feedback control - temp & other signs Flashcards
what are commonly assessed vital signs?
-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)
what is core body temp and how do you find it?
temp of blood & internal organs
= indirect measure
= 37.8 degrees C
what does outer shell consist of?
consists of skin & subcutaneous tissue
what is normothermia?
narrow range of normal body temp
= optimum for cellular function 7 metabolism
what happens if normothermia
a) increased
b) decreased
a) speeds up cellular metabolism, overheating causes protein denaturation, nerve malfunction, convulsions
b) slows down cellular
what is indirect estimate of core body temp?
infrared tympanic thermometer (forehead strips)
- ear drum (tympanic)
what is normal ear drum temp range?
36-37.5 degrees C
what is fever temp?
above 38 degrees C
what is hyperthermia temp?
above 40 degrees C
what is hypothermia temp?
below 35 degrees C
what is direct estimate of core body temp?
rectal or oesophageal (slightly higher than tympanic temp)
what does dirunal variation in body temp mean?
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)
why are heat gain and heat loss important?
to maintain constant core body temp they must be balanced
what are heat gain examples? (internal & extrenal)
internal environment = metabolic heat gain
external = radiation, convection, conduction
what are heat loss examples?
external = radiation, conduction, convection, evaporation
what is basal metabolic rate (BMR)?
minimum amount of energy required to sustain vital body functions
how does shivering increase heat production?
by increasing muscle activity (as that increases BMR)
what can BMR be increased by?
hormones like adrenaline, noradrenaline, thyroxine
how is heat produced internally?
metabolic heat = even when doing nothing, heat still being produced
- oxidation of metabolic fuel derived from food in body
how is radiation involved in heat exchange with external environment?
- 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
how is conduction involved in heat exchange with external environment?
- 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
how is convection involved in heat exchange with external environment?
- 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
how is evaporation involved in heat exchange with external environment?
- 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)
how does human maintain core body temp at set point?
The human body maintains its core temperature at a set point by homeostatic mechanisms involving a negative feedback control system
what are sensor examples?
central thermoreceptors (hypothalamus, abdominal organs etc)
peripheral thermoreceptors (skin)
where is control centre for negative feedback temperature control?
hypothalamus
what are effectors examples for negative feedback temp control?
- skeletal muscles
- skin arterioles (vasoconstriction & vasodilation)
- sweat glands
what does negative feedback control try to do for temp control?
tries to cancel out any disturbance to core body temp
what is hypothalamus?
- 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)
what are neural inputs to hypothalamus example?
neural inputs from negative feedback control receptors for temp regulation
what is
a) posterior hypothalamus triggered by and what response does it evoke?
b) anterior hypothalamus triggered by and what response does it evoke?
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
what is effector response to cold exposure?
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
what is effector response to heat exposure?
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
how is temp set point changes in fever?
- 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
how is normal temp set point restored after 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 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
