feedback control - temp & other signs

Question 1

what are commonly assessed vital signs?

Answer 1

-pulse (60-100)
-blood pressure (120/80)
- respiratory rate (12-20 breaths/min)
- oxygen saturation (>/=96%)
- temperature (37.8)
- consciousness (AVPU)
- capillary refill time (<2 seconds)

Question 2

what is core body temp and how do you find it?

Answer 2

temp of blood & internal organs
= indirect measure
= 37.8 degrees C

Question 3

what does outer shell consist of?

Answer 3

consists of skin & subcutaneous tissue

Question 4

what is normothermia?

Answer 4

narrow range of normal body temp
= optimum for cellular function 7 metabolism

Question 5

what happens if normothermia
a) increased
b) decreased

Answer 5

a) speeds up cellular metabolism, overheating causes protein denaturation, nerve malfunction, convulsions
b) slows down cellular

Question 6

what is indirect estimate of core body temp?

Answer 6

infrared tympanic thermometer (forehead strips)
- ear drum (tympanic)

Question 7

what is normal ear drum temp range?

Answer 7

36-37.5 degrees C

Question 8

what is fever temp?

Answer 8

above 38 degrees C

Question 9

what is hyperthermia temp?

Answer 9

above 40 degrees C

Question 10

what is hypothermia temp?

Answer 10

below 35 degrees C

Question 11

what is direct estimate of core body temp?

Answer 11

rectal or oesophageal (slightly higher than tympanic temp)

Question 12

what does dirunal variation in body temp mean?

Answer 12

temp varies in day - lowest temp in early morning
- altered by activity, exercise, exposure to extreme temp
- varies during menstrual cycle (higher during 2nd half of cycle)

Question 13

why are heat gain and heat loss important?

Answer 13

to maintain constant core body temp they must be balanced

Question 14

what are heat gain examples? (internal & extrenal)

Answer 14

internal environment = metabolic heat gain

external = radiation, convection, conduction

Question 15

what are heat loss examples?

Answer 15

external = radiation, conduction, convection, evaporation

Question 16

what is basal metabolic rate (BMR)?

Answer 16

minimum amount of energy required to sustain vital body functions

Question 17

how does shivering increase heat production?

Answer 17

by increasing muscle activity (as that increases BMR)

Question 18

what can BMR be increased by?

Answer 18

hormones like adrenaline, noradrenaline, thyroxine

Question 19

how is heat produced internally?

Answer 19

metabolic heat = even when doing nothing, heat still being produced
- oxidation of metabolic fuel derived from food in body

Question 20

how is radiation involved in heat exchange with external environment?

Answer 20

• Emission of heat energy in the form of electromagnetic waves from a surface, the waves travel through the space and transformed into heat on striking another surface
• The human body both emits and
  absorbs radiant heat
• Net heat transfer depends upon the relative temperature of body and surrounding objects (including the sun)
• In humans, about half the body’s heat loss is through radiation

Question 21

how is conduction involved in heat exchange with external environment?

Answer 21

• Transfer of heat between objects in contact
• Heat moves from warmer to cooler object
• Heat conduction depends on temperature gradient and thermal conductivity (e.g. water is a better thermal conductor than air)
• In humans, a small percentage of total heat exchange takes place through conduction alone

Question 22

how is convection involved in heat exchange with external environment?

Answer 22

• 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

Question 23

how is evaporation involved in heat exchange with external environment?

Answer 23

• Energy is required to convert water in the skin surface and the lining of the respiratory airways into vapour (by converting water that was leaking from skin cells, this means you’re using energy by cooling water) - energy comes from body & cools
• Passive evaporative heat loss occurs continuously - water molecules continuously passively diffuse from the surface of the skin and the linings of the respiratory airways (always happening, not subjective to physiological control)
• Passive evaporative heat loss from skin & 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 atmosphere affects the extent of evaporation and hence evaporation heat loss (humidity of surroundings can affect body temp)

Question 24

how does human maintain core body temp at set point?

Answer 24

The human body maintains its core temperature at a set point by homeostatic mechanisms involving a negative feedback control system

Question 25

what are sensor examples?

Answer 25

central thermoreceptors (hypothalamus, abdominal organs etc)
peripheral thermoreceptors (skin)

Question 26

where is control centre for negative feedback temperature control?

Answer 26

hypothalamus

Question 27

what are effectors examples for negative feedback temp control?

Answer 27

• skeletal muscles
• skin arterioles (vasoconstriction & vasodilation)
• sweat glands

Question 28

what does negative feedback control try to do for temp control?

Answer 28

tries to cancel out any disturbance to core body temp

Question 29

what is hypothalamus?

Answer 29

• small area in the brain that has a variety of neural and hormonal inputs and outputs
• acts as bodies thermostat (maintains temp at set point)

Question 30

what are neural inputs to hypothalamus example?

Answer 30

neural inputs from negative feedback control receptors for temp regulation

Question 31

what is
a) posterior hypothalamus triggered by and what response does it evoke?
b) anterior hypothalamus triggered by and what response does it evoke?

Answer 31

a) triggered by cold sensation →works to preserve heat by increased muscle tone & shivering
b)triggered by warm sensation →works to release heat by vasodilation, sweating, decreased muscle tone

Question 32

what is effector response to cold exposure?

Answer 32

skin arterioles = vasoconstriction - reduced blood flow to skin surface so heat conservation

skeletal muscles = increased muscle tone, shivering & increased voluntary movement (behavioural) which all increase heat production

other behavioural - postural changes (reduced exposed surface area) and warm clothing - for decreased heat loss

Question 33

what is effector response to heat exposure?

Answer 33

skin arterioles = vasodilation - increase blood flow to skin surface for increased heat loss

sweat glands = sweating = evaporation of sweat (increased heat loss)

skeletal muscles = decreased muscle tone, decreased voluntary movement (behavioural) so decreased heat production

Question 33

how is temp set point changes in fever?

Answer 33

• Chemicals released from macrophages in response to infection or inflammation act as an endogenous pyrogen (cytokine)
• Endogenous pyrogen (e.g. interleukins) stimulate the release of prostaglandin E 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

Question 34

how is normal temp set point restored after fever?

Answer 34

• 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 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