Thermoregulation

Body temperature

Heat produced - heat lost = body temp

Core body temperature range

36-37.5

Thermoregulation

Processes which maintain the balance between heat production and heat loss

Core temperature measured at

Tympanic or rectal sites (may also be measured in eosophagus, pulmonary artery or bladder by invasive monitoring devices)

Surface temperature measured at

oral or sublingual sites

Heat production

• Primary source is metabolism as heat is a by-product of metabolic activities

• Hormones

• Muscle movements - shivering and exercise

• Dietary induced

Heat loss

• Skin (primary source) - arteriovenous shunts, evaporation of sweat

• Lungs humidifying inspired air, exhaling warm air

• Eliminating urine and faeces

Maintenance of body temperature

• Behavioral and physiological responses

• Negative feedback system

• Maintained within a constant range by thermoregulatory centre in the hypothalamus

• Centre receives messages from cold and warm thermal receptors in the body

• Then the centre initiates responses to produce or conserve body heat or increase heat loss

Heat sensitive processes

Chemical reactions occuring in cells, enzymes that control cellular activity

Processes for maintaining thermoregulation are

Behavioral and physiological

Thermoregulation processes utilise mechanisms of…

heat transfer

Heat energy can be transferred by:

• conduction

• convection

• radiation

• evaporation

Conduction

• A diffusion process where molecules transmit their kinetic energy to other molecules by colliding with them

• Heat energy is transferred by adjacent molecular collisions inside a material. The medium itself does not move

Convection

• The transfer of heat of heat by circulating it through air or liquids

• associated with the circulating motion of the molecules (air or liquid)

• An invisible conveyor belt with hot particles rising, forcing cooler particles to flow down beneath

Radiation

• Electromagnetic waves carry energy from one place to another

• Unlike conduction and convection, which need material for energy transfer, this mechanism can transfer energy across empty space

• When temperature of things in environment exceeds skin temperature, radiant heat energy is absorbed by surroundings

Vaporisation/evaporation

• Change of the state of water from liquid to vapour results in the loss of heat from the surrounding structure

• Moisture from respiratory tract

• From the skin

• Dependant on rate of ventilation and the temperature and humidity of the air

Behavioural responses for heat reduction

• Staying still (decrease activity)

• Staying in the shade

• Air conditioning

• wearing less clothing

• Drink water

Physiological responses for heat reduction

• Increase blood flow to the skin

• Decrease metabolic rate

• Sweating

Vasodilation

• controlled by autonomic nervous system

• Results in an increase in blood flow to the skin, allowing heat loss via radiation, conduction, convection and evaporation

• Prompts cooling of the blood that is flowing through the skin

Metabolic rate

• Changes through a reduction in the secretion of thyroxine

• Results in decreased rate

• Causes less heat to be produced in body

Sweat

• Controlled by sympathetic nervous system

• secreted from sweat glands to skin

• Contains sodium chloride, urea, lactic acid and potassium ions

• Cools from evaporating from body

• Does not work in a humid environment

• Environmental temperature must be higher than body temp to be effective

Behavioural responses for increasing body heat

• Huddling

• Curling into a ball

• putting on more clothes

• using a heating device

Physiological processes for increasing body heat

• Reduce blood flow to the skin

• Increase metabolic rate

• shivering

Vasoconstriction

• controlled by sympathetic nervous system

• deceases blood flow to the skin from internal organs

  • decreases transfer of heat from organs to skin

  • allow heat to be lost from body surface

  • cools skin but keeps internal organs warm

Shivering

• Rhythmic muscle tremors occuring at a rate of around ten to twenty per second

• hypothalamus stimulates parts of the brain that increase skeletal muscle movement

Piloerection

• Traps an insulating layer of still, warm air next to skin — goosebumps

• not as effective in humans

Hypothalamus stimulates…

• adrenal medulla via sympathetic nerves

• anterior lobe of the pituitary

Medulla secretes…

adrenaline and noradrenaline in the blood

Hypothalamus and adrenal medulla increase…

• cellular metabolism, increasing heat production

• Helps maintain internal body temperature

Anterior pituitary secretes…

Thyroid stimulating hormone, causing thyroid gland to release thyroxine into the blood

Hypothalamus and anterior pituitary increase…

• Metabolic rate

• Increase body temperature

Factors affecting body temperature

• Circadian rhythms

• Age + gender

• Environmental temperature

• Different body parts

• Exercise

• Hormone levels

• Stress

• Infection + disease

• Medication

Factors increasing body temperature

• Fever as part of an inflammatory response

  • set point of thermoregulatory centre changes

  • whole body temperature increases by 2-3 degrees

  • Acts an defence from invading organisms

• Hyperthermia

  • caused by inability to promote heat loss and reduce heat production

  • Overload of thermoregulatory mechanisms such as in heat stroke or malignant hyperthermia

Stages of a fever

1. Chill phase

2. Plateau (hot) phase

3. Defervescence (breaking) phase

Chill phase

Characterised by heat production responses due to a high hypothalamic temperature set point

Plateau phase

Core temperature reaches a new set point

Defervescence phase

Characterised by heat loss mechanisms as the hypothalamic set point has been readjusted to normal body temperature

Complications of elevated temperature

• fluid loss + dehydration

• Electrolyte imbalances

• decreased urine output

• increased physiological demands

• tachycardia and tachypnea

• cellular/tissue damage

• Neurological damage

• confusion/delirium

• febrile convulsions

Fever (febrile response) treatment and nursing management

• Support physiological mechanisms for each stage of fever (warming or cooling processes)

• Avoid promotion of shivering

• Administer antipyretic medications

• Promote comfort

• Monster nutrition and fluid

• Remove cause of infection

Heat exhaustion/stroke treatment and nursing management

• Facilitate cooling mechanisms

• Rehydration

• monitor for complications

Hypothermia

• Defined as body temp 35 degrees or below

• Thermoregulation mechanisms not enough to restore normal body temp

• Rates of chemical reactions in the body are slowed

Hypothermia caused by:

• Excessive heat loss

• Inadequate heat production

• Impaired hypothalamic regulation

Accidental or induced, can lead to death

Hypothermia treatment and nursing management

Involves rewarming methods and close monitoring of body temperature

Frostbite

• Ice crystals form inside cells resulting in permanent circulatory damage

• Temperatures below 0

Frostbite susceptible areas

• Earlobes

• tip of nose

• fingers and toes

Frostbite treatment and nursing management

• Gradual rewarming

• analgesia (medication relieving pain)

• protection of injured tissue

Body temperature can be measured ______ or ________

Invasively, non-invasively

Accurate methods for measuring body temperature

• Oral

• Rectal

• Tympanic

• Axillary

• Temperature strips

• Temporal artery thermometer

• Bladder temperature sensor

• Oesophageal temperature probe

• Invasive cardiovascular catheter sensor

Factors affecting site choice

• age

• state of consciousness

• amount of pain

• other care

• other conditions