Thermoregulation Practice Questions

Q: Body temperature is maintained by:

All of the above. ***Correct: All of the above*** Body temperature maintenance is achieved through the **integrated functioning of multiple mechanisms**: **1. Hypothalamic thermoregulation** - The **preoptic area of the anterior hypothalamus** acts as the body's thermostat - Contains thermoreceptors that detect core temperature changes - **Integrates** thermal information from peripheral and central thermoreceptors - Coordinates appropriate heat production and heat loss responses **2. Shivering and non-shivering thermogenesis** - **Shivering thermogenesis**: Involuntary muscle contractions generate heat when body temperature drops - **Non-shivering thermogenesis**: Heat production primarily in **brown adipose tissue (BAT)** via uncoupling protein-1 (UCP-1), important in neonates and cold adaptation **3. Peripheral vasoconstriction and vasodilation** - **Vasoconstriction**: Reduces cutaneous blood flow to **conserve heat** in cold environments - **Vasodilation**: Increases cutaneous blood flow to **dissipate heat** in warm environments - Controlled by sympathetic nervous system under hypothalamic regulation **Key Concept**: Temperature homeostasis requires the **coordinated action of all these mechanisms**. The hypothalamus serves as the control center, while thermogenesis and vasomotor responses are the effector mechanisms. **None of these work in isolation** - they function as an integrated thermoregulatory system.

Q: Fever causes:

Thermoregulatory centre to shift to new level. ***Thermoregulatory centre to shift to new level*** - Fever is characterized by a **resetting of the hypothalamic thermoregulatory set point** to a higher level. - This higher set point prompts the body to increase heat production and decrease heat loss, leading to a rise in core body temperature. *Resetting of skin temperature* - While skin temperature does change during fever (initially feeling cold, then warm), the primary change is the **core body temperature's set point** in the hypothalamus. - Skin temperature is a reflection of peripheral thermoregulation and the body's attempts to reach the new set point, rather than the primary cause of fever. *Both of the options* - Resetting of skin temperature is not the primary cause or mechanism of fever; rather, it is a consequence of the body attempting to reach the elevated core temperature set point. - The fundamental change in fever is the **thermoregulatory center's set point**. *None of the options* - The second option accurately describes the underlying mechanism of fever, which involves the alteration of the thermoregulatory center's set point. - Therefore, this option is incorrect as one of the provided mechanisms is correct.

Q: O2 consumption is minimal when temperature gradient between skin and external environment is:

< 0.5°C. ***< 0.5°C*** - A minimal temperature gradient between the skin and the external environment means that there is very little heat transfer occurring, either in or out of the body. - This scenario represents a **thermoneutral state**, where the body does not need to actively engage in thermoregulation (e.g., shivering, sweating) to maintain its core temperature, thus minimizing **metabolic demand** and **oxygen consumption**. *< 2.5°C* - While a small gradient, it is still large enough to require some degree of **thermoregulatory effort** from the body to maintain core temperature, which would increase **O2 consumption** compared to a near-zero gradient. - The body would likely be making slight adjustments to blood flow or metabolic rate to prevent heat loss or gain. * 3.5°C* - A temperature gradient greater than 3.5°C signifies a significant difference between skin and ambient temperature, necessitating substantial **thermoregulatory responses**. - These responses, such as **shivering** (to generate heat) or **sweating** (to lose heat), are metabolically intensive and would lead to a significantly **increased O2 consumption**.

Q: The hormone associated with cold adaptation is:

Thyroxine. ***Thyroxine*** - **Thyroxine (T4)** and **triiodothyronine (T3)**, produced by the thyroid gland, play a crucial role in regulating basal metabolic rate and heat production. - In cold environments, the release of these **thyroid hormones** increases, stimulating metabolism and generating more body heat to maintain core temperature. *Melanocyte Stimulating Hormone* - **Melanocyte-stimulating hormone (MSH)** primarily regulates **melanin production** in the skin, which determines skin pigmentation. - It has no direct significant role in **cold adaptation** or thermoregulation. *Insulin* - **Insulin** is essential for **glucose metabolism** by facilitating glucose uptake into cells from the bloodstream. - While energy metabolism is relevant to heat production, insulin's primary role is not direct **cold adaptation**. *Growth hormone* - **Growth hormone (GH)** is critical for **growth**, development, and metabolism of proteins, carbohydrates, and fats. - While it has some metabolic effects that contribute to overall energy balance, it is not a primary hormone specifically associated with **cold adaptation**.

Q: Which is the primary gland responsible for thermoregulatory sweating in humans?

