Thermoregulation Quiz

Health Sciences: Heat Energy & Body Temperature Control

• This lecture covers heat energy, body temperature, and control mechanisms.
• The body maintains a stable internal temperature (homeostasis) around 37°C.
• Heat energy is caused by the internal motion of particles (kinetic energy).
• The more motion, the higher the energy and temperature.

Kinetic Theory of Matter

• Matter consists of tiny particles in constant motion (atoms, ions, or molecules).
• Gas particles are far apart, have weak attractive forces, and no fixed shape or size.
• Liquid particles are relatively far apart, have strong attractive forces, and take the shape of the container.
• Solid particles are close together, have very strong attractive forces, and maintain a fixed shape and size.

Heat Energy

• Heat transfer is the movement of kinetic energy from a high-temperature region to a low-temperature area.
• Heat is a form of energy caused by the internal motion of particles.
• The extent of this motion is proportional to the temperature.

Temperature & Temperature Scales

• Temperature is a measure of the degree of hotness or coldness.
• Celsius (°C), Fahrenheit (°F), and Kelvin (K) are different scales.
• Conversion formulas exist between these scales.
• Water's freezing point is 0°C, and its boiling point is 100°C.
• Normal body temperature is approximately 37.0°C.

Specific Heat Capacity of Water

• Water requires a relatively large amount of heat energy to change its temperature.
• Its specific heat capacity (high ability to absorb and store heat energy) is 4200 J kg⁻¹ K⁻¹.
• Water's high specific heat capacity stabilizes temperature fluctuations within the body and helps regulate body temperature.
• Specific heat capacity also influences factors like water's ability to transfer heat energy.

Change the State of Matter

• Changing the state of matter involves gaining or losing kinetic energy.
• Evaporation occurs on the surface of a liquid.
• In a physical change, the substance changes its physical state, but the chemical composition remains unchanged.
• This often occurs when adding or removing heat.

Latent Heat of Fusion & Vaporization

• Latent heat of fusion is the energy needed for a substance to change from a solid to a liquid.
• Latent heat of vaporization is the energy needed for a substance to change from a liquid to a gaseous state.
• These changes of state occur without the substance changing its overall temperature.

Specific Latent Heat of Fusion or Vaporization

• Specific latent heat of fusion or vaporization is a measure of the heat required to change one kilogram of a substance from a solid to liquid or from a liquid to a gas.
• Water has a relatively high specific latent heat of fusion and vaporization, which is important in regulating temperature.

Processes of Heat Transfer

• Heat exchange occurs through processes like conduction, convection, and radiation.
• Conduction involves the transfer of heat through direct contact.
• Convection involves the transfer of heat through the movement of fluids (e.g., air or water).
• Radiation involves the transfer of heat energy through electromagnetic waves.

Factors Affecting Heat Transfer by Radiation

• Surface temperature affects the rate of radiant heat emission.
• Dark or dull surfaces are better absorbers of radiant heat.
• Shiny or light-colored surfaces are better reflectors of radiant heat.
• Shielding can block or deflect radiant heat transfer.

Working Principle of a Thermal Flask

• Heat transfer in a vacuum flask is minimized.
• Double-walled construction with a vacuum between the walls reduces conduction.
• Silver coating on the glass walls minimizes radiant heat transfer.

Core & Shell Body Temperature

• Core temperature refers to the temperature of vital organs (brain, thoracic, and abdominal organs).
• Shell temperature refers to the temperature of the peripheral body parts like skin.
• The core temperature is usually higher than the shell temperature.
• Environmental changes influence body core and shell temperature.

Heat Exchange Between Our Body and the Environment

• The heat exchange between the body and the environment follows four main processes.
• Evaporation, conduction, convection, and radiation.
• These processes are driven by the difference in core and ambient temperature.

Heat Exchange Between the Body and the Environment the 2 Steps

• Body heat exchange between the body and the environment is characterized by two-step processes.
• The first process involves peripheral heat transfer between the body core and the skin, regulated by cutaneous blood flow.
• The second involves shell-to-exterior transfer through conduction, convection, radiation, and evaporation.

Heat Transfer Between the Body Core & Shell

• Heat transfer between the core and the shell (e.g., the skin) occurs primarily through convection mediated by cutaneous blood flow.
• Blood vessels dilate to increase heat loss in hot environments and constrict to conserve heat in cold environments.

Heat Transfer Between The Body Shell & The Exterior

• Heat transfer between the body shell and the external environment involves different mechanisms.
• Conduction, convection, and radiation are key factors based on environmental temperature influences.
• Body surface temperature regulation is critical for overall thermal homeostasis.

