Thermoregulation in the Human Body
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Questions and Answers

What is the primary function of thermoregulation in the human body?

  • To maintain a constant body temperature of 98.6F
  • To control the body's hydration levels
  • To regulate the body's metabolic rate
  • To maintain a stable core temperature despite changes in environmental temperature (correct)

    • What is the range of normal core temperature?

  • Less than 36C to greater than 37.5C (correct)
  • Between 96F and 100.4F
  • Between 98F and 98.6F
  • Between 95F and 100F

    • What is the main source of heat production in the body?

  • Muscle activity
  • Thyroxine production
  • Metabolic rate (correct)
  • Heat gained from the environment

    • What is the role of subcutaneous tissues in thermoregulation?

    <p>To act as heat insulators</p> Signup and view all the answers

    What is the mechanism by which the body controls heat conduction to the skin?

    <p>Vasoconstriction of arterioles</p> Signup and view all the answers

    What is the primary mechanism of heat loss from the skin surface?

    <p>Radiation</p> Signup and view all the answers

    What happens to the body's core temperature during extreme physical activity?

    <p>It increases</p> Signup and view all the answers

    What is the role of the skin in thermoregulation?

    <p>To act as a heat radiator</p> Signup and view all the answers

    What is the effect of thyroxine on the body's heat production?

    <p>It increases heat production</p> Signup and view all the answers

    What is the role of blood flow in thermoregulation?

    <p>To provide heat transfer from the body core to the skin</p> Signup and view all the answers

    What percentage of heat loss from the body occurs through direct conduction?

    <p>3%</p> Signup and view all the answers

    What happens to air convection when there is an equal amount of heat in the air and body?

    <p>It remains the same</p> Signup and view all the answers

    How much more effective is conduction and convection of heat from a person suspended in water compared to air?

    <p>Thousand times</p> Signup and view all the answers

    How many calories of heat are lost for each gram of water that evaporates?

    <p>0.58 calories</p> Signup and view all the answers

    Why is evaporation a necessary cooling mechanism at very high air temperatures?

    <p>Because body temperature increases when surroundings are hot and body starts to evaporate</p> Signup and view all the answers

    What happens to the rate of heat loss from the body when wearing clothing?

    <p>It is depressed to 1/6th</p> Signup and view all the answers

    What happens to the flow of convection air currents when wearing clothing in private areas?

    <p>It decreases</p> Signup and view all the answers

    Why is it hard to radiate heat out when clothing is wet?

    <p>Because wet clothing is less breathable</p> Signup and view all the answers

    How much water is lost through evaporation in the skin and breath per day?

    <p>600-700ml</p> Signup and view all the answers

    What is the effect of vasodilation of skin blood vessels on heat transfer?

    <p>Increases the rate of heat transfer to the skin</p> Signup and view all the answers

    What happens to sweat production when the body core temperature rises?

    <p>Sweat production increases by 10 times the basal rate of body heat production</p> Signup and view all the answers

    What is the effect of skin vasoconstriction on heat loss?

    <p>Decreases heat loss</p> Signup and view all the answers

    What is the function of piloerection?

    <p>To create a thick layer to protect skin from cold surroundings</p> Signup and view all the answers

    What is the effect ofthyroxine secretion on heat production?

    <p>Increases heat production</p> Signup and view all the answers

    What is the primary motor center for shivering located in?

    <p>Posterior hypothalamus</p> Signup and view all the answers

    What is the term for the increase in metabolic rate due to sympathetic stimulation?

    <p>Chemical thermogenesis</p> Signup and view all the answers

    What is the effect of cooling the anterior hypothalamic-preoptic area on thyrotropin-releasing hormone production?

    <p>Increases thyrotropin-releasing hormone production</p> Signup and view all the answers

    What is the effect of sympathetic excitation on heat production?

    <p>Increases heat production</p> Signup and view all the answers

    What is the set point temperature for temperature control mechanisms in the human body?

    <p>37.1°C</p> Signup and view all the answers

    What is the feedback gain of the temperature control system equal to?

    <p>The ratio of the change in environmental temperature to the change in body core temperature minus 1.0</p> Signup and view all the answers

    How much does the body temperature change for each 25- to 30°C change in environmental temperature?

    <p>1°C</p> Signup and view all the answers

    What happens to the set point for core temperature control when skin temperature changes?

