Vital Signs: Body Temperature

Video 4.1: Introduction to Thermoregulation

- metabolic rate: measure of all of the chemical reactions going on in the body at a given time

o certain organs have continuous rate of metabolism that contributes significantly to establishing our resting metabolic rate --e.g., the heart, brain, liver, kidneys

o body core –the internal region of body where we normally maintain a fairly constant temperature

o heat is released with an increase in metabolic rate because cells are not 100% efficient –increased metabolism, as occurs during exercise, creates more heat

o core body temperature-

normal range: 35.8°C-38.2°C

normal core temperatures vary between individuals and throughout the day

lowest during-

highest during-

important to maintain a normal temperature for optimal enzyme activity-

o body shell

more temperature fluctuation occurs in the body shell based on atmospheric temperature and body’s metabolic

rate

blood – mechanism of heat transfer in body

picks up heat in body core > carries heat to less metabolically active parts of body

- types of heat transfer:o conduction –heat transfer between 2 objects in direct content

o radiation –transfer of heat in the form of infrared waves

o convection –heat loss that occurs because a warm fluid (which could be air or liquid) rises away from the body surface and is replaced by a cooler fluid

body heat will transfer to the cold fluid, which will then rise away from the body surface and be replaced by cooler fluid

the cooler fluid will warm (due to heat transfer from the body) –and then it will rise away from the body surface

the greater the temperature gradient between the body and the cool fluid that replaces the warm fluid, the greater will be the heat loss

wind chill

o evaporation heat is required to vaporize water (called the “heat of

vaporization”) it is not sweating per se that makes us feel cooler –it is

the evaporation of sweat that cools us when sweat evaporates, it is body heat that vaporizes the

water in sweat

heat index

- heat loss from the body can be sensible or insensible:

o sensible heat loss-

example: sweating

o insensible heat loss-

example: evaporation that occurs as air moves past the airway surfaces during inhalation

Video 4.2: Maintaining Body Temperature

Reflex arc:

- all reflex arcs begin with a sensory receptor –the temperature sensors of the body are called thermoreceptors

o peripheral thermoreceptors

sensitive to hot and cold peripheral thermoreceptors provide the information which helps

us cope with environmental temperature changes

body has high water content which creates thermal inertia –peripheral thermoreceptors make the brain aware of changes in environmental temperature so that adjustments can be made to maintain core temperature

o central thermoreceptors

- neurons carry the sensory input to the hypothalamus, which is the control center for body temperature regulation

o temperature control center is located in the preoptic nucleus of the hypothalamus

- motor effects allow us to maintain our temperature

o temperature homeostasis –state of dynamic equilibrium in which we maintain our body core temperature within the normal range (35.8°C-38.2°C)

o decreased body temperature –when body temperature falls below the hypothalamic set point it causes:

vasoconstriction of subcutaneous blood vessels

shivering- the slight shaking or shuddering that we call “shivering” is

due to rapid involuntary muscle contractions remember: about 60% of the energy stored in the

molecular bonds of fuel molecules is released as heat thus, as skeletal muscles generate ATP to fuel shivering,

they also generate a lot of heat

hormonal secretion in prolonged cold, hormones can stimulate metabolism &

help to maintain a normal body temperature

o increased body temperature – body/blood is warmer than the hypothalamic set point

vasodilation of subcutaneous blood vessels

increases heat loss via radiation (and possibly convection)

sweating

o negative feedback is built into the temperature regulating system

Video 4.3: Hypothermia & Hyperthermia

- hypothermia –condition in which the body core temperature falls below the normal range

o normal physiological mechanisms to warm body (constriction of subcutaneous blood vessels, shivering) are not enough to raise body temperature back to the normal range

o manifestations - decreased heart rate decreased respiration rate decreased blood pressure brain functions will also begin to fail if the hypothermia become

severe enough and/or prolonged

o interventions -

- hyperthermia:

o varies in severity

heat exhaustion

blood cannot circulate effectively due to blood volume loss from excessive sweating

conflicting signals

can occur after prolonged exercise in heat

manifestations

interventions:

heat stroke –condition is more severe than heat exhaustion

positive feedback cycle created that generates heat loss mechanisms that worsen the condition

manifestations: o hot, dry skin

o organs shut down (i.e., organ failure)

predisposing factors can put some people at higher risk :o older adults

o young children and neonates

o people with cardiovascular disease-

o pregnant women-

o people who have impaired fluid regulation capability (as in chronic kidney failure)-

interventions :

Video 4.4: Fever

- Fever:

o pyrogens –molecules released by the cells of the immune system that have the ability to raise the hypothalamic set point

released by cells of the immune system (mainly) and can circulate in the blood

when they arrive in the brain, they affect hypothalamic function when hypothalamus set point is increased, the higher body

temperature of a fever is interpreted by the hypothalamus as “normal”

o may feel cool despite high temperature

o a fever “breaks” when the pyrogens are removed from body and hypothalamus returns to normal set point

o fever is not always a bad thing

Video 4.5: Assessing Body Temperature Demo

- Types of thermometers-

o oral

place probe of thermometer in sublingual pocket-

close to sublingual artery – a deep artery, which gives a more accurate measure of core body temperature

o temporal

run probe over patient’s forehead –assesses temperature in temporal artery, which also carries blood a short distance from the core and gives a relatively accurate measure of core temperature

o tympanic

placed in external auditory canal against tympanic membrane (or ear drum)

close to hypothalamus --thus, gives a fairly accurate measure of core temperature

o axillary

measured in axilla (or armpit) it is difficult to get an accurate reading at this site, for

various reasons

o rectal

sensor probe is placed in rectum requires practice and training for accurate readings

- important to take a temperature when patient is healthy –then, are able to compare future readings to this baseline temperature