4) Body Temperature: Physiology Flashcards
What determines body temperature?
- The difference between heat produced by body processes
- And the amount of heat lost to the external environment
How do temperature control mechanisms work?
- They keep the body’s core temperature relatively constant
- Despite environmental extremes and physical activity levels
How does body surface temperature differ from core temperature?
- Surface temperature fluctuates
- Depending on blood flow to skin and heat lost to environment
What is the acceptable body temperature range?
- 36°C to 38°C
- A narrow range for optimal tissue/cell function
What is the aim when measuring body temperature?
- To obtain average temperature of core body tissues/organs
Which temperature measurement sites reflect core temperature?
Rectum
Tympanic membrane
Temporal artery
Esophagus
Pulmonary artery
Urinary bladder
Nasopharynx
Which sites reflect surface temperature?
Skin
Mouth
Axillae
Can temperature values differ between measurement sites?
- Yes, values may differ between sites
What should nurses recognize about temperature readings?
- No single reading is normal for all people
- Learn the temperature range for individual patients
How is body temperature regulation controlled?
- Thermoregulation is regulated by physiological and behavioral mechanisms
- The balance between heat production and heat loss must be closely maintained
What controls body temperature regulation?
- The hypothalamus controls body temperature like a thermostat
- The anterior hypothalamus controls heat loss, the posterior controls heat production
How does the anterior hypothalamus regulate temperature?
- When heated above set point, it sends impulses to reduce body temperature
- Mechanisms include sweating, vasodilation, inhibiting heat production
How does the posterior hypothalamus regulate temperature?
- When body temperature is below set point, it institutes heat conservation
- Mechanisms include vasoconstriction, muscle contraction, and shivering
What can disrupt temperature regulation?
- Disease or trauma to the hypothalamus or spinal cord
- Can cause serious alterations in temperature control
What is the basis for heat production in the body?
- Heat is produced as a by-product of metabolism in all body cells
- Food is the primary fuel source for metabolism
How does activity level affect heat production?
- Additional chemical reactions from activities increase metabolic rate
- As metabolism increases, more heat is produced
What processes produce heat in the body?
- Heat production occurs during rest, voluntary movements, shivering, nonshivering thermogenesis
What is basal metabolism?
- Accounts for heat produced by the body at absolute rest
- Average basal metabolic rate depends on body surface area
How do thyroid hormones affect heat production?
- Promote breakdown of glucose and fat, increasing metabolic rate
- Large amounts can increase basal metabolic rate by 100%
How does gender affect basal metabolic rate?
- Testosterone increases basal metabolic rate
- Men have a higher basal metabolic rate than women
How does exercise affect heat production?
- Voluntary movements like exercise require additional energy
- Metabolic rates can increase up to 2000 times normal during exercise
What is shivering and how does it produce heat?
- Involuntary muscle movement in response to temperature differences
- Skeletal muscle movement requires significant energy, increasing heat production
Who is at increased risk for hypothermia related to heat production?
- Newborns and older persons are less able to shiver or vasoconstrict
- Puts them at increased risk for hypothermia
What is nonshivering thermogenesis?
- Occurs primarily in newborns as main heat source due to inability to shiver
- Stimulates fat metabolism to produce internal heat
How does heat loss occur in the body?
- Through radiation, conduction, convection, and evaporation
- Due to skin’s structure and exposure to environment
What is radiation heat loss?
- Transfer of heat from body surface to environment without direct contact
- Up to 85% of body surface area radiates heat
How does vasodilation/vasoconstriction affect radiation heat loss?
- Vasodilation increases blood flow to skin, increasing radiant heat loss
- Vasoconstriction minimizes radiant heat loss
What factors increase radiation heat loss?
- Removing clothing/blankets
- Standing position exposes more surface area
- Temperature difference between body and environment
How can radiation heat loss be reduced?
- Fetal position minimizes exposed surface area
- Wearing dark, closely woven clothing
What is conduction heat loss?
- Transfer of heat through direct contact with solids/liquids/gases
- Normally accounts for small amount of heat loss
How can conduction heat loss be increased/decreased?
- Applying cool cloths increases conductive loss
- Layering clothing reduces conductive loss
What is convection heat loss?
- Transfer of heat away from body by air movement
- Fans promote convection heat loss
What increases convection heat loss?
- Moistened skin coming into contact with moving air
What is evaporation in relation to heat loss?
- Transfer of heat energy when liquid changes to gas
- Body continuously loses heat through evaporation
How much water/heat is lost through evaporation daily?
- About 600-900 mL evaporates from skin and lungs
- Resulting in water and heat loss
How does the body promote additional evaporative heat loss?
- By regulating perspiration (sweating)
- Sweat glands in skin secrete sweat that evaporates
What triggers sweat gland secretion?
- When body temperature rises
- Anterior hypothalamus signals sweat glands to release sweat
When does sweating occur to lose excessive heat?
- During exercise
- During emotional or mental stress
What is diaphoresis?
- Visible perspiration
- Occurs primarily on forehead and upper thorax
What can excessive evaporation cause?
- Skin scaling and itching
- Drying of nares and pharynx
How does lowered body temperature affect sweating?
- Inhibits sweat gland secretion
Who cannot tolerate warm temperatures due to impaired sweating?
- Those with congenital absence of sweat glands
- Those with skin diseases impairing sweating
How does the skin help regulate body temperature?
- Insulates the body
- Controls blood flow/heat loss through vasoconstriction/vasodilation
- Provides temperature sensation
What provides insulation to keep heat inside the body?
- Skin
- Subcutaneous tissue
- Body fat
Who has more natural insulation?
- People with more body fat
- Compared to slim/muscular people
Where is heat produced in the body?
- Internal organs
- Amount increases during exercise/sympathetic stimulation
How does blood carry heat to the skin surface?
- Blood flows from internal organs carrying heat
- To well-vascularized areas like hands, feet, ears
How much blood can flow through vascular skin areas?
- May vary from minimal to 30% of heart’s output
How is heat lost from the skin surface?
- Heat transfers from blood vessels to skin surface
- Then lost to environment through heat loss mechanisms
What determines blood flow and heat loss to skin?
- Degree of vasoconstriction
How does the body respond to high core temperature?
- Hypothalamus inhibits vasoconstriction
- Blood vessels dilate, increasing blood/heat to skin surface
How does the body respond to low core temperature?
- Hypothalamus initiates vasoconstriction
- Reducing blood flow/heat loss to skin to conserve heat
What allows healthy individuals to maintain comfortable body temperature?
- Voluntarily acting when exposed to temperature extremes
- Ability depends on degree of temperature extreme
What abilities are needed to control body temperature?
- Sensing feeling comfortable/uncomfortable
- Intact thought processes and emotions
- Mobility to remove/add clothes
Who may have difficulty controlling body temperature?
- Those lacking the required abilities
- Infants, older adults, spinal cord injuries
What can impair temperature control?
- Illness
- Altered consciousness
- Impaired thought processes
How effective are behavioral changes in extreme temperatures?
- Have limited effect on controlling temperature
- Like removing/adding clothes
What is important for nurses regarding thermoregulation?
- Assessing factors that place patients at high risk
- For ineffective thermoregulation
