CNS 2nd Year Temperature Control Overview

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What happens to skin vessels during vasoconstriction?

They increase blood flow to the skin.

They completely stop all blood flow.

They decrease blood flow to the skin. (correct)

They become more permeable to heat.

What is the primary function of sweating?

To cool the body through evaporation. (correct)

To increase blood pressure.

To enhance metabolic activity.

To provide insulation to the skin.

What physiological response prevents heat loss when body temperature decreases?

Vasoconstriction of skin vessels. (correct)

Increased sweating.

Vasodilation of skin vessels.

Increased metabolic activity.

How does high humidity affect the sweating process?

It limits the evaporation of sweat. Signup and view all the answers

Which physiological mechanism is NOT involved in temperature regulation?

Increased heart rate. Signup and view all the answers

What is the purpose of the thermoneutral zone in temperature regulation?

To maintain core temperature without other mechanisms. Signup and view all the answers

What creates the cooling effect of sweat on the body?

The evaporation of water from the skin. Signup and view all the answers

What role do arterioles play in heat regulation?

They adjust blood flow to the skin. Signup and view all the answers

Which mechanism of heat transfer is primarily responsible for the human body emitting heat as infrared radiation?

Radiation Signup and view all the answers

In which scenario would conductive heat loss be most significant?

When lying on a cold operating room table Signup and view all the answers

What primarily causes the transfer of heat in conduction?

Molecular agitation and kinetic energy transfer Signup and view all the answers

Approximately what percentage of heat energy do humans lose through radiation?

50% Signup and view all the answers

What is the primary source of heat gain for the human body through radiation?

Infrared radiating sources like the sun Signup and view all the answers

Which of the following best describes convection as a mechanism of heat transfer?

Heat transfer through warmed air or water currents Signup and view all the answers

What can significantly influence the net transfer of radiant energy?

Ambient temperature Signup and view all the answers

Which of the following materials is considered a poor conductor of heat, impacting conductive heat loss?

Air Signup and view all the answers

What is the primary involuntary mechanism for heat production in the body?

Skeletal muscle activity Signup and view all the answers

How does shivering contribute to heat production?

By increasing muscle contractions and tone Signup and view all the answers

Which mechanism for heat production is specifically mentioned for use in animals and newborns?

Brown fat metabolism Signup and view all the answers

What role does piloerection play in heat retention?

Traps warm air close to the skin Signup and view all the answers

What influences the basal metabolic rate (BMR) regarding heat production?

Thyroid hormone levels Signup and view all the answers

Which of the following best describes the body's thermoregulatory feedback mechanisms?

They involve afferent signalling to the hypothalamus Signup and view all the answers

Where are core thermoreceptors located?

In the CNS and internal abdominal organs Signup and view all the answers

Which behavioral changes might occur in response to cold conditions?

Finding a warm beverage Signup and view all the answers

What type of thermoreceptors monitor the body's core temperature?

Central thermoreceptors Signup and view all the answers

Which TRP channel is activated by high temperatures?

TRPV1 Signup and view all the answers

What ions flow into a neuron upon activation of a TRP channel?

Calcium and sodium Signup and view all the answers

Where are central thermoreceptors primarily located?

In the hypothalamus and internal organs Signup and view all the answers

What is the effect of TRPM8-/- mice on cold sensing?

They do not respond to cold. Signup and view all the answers

What is the main function of peripheral thermoreceptors?

To provide information about external temperature Signup and view all the answers

Which TRPM8 genotype has a reduced expression compared to wild type?

TRPM8+/- Signup and view all the answers

What is the response of TRPM8 to cold temperatures?

It opens and allows ion flow Signup and view all the answers

What characterizes the TRPV1 receptor?

It is activated by capsaicin. Signup and view all the answers

What is the consequence of sufficient depolarization in temperature-sensitive neurons?

It triggers an action potential. Signup and view all the answers

How do conformational changes in the TRP ion channels affect temperature sensitivity?

They stabilize the open state in response to cold Signup and view all the answers

How are TRPM8 channels characterized?