Eccrine gland. ***Eccrine gland*** - **Eccrine glands** are the most numerous sweat glands and are primarily responsible for producing the watery sweat involved in **thermoregulation**. - Their ducts open directly onto the skin surface, allowing for efficient evaporative cooling, which is crucial for maintaining **body temperature homeostasis**. *Apocrine gland* - **Apocrine glands** are mainly located in the axilla and anogenital regions and produce a thicker, milkier secretion that becomes odorous when metabolized by skin bacteria. - They are primarily involved in emotional sweating and have a minimal role in body temperature regulation. *Holocrine gland* - **Holocrine glands** are a type of exocrine gland (e.g., sebaceous glands) where the entire cell ruptures and becomes part of the secreted product. - This term describes a mode of secretion rather than a specific gland type responsible for thermoregulation. *Sebaceous gland* - **Sebaceous glands** produce **sebum**, an oily substance that lubricates the skin and hair, and helps prevent water loss. - They are not involved in thermoregulatory sweating.

Q: In human physiology, the amount of heat required to convert water to vapor during processes like sweating and respiratory humidification is referred to as

Latent Heat of vaporization. ***Latent Heat of vaporization*** - This term specifically refers to the **amount of heat energy absorbed** by a substance during a phase change from a **liquid to a gas** at a constant temperature. - In physiological processes like **sweating**, the absorption of this heat from the body's surface causes a **cooling effect** as the sweat evaporates. *Latent Heat of condensation* - This is the **heat released** when a substance changes from a **gas to a liquid**, which is the opposite of the process described in the question. - It describes the energy released when water vapor condenses, not the energy absorbed for vaporization. *Latent Heat of sublimation* - This term refers to the **heat required to change a substance directly from a solid to a gas** without passing through a liquid phase. - This process is not directly applicable to the conversion of liquid water to vapor in human physiology. *Latent heat of fusion* - This is the **heat absorbed** when a substance changes from a **solid to a liquid** (melting) at a constant temperature. - It is relevant to processes like ice melting but not to the liquid-to-gas conversion of water in the body.

Q: What is the temperature threshold that defines hyperthermia?

> 40 with autonomic dysfunction. ***> 40 with autonomic dysfunction*** - Hyperthermia is defined as **unregulated elevation of body temperature** where the hypothalamic set point remains normal but heat dissipation mechanisms fail or heat production is excessive. - The threshold of **> 40°C (104°F)** with autonomic dysfunction is characteristic of **severe hyperthermia** such as **heatstroke**, **malignant hyperthermia**, or **neuroleptic malignant syndrome**. - This distinguishes hyperthermia from fever, where the hypothalamic set point is actively raised by pyrogens. In hyperthermia, antipyretics are ineffective because the thermoregulatory center is functioning normally but overwhelmed. *> 38.3 degC* - This threshold typically defines **fever (pyrexia)**, not hyperthermia. - Fever is a **regulated** increase in body temperature due to cytokine-mediated resetting of the hypothalamic set point, often in response to infection or inflammation. - This is fundamentally different from hyperthermia, where thermoregulation is intact but overwhelmed by external or internal heat stress. *36.5-37.5 degC* - This range represents **normal human body temperature** or **normothermia**. - This reflects the body's homeostatic balance with intact thermoregulation. *>37.5-38.3 degC* - This range indicates a **low-grade fever** or mild elevation in body temperature. - While above normal, this represents early fever, not hyperthermia, and the hypothalamic set point is elevated but thermoregulation is still functioning.

Q: Which of the following measurement sites most closely reflects core body temperature?

Rectal. ***Rectal*** - **Rectal temperature** is considered the most accurate non-invasive measure of **core body temperature** because of its proximity to the body's internal organs and consistent blood supply. - It is typically about **0.5-0.7°C higher than oral temperature** and reflects the true core warmth of the body. *Axillary* - **Axillary temperature** is taken in the armpit and is generally the **least accurate** and lowest reading. - It often **underestimates core body temperature** by 1°C or more due to exposure to ambient air. *Oral* - **Oral temperature** is a common and convenient site for temperature measurement but can be influenced by recent ingestion of hot or cold foods/liquids, or breathing through the mouth. - While generally reliable, it typically measures about **0.5°C lower than rectal temperature**. *Surface* - **Surface temperature**, such as that taken on the skin (e.g., forehead thermometer), is highly variable and easily affected by environmental factors like ambient temperature, airflow, and sweating. - It provides a less accurate reflection of the **body's internal core temperature** compared to deeper measurements.

