53 Questions
What is the primary mechanism of heat transport from the core of the body to the skin?
Radiation
During fever and recovery, what are the primary mechanisms of heat production and heat dissipation?
Heat production: shivering; Heat dissipation: vasodilation and sweating
What is the primary function of the thermoregulatory center in the body?
To maintain the body temperature within a narrow range around the hypothalamic set point
What is the primary mechanism by which heat is lost from the body at room temperature?
Radiation
At what core body temperature can hypothermia be diagnosed?
35°C
Vasoconstriction of cutaneous blood vessels in response to changes in core body temperature is mediated by binding of a hormone/neurotransmitter to what receptor?
Alpha-1 adrenergic receptor
What contributes to the production of body heat?
Muscular exercise, food assimilation, and vital processes contributing to Basal Metabolic Rate (BMR)
What are the mechanisms for heat loss from the body?
Radiation, conduction, convection, and water evaporation
What determines body temperature?
The balance between heat production and loss
Which part of the body primarily controls the regulation of body temperature?
Hypothalamus
What is the 'normal' core body temperature (Tb)?
37ᵒC (98.6ᵒF)
How does rectal temperature compare to oral temperature?
Approximately 0.5°C higher
What contributes to the fluctuation in body temperature?
Circadian and female monthly rhythms
How is heat balance achieved in the body?
When heat gain equals heat loss
What determines heat storage in the body?
Heat capacity, with water having a high heat capacity
What percentage of the energy liberated through catabolism is released as heat?
60%
What factors influence Basal Metabolic Rate (BMR)?
Age, sex, hormones, and digestive state
What is the average Basal Metabolic Rate (BMR) in a 70 kg male?
Around 70 kcal/hr
Which mechanism primarily contributes to heat production during moderate exercise?
Muscular activity
What is the primary mechanism of heat loss during physical activity at high temperatures?
Evaporation
Which organs are the primary heat producers in the body during cellular processes?
Brain, skeletal muscle, and visceral organs
What is the approximate percentage of total heat produced by internal organs at rest?
56%
What is the chief determinant of heat transfer to the skin?
Blood flow to the skin
Which mechanism is responsible for heat dissipation at low temperatures?
Shivering
What is the primary mechanism of heat transfer from the body core to the skin?
Convection
What is the primary mechanism of heat production after a meal?
Digestion, absorption, and storage of food
What regulates heat dissipation at high temperatures?
Vasodilation
What is the primary mechanism of heat transfer at low temperatures?
Conduction
What is the primary mechanism of heat transfer by conduction across subcutaneous fat?
Relatively constant
Which mechanism contributes to heat production in brown adipose tissue?
Non-shivering thermogenesis
What is the primary mechanism for heat loss from the skin surface for naked individuals in a 20°C room?
Radiation
What is the primary mechanism for heat loss from the skin surface for naked individuals in a 30°C room?
Evaporation
How much heat does 1 L of water remove through evaporation from the skin surface?
580 kcal
What is the primary method for heat dissipation in hot environments when evaporation becomes ineffective?
Radiation
At what relative humidity does evaporation become ineffective for heat dissipation?
75%
Where is the thermoregulatory center located in the human body?
Anterior hypothalamus
What does the thermoregulatory center do when body temperature is below the set-point?
Activates heat-generating mechanisms
What type of nerves innervate the sweat glands?
Sympathetic cholinergic nerves
At high humidity, what happens to the effectiveness of sweating as a heat loss mechanism?
Decreases
What happens to the body's evaporation rate at high temperatures with high humidity?
Declines
What can potentially lead to hypothermia or hyperthermia according to the heat balance equation?
Shifts in heat storage
What does the hypothalamic thermoregulatory center do when body temperature is above the set-point?
Activates heat-dissipating mechanisms
What are the mechanisms through which the hypothalamus controls thermoregulation?
Cholinergic and adrenergic mechanisms
What happens to skin blood vessels to release heat?
They dilate
What are common causes of hyperthermia?
Prolonged heat exposure, high humidity, and physical exertion
What are symptoms of hyperthermia?
Weakness, sweating, nausea, vomiting, and collapse
What can heat stroke lead to if untreated?
Disorientation, seizures, coma, and death
What occurs during hypothermia?
Thermoregulatory mechanisms activated to raise body temperature
What induces fever?
Cytokines released during infections
How can fever be reduced?
Inhibitors of PG synthesis, like NSAIDs, can reduce fever
What is the benefit of fever?
It slows microorganism growth and stimulates antibody production
What stimulates PGE2 release, leading to fever?
Cytokines, such as IL1, IL6, and TNFa
What can fever cause?
Increased heart rate, fatigue, joint aches, headache, and disturbances of consciousness
Study Notes
Hypothalamic Control of Thermoregulation and Temperature Disorders
- The hypothalamus controls thermoregulation through cholinergic and adrenergic mechanisms
- Skin blood vessels dilate to release heat, while vasoconstriction minimizes heat loss
- Hyperthermia results from the body's inability to dissipate heat, leading to heat collapse, heat stroke, and malignant hyperthermia
- Common causes of hyperthermia include prolonged heat exposure, high humidity, and physical exertion
- Hyperthermia symptoms include weakness, sweating, nausea, vomiting, and collapse
- Heat stroke can lead to disorientation, seizures, coma, and death if untreated
- Hypothermia occurs in mild, moderate, and severe stages, with thermoregulatory mechanisms activated to raise body temperature
- Fever is induced by cytokines released during infections, which stimulate prostaglandin E2 (PGE2) release and elevate the thermoregulatory set-point
- Inhibitors of PG synthesis, like NSAIDs, can reduce fever
- Fever is beneficial as it slows microorganism growth and stimulates antibody production
- Cytokines, such as IL1, IL6, and TNFa, stimulate PGE2 release, leading to fever
- Fever can cause increased heart rate, fatigue, joint aches, headache, and disturbances of consciousness
Test your knowledge of hypothalamic control of thermoregulation and temperature disorders with this quiz. Explore the mechanisms of heat regulation, hyperthermia, heat stroke, and hypothermia, as well as the role of fever in combating infections.
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