Week 9 (Body Temperature Regulation) Flashcards
Normal Core Body Temperature
Average normal core body temperature of an adult: 37ºC (98.6ºF)
Normal core body temperature range: 35.5ºC (96.0ºF) to 37.7ºC (99.9ºF)
Measurement sites:
Rectal, temporal artery, tympanic membrane (eardrum), esophagus, pulmonary artery, urinary bladder
The Hypothalamus
The Body’s Thermostat
Receives nerve impulses from heat and cold thermoreceptors in the skin
Regulates core temperature via homeostasis
Precisely maintained in dynamic equilibrium
Core and Shell Temperature
Core temperature: Internal body structures (organs within cranial, thoracic, and abdominal cavities, skeletal muscles)
Most important temperature
Maintained fairly constant
Shell temperature: Skin and subcutaneous fat
Generally cooler and varies significantly
Affected by external/ambient temperature
Can fluctuate between 20ºC and 40ºC
Blood is the major agent of heat exchange between the core and shell
Shell thickens in cold environments and thins in warm environments
Factors Affecting Body Temperature
Age: Infants, children, elderly are more sensitive to temperature changes due to decreased thermoregulatory control
Gender: Slightly higher in women due to hormonal influence
Hormonal Levels: Women experience more fluctuations (e.g., menstrual cycle)
Race and Body Mass
Diurnal Variation (Circadian Rhythm): Lower in morning, higher in evening
Physical Activity & Exercise
Food Intake: Malnourished individuals have lower body temperatures
Ingestion of Hot/Cold Liquids
Environmental Temperature, Humidity, Climate
Duration of exposure matters
Heat Acclimatization
Clothing
Illness/Disease
Medications
Emotional State & Stress
Smoking: Produces body heat
Heat Balance: Thermal Regulation
To maintain a steady-state core temperature, heat gain must balance heat loss
Methods of Heat Gain:
Basal metabolism
Environmental heat (conduction, convection, radiation)
Muscular activity (shivering)
Hormones (thyroxine, epinephrine)
Thermic effect of food
Postural changes (huddling, crossing arms)
Methods of Heat Loss:
Radiation: Transfer of heat as infrared rays (60% of heat loss)
Conduction: Direct contact heat transfer (e.g., to objects: 3%, to air: 15%)
Convection: Heat transfer via air or water movement
Evaporation: Conversion of water to gas (22% of heat loss)
Insensible heat loss: Water evaporation from lungs, oral mucosa, skin
Sensible heat loss: Sweating
Thermoregulation
The body’s ability to maintain a stable internal temperature despite environmental changes
Goal: Balance heat gain and heat loss
Controlled by the Hypothalamus (thermoregulatory center)
Monitors blood temperature
Receives signals from thermoreceptors:
Central thermoreceptors: Located in the hypothalamus
Peripheral thermoreceptors: Located in the skin
Deep thermoreceptors: Found in abdominal organs and spinal cord
Regulation via Negative Feedback Loop
Heat loss center activates cooling mechanisms
Heat gain center activates warming mechanisms
Effectors in Thermoregulation
Skin Arterioles:
Vasodilation (heat loss): Increases blood flow to the skin
Vasoconstriction (heat conservation): Reduces blood flow
Sweat Glands:
Sweating (heat loss): Activated by sympathetic cholinergic nerves and adrenal medulla
No sweating (heat conservation): When body temperature drops
Skeletal Muscles:
Shivering (heat production): Increases muscle contraction to generate heat
No shivering (heat loss): To prevent overheating
Skin Hairs:
Piloerection (goosebumps, heat conservation): Hairs stand up to trap heat (minimal effect in humans)
Relaxation (heat loss): Hairs lie flat
Adrenal & Thyroid Glands:
Heat production: Secretion of epinephrine, norepinephrine, and thyroxine
Heat loss: No hormone secretion
Voluntary Control (Cerebral Cortex)
Increase in Body Temperature:
Taking off clothes
Moving into shade
Turning down heat
Reducing physical activity
Drinking cold fluids
Postural changes
Decrease in Body Temperature:
Putting on clothes
Moving into warmth
Turning up heat
Increasing physical activity
Drinking hot fluids
Huddling, crossing arms
Heat Acclimatization
Body adapts to repeated heat exposure
Improves ability to regulate temperature and enhance performance
Takes 6 to 7 days (may vary among individuals)
Gradual loss when moving away from heat
Heat Illnesses
Heat Rash
Heat Cramps
Heat Syncope
Heat Exhaustion
Heat Stroke
Hyperthermia: Elevated body temperature without hypothalamic set-point change
