Metabolism and Hormonal Regulation
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Questions and Answers

Which hormone primarily increases substrate availability for cellular metabolism, particularly by stimulating triglyceride breakdown and oxidation in adipocytes?

  • Growth Hormone (GH) (correct)
  • Norepinephrine (NE)
  • Thyroxine
  • Epinephrine

Non-shivering thermogenesis, stimulated by the sympathetic nervous system (SNS), serves as the primary defense against hypothermia.

False (B)

What are the two main hormones secreted by the adrenal medulla upon stimulation by the sympathetic nervous system (SNS)?

Epinephrine and Norepinephrine

__________ increases the synthesis of beta receptors, enhancing the synergistic effect of epinephrine and norepinephrine on cellular metabolism.

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

Match the hormone with its primary effect on metabolism:

<p>Epinephrine = Increases cellular metabolism (in synergy with thyroxine and norepinephrine) Norepinephrine = Main neurotransmitter released from sympathetic nerve fibers; elevates plasma concentrations during high SNS activation Growth Hormone = Increases substrate availability by stimulating triglyceride breakdown and oxidation Thyroxine = Increases synthesis of beta receptors, enhancing hormone action</p> Signup and view all the answers

Why does the human body have a limited ability to adapt to cold when exercising in water?

<p>Because heat loss by convection is faster in cold water than in cold air. (C)</p> Signup and view all the answers

Heat loss through convection is slower in cold water than in cold air.

<p>False (B)</p> Signup and view all the answers

By approximately how many times does the human body lose heat faster in water compared to air?

<p>4</p> Signup and view all the answers

Moving water increases heat loss through the process of ______ heat loss.

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

What is the primary reason for the faster heat loss in water compared to air?

<p>Water conducts heat more efficiently than air. (B)</p> Signup and view all the answers

Which of the following is the primary physiological role of the preoptic-anterior hypothalamus (POAH) in thermoregulation?

<p>Acting as the body's thermostat by receiving and responding to temperature changes. (A)</p> Signup and view all the answers

Humans are poikilotherms, meaning they must maintain a constant body temperature regardless of the environment.

<p>False (B)</p> Signup and view all the answers

What is the primary function of peripheral thermoreceptors in the skin regarding temperature regulation?

<p>reporting temperature to the POAH and cerebral cortex</p> Signup and view all the answers

The transfer of heat from one solid material to another through direct molecular contact is known as ______.

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

Match the following heat loss mechanisms with their descriptions:

<p>Radiation = Heat loss via infrared rays Convection = Heat removal by gas or liquid motion Conduction = Heat transfer through direct contact Evaporation = Heat loss through conversion of liquid to gas</p> Signup and view all the answers

During exercise, which heat loss mechanism becomes the primary way the body gets rid of excess heat?

<p>Evaporation (B)</p> Signup and view all the answers

Central thermoreceptors monitor blood temperature changes. What is the sensitivity of these receptors to detect changes in blood temperature?

<p>0.01°C (A)</p> Signup and view all the answers

Heat gain must always exceed heat loss in order for the body to maintain a steady-state core temperature.

<p>False (B)</p> Signup and view all the answers

During rest, what percentage of the body's blood supply is directed to the skin?

<p>10-20% (C)</p> Signup and view all the answers

Sweat production decreases as the body core temperature increases.

<p>False (B)</p> Signup and view all the answers

What is the primary function of subcutaneous fat in relation to body temperature?

<p>To act as an excellent insulator and reduce heat loss (A)</p> Signup and view all the answers

What is the body's first line of defense against hypothermia?

<p>Peripheral Vasoconstriction (B)</p> Signup and view all the answers

The sympathetic nervous system (SNS) activates vascular smooth muscle cells (VSMC) through ________ receptors.

<p>Adrenergic Cholinergic</p> Signup and view all the answers

Eccrine sweat glands are primarily activated in response to a decrease in core or skin temperature.

<p>False (B)</p> Signup and view all the answers

Windchill is best described as:

<p>An index based on the cooling effect of wind. (A)</p> Signup and view all the answers

Which hormone increases cellular metabolism by 60-100% to help maintain body temperature?

<p>Thyroxine (B)</p> Signup and view all the answers

How does growth hormone (GH) influence protein metabolism?

