Thermoregulation — MCQs

Thermoregulation Indian Medical PG Practice Questions and MCQs

Question 51: What is the most consistent cardiovascular effect of hypothermia in elderly patients?

A. May cause myocardial infarction
B. Decreased heart rate (Correct Answer)
C. Decreased cardiac output
D. All of the options

Explanation: ***Decreased heart rate*** - In elderly patients, **hypothermia consistently leads to a decrease in heart rate (bradycardia)**, a physiological response to conserve energy and reduce metabolic demand - This **bradycardia** is a hallmark sign of hypothermia across various age groups, but it is particularly pronounced and dangerous in the elderly due to their reduced physiological reserve - **Heart rate decreases by approximately 3-5 beats per minute for every 1°C drop in core temperature** below 35°C, making it the most predictable and consistent cardiovascular finding *May cause myocardial infarction* - While severe hypothermia can precipitate **myocardial ischemia or infarction** due to increased myocardial oxygen demand from shivering, catecholamine release, and coronary vasoconstriction, it is not the *most consistent* cardiovascular effect across all degrees of hypothermia - **Myocardial infarction** is a serious complication, but occurs less predictably than bradycardia and depends on pre-existing coronary artery disease *Decreased cardiac output* - **Cardiac output** does generally decrease in hypothermia due to the combined effects of **bradycardia and reduced myocardial contractility** - However, the initial and most consistent direct effect is the **slowing of the heart rate**, which then contributes to the overall decrease in cardiac output - Cardiac output falls by approximately **25-40% at core temperatures below 32°C** *All of the options* - While hypothermia can contribute to myocardial infarction and does decrease cardiac output, the **most consistent and universal cardiovascular effect is bradycardia** - Not all hypothermic patients will develop MI, and the decrease in cardiac output is a *consequence* of bradycardia and reduced contractility rather than a primary direct effect

Question 52: In human beings, the least useful physiological response to low environmental temperature is:

A. Shivering
B. Vasoconstriction
C. Release of thyroxine
D. Piloerection (Correct Answer)

Explanation: ***Piloerection*** - **Piloerection**, or 'goosebumps,' is a vestigial reflex in humans, meaning it has lost most of its original function. - While it causes hair to stand on end, which would trap an insulating layer of air in furry animals, humans lack sufficient body hair for this to be an **effective heat retention mechanism**. *Shivering* - **Shivering** involves involuntary muscle contractions that generate heat through increased metabolic activity. - This is a highly effective and significant physiological response for **acute heat production** in response to cold. *Vasoconstriction* - **Vasoconstriction** of peripheral blood vessels reduces blood flow to the skin, thereby decreasing heat loss to the environment through conduction, convection, and radiation. - This is a crucial mechanism for **conserving core body heat** in cold conditions. *Release of thyroxine* - The **release of thyroxine** (thyroid hormone) increases the body's basal metabolic rate over a longer term, leading to increased heat production. - This is an important **adaptive response to prolonged cold exposure**, rather than an immediate one.

Question 53: Which of the following statements about cutaneous shunt vessels is true:

A. Not under the control of autonomic nervous system
B. Have role in thermoregulation (Correct Answer)
C. These vessels are evenly distributed throughout the skin
D. Perform nutritive function

Explanation: ***Have role in thermoregulation*** - **Cutaneous shunt vessels**, specifically **arteriovenous anastomoses**, are abundant in the skin of the **fingertips**, **toes**, **ears**, and **nose**. - They allow for direct shunting of blood from arterioles to venules, bypassing the capillaries, which is crucial for **regulating heat loss** from the body. *Not under the control of autonomic nervous system* - **Cutaneous shunt vessels** are indeed under the **control of the autonomic nervous system**, specifically the **sympathetic nervous system**. - **Sympathetic stimulation** causes vasoconstriction of these shunts, reducing blood flow to the skin and conserving heat. *These vessels are evenly distributed throughout the skin* - **Cutaneous shunt vessels** are **not evenly distributed** throughout the skin; they are primarily concentrated in areas important for thermoregulation, such as the digits, ears, and nose. - Their presence is more prominent in areas exposed to the environment, facilitating rapid heat exchange. *Perform nutritive function* - While all blood vessels deliver nutrients, the primary function of **cutaneous shunt vessels** is **thermoregulation**, not **nutritive exchange**. - They largely **bypass the capillary beds**, where the majority of nutrient and waste exchange occurs.

