Thermoregulation — MCQs

Thermoregulation Indian Medical PG Practice Questions and MCQs

Question 91: The temperature centre is?

A. Supraoptic nucleus of hypothalamus
B. Paraventricular nucleus of hypothalamus
C. Preoptic nucleus of hypothalamus (Correct Answer)
D. Suprachiasmatic nucleus of hypothalamus

Explanation: **Preoptic nucleus of hypothalamus** - The **preoptic nucleus** within the **hypothalamus** serves as the primary **thermoregulatory center** in the brain. - It contains both **heat-sensitive** and **cold-sensitive neurons** that monitor core body temperature and initiate appropriate responses to maintain homeostasis. *Supraoptic nucleus of hypothalamus* - The **supraoptic nucleus** is primarily involved in the production of **antidiuretic hormone (ADH)**, which regulates water balance. - It plays a crucial role in **fluid and electrolyte balance**, not temperature regulation. *Paraventricular nucleus of hypothalamus* - The **paraventricular nucleus** is multifunctional, producing **oxytocin** and **vasopressin** (ADH), and is involved in stress response and feeding. - While it has broad regulatory roles, it is not the primary center for **temperature control**. *Suprachiasmatic nucleus of hypothalamus* - The **suprachiasmatic nucleus (SCN)** is the body's main **circadian clock**, regulating daily rhythms like the sleep-wake cycle. - Its primary function is to synchronize biological activities with the **24-hour light-dark cycle**, not directly control body temperature.

Question 92: Hot water bottle relieves pain of abdominal spasm by:

A. Activation of heat receptors leading to pain pathway inhibition (Correct Answer)
B. Stimulation of parasympathetic fibers
C. Inhibition of cold pain receptors
D. Inhibition of heat pain receptors

Explanation: ***Activation of heat receptors leading to pain pathway inhibition*** - Heat stimulates **thermoreceptors** in the skin, sending signals to the brain that can override or diminish the perception of pain signals originating from the abdominal spasm. This is an example of the **gate control theory of pain**. - Heat causes local **vasodilation**, increasing blood flow to the area, which can help relax smooth muscles and reduce the intensity of the spasm indirectly. *Stimulation of parasympathetic fibers* - While the **parasympathetic nervous system** is involved in regulating gut motility, direct external heat application primarily affects sensory nerve fibers and local tissue physiology, not directly stimulating specific autonomic fibers to alleviate the spasm. - Relief from a hot water bottle is more attributed to **sensory nerve modulation** and local tissue effects rather than direct autonomic stimulation at this level. *Inhibition of cold pain receptors* - Applying heat would primarily **activate heat receptors** and potentially inhibit nociceptors (pain receptors), but it would not directly inhibit 'cold pain receptors'. - While cold can sometimes relieve pain (e.g., through vasoconstriction and reduced nerve conduction), this option describes an action contrary to the mechanism of heat application. *Inhibition of heat pain receptors* - Applying heat would typically **activate heat receptors** and, if the heat is extreme, activate heat-sensitive nociceptors (pain receptors), not inhibit them at therapeutic temperatures. - The mechanism of pain relief by a hot water bottle at comfortable temperatures is through the **activation of non-painful heat sensation pathways** that interfere with pain transmission, rather than by inhibiting heat-specific pain receptors.

Question 93: What is the PRIMARY pathophysiological feature that defines severe heat stress?

A. Hyperpyrexia (Correct Answer)
B. Hypothermia
C. Syncope
D. Cramps

Explanation: ***Hyperpyrexia*** - **Hyperpyrexia** (a core body temperature typically exceeding 40°C or 104°F) is the hallmark of severe heat stress, indicating a failure of the body's thermoregulatory mechanisms. - This extreme elevation in body temperature can lead to **cellular damage**, organ dysfunction, and is a defining characteristic of conditions like heat stroke. *Syncope* - **Syncope** (fainting) can occur in heat exhaustion due to **vasodilation** and **orthostatic hypotension**, but it is not the primary defining pathophysiological feature of severe heat stress itself. - While a symptom, it does not represent the overarching systemic thermoregulatory failure that defines severe heat stress. *Cramps* - **Heat cramps** are painful muscle spasms resulting from **electrolyte imbalances** and **dehydration**, usually occurring during strenuous activity in a hot environment. - Though a heat-related illness, cramps represent a milder form of heat stress and do not signify the systemic danger of **thermoregulatory collapse** seen in severe cases. *Hypothermia* - **Hypothermia** is a condition where the body loses heat faster than it can produce it, leading to a dangerously low body temperature, usually below 35°C (95°F). - This is the **opposite** of what occurs in heat stress; severe heat stress is characterized by an excessive **increase** in body temperature.

Question 94: Which of the following statements about sweat glands is true?

A. Sweat glands are most numerous on the back and least on the sole.
B. Palm and sole sweat glands are the last to appear.
C. Sweat ducts produce hypotonic sweat.
D. The hypothalamic preoptic nucleus plays a key role in sweating. (Correct Answer)

Explanation: ***The hypothalamic preoptic nucleus plays a key role in sweating.*** - The **hypothalamic preoptic nucleus** is the primary thermoregulatory center in the brain, integrating temperature signals and initiating responses such as sweating to maintain **homeostasis**. - Its activation leads to the stimulation of sympathetic cholinergic nerves that innervate the **eccrine sweat glands**, driving sweat production. *Sweat glands are most numerous on the back and least on the sole.* - **Eccrine sweat glands** are most numerous on the **palms, soles**, and forehead, areas critical for grip and fine motor control. - The back has a moderate density of sweat glands, but not the highest, and the soles have one of the highest densities. *Palm and sole sweat glands are the last to appear.* - **Palm and sole sweat glands** are among the first to develop during fetal development, appearing around the **4th gestational month**. - Other sweat glands, such as those on the trunk and limbs, develop later. *Sweat ducts produce hypotonic sweat.* - Sweat is initially **isotonic** as it is formed by the secretory coil of the gland. - As sweat passes through the sweat duct, **sodium and chloride** are reabsorbed, making the final sweat secreted onto the skin surface **hypotonic**.

Question 95: At what temperature does heat stiffening occur in the body?

A. 30°C
B. 40°C
C. 50°C
D. > 60°C (Correct Answer)

Explanation: ***> 60°C*** - **Heat stiffening**, or **heat rigor**, primarily results from the **coagulation of muscle proteins** and occurs at temperatures significantly above physiological ranges [1]. - At temperatures exceeding **60-65°C**, proteins begin to denature irreversibly, leading to macroscopic stiffening of tissues [1]. *30°C* - This temperature is within the normal physiological range or slightly below it; **hypothermia** can occur, but not heat stiffening. - Muscle function may be impaired, leading to **shivering or reduced coordination**, but not the structural changes associated with heat rigor. *40°C* - This temperature represents a **moderate fever** or **mild hyperthermia**, which can cause discomfort, but does not induce tissue stiffening [3]. - While metabolic processes are affected, **protein denaturation** leading to rigor does not occur at this level. *50°C* - Exposure to 50°C can cause significant **tissue damage** and **burns**, but direct **heat stiffening** requires higher temperatures for widespread protein coagulation. - At this temperature, cellular damage, including enzyme denaturation, begins to be severe, but full body rigor is not typically observed [2].

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

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free