Thermoregulation — MCQs

Thermoregulation Indian Medical PG Practice Questions and MCQs

Question 61: Which is the primary gland responsible for thermoregulatory sweating in humans?

A. Apocrine gland
B. Holocrine gland
C. Sebaceous gland
D. Eccrine gland (Correct Answer)

Explanation: ***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.

Question 62: What is the temperature threshold that defines hyperthermia?

A. > 40 with autonomic dysfunction (Correct Answer)
B. 36.5-37.5 degC
C. >37.5-38.3 degC
D. > 38.3 degC

Explanation: ***> 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.

Question 63: Which of the following measurement sites most closely reflects core body temperature?

A. Axillary
B. Oral
C. Surface
D. Rectal (Correct Answer)

Explanation: ***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.

Question 64: Febrile response in CNS is mediated by all except:

A. Interferon
B. IL-10 (Correct Answer)
C. Bacterial toxin
D. IL-1

Explanation: ***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.

Question 65: The first physiological response to high environmental temperature is:

A. Sweating
B. Decrease heat production
C. Vasodilatation (Correct Answer)
D. Non-shivering thermogenesis

Explanation: ***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 66: Which of the following physiological changes occur during heat acclimatization?

A. Decreased Renal Blood Flow
B. Increased urine sodium
C. Increased aldosterone secretion (Correct Answer)
D. Decreased sweat sodium concentration

Explanation: ***Increased aldosterone secretion*** - Heat acclimatization leads to **increased aldosterone secretion** as part of the body's effort to conserve sodium and water due to increased sweating. - This hormonal response helps maintain **fluid and electrolyte balance** in hot environments. - Aldosterone acts on the **sweat glands** and **renal tubules** to reduce sodium loss. *Decreased Renal Blood Flow* - While there might be some transient changes during acute heat exposure, **sustained decreases in renal blood flow** are not a primary or beneficial physiological change in heat acclimatization. - The body aims to maintain adequate renal perfusion to excrete metabolic waste, even in hot environments. *Increased urine sodium* - Heat acclimatization results in **decreased urine sodium concentration** because aldosterone promotes sodium reabsorption in the kidneys. - This mechanism is crucial for conserving sodium that is lost through increased sweating. *Decreased sweat sodium concentration* - While this IS a feature of heat acclimatization, it occurs as a **consequence of increased aldosterone secretion**, making aldosterone the more fundamental physiological change. - Acclimatized individuals produce **more dilute sweat** with lower sodium concentration, which helps conserve electrolytes. - The **primary mechanism** is the hormonal adaptation (aldosterone), not just the secondary effect on sweat composition.

Question 67: Thermoregulatory response activated by cold is:

A. Increased respiration
B. Cutaneous vasodilatation
C. Increased voluntary activity (Correct Answer)
D. Anorexia

Explanation: ***Increased voluntary activity*** - Among the given options, **increased voluntary activity** is the correct answer as it represents a behavioral thermoregulatory response that generates heat through **muscle contraction** (e.g., moving around, exercising, stamping feet). - While the **primary physiological responses** to cold include **shivering** (involuntary muscle contraction), **vasoconstriction**, and **non-shivering thermogenesis** (brown fat), voluntary physical activity does contribute to heat production and is a recognized cold-adaptive behavior. - Voluntary activity increases metabolic rate and heat generation, helping maintain core body temperature in cold environments. *Increased respiration* - While respiration rate may increase slightly in cold due to metabolic changes, it is **not a primary thermoregulatory mechanism** for heat production. - The main purpose of respiration is **gas exchange**, not heat generation. - This is not a recognized thermoregulatory response to cold exposure. *Cutaneous vasodilatation* - **Cutaneous vasodilatation** (widening of skin blood vessels) leads to increased blood flow to the skin, which facilitates **heat loss** and is a response to **heat**, not cold. - In cold conditions, the body undergoes **cutaneous vasoconstriction** (narrowing of skin blood vessels) to minimize heat loss and preserve core temperature. - This option represents the **opposite** of what occurs in cold. *Anorexia* - **Anorexia** (loss of appetite) is not a thermoregulatory response to cold. - In fact, cold exposure typically **increases appetite and food intake** to support increased metabolic heat production. - Reduced food intake would impair the body's ability to generate heat through metabolism.

Question 68: Which of the following is the primary neurotransmitter responsible for lowering the thermoregulatory set point and triggering hot flushes?

