange takes place through conduction alone?

Answer 33

A small percentage.

Question 34

What is the definition of convection?

Answer 34

Convection is the transfer of heat energy by air (or water) currents that help t carry the heat away from the body.

Question 35

What is the method by which convection is carried out?

Answer 35

Convection combines with conduction to dissipate heat from the body.
Air next to the skin is warmed by conduction, warmed air becomes less dense and rises wile cooler air moves in next to the skin.
Forced air movement across the body sauce (caused by e.g. wind or a fan) increases the combined effect of conduction-convection.
Forced air movement allows a greater total amount of heat to b carried away from the body in given period of time - the wind chill factor.
Air trapping clothes reduce convection.

Question 36

What is the definition of evaporation?

Answer 36

Evaporation is the energy 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 hat loss and hence cooling of the body.

Question 37

What is the method by which evaporation is carried out?

Answer 37

Passive evaporative heat loss occurs continuously - water molecules continuously passively diffuse from the surface of the skin and the linings of the respiratory airways.
Passive evaportative heat loss from skin and respiratory airways is not subjected to physiologic control.
Sweating is an active evaporative heat loss process controlled by the sympathetic nervous system.
Relative humidity of the atmosphere affects the extent of evaporation an hence evaporative heat loss.

Question 38

How does the human body maintain it’s core temperature at a set point?

Answer 38

Homeostatic mechanisms involving a negative feedback control system.
Negative feedback tends to cancel out any disturbance to controlled variable.

Question 39

What is the hypothalamus?

Answer 39

It is a small area in the brain and ha a variety of neutral and hormonal inputs and outputs.

Question 40

What sort of inputs are received by the hypothalamus?

Answer 40

The neutral inputs to the hypothalamus include those from the negative feedback receptors for temperature regulation.
(The temperature control centre is in the hypothalamus)

Question 41

What is the role of the hypothalamus?

Answer 41

The hypothalamus acts as the body’s thermostat (maintains the temperature at a set point).
The posterior hypothalamic centre is activated by cold.
THe anterior hypothalamic centre is activated by warmth.
The hypothalamus has neutral connections with e.g. the limbic system and cerebral cortex, the motor neurons which controls skeletal muscles and the sympathetic nervous system.

Question 42

What is the coordinated Effectors’ Responses to cold exposure

Answer 42

Skin arterioles - vasoconstriction (contraction of the arterioles’ smooth muscles) - blood flow to the skin surface is reduced - heat conservation (decreased heat loss)
Skeletal muscles - Increased muscle tone
- Shivering
- Increased voluntary movement (behavioural)
(these all increase heat production)
Other behavioural adaptations - postural changes (reduce exposed surface area)
- Warm clothing
(decreased heat loss)

Question 43

Coordinated Effectors’ Responses to heat exposure

Answer 43

Skin Arterioles - Vasodilation (relaxation of the arterioles smooth muscles) - blood flow to the skin surface is increased (increased heat loss)
Sweat glands - Sweating (evaporation of sweat), increased heat loss
Skeletal muscles - decreased muscle tone
- decreased voluntary movement (behavioural), decreased heat production
Other behavioural adaptations - cool clothing, increased heat loss

Question 44

What is the Hypothalamic temperature’s response to it’s set point being raised in fever.

Answer 44

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 hypothalmus initiates mechanisms to heat the body's "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".
The hypothalamic set point would be restored to normal if the pyrogen release is reduced/stopped or the prostaglandins synthesis is decreased/ceased.
The hypothalamus then initiates mechanisms to cool the body "hot response" (e.g. sweating and skin vasodilation) to reduce the body temperature to the normal hypothalamic set point.

Question 45

If the temperature set point is raised to a new higher level this results in “fever”, at what temperature would this happen?

Answer 45

38-40°C

Question 46

What is hyperthermia and at what temperatures is considered to be occurring?

Answer 46

Hyperthermia is the extreme uncontrolled increase in body temperature (elevation of body temperature beyond accepted range due to failure of heat regulating mechanisms).
This occurs at temperature above 40°C

Question 47

What is hypothermia and at what temperatures is it considered to be occurring?

Answer 47

Hypothermia is the drop in body temperature blow that required for cellular metabolism and function.
This occurs at 35°C or below.