Physiology - Thermoregulation

37°C (98.6°F)

What is the optimal core body temperature for adults?

Homeostasis

What is the term for the body’s effort to maintain a stable internal temperature?

Upper limit compatible with life

What happens when body temperature rises above 43.3°C?

20–29°C

Which temperature range is associated with cardiac fibrillation?

Cardiovascular system (heart)

What organ system benefits from induced hypothermia during cardiac surgery?

True

T/F: Overheating is more dangerous than cooling.

False

T/F: All tissues can tolerate high temperatures for prolonged periods.

True

T/F: Cellular metabolism slows down with hypothermia.

True

T/F: Fever increases enzymatic reactions.

False

T/F: Measuring skin temperature gives an accurate value of core body temperature.

External environment and internal metabolism

What are the two sources of heat input?

Thyroxine

Which hormone significantly increases metabolic heat production?

Sympathetic nervous system

Name one nervous system component that increases heat production.

Specific dynamic action (thermogenic effect of food)

What metabolic process increases after eating food?

Basal metabolic rate

What is the most significant source of internal heat at rest?

True

T/F: Muscle activity increases heat production.

False

T/F: Testosterone has a greater thermogenic effect than thyroxine.

True

T/F: Heat input must equal heat output for temperature homeostasis.

True

T/F: External radiation contributes to body heat gain.

False

T/F: Shivering does not affect heat production.

Radiation, Conduction. Convection, Evaporation

What are the four main mechanisms of heat loss?

Radiation (~60%)

Which mechanism accounts for the greatest heat loss?

Skin and its vasculature

Which organ system primarily controls heat dissipation?

Insensible evaporation

What term refers to heat loss without visible sweat?

Sweat glands (innervated by sympathetic cholinergic neurons)

Which gland is responsible for sweat production?

True

T/F: Sweating must evaporate to cause effective heat loss.

False

T/F: Conduction to objects accounts for the majority of heat loss.

True

T/F: Vasodilation increases heat loss.

True

T/F: Convection enhances heat loss by replacing warm air with cool air.

False

T/F: Fat conducts heat more efficiently than other tissues.

Hypothalamic preoptic area

What region of the brain serves as the thermostat?

Skin, sweat glands, and skeletal muscles

What are the effectors for thermoregulation?

Cold receptors

Which type of thermoreceptor is more numerous in the skin?

Posterior hypothalamus

Which pathway integrates thermal signals?

Receptors, control center, effector organs

What are the three components of the thermoregulatory feedback system?

True

T/F: The hypothalamus receives signals from both skin and internal sensors.

False

T/F: Warm receptors outnumber cold receptors in the skin.

True

T/F: Sweating is mediated by cholinergic sympathetic neurons.

True

T/F: Cutaneous vasoconstriction conserves heat.

False

T/F: Piloerection is ineffective in humans.

Dorsomedial posterior hypothalamus

What part of the brain controls shivering?

Cold signals from skin and spinal cord

What stimulates the shivering center?

No (it increases tone without rhythmic shaking)

Does shivering involve rhythmic muscle movement?

Anterior hypothalamic preoptic area

Which area inhibits shivering?

Anterior motor neurons

What type of motor neurons are activated during shivering?

True

T/F: Infants cannot shiver effectively.

False

T/F: Shivering is a form of non-metabolic thermogenesis.

True

T/F: Shivering increases heat by muscle tone.

True

T/F: Shivering is triggered just below the set point.

False

T/F: Shivering occurs regardless of temperature levels.

Brown adipose tissue (brown fat)

What special tissue supports non-shivering thermogenesis?

Thermogenin (UCP1)

Which hormone uncouples oxidative phosphorylation in brown fat?

Interscapular space

Where is brown fat most abundant in infants?

Epinephrine

Which hormone increases with cold stress to activate brown fat?

More mitochondria and generates heat

What is the main difference between white and brown fat?

True

T/F: Brown fat is richly supplied with sympathetic nerves.

False

T/F: Brown fat produces large amounts of ATP during thermogenesis.

True

T/F: Cold exposure increases TSH and epinephrine.

True

T/F: Non-shivering thermogenesis can double heat production.

False

T/F: Brown fat is abundant in adults.

Sympathetic cholinergic neurons

What type of neuron activates sweat glands?

Vasodilation and sweating

What is the result of activating the heat-loss center?

Triggers vasoconstriction, shivering, and brown fat activation

What is the function of the heat-promoting center?

37.1°C (98.8°F)

What is the hypothalamic set point for body temperature?

Decreased blood temperature relative to set point

What triggers a reflex to increase body temperature?

True

T/F: Thermoregulatory reflexes rely on sensory input and hypothalamic control.

False

T/F: Cutaneous vasodilation helps conserve heat.

True

T/F: Reflexes are triggered by changes sensed by skin and central thermoreceptors.

False

T/F: Vasoconstriction increases heat loss.

True

T/F: Shivering is a reflex response to low core temperature.

Involves a raised hypothalamic set point

What differentiates fever from other forms of hyperthermia?

Interleukin-1 (IL-1)

What cytokine initiates fever via the hypothalamus?

Aspirin

What drug impedes fever by blocking prostaglandins?

Malignant hyperthermia

What is a dangerous reaction to anesthesia causing severe hyperthermia?

Below 35°C (risk of cardiac fibrillation < 32°C)

What core body temperature defines hypothermia?

True

T/F: Heat stroke is a medical emergency with dry, flushed skin.

False

T/F: Hyperthermia involves a raised set point like fever.

True

T/F: Malignant hyperthermia is genetically linked to the RYR1 gene.

True

T/F: Hypothermia reduces enzymatic activity and oxygen use.

False

T/F: Fever causes the hypothalamus to lower the set point.