A. Neurokinin B (NKB) (Correct Answer)
B. Estrogen
C. Serotonin
D. Norepinephrine

Explanation: ***Neurokinin B (NKB)*** - **Neurokinin B (NKB)** is a key neuropeptide produced by **KNDy (Kisspeptin, Neurokinin B, Dynorphin) neurons** in the hypothalamus. - It plays a crucial role in regulating the **thermoregulatory set point**, and its dysregulation is implicated in the genesis of hot flushes, particularly in menopausal women. *Estrogen* - **Estrogen deficiency** is the *underlying cause* of hot flushes but is not the direct neurotransmitter that acutely lowers the thermoregulatory set point. - Low estrogen levels lead to changes in hypothalamic neurotransmitter function, which then trigger the flushing response. *Serotonin* - **Serotonin** is involved in thermoregulation, and certain **serotonin reuptake inhibitors (SSRIs)** can alleviate hot flushes. - However, serotonin itself is not considered the primary neurotransmitter responsible for acutely lowering the thermoregulatory set point in the context of hot flushes. *Norepinephrine* - **Norepinephrine** is a neurotransmitter involved in various physiological processes, including thermoregulation. - While it can influence heat dissipation mechanisms, it is not primarily responsible for the *initial lowering of the thermoregulatory set point* that triggers hot flushes; rather, it often acts downstream of other signals.

Question 69: A cold exposure which is expected to bring the body temperature from 37°C to 20°C, actually brings it down to only 36.5°C. Calculate the 'Gain' of the thermoregulatory system.

A. 33 (Correct Answer)
B. 34
C. 16.5
D. 66

Explanation: ***33*** - The **error signal** (or uncorrected temperature drop) is the difference between the actual drop and the expected drop without regulation. Here, the expected drop is 37°C - 20°C = 17°C. The actual drop is 37°C - 36.5°C = 0.5°C. So, the error signal caused by the regulatory system's action is 36.5°C - 20°C = 16.5°C. Alternatively calculated as 17°C (expected) - 0.5°C (actual) = 16.5°C. - The **gain** of a thermoregulatory system is calculated as the expected change in temperature (without regulation) divided by the actual observed change in temperature after regulation when the body resists the change. Here, the body would have cooled by 17°C (37°C - 20°C) without compensation, but it only cooled by 0.5°C (37°C - 36.5°C). The gain is therefore 16.5 / 0.5 = 33. *34* - This answer likely arises from a miscalculation of the error signal or the expected temperature drop. - The key is to correctly identify the **change that would have occurred without regulation** and the **change that actually occurred.** *16.5* - This value represents the **change in temperature that was prevented by the thermoregulatory system** (17°C expected drop minus 0.5°C actual drop), but it is not the gain. - The gain is a ratio, not an absolute temperature difference. *66* - This value would result from an incorrect calculation, possibly by inverting the gain formula or multiplying by an incorrect factor. - The gain is specifically the ratio of the "corrected" change to the "uncorrected" error.

Question 70: Heat loss from the body depends mostly on:

A. Warming of air during inspiration
B. Environmental temperature
C. Radiation and evaporation (Correct Answer)
D. Thermoregulatory center

Explanation: ***Radiation and evaporation*** - **Radiation** is the primary mechanism of heat loss in a cool environment, accounting for approximately 60% of heat loss at room temperature, as the body emits infrared electromagnetic waves. - **Evaporation** of sweat from the skin surface is crucial for heat dissipation, especially in warmer conditions. It accounts for 20-25% of heat loss at rest and can increase to 100% when ambient temperature equals or exceeds skin temperature. - Together, these two mechanisms represent the **most significant pathways** for body heat loss under normal physiological conditions. *Warming of air during inspiration* - While warming inspired air does consume some body heat, it is a relatively minor mechanism compared to radiation and evaporation. - Respiratory heat loss accounts for only 2-9% of total heat loss, depending on the temperature and humidity of the inhaled and exhaled air. *Environmental temperature* - Environmental temperature certainly influences the *rate* of heat loss but is not a *mechanism* of heat loss itself. - It determines the gradient for heat exchange through radiation, convection, and conduction, as well as the need for evaporative cooling. *Thermoregulatory center* - The thermoregulatory center (in the hypothalamus) *controls* heat loss and production mechanisms through coordinating physiological responses, but it is not a direct mechanism of heat loss. - It receives input from peripheral and central thermoreceptors and initiates responses like sweating, vasoconstriction/vasodilation, or shivering to maintain body temperature homeostasis.

Practice by Chapter

Heat Production and Loss

Practice Questions

Temperature Sensing Mechanisms

Practice Questions

Hypothalamic Regulation of Temperature

Practice Questions

Behavioral Thermoregulation

Practice Questions

Fever and Hyperthermia

Practice Questions

Hypothermia

Practice Questions

Exercise and Thermoregulation

Practice Questions

Thermoregulation in Extreme Environments

Practice Questions

Age-Related Changes in Thermoregulation

Practice Questions

Disorders of Thermoregulation

Practice Questions

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