<p>GH facilitates amino acid uptake and increases protein synthesis. (B)</p> Signup and view all the answers

Shivering is the primary mechanism coordinated by the endocrine system to defend against hypothermia.

<p>False (B)</p> Signup and view all the answers

Explain how a larger body size (BSA to body mass ratio) can affect heat loss in cold environments.

<p>Individuals with a smaller BSA to body mass ratio lose less heat to the environment because they have less surface area relative to their mass.</p> Signup and view all the answers

Inactive peripheral muscles and subcutaneous fat act as excellent ______ against heat loss.

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

Why might high-intensity exercise be recommended as an immediate response for someone experiencing cold?

<p>High-intensity exercise creates greater metabolic heat production. (C)</p> Signup and view all the answers

Exercising in the cold presents no unique physiological challenges as long as clothing insulation and exercise metabolism maintain core temperature.

<p>False (B)</p> Signup and view all the answers

Which of the following is a potential risk associated with exercising in cold conditions, even if core temperature is adequately maintained?

<p>Muscle and/or metabolic fatigue (B)</p> Signup and view all the answers

Match the defense mechanism with the bodily function.

<p>Shivering = Skeletal Muscle Gluconeogenesis = GH (Growth Hormone) Vasoconstriction = SNS (Sympathetic Nervous System) Insulation = Subcutaneous Fat</p> Signup and view all the answers

At approximately what core temperature does the hypothalamus begin to lose its ability to regulate body temperature?

<p>34.5°C (D)</p> Signup and view all the answers

Breathing very cold air will always freeze the respiratory passages or lungs, regardless of ventilation rate.

<p>False (B)</p> Signup and view all the answers

What is one physiological effect of cardiac cooling that can lead to cardiac arrest?

<p>SA node firing can slow to a complete stop</p> Signup and view all the answers

Exposure to extreme cold decreases respiratory ______ and volume.

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

Which of the following hormones are released in response to cold stress to stimulate lipolysis?

<p>Epinephrine, norepinephrine, and cortisol (D)</p> Signup and view all the answers

What is the primary mechanism by which muscle cooling leads to a loss of force and power?

<p>Slowed nerve conduction velocity (NCV) and altered motor unit recruitment (D)</p> Signup and view all the answers

Frostbite is a superficial condition that does not typically lead to long-term tissue damage.

<p>False (B)</p> Signup and view all the answers

Match the following conditions with their primary physiological effect during hypothermia:

<p>Cardiac Cooling = Decreased SA node firing rate Muscle Cooling = Slowed nerve conduction velocity Hormone Release = Stimulation of lipolysis Hypothalamus Dysfunction = Impaired body temperature regulation</p> Signup and view all the answers

Flashcards

Homeothermy

Maintaining a stable internal body temperature, around 37°C (98.6°F), regardless of external environment.

Hypothalamus (POAH)

The brain region acting as the body's thermostat; monitors blood temperature and triggers responses.

Peripheral Thermoreceptors

Sensors in the skin that send temperature information to the hypothalamus and cerebral cortex.

Central Thermoreceptors

Sensors in the brain and spinal cord that monitor blood temperature.

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Effector Organs (Temperature Regulation)

Organs such as skin arterioles, endocrine glands, skeletal muscle, and sweat glands regulated by the hypothalamus to control body temperature.

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Radiation (Heat Loss)

Heat transfer through infrared rays.

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Convection (Heat Loss)

Heat transfer via movement of gas or liquid across a heated surface.

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Conduction (Heat Loss)

Heat transfer through direct contact between solid materials.

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Resting Heat Dissipation

At rest, the body dissipates heat, with only 10-20% of the energy expenditure converted to external work.

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Sweat and Cooling

Sweat production escalates to facilitate cooling when the body core temperature rises.

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Erector Muscles & Insulation

Tiny muscles at the base of hairs contract to make them stand up. This traps air, providing insulation and reducing heat loss.

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Subcutaneous Fat

Subcutaneous fat is a thermal insulator, limiting heat transfer from deep tissues to the skin surface.

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Vasoconstriction

Peripheral vasoconstriction narrows blood vessels near the skin surface, reducing heat loss by keeping blood away from the cold.

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Eccrine Sweat Glands Activation

Eccrine sweat glands, activated by the sympathetic nervous system (SNS), release sweat in response to increased core or skin temperature.