As non-selective cation channels Signup and view all the answers

Which of the following is true regarding TRPV2?

It has a higher activation threshold than TRPV1. Signup and view all the answers

Which of the following receptors responded to warm temperatures ranging from 33°C to 40°C?

TRPV3 Signup and view all the answers

What distinguishes TRPM8+/- mice compared to TRPM8++ mice?

TRPM8+/- mice show an intermediate cold response. Signup and view all the answers

What temperature range activates the TRPV1 receptor?

Above 43°C Signup and view all the answers

Which of the following adaptations do the skeletal muscles undertake to control heat production?

Muscle tone Signup and view all the answers

What is a significant factor that affects thermoregulatory efficiency in young and elderly individuals?

Less efficient thermoregulatory responses Signup and view all the answers

During which phase of the menstrual cycle do women typically experience a rise in basal body temperature?

Luteal phase Signup and view all the answers

Which thermoreceptors are involved in the central regulation of body temperature?

Core thermoreceptors Signup and view all the answers

What time of day is body temperature typically at its lowest?

Early morning Signup and view all the answers

Which physiological response is responsible for heat loss through sweating?

Vasodilation of skin blood vessels Signup and view all the answers

How does the body's core temperature change throughout the day?

It typically exhibits diurnal variations. Signup and view all the answers

What role does the sympathetic nervous system play in thermoregulation?

It controls heat loss via sweat glands and blood vessel adjustments. Signup and view all the answers

What is the primary means through which the human body loses approximately 50% of its heat energy?

Radiation Signup and view all the answers

Which mechanism of heat transfer relies on direct contact between objects of differing temperatures?

Conduction Signup and view all the answers

What factors influence the rate of conductive heat transfer?

Temperature difference and thermal conductivity Signup and view all the answers

In a clinical scenario, conductive heat loss is most significant when patients are in contact with which of the following?

Colder surfaces Signup and view all the answers

What form of electromagnetic radiation does the human body primarily emit?

Infrared Signup and view all the answers

Which of these statements is true regarding the influences on net radiant energy transfer?

It considers the temperature of surrounding objects. Signup and view all the answers

What is the relationship between faster-moving molecules and cooler molecules during conductive heat transfer?

Faster-moving molecules pass on some of their kinetic energy to the cooler molecules. Signup and view all the answers

Which factor is a poor conductor of heat, thus impacting conductive heat loss?

Air Signup and view all the answers

What type of TRP channel is specifically activated by cold temperatures?

TRPM8 Signup and view all the answers

What is the role of central thermoreceptors in the body?

They monitor core body temperature. Signup and view all the answers

Which ion is primarily involved in the depolarization of temperature-sensitive neurons when TRP channels open?

Calcium Signup and view all the answers

What depicts the mechanism of temperature sensitivity in cold fibers?

Conformational change in receptor domains Signup and view all the answers

Which of the following best describes the TRPM8 channel?

A non-selective cation channel activated by cold Signup and view all the answers

In wild-type mice with two copies of the functional TRPM8 gene, what is expected about their sensitivity to cold?

Higher sensitivity than TRPM8-/- mice Signup and view all the answers

What is the likely impact of temperature fluctuations on TRP channel states?

Cold stabilizes the open state, while warmth causes fluctuations. Signup and view all the answers

Where are peripheral thermoreceptors primarily located?

In the skin and mucous membranes Signup and view all the answers

What characterizes TRPM8+/- mice compared to TRPM8+/+ mice?

They have reduced TRPM8 expression and an intermediate cold-sensing response. Signup and view all the answers

Which receptor has the highest threshold for activation among the TRP receptors mentioned?

TRPV2 Signup and view all the answers

What is the effect on cold sensing in TRPM8-/- mice?

They exhibit a complete lack of cold sensing through the TRPM8 pathway. Signup and view all the answers

In terms of temperature range, which receptor is sensitive to warm temperatures ranging from 33°C to 40°C?

TRPV3 Signup and view all the answers

What type of neurons are TRPV1 receptors primarily found in?