Question 54: Body temperature is controlled by:

A. Precentral gyrus
B. Diencephalon
C. Medulla
D. Hypothalamus (Correct Answer)

Explanation: ***Hypothalamus*** - The **hypothalamus** acts as the body's **thermostat**, integrating sensory information about body temperature and initiating responses to maintain a narrow range. - It contains specialized neurons sensitive to temperature (thermoreceptors) and coordinates various physiological processes such as **shivering**, **sweating**, and changes in blood flow to regulate heat production and loss. *Precentral gyrus* - The **precentral gyrus** is primarily involved in **motor control**, specifically initiating voluntary movements. - It forms the primary **motor cortex** and has no direct role in temperature regulation. *Diencephalon* - The **diencephalon** is a region of the brain that includes the **thalamus**, **hypothalamus**, epithalamus, and subthalamus. While the hypothalamus within it controls temperature, the term diencephalon is too broad and not specific enough. - The **thalamus**, a major component of the diencephalon, acts as a relay station for sensory information but not for direct temperature regulation. *Medulla* - The **medulla oblongata** is part of the brainstem and controls vital involuntary functions such as **heart rate**, **breathing**, and **blood pressure**. - It does not directly regulate body temperature; its functions are more focused on autonomic control of basic life-sustaining processes.

Question 55: A 17-year-old boy is admitted to the hospital with a traumatic brain injury, sustained when he fell off his motorcycle. He develops a fever of 39°C, which is unrelated to an infection or inflammation. The fever is most likely due to a lesion of which of the following?

A. The posterior nucleus
B. The anterior hypothalamus (Correct Answer)
C. The arcuate nucleus
D. The lateral hypothalamus

Explanation: ***The anterior hypothalamus*** - The **anterior hypothalamus** is responsible for **heat dissipation**, including sweating and vasodilation. A lesion here impairs the body's ability to cool down, leading to **hyperthermia** (fever) even without infection or inflammation. - This type of fever, often seen after traumatic brain injury, is referred to as **central fever** or **hypothalamic fever**. *The posterior nucleus* - The **posterior hypothalamus** is primarily involved in **heat conservation** and production, such as shivering and vasoconstriction. - A lesion here would more likely lead to **hypothermia** due to impaired heat generation, rather than hyperthermia. *The arcuate nucleus* - The **arcuate nucleus** plays a crucial role in regulating **appetite** and **satiety** through the production of neuropeptides like NPY and POMC. - It is not directly involved in the central control of body temperature, so a lesion here would not cause fever. *The lateral hypothalamus* - The **lateral hypothalamus** contains the **feeding center** and is primarily involved in stimulating appetite. - Damage to this area typically leads to **anorexia** and weight loss, not an uncontrolled increase in body temperature.

Question 56: The primary motor area for shivering is:

A. Red nucleus
B. Ventromedial anterior hypothalamus
C. Dorsomedial posterior hypothalamus (Correct Answer)
D. Cerebrum

Explanation: ***Dorsomedial posterior hypothalamus*** - The **dorsomedial posterior hypothalamus** is considered the primary motor area for shivering, integrating thermal signals to initiate muscle contractions for heat production. - This region coordinates the involuntary **phasic muscle contractions** that characterize shivering in response to cold. *Red nucleus* - The **red nucleus** is involved in motor coordination, particularly of the upper limbs, but it is not the primary center for initiating shivering. - It primarily contributes to the **rubrospinal tract**, which influences muscle tone and posture. *Ventromedial anterior hypothalamus* - The **ventromedial anterior hypothalamus** is primarily associated with responses to heat, such as **sweating** and **vasodilation**, to promote heat loss. - Its function is antagonistic to shivering; it would inhibit mechanisms for heat production rather than initiate them. *Cerebrum* - The **cerebrum** is responsible for higher cognitive functions, voluntary movements, and conscious perception of temperature but does not directly control the automatic reflex of shivering. - While it can influence thermal comfort and behavioral responses to cold, the subcortical control of shivering is located in the hypothalamus.

Question 57: Body temperature is maintained by:

A. Hypothalamic thermoregulation
B. Shivering and non-shivering thermogenesis
C. Peripheral vasoconstriction and vasodilation
D. All of the above (Correct Answer)

Explanation: ***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.

Question 58: Fever causes:

A. Resetting of skin temperature
B. Thermoregulatory centre to shift to new level (Correct Answer)
C. Both of the options
D. None of the options

Explanation: ***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.

Question 59: O2 consumption is minimal when temperature gradient between skin and external environment is:

A. < 2.5°C
B. < 1.5°C
C. < 0.5°C (Correct Answer)
D. > 3.5°C

Explanation: ***< 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. *< 1.5°C* - This gradient is larger than 0.5°C, indicating that the body would need to expend some energy for **thermoregulation**. - A greater heat exchange would occur, prompting the body to increase its **metabolic rate** to either generate or dissipate heat. *> 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**.

Question 60: The hormone associated with cold adaptation is:

A. Melanocyte Stimulating Hormone
B. Insulin
C. Growth hormone
D. Thyroxine (Correct Answer)

Explanation: ***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**.

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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