    <p>It can slightly alter</p> Signup and view all the answers

    What is the primary function of the temperature controlling area in the brain?

    <p>To provide psychic sensation of being overheated or cold</p> Signup and view all the answers

    What is the primary cause of fever?

    <p>Abnormalities in the brain causing high body temperature</p> Signup and view all the answers

    What is the normal body temperature range?

    <p>Above 99 degree F</p> Signup and view all the answers

    What is the role of peripheral thermoreceptors?

    <p>To detect changes in the balance between heat loss and production</p> Signup and view all the answers

    What stimulates sweat glands to produce sweat?

    <p>Nerve impulses from the anterior hypothalamus-preoptic area</p> Signup and view all the answers

    What is the role of the hypothalamus in thermoregulation?

    <p>To integrate thermoregulatory information</p> Signup and view all the answers

    What happens to the body's core temperature when the anterior hypothalamus-preoptic area is stimulated?

    <p>It decreases</p> Signup and view all the answers

    What is the role of cholinergic nerve fibers in thermoregulation?

    <p>To innervate sweat glands</p> Signup and view all the answers

    What is the effect of sympathetic stimulation on sweat glands?

    <p>It increases sweat production</p> Signup and view all the answers

    What is the role of the autonomic nervous system in thermoregulation?

    <p>To transmit nerve impulses to sweat glands</p> Signup and view all the answers

    What is the effect of norepinephrine on sweat glands?

    <p>It increases sweat production</p> Signup and view all the answers

    What is the main function of the coiled portion of the sweat gland?

    <p>To secrete a primary fluid</p> Signup and view all the answers

    What happens to the primary secretion as it flows through the duct portion of the sweat gland?

    <p>Its constituents are modified</p> Signup and view all the answers

    What is the relationship between the secretory portion and the duct portion of the sweat gland?

    <p>The secretory portion secretes the sweat, and the duct portion modifies it</p> Signup and view all the answers

    What is the significance of the tubular structure of the sweat gland?

    <p>It enables the sweat gland to secrete and transport sweat efficiently</p> Signup and view all the answers

    What is the result of the modification of the primary secretion as it flows through the duct portion of the sweat gland?

    <p>The sweat is made suitable for secretion onto the skin surface</p> Signup and view all the answers

    What is the primary regulator of body temperature?

    <p>The hypothalamus</p> Signup and view all the answers

    What is the range of environmental temperatures within which a nude person can maintain a normal body core temperature?

    <p>55°F to 130°F</p> Signup and view all the answers

    What is the purpose of the temperature detectors in the body?

    <p>To determine when body temperature becomes either too high or too low</p> Signup and view all the answers

    What happens when the hypothalamic temperature centers detect that the body temperature is either too high or too low?

    <p>They institute appropriate temperature-decreasing or temperature-increasing procedures</p> Signup and view all the answers

    What is the primary location of the temperature-regulating centers in the body?

    <p>The hypothalamus</p> Signup and view all the answers

    What is the mechanism by which the body regulates its core temperature?

    <p>Nervous feedback mechanisms</p> Signup and view all the answers

    What is necessary for the feedback mechanisms to operate and maintain a normal body core temperature?

    <p>Both temperature detectors and nervous feedback mechanisms</p> Signup and view all the answers

    When the body temperature is too high or too low, what is the response of the hypothalamic temperature centers?

    <p>They institute temperature-decreasing or temperature-increasing procedures.</p> Signup and view all the answers

    What is the main purpose of the hypothalamic temperature centers?

    <p>To maintain the body's temperature within a narrow range.</p> Signup and view all the answers

    What happens when the hypothalamic temperature centers detect that the body temperature is too high or too low?

    <p>They institute temperature-decreasing or temperature-increasing procedures.</p> Signup and view all the answers

    What is the result of the hypothalamic temperature centers detecting a change in body temperature?

    <p>The body's thermoregulation mechanisms are activated.</p> Signup and view all the answers

    What is the role of the hypothalamic temperature centers in maintaining the body's temperature?

    <p>They maintain the body's temperature within a narrow range.</p> Signup and view all the answers

    Study Notes

    Thermoregulation

    • Thermoregulation is a homeostatic process that maintains the body's core temperature at a constant 37°C (98°F) despite changes in external temperatures.
    • Core temperature remains constant even when exposed to extreme temperatures, ranging from 55°F to 130°F.
    • Skin temperature refers to the skin's ability to lose heat to the surroundings.