Thermal Balance of Our Body

• The body maintains heat balance.
• Heat gained from the environment must be equal to heat lost.
• Various physiological and behavioral mechanisms maintain this balance, including the metabolic rate, skin vasodilation/vasoconstriction, sweating, and shivering.

The Need for Thermoregulation

• Body functions within a narrow temperature range.
• Enzymes and metabolic reactions operate optimally around 37°C.
• Failure in thermoregulation can disrupt biochemical reactions and cellular activities.

Concept of Homeostasis

• Our body regulates internal environment stability (homeostasis).
• Our body's internal environment is mainly regulated by the nervous and endocrine systems.

Components of a Homeostatic Control System

• A homeostatic control system consists of three key components: sensors/receptors, integrating/control centers, and effectors
• Two pathways: afferent and efferent (sensory and motor) pathways

Feedback/Homeostatic Control of Body Temperature

• Body temperature regulation uses a feedback loop.
• Receptors sense temperature changes.
• The control center (hypothalamus) compares this with the set point.
• Effectors (e.g., sweat glands, blood vessels) generate appropriate responses to return temperature to normal.

Structural & Functional Organization of the Nervous System

• The nervous system is crucial for thermoregulation.
• Analysis and integration of sensory and motor information occur in different brain regions.
• Sensory components include receptors, nerve cells/ganglia, and nerves that transmit information from internal and external environments.
• Motor components consist of nerves and muscles that adjust responses based on information processing.

Organization of Body Temperature Control

• Thermoregulation maintains internal body temperature in a narrow range
• Hypothalamus plays a crucial role as the central control center.
• Homeostatic responses regulate heat gain and heat loss mechanisms.
• Responses to temperature changes include cutaneous blood vessel dilation/constriction.

Thermoreceptors

• Central and peripheral/cutaneous thermoreceptors sense temperature.
• Central thermoreceptors are located in the hypothalamus and monitor core body temperature.
• Peripheral thermoreceptors, located in the skin, sense ambient temperature.

Thermoregulatory Center

• The thermoregulatory center coordinates the body's response to maintain homeostasis of internal body temperature through heat gain and heat loss mechanisms.
• The center is located in the preoptic area of the hypothalamus.
• The posterior nucleus manages heat gain while the anterior nucleus regulates heat loss.

Physiological & Behavioral Thermoregulatory Responses

• Physiological responses include autonomic nervous system regulation of blood vessels and sweating, non-shivering thermogenesis, and somatic responses.
• Behavioral responses, such as seeking shade or clothing adjustments, are crucial components too.

Thermoregulatory Responses

• Maximize heat loss in high temperatures via vasodilation, increased sweating, and behavioral adjustments.
• Minimize heat loss in cold environments via vasoconstriction and seeking warmth.
• Maximum heat production through shivering and nonshivering mechanisms.
• Hormones like epinephrine, norepinephrine, and thyroxine play key roles.

Hormones in Physiological Thermoregulation

• Hormones like epinephrine, norepinephrine, and thyroxine regulate bodily functions in response to internal temperature changes.
• Their secretion increases or decreases as directed by the thermoregulatory center.

Mechanisms of Fever

• Fever is regulated by an increase in the hypothalamic set-point.
• Pyrogens trigger an elevation of the internal body temperature.
• Mechanisms of fever involve the production of prostaglandins, the suppression of pathogens, and the increased metabolic rate for heat production and heat conservation.

Mechanisms of Fever

• The pyrogens raise the hypothalamic set point, increasing the body temperature, resulting in fever.
• This response is associated with the body's defense mechanisms, mainly the immune response.

The Course of An Episode of Fever

• The sequence of a fever episode involves an increase in the hypothalamic temperature set point due to pyrogens, triggering increased heat production and conservation.
• Symptoms are typically resolved when the hypothalamic set point returns to normal through heat dissipation mechanisms like sweating and adjusting blood flow to the skin.

Normal Variations in Body Temperature

• Body temperature variations exist based on circadian rhythms, seasonal changes, exercise, stress, and the menstrual cycle.
• Progesterone fluctuations during the luteal phase of the menstrual cycle have implications due to its effect on the set point of the thermoregulatory center.

Measure Body Temperature: Core or Shell Temperature?

• Measuring core temperature is preferred for diagnosis, as it reflects the body's internal metabolic state.
• Shell temperature varies according to environmental conditions.

Sites of Measuring Temperature

• Various sites can be used for body temperature measurement.
• Oral, rectal, and axillary measurements are common, each having slight variations depending on the location.
• The location of the measurement and its interpretation should be considered with the context of the health evaluation.

Temperature Measurement Device

• Different devices are available to measure body temperature, each with its advantages and limitations.
• Clinical thermometers, thermistors, infrared thermometers, and liquid crystal devices are common methods.
• Accurate measurement methods are important to allow for good diagnosis.