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Windchill Definition

Windchill is the cooling sensation caused by the combination of air temperature and wind speed.

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Hormonal Thermogenesis

Hormones like thyroxine, epinephrine and norepinephrine can increase metabolic rate and generate heat to raise body temperature.

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Heat Loss in Cold Water

In cold water, the body loses heat much faster due to convection.

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Adapting to Cold

The process of the body adjusting to colder temperatures.

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Effect of Moving Water

Moving water increases the rate of heat loss, making it feel colder.

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Thermal Stress in Water

Extended exercise in cold water can pose significant thermal challenges to the body.

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Adrenal Medulla Secretion

SNS stimulation of the adrenal medulla releases epinephrine (80%) and norepinephrine (20%) into the blood.

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Thyroxine's Role in Metabolism

Thyroxine increases beta receptor synthesis, synergistically boosting cellular metabolism with epinephrine and norepinephrine.

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Non-Shivering Thermogenesis

SNS-stimulated metabolism, known as non-shivering thermogenesis, is a secondary defense against hypothermia.

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Norepinephrine (NE)

Norepinephrine (NE) is the primary neurotransmitter from sympathetic nerve fibers; it spills into the blood during high SNS activation.

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Growth Hormone (GH) & Fat Metabolism

GH enhances fat utilization by stimulating triglyceride breakdown and oxidation in adipocytes.

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GH & Gluconeogenesis

Growth hormone stimulates glucose production in the liver.

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GH on Protein Metabolism

Growth hormone (GH) increases amino acid uptake & protein synthesis, but decreases protein oxidation.

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Shivering

Skeletal muscle's shivering thermogenesis helps defend against hypothermia

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Insulating Tissues

Inactive muscle and subcutaneous fat provide insulation against heat loss.

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Exercise in the Cold

If clothing insulation and exercise metabolism are adequate, there shouldn't be any problems with exercising in the cold.

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Exercise Intensity & Heat

High intensity exercise generates more metabolic heat.

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Cold-Impaired Muscles

Cold exposure can impair muscle function through muscle &/or metabolic fatigue.

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Hypothermia & Exercise

Exercising in the cold can lead to hypothermia if heat loss exceeds heat production.

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Lethal Hypothermia Limit

The lethal lower limit of body temperature is between 23 - 25°C or 73.4 - 77°F.

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Cold Air and Lungs

Breathing cold air typically doesn't freeze the respiratory passages or lungs, especially with low ventilation.

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Cold's Effect on Respiration

Exposure to extreme cold decreases respiratory rate and volume.

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Frostbite Risk

Exposed skin can freeze quickly, leading to frostbite, gangrene, and tissue loss.

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Muscle Cooling Effects

Muscle cooling slows nerve conduction velocity, alters motor recruitment, and causes loss of force and power.

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Cardiac Cooling Risks

Cardiac cooling decreases the SA node's spontaneous depolarization, decreasing heart rate and potentially leading to cardiac arrest.

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Hypothalamus function temperature

Hypothalamus loses its ability to regulate body temperature, starting at around 34.5°C and being completely lost by 29.5°C

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Hormones in Cold Stress

Epinephrine, norepinephrine and cortisol stimulate lipolysis in response to cold stress to generate heat.

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Study Notes

  • The physiology of cold covers the body's responses to cold environments, including temperature regulation, physiological responses to exercise in the cold, how cold stress influences fuel utilization, and the health risks associated with hypothermia.

Body Temperature Regulation

  • Humans are homeotherms and must maintain a body temperature of approximately 37°C or 98.6°F regardless of the environment.
  • The hypothalamus (specifically the preoptic-anterior hypothalamus or POAH) functions as the body's thermostat.
  • Peripheral thermoreceptors in the skin report to the POAH for physiological responses and to the cerebral cortex for behavioral responses.
  • Central thermoreceptors in the hypothalamus, brain, and spinal cord monitor blood temperature and respond to changes as small as 0.01° C or 0.018°F.
  • Effector organs involved in temperature regulation include skin arterioles, endocrine glands, skeletal muscle, and eccrine sweat glands.