    Normal Core Temperature

    • Normal core temperature ranges from less than 36°C to greater than 37.5°C.
    • The average normal core temperature is between 98°F and 98.6°F orally, and 1°F higher when measured rectally.
    • Core temperature can increase during exercise and vary depending on surrounding temperatures.
    • It can rise to 101°F to 104°F when extremely active, and drop to 96°F when cold.

    Heat Production

    • Heat is a by-product of metabolism, influenced by the metabolic rate of the body.
    • Factors that affect heat production include:
      • Basal metabolic rate
      • Muscle activity (shivering)
      • Thyroxine
      • Epinephrine and norepinephrine
      • Sympathetic stimulation
      • Chemical activity
      • Digestion and absorption

    Heat Loss

    • Heat loss occurs through the transfer of heat from organs and tissues to the skin, and then to the air.
    • The rate of heat loss is influenced by the speed of heat transfer to the skin and the surrounding air.
    • The insulator system of the body, comprising subcutaneous tissues, acts as a heat insulator, conducting heat ⅓ as readily as other tissues.
    • Blood flow to the skin from the body core provides an effective means of heat transfer.

    Control of Heat Conduction to the Skin

    • The sympathetic nervous system controls heat conduction to the skin by regulating blood flow through arterioles and arteriovenous anastomoses.
    • Vasoconstriction and vasodilation play a crucial role in this process.

    Basic Physics of Heat Loss

    • Heat loss from the skin surface occurs through three mechanisms:
      • Radiation: when the body temperature is higher than surrounding objects, heat is radiated towards the surroundings.
      • Conduction: direct contact between the skin and an object results in heat loss (about 3% of total heat loss).
      • Evaporation: 0.58 calories of heat are lost for each gram of water evaporated.

    Cooling Effect of Air and Water

    • Air movement increases heat loss, with low velocity air resulting in a cooling effect proportional to the square root of wind velocity.
    • Conduction and convection of heat from a person suspended in water are significantly more effective than in air, resulting in faster cooling.

    Conductive Heat Loss

    • Conductive heat loss occurs through direct contact with an object, accounting for approximately 3% of body heat loss.
    • Molecules of skin undergo vibratory motion, facilitating heat transfer.

    Convective Heat Loss

    • Convective heat loss occurs when there is equal heat in the air and body, resulting in air convection.
    • When a person is sitting, 15% of body heat loss is due to convective heat loss, assuming no gross air movement.
    • Air movement enhances convective heat loss, with increased cooling effects at higher wind velocities.

    Cooling Effect of Wind

    • Wind replaces air constantly, increasing heat loss, with the cooling effect proportional to the square root of wind velocity.
    • Faster wind currents result in more efficient cooling.

    Conduction and Convection in Water

    • Heat conduction and convection in water are approximately 1,000 times more efficient than in air.
    • When in water, the body cools more efficiently than in air.

    Evaporation

    • Evaporation results in heat loss of approximately 0.58 calories per gram of water evaporated.
    • Even without sweating, evaporation occurs through breathing and skin, resulting in a loss of around 600-700ml of water per day, equivalent to 16-19 calories per hour.
    • Evaporation is a necessary cooling mechanism at high air temperatures, as body heat increases when surroundings are hot.
    • People without sweat glands are at risk of heat stroke due to their inability to cool themselves through evaporation.

    Clothing and Heat Loss

    • Clothing reduces conductive and convective heat loss, depressing the rate of heat loss to about 1/6th.
    • Wet clothing makes it difficult to radiate heat out, further reducing heat loss.

    Temperature-Decreasing Mechanisms When the Body Is Too Hot

    • Vasodilation of skin blood vessels increases the rate of heat transfer to the skin, allowing the body to cool down
    • Sweating is an effective way to remove heat, as a 1°C increase in body core temperature causes sweat to remove 10 times the basal rate of body heat production
    • Decrease in heat production is achieved through the inhibition of shivering and chemical thermogenesis

    Temperature-Increasing Mechanisms When the Body Is Too Cold

    • Skin vasoconstriction occurs throughout the body, stimulated by the posterior hypothalamic sympathetic centers
    • Piloerection (hair standing upright) helps to create a thick layer to protect the skin from cold surroundings
    • Increase in thermogenesis (heat production) is achieved through:
      • Shivering, stimulated by the primary motor center in the posterior hypothalamus
      • Chemical thermogenesis (non-shivering thermogenesis), which increases the rate of cellular metabolism through sympathetic circulation, norepinephrine, and epinephrine
      • Thyroxine secretion, which is stimulated by the cooling of the anterior hypothalamic-preoptic area and the release of thyrotropin-releasing hormone from the hypothalamus

    Body Temperature Control

    • The set point for temperature control is 37.1°C, which the body continually attempts to maintain.
    • The body temperature control mechanisms work to bring the body temperature back to this set point level.