Q: Febrile response in CNS is mediated by all except:

IL-10. ***IL-10*** - **IL-10 (Interleukin-10)** is a potent **anti-inflammatory cytokine** that primarily functions to suppress immune responses. It is not involved in mediating fever; rather, it would counteract pro-inflammatory mechanisms that lead to fever. - Its main roles include inhibiting the production of **pro-inflammatory cytokines** (like IL-1, TNF-α, and IL-6) and downregulating antigen presentation, thereby promoting immune tolerance. *Interferon* - **Interferons (IFNs)**, particularly **IFN-α and IFN-β**, are **pro-inflammatory cytokines** primarily known for their antiviral effects, but they also contribute to the febrile response. - They induce the production of pyrogenic cytokines and prostaglandin E2 within the hypothalamus, leading to an elevation in body temperature. *Bacterial toxin* - **Bacterial toxins**, such as **lipopolysaccharide (LPS)** from gram-negative bacteria, are potent **exogenous pyrogens**. - LPS directly stimulates immune cells (e.g., macrophages) to release **endogenous pyrogens** like IL-1, TNF-α, and IL-6, which then act on the hypothalamus to raise the body's set point temperature, causing fever. *IL-1* - **IL-1 (Interleukin-1)**, specifically **IL-1β**, is a key **endogenous pyrogen** and a central mediator of the febrile response. - It acts directly on the **hypothalamus** to induce the production of **prostaglandin E2 (PGE2)**, which then raises the body's thermostatic set point, resulting in fever.

Q: The first physiological response to high environmental temperature is:

Vasodilatation. ***Vasodilatation*** - **Cutaneous vasodilation** is the initial physiological response to dissipate heat when the body senses an increase in environmental temperature. This increases blood flow to the skin, allowing heat to radiate away from the body. - This process is mediated by the **autonomic nervous system** and precedes other heat loss mechanisms. *Sweating* - **Sweating** is a primary mechanism for heat loss through evaporation, but it is typically activated *after* vasodilation has begun to increase skin blood flow, facilitating the transfer of heat to the skin surface for evaporation. - While very effective, it is not the *first* physiological change in response to elevated environmental temperature. *Decrease heat production* - Reducing **metabolic heat production** is a long-term adaptation rather than an immediate physiological response to acute high environmental temperature. - The body's immediate focus is on dissipating existing heat, not altering basal metabolic rate for thermoregulation. *Non-shivering thermogenesis* - **Non-shivering thermogenesis** is a mechanism for *increasing* heat production, primarily through the metabolism of brown fat. - This response is activated during **cold exposure** to maintain body temperature, not in response to high environmental temperatures.

Question 1

Body temperature is maintained by:

Accepted Answer

All of the above

Answer

Hypothalamic thermoregulation

Answer

Shivering and non-shivering thermogenesis

Answer

Peripheral vasoconstriction and vasodilation

Question 2

Fever causes:

Accepted Answer

Thermoregulatory centre to shift to new level

Answer

Resetting of skin temperature

Answer

Both of the options

Answer

None of the options

Question 3

O2 consumption is minimal when temperature gradient between skin and external environment is:

Accepted Answer

< 0.5°C

Answer

< 2.5°C

Answer

< 1.5°C

Answer

> 3.5°C

Question 4

The hormone associated with cold adaptation is:

Accepted Answer

Thyroxine

Answer

Melanocyte Stimulating Hormone

Answer

Insulin

Answer

Growth hormone

Question 5

Which is the primary gland responsible for thermoregulatory sweating in humans?

Accepted Answer

Eccrine gland

Answer

Apocrine gland

Answer

Holocrine gland

Answer

Sebaceous gland

Question 6

In human physiology, the amount of heat required to convert water to vapor during processes like sweating and respiratory humidification is referred to as

Accepted Answer

Latent Heat of vaporization

Answer

Latent Heat of condensation

Answer

Latent Heat of sublimation

Answer

Latent Heat of fusion

Question 7

What is the temperature threshold that defines hyperthermia?

Accepted Answer

> 40 with autonomic dysfunction

Answer

36.5-37.5 degC

Answer

>37.5-38.3 degC

Answer

> 38.3 degC

Question 8

Which of the following measurement sites most closely reflects core body temperature?

Accepted Answer

Rectal

Answer

Axillary

Answer

Oral

Answer

Surface

Question 9

Febrile response in CNS is mediated by all except:

Accepted Answer

IL-10

Answer

Interferon

Answer

Bacterial toxin

Answer

IL-1

Question 10

The first physiological response to high environmental temperature is:

Accepted Answer

Vasodilatation

Answer

Sweating

Answer

Decrease heat production

Answer

Non-shivering thermogenesis

Thermoregulation — MCQs

Thermoregulation — MCQs

On this page

Practice by Chapter

Want unlimited practice?