Nociceptive neurons Signup and view all the answers

When sufficient depolarization is achieved in temperature-sensitive neurons, what occurs?

An action potential is triggered. Signup and view all the answers

Which other stimuli, apart from temperature, can activate TRPV1 receptors?

Capsaicin and protons Signup and view all the answers

What physiological role do TRPV3 receptors play?

They respond to normal body temperature and warmer stimuli. Signup and view all the answers

What thermoregulatory response occurs in the skin during high temperatures?

Skin vasodilation Signup and view all the answers

Which factors contribute to the thermoregulatory inefficiency in the elderly?

Reduced metabolic rate and impaired vasodilation Signup and view all the answers

During which phase of the menstrual cycle does the basal body temperature typically rise?

Luteal phase Signup and view all the answers

What is the typical pattern of core body temperature throughout the day?

Lowest in the early morning and highest in the late afternoon Signup and view all the answers

What physiological adaptation do skeletal muscles invoke to regulate heat production in response to cold?

Increased shivering Signup and view all the answers

What role do central thermoreceptors play in body temperature regulation?

They detect temperature variations in the body's core. Signup and view all the answers

Which population is particularly at risk for temperature extremes due to thermoregulatory inefficiency?

Young children and elderly individuals Signup and view all the answers

What circadian pattern is observed in core body temperature?

Temperature varies with time of day independent of activity. Signup and view all the answers

What mechanism primarily facilitates heat dissipation from the body during a fever response?

Vasodilation Signup and view all the answers

How do antipyretic medications like paracetamol affect the hypothalamus?

Inhibit prostaglandin synthesis Signup and view all the answers

What is the likely physiological sensation experienced when body temperature returns to normal after a fever?

Sweating and feeling chilled Signup and view all the answers

What role does behavioural change play in the body's response during hyperthermia?

It facilitates cooling by seeking a cooler environment Signup and view all the answers

Which of the following correctly describes the body's cooling mechanisms once fever resolves?

Vasodilation and sweating help to lower body temperature Signup and view all the answers

What is a significant risk associated with aspirin use in children for fever management?

Reye’s syndrome Signup and view all the answers

Which physiological change occurs during the initiation of cooling mechanisms in response to lowered pyrogen levels?

Enhanced blood flow to the skin Signup and view all the answers

Which general statement about endogenous pyrogens is accurate?

They cause the hypothalamus to increase temperature set-point. Signup and view all the answers

What physiological mechanism is primarily responsible for the elevation of body temperature during a fever?

Action of pyrogens on the hypothalamic thermoregulatory centre Signup and view all the answers

Which of the following is NOT a cause of hypothermia?

Hyperthyroidism Signup and view all the answers

In the condition of hyperthermia, what happens when the core temperature exceeds 39°C?

Onset of heat stroke symptoms Signup and view all the answers

How do pyrogens contribute to fighting infections?

By elevating the hypothalamic set-point, inducing fever Signup and view all the answers

What is the primary reason for cognitive impairment during hypothermia?

Loss of judgment due to rapid cooling of cerebral functions Signup and view all the answers

Which of the following is a mechanism used for treating hyperthermia?

Employing ice packs or water sprays for cooling Signup and view all the answers

What is one effect of elevated thyroid hormone levels in pathologic hyperthermia?

Elevated metabolic rate and heat production Signup and view all the answers

Which of the following statements best describes the adaptive response of fever?

It serves as a defense mechanism by inhibiting pathogen growth. Signup and view all the answers

Study Notes

Temperature Control Overview

Course code: CNS
Year: 2, Semester: 1
Date: 30.11.2023
Lecturer: Prof David Henshall (RCSI-IE) and Dr. Colin Greengrass (RCSI-BH)
Topic: Temperature Control

Learning Objectives

Recognize the main mechanisms of heat transfer
Discuss the mechanisms of heat gain and loss in the body
Describe how heat is sensed (warm and cold receptors)
Describe the role of the hypothalamus in regulating temperature
Explain the coordinated response to hot and cold
Explain the causes of temperature change in fever

Thermoregulation

The process of maintaining internal balance between heat production and heat loss
A complex homeostatic function involving multiple body systems.
Crucial for optimal biochemical reactions and physiological processes for health and survival.