    Feedback Gain for Body Temperature Control

    • Feedback gain is the ratio of the change in environmental temperature to the change in body core temperature minus 1.0.
    • For every 25°- to 30°C- change in environmental temperature, the body core temperature changes about 1°C.

    Skin Temperature and Body Temperature Control

    • Skin temperature can slightly alter the set point for core temperature control.

    Behavioral Control of Body Temperature

    • The temperature controlling area in the brain gives a psychic sensation of being overheated.
    • When the body is cold, it receives signals from skin and deep body receptors, resulting in a feeling of being cold.
    • Behavioral control of body temperature is most effective in cold environments.

    Fever

    • Fever is an elevation of body temperature (> 99°F) caused by the "resetting of the thermostat" due to toxic substances or abnormalities in the brain's temperature-regulating centers
    • Causes of fever include bacterial/viral infections, trauma, lesions of CNS, exposure to high temperatures, and drug-induced factors
    • Fever is characterized by increased heat production (shivering, increased metabolism) and diminished heat loss (vasoconstriction, warm and flushed skin)
    • Fever subsides through sweating

    Thermoregulation

    • Thermoreceptors detect changes in the balance between heat loss and production due to metabolic rate (exercise)
    • There are two types of thermoreceptors: peripheral (on skin) and central (in hypothalamus, spinal cord, and abdominal organs)
    • Output from the hypothalamus is sent to effectors via sympathetic nerves to sweat glands, skin arterioles, and adrenal medulla, and to motor neurons to skeletal muscles
    • Core temperature is maintained relatively constantly
    • Peripheral thermoreceptors help identify heat and cold

    Sweating and Its Regulation

    • Stimulation of the anterior hypothalamus-preoptic area in the brain causes sweating through the autonomic pathways to the skin
    • Sweat glands are innervated by cholinergic nerve fibers (acetylcholine-secreting) that run in sympathetic nerves
    • Sweat glands can also be stimulated by epinephrine or norepinephrine in the blood, particularly during exercise when these hormones are secreted by the adrenal medullae to help the body lose excessive heat

    Sweat Gland Structure

    • A sweat gland is a tubular structure consisting of two main parts: a deep subdermal coiled portion and a duct portion.
    • The coiled portion is responsible for secreting sweat and is located deep in the subdermal layer.
    • The duct portion passes outward through the dermis and epidermis of the skin.

    Sweat Secretion Process

    • The secretory portion of the sweat gland produces a fluid called primary secretion or precursor secretion.
    • The primary secretion undergoes modification as it flows through the duct, resulting in changes to the concentrations of its constituents.

    Regulation of Body Temperature

    • The precise regulation of body temperature depends on various factors, including wind movement, air moisture, and surroundings.
    • A nude person in dry air between 55°F and 130°F can maintain a normal body core temperature between 97°F and 100°F.

    Role of the Hypothalamus

    • The hypothalamus plays a crucial role in regulating body temperature, with almost all temperature-regulating mechanisms operating through it.
    • The hypothalamus contains temperature-regulating centers that detect changes in body temperature.

    Temperature Regulation Mechanisms

    • When the hypothalamus detects abnormal body temperature, it institutes procedures to decrease or increase body temperature.
    • These procedures are activated through neuronal effector mechanisms.

    Neuronal Effector Mechanisms for Thermoregulation

    • Hypothalamic temperature centers play a crucial role in detecting deviations in body temperature from the normal range.
    • When the body temperature is too high or too low, the hypothalamic temperature centers trigger mechanisms to decrease or increase the body temperature.
    • These mechanisms are activated to maintain a stable body temperature, which is essential for proper bodily functions.

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    Learn about the homeostatic process of thermoregulation, maintaining a constant body core temperature despite external temperature changes, and normal core temperature ranges.

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