Environmental Challenge

  • To maintain a steady-state core temperature, the body must balance heat gain with heat loss.
  • Heat gain sources include metabolic heat and environmental heat (conduction, convection, radiation).
  • Heat Loss sources include radiation, conduction, convection and evaporation.

Heat Loss Mechanisms

  • Radiation: Heat is emitted away from the body in the form of infrared rays.
  • Conduction: Heat is transferred from one solid to another through direct molecular contact.
  • Convection: Heat is removed by the motion of gas or liquid across a heated surface.
  • Evaporation: Heat dissipates as sweat evaporates.
  • Primary avenue for heat dissipation during exercise.
  • Evaporation accounts for 80% of heat lost during exercise vs. 10-20% at rest.
  • As body core temperature increases, sweat production increases.

Physiological Response to Cold

  • Decreased blood/skin temperature is sensed by the hypothalamus.
  • Vasoconstriction occurs in skin blood vessels to reduce heat loss to the environment.
  • Skeletal muscles activate, causing shivering, which increases metabolism and generates heat.
  • The skin plays a role in insulation through the erection of hairs via muscle erectors, trapping air and reducing heat loss.

Skin Structure and Function

  • Hairs become erect, trapping air for insulation to reduce heat loss.
  • Temperature receptors: Free-nerve endings in the skin detect temperature changes.
  • Subcutaneous fat is an excellent insulator with low capacity to transfer heat from deep tissues to the body surface.

Skin Arterioles

  • Peripheral vasoconstriction of skin arterioles is the body's first line of defense against hypothermia.
  • The sympathetic nervous system (SNS) activates the vascular smooth muscle cells (VSMC)
  • Arterioles become constricted, and shunt vessels dilate to keep blood away from the skin surface, cooled by the environment.

Eccrine Sweat Glands

  • Activated by the SNS in response to an increase in core or skin temperature.
  • Not typically needed in response to cold, unless the individual is overdressed.

Windchill

  • An index based on the cooling effect of wind, not the actual temperature.

Non-Shivering Thermogenesis

  • The body's second line of defense against cold.
  • Involves hormones that increase metabolic rate.
  • Thyroxine increases cellular metabolism.
  • Epinephrine and norepinephrine, secreted due to SNS stimulation, also increase cellular metabolism.
  • Thyroxine increases the synthesis of beta receptors, aiding in the synergistic effect of these hormones.
  • Growth hormone increases substrate availability but doesn't play a large part in cellular metabolism.

Skeletal muscle

  • Skeletal muscle is the third defense line against hypothermia.
  • Shivering is an involuntary muscle contraction that generates heat.
  • Both inactive peripheral muscles and subcutaneous fat are excellent insulators.

Exercise in the Cold

  • High-intensity exercise can generate metabolic heat, which can offset the cold, but prolonged exercise can lead to hypothermia if heat is not effectively generated.

Challenges of Cold Water Immersion

  • Exercise in water poses a thermal challenge.
  • Heat Loss by convection is faster in cold water compared to air.
  • Heat is lost 4x faster in water when compared to air!

Hypothermia

  • The lethal lower limit of body temperature is between 23 - 25°C or 73.4 - 77°F.
  • Exposure to extreme cold decreases respiratory rate and volume.
  • As cellular metabolism slows with a lower core temperature, the hypothalamus cannot regulate body temperature.
  • By ~29.5 °C the hypothalamus has completely lost the ability to to regulate body temperature.
  • Cardiac cooling:spontaneous depolarization of the SA node decreases→ decreasing HR. SA node firing can slow to a complete stop, resulting in cardiac arrest.
  • Exposed skin can quickly freeze from frostbite, leading to gangrene and tissue loss.
  • Muscle cooling: slows nerve conduction velocity affecting motor recruitment, resulting in a loss of force and power.

Influence of Cold Stress on Fuel Utilization

  • Epinephrine, norepinephrine, and cortisol stimulate lipolysis
  • Vasoconstriction in skin arterioles reduces the availability of free fatty acids from subcutaneous fat.
  • Muscle glycogen's consumption increases for thermogenesis.

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Physiology of Cold: Lessons from Everest PDF

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Explore the intricate relationship between hormones and metabolism, focusing on substrate availability and thermogenesis. Understand how hormones like epinephrine and norepinephrine influence cellular metabolism. Learn about the body's adaptation to cold and heat loss in different environments.

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