Homeothermic

The ability of the human body to maintain a relatively constant internal body temperature regardless of external environmental conditions

Homeotherms vs. Poikilotherms

Homeotherms: Maintain a stable internal temperature
Poikilotherms: Body temperature varies with the environment

Advantages of Homeothermy

Homeothermic animals (and humans) can adapt metabolically to environmental challenges.
Maintain metabolic processes and adapt to environmental challenges
Relatively unaffected by changes in ambient temperature
Can function in subzero conditions

Disadvantages of Homeothermy

Expend considerable chemical energy to maintain the homeothermic condition
Complex regulatory systems

Normal Human Body Temperature

Average normal body temperature for a healthy adult human is approximately 37°C (98.6°F)
Individual variations exist
Understanding the factors affecting the set point is vital for assessing and managing thermoregulatory disorders

Temperature Range Variations

Normal human temperature range: ~35.5°C to 37.7°C
Above 37.8°C: protein denaturation, cell damage
Below 35.5°C: compromised metabolic function (generally less harmful)
Temperature measured by mouth varies internally from organ to organ

Consequences of Body Temperature Deviations

40-44°C: Heat stroke, brain lesions
38-40°C: Fever or exercise
36-38°C: Normal range
34-36°C: Mild hypothermia
30-34°C: Impairment of temperature regulation
27-29°C: Cardiac fibrillation

Variation in Body Temperature

Body temperature fluctuates daily between 35.5°C and 37.7°C, influenced by circadian rhythms.
Lowest in early morning, peaks late afternoon.
Circadian fluctuations driven by hormone levels like cortisol and melatonin

Measuring Body Temperature

Common methods: oral, axillary, rectal, tympanic, or using non-contact infrared thermometers
Each method has implications for clinical interpretation
e.g., rectal temperatures are closer to core temperature (averaging 0.56°C higher).

Core vs Shell Temperature

Core: vital organs and CNS; maintains a stable temperature
Shell: skin and extremities; more variable
Core-shell model vital for understanding different heat exchange mechanisms
Core protected by vasoconstriction and countercurrent heat exchange in extremities to minimize heat loss
Specialized receptors in skin and core for sensing temperature changes

Maintaining Stability of Core Temperature

Heat input: external environment, metabolic activity, movement-generated heat
Heat output: exposed body surfaces, balance affected by internal heat production changes (e.g., exercise) and external environmental changes
Need to maintain body temperature at an optimal level for cell metabolism

Heat Production: Muscular Activity

Muscle contractions significantly increase heat production during physical activity
Muscular thermogenesis (both exercise-associated and shivering-induced) is critical for responding to cold stress
Heat production through muscle activity is increased by thyroxine and catecholamines

Heat Production: Metabolism

Heat is a byproduct of metabolic reactions during food and muscle use.
Metabolic heat production is influenced by basal metabolic rate and the thermic effect of food.
Thyroid hormone levels and sympathetic nervous system activity are key regulators of these metabolic processes

Heat Input and Output

Heat balance is a dynamic process involving heat input from metabolic processes and the external environment, and heat output through various mechanisms.
Maintained by the balance between internal heat production and heat loss to the environment.
Balance orchestrated by the central nervous system, integrating internal and external thermal signals

Heat Transfer Principles

The body follows similar heat transfer principles as inanimate objects, moving heat from warmer to cooler areas.
Heat is transferred via radiation, conduction, convection, and evaporation

Body Heat Emission (Infrared)

Cellular metabolism (predominantly oxidative phosphorylation) generates heat
Thermal energy elevates vibrational states of intracellular water and biomolecules.
Molecules return to ground state, emitting infrared photons (electromagnetic radiation beyond the visible light spectrum)

Mechanisms of Heat Gain and Loss: Radiation

Body constantly emits infrared radiation, significant source of heat loss.
Gain/loss depends on ambient temperature.
Transfers from warmer to cooler.
Sources of gain: sun, heater. Sources of loss: furniture, building walls.
Humans lose ~50% heat through radiation.

Mechanisms of Heat Transfer: Conduction

Heat transfer between objects in direct contact.
Faster-moving “warmer” molecules transfer kinetic energy to cooler molecules.
Rate influenced by temperature difference and thermal conductivity (air is poor, water is good)

Mechanisms of Heat Transfer: Convection

Heat transfer by air or water currents.
Warm air/water is less dense than cold, and rises, dissipating heat.
Enhanced by forced air movements (wind, fan, bike riding) and “wind chill factor”

Mechanisms of Heat Transfer: Evaporation

Heat loss from an object through evaporation of water from its surface.
Heat needed to change water from liquid to gas is absorbed from the skin.
Cools the body.
Evaporative heat loss is critical during hypermetabolic states, fever, or exercise
Effectiveness modified by ambient humidity and air flow

Heat Loss Through Breathing

Pulmonary heat loss occurs when cooler/dryer air is inhaled
Air is warmed and humidified in the respiratory tract to reach the lungs (needs energy = heat loss to the air).

Thermoregulatory System

A homeostatic system, relying on anticipatory controls and negative feedback.
Involves thermal sensors like afferent pathways, integration within the central nervous system, effector pathways, and target organs (muscles, sweat glands).

Core vs Shell

Core: vital organs and CNS. Stable temperature, tightly regulated
Shell: skin and extremities. Variable temperature, adjusts based on needs
Insulation and heat exchange: shell exchanges heat based on ambient temperature

Main Physiological Mechanisms for Regulating Temperature

Metabolic activity
Vasomotor responses (vasoconstriction and vasodilation of blood vessels in the skin)
Sweating
Shivering
Brown fat metabolism
Hair-raising (piloerection)
Behavioral changes

Vasomotor Responses

Conserving Heat:
Vasoconstriction: reduced blood flow to the skin (good insulator for warmth)
Losing Heat:
Vasodilation: increased blood flow to the skin (releases heat to the environment)
Control: sympathetic vasoconstriction activity

Thermoregulatory Responses to Cold

Shivering (involuntary muscle contractions generate heat)
Increasing metabolic activity increases core temperature, and metabolic responses are influenced by thyroid hormone
Stimulating "brown fat" metabolism (heat-generating chemical activity, especially in animals and newborns – limited understanding in adults
Hair-raising (piloerection)

Behavioral Changes to Cold

Heat-avoiding behavior (find shade or water)
Increase activity (hand-clapping, jumping, or more clothing) and/or
Heat-generating behaviors
More clothing

Metabolic Rate and Thermoregulation

Basal metabolic rate (BMR) influences heat production; higher BMR results in greater heat generation.
BMR affected by thyroid hormone levels (BMR, influencing heat production)

Thermoregulatory Feedback Mechanisms

Feedback loops involve afferent signaling to the hypothalamus, integration of thermal information, efferent responses to adjust heat production and loss, maintaining thermal homeostasis.

Thermoregulation: Central Control & Detection

Temperature detection: controlled by peripheral and central nervous systems.
Comprises: peripheral and core thermoreceptors, and a central control center (hypothalamus).
Peripheral thermoreceptors monitor skin temperature
Core thermoreceptors within hypothalamus, CNS and abdominal organs monitor core temperature and feedback to hypothalamus.

Peripheral Thermoreceptors

Located in the skin, mucous membranes, and other tissues.
Sense external temperatures, and relay information to the hypothalamus.

Central (or Core) Thermoreceptors

Located in the hypothalamus, spinal cord, and abdominal organs.
Monitor the body's core temperature, and provide feedback on internal thermal states.

Mechanisms of Signal Transduction

Thermal sensitivity mediated by transient receptor potential (TRP) channels (e.g., TRPV1, TRPM8).
TRP channels respond to specific temperature ranges.
Opening of TRP channels leads to depolarization of the neuron.

What is the Mechanism of Temperature Sensitivity? (Cold fibers)

TRPM8 is a non-selective cation channel
Activated by cold temperatures
Exhibits a conformational change in response to cold, which likely influences its open-closed activation state

What is the Mechanism of Temperature Sensitivity? (TRPM8 types)

TRPM8+/+: Normal TRPM8 expression and function, robust firing to decreasing temperature
TRPM8+/-: Intermediate firing rate response to decreasing temperatures, partial function.
TRPM8-/-: Non-functional TRPM8, no firing rate response to decreasing temperatures.

Heat General Receptors

The various general receptors respond to warmth or heat with different ranges

Temperature-sensitive Neurons

Generation of action potentials
Threshold potential reached = action potential; all-or-nothing
Signal travels along the neuron’s axon to the central nervous system (CNS)

Thermoregulatory Centre: The Hypothalamus

The hypothalamus acts as the thermostat, integrating peripheral and central thermoreceptor feedback, initiating endocrine and/or behavioral responses.
Different hypothalamic areas (e.g., preoptic area) respond to heat and cold to determine the best response (increase or decrease production)
Inputs: from cold & heat receptors in the skin and body core
Integrating signals, initiating responses (e.g., vasodilation/vasoconstriction, sweating, shivering).

Anterior Hypothalamus Role & Posterior Hypothalamus

Anterior hypothalamus: detects heat; involved in heat-loss mechanisms (vasodilation, sweating)
Posterior hypothalamus: detects cold; more involved in cold-responses and heat-conservation (shivering, vasoconstriction)

Hypothalamus: Thermoregulatory Integrating Centre

Anterior region: mediates decreased body temperature (triggers heat-loss reflexes).
Posterior region: mediates increased body temperature (triggers heat-production and conservation)
Evidences: electrical stimulation or ablation studies in animal models provide supporting evidence

Hypothalamus Diagrams

Several diagrams showing the hypothalamus's role in integrating signals and triggering responses.

Age can affect thermoregulatory efficiency. The very young and elderly are more vulnerable to temperature extremes.
E.g., reduced sweat gland function, decreased skin blood flow, smaller increases in cardiac output

Diurnal Variations in Body Temperature

Body temperature varies throughout the day.
Lowest temperatures in the early morning and highest in the late afternoon.
Driven by circadian rhythms.

The Menstrual Cycle & Body Temperature

Women may experience a rise in basal body temperature during the luteal phase of the menstrual cycle (due to progesterone's effect).
Body temperature follows a biphasic pattern during the menstrual cycle.

Hypothermia

Fall in core body temperature below normal range.
Common causes: accidents, mountaineering/diving, old age, secondary (e.g., hypothyroidism, malnutrition, stroke, trauma)
Leads to impaired metabolic processes and reduced responsiveness.

Hyperthermia

Elevation in core body temperature beyond normal range.
Common causes: exercise-induced heat production, high thyroid hormone, or hypothalamus malfunction
High core temperatures trigger heat-stroke and require immediate intervention

Fever as an Adaptive Response

Controlled and adaptive immune response.
Raises body temperature to combat infection.
Many pathogens have temperature limitations, making high temperatures unfavorable to them.
Increased body temperature slows pathogen growth and boosts immune response

The Role of Pyrogens in Fever

Pyrogens are released in response to pathogens.
They act on the hypothalamic thermoregulatory center, elevating the set point for body temperature (inducing fever).
Examples: Interleukin-1b (IL-1β), tumor necrosis factor-alpha (TNF-α)

Fever Stages

Detailed description of the stages involved in the induction of fever, maintenance of the elevated set point, resolution of infection.

Pharmacological Management of Fever

Antipyretic medications (e.g., paracetamol and aspirin) lower the set-point temperature of the hypothalamus
Reduce fever by inhibiting prostaglandin synthesis
Lowering the set-point brings the body back toward a normal range reducing fever.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz covers the key concepts surrounding temperature control and thermoregulation in the human body. Students will learn about heat transfer mechanisms, the role of the hypothalamus, and how the body responds to temperature changes. Prepare to discuss the importance of maintaining internal temperature for overall health.