Exercise and thermoregulation US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Exercise and thermoregulation. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Exercise and thermoregulation US Medical PG Question 1: A 35-year-old woman presents to the clinic for a several-month history of heat intolerance. She lives in a small apartment with her husband and reports that she always feels hot and sweaty, even when their air conditioning is on high. On further questioning, she's also had a 4.5 kg (10 lb) unintentional weight loss. The vital signs include: heart rate 102/min and blood pressure 150/80 mm Hg. The physical exam is notable for warm and slightly moist skin. She also exhibits a fine tremor in her hands when her arms are outstretched. Which of the following laboratory values is most likely low in this patient?
- A. Triiodothyronine (T3)
- B. Thyroxine (T4)
- C. Calcitonin
- D. Glucose
- E. Thyroid-stimulating hormone (Correct Answer)
Exercise and thermoregulation Explanation: ***Thyroid-stimulating hormone***
- The patient's symptoms (heat intolerance, weight loss, tachycardia, hypertension, warm/moist skin, fine tremor) are classic for **hyperthyroidism**.
- In primary hyperthyroidism, the thyroid gland overproduces T3 and T4, which **negatively feedbacks** on the pituitary, leading to a **low TSH** level.
*Triiodothyronine (T3)*
- In hyperthyroidism, **T3 levels are typically elevated**, not low, as the thyroid gland is overactive.
- T3 is one of the primary thyroid hormones responsible for the patient's metabolic symptoms.
*Thyroxine (T4)*
- In hyperthyroidism, **T4 levels are typically elevated**, not low, alongside T3.
- T4 is the other key thyroid hormone produced in excess, contributing to the hypermetabolic state.
*Calcitonin*
- Calcitonin is a hormone involved in **calcium regulation** and is produced by the parafollicular C cells of the thyroid gland.
- Its levels are not directly affected by hyperthyroidism and would not be consistently low in this scenario.
*Glucose*
- While hyperthyroidism can affect glucose metabolism, causing increased gluconeogenesis and glycogenolysis, it more commonly leads to **elevated or normal glucose levels**, not consistently low levels.
- Low glucose would typically suggest other conditions like insulinoma or adrenal insufficiency.
Exercise and thermoregulation US Medical PG Question 2: An investigator is studying the function of the lateral nucleus of the hypothalamus in an experimental animal. Using a viral vector, the genes encoding chloride-conducting channelrhodopsins are injected into this nucleus. Photostimulation of the channels causes complete inhibition of action potential generation. Persistent photostimulation is most likely to result in which of the following abnormalities in these animals?
- A. Hyperthermia
- B. Anorexia (Correct Answer)
- C. Nocturnal hyperactivity
- D. Polydipsia
- E. Hypothermia
Exercise and thermoregulation Explanation: ***Anorexia***
- The **lateral nucleus of the hypothalamus** is primarily associated with **hunger** and **feeding behavior**; its destruction or inhibition leads to aphagia and reduced food intake.
- Inhibiting action potential generation in this region would mimic a lesion, preventing the animal from feeling hunger and consequently leading to anorexia.
*Hyperthermia*
- The **anterior hypothalamus** is more involved in **heat dissipation** (cooling), while the posterior hypothalamus handles heat conservation.
- Disrupting the lateral hypothalamus would not directly lead to hyperthermia.
*Nocturnal hyperactivity*
- The **suprachiasmatic nucleus** and other areas of the hypothalamus regulate circadian rhythms, but the lateral hypothalamus is not primarily associated with activity levels or sleep-wake cycles in this manner.
- Activation or inhibition of the lateral hypothalamus typically affects feeding, not general activity levels in a nocturnal pattern.
*Polydipsia*
- **Thirst regulation** is primarily attributed to the **supraoptic** and **paraventricular nuclei** and the **organum vasculosum of the lamina terminalis (OVLT)**.
- The lateral hypothalamus also plays a role in **drinking behavior**, and its inhibition would cause **adipsia** (decreased drinking), not polydipsia (increased drinking).
*Hypothermia*
- While the hypothalamus regulates body temperature, direct inhibition of the lateral **"hunger center"** would not cause systemic hypothermia.
- **Heat conservation** and **production** are more closely linked to the **posterior hypothalamus**.
Exercise and thermoregulation US Medical PG Question 3: During exercise, what is the primary mechanism for increased oxygen delivery to active muscles?
- A. Decreased blood viscosity
- B. Increased cardiac output (Correct Answer)
- C. Increased hemoglobin affinity
- D. Enhanced oxygen diffusion
Exercise and thermoregulation Explanation: ***Increased cardiac output***
- During exercise, **cardiac output** increases significantly due to both an elevated **heart rate** and increased **stroke volume**, directly pushing more oxygenated blood to the active muscles.
- This augmentation in blood flow is the primary factor ensuring a sufficient supply of oxygen and nutrients to meet the heightened metabolic demands of exercising muscles.
*Decreased blood viscosity*
- While factors like **hemodilution** can decrease blood viscosity during prolonged exercise, this effect is relatively minor and not the primary mechanism for acute increases in oxygen delivery compared to the dramatic increase in cardiac output.
- A decrease in blood viscosity can slightly improve flow efficiency, but it doesn't fundamentally change the amount of blood pumped per minute to the muscles.
*Increased hemoglobin affinity*
- An *increased* hemoglobin affinity for oxygen would actually make it *harder* for oxygen to unload from hemoglobin to the tissues, which is counterproductive for oxygen delivery during exercise.
- In fact, during exercise, local conditions like increased temperature, decreased pH (**Bohr effect**), and increased 2,3-BPG tend to *decrease* hemoglobin's affinity for oxygen, facilitating oxygen release to active muscles.
*Enhanced oxygen diffusion*
- While exercise does improve the efficiency of oxygen extraction at the tissue level due to a steeper partial pressure gradient and increased capillary recruitment, the *rate* of oxygen diffusion across the capillary membrane isn't the primary modulator of overall oxygen delivery.
- The main determinant is the *amount* of oxygenated blood reaching the muscle, which is governed by cardiac output and local blood flow regulation.
Exercise and thermoregulation US Medical PG Question 4: A 19-year-old woman is brought to the emergency department by ambulance 30 minutes after her neighbor found her unconscious on a running trail. Her neighbor reports that she has been training for a marathon since the beginning of the summer. She is alert and oriented but becomes irritable when realizing that she is at a hospital and refuses to answer questions. She appears tired. She is 174 cm (5 ft 7 in) tall and weighs 51 kg (112 lb). Her temperature is 35.5°C (96°F), pulse is 44/min, respirations are 20/min, and blood pressure is 84/48 mm Hg. Examination shows dry, scaly skin and dry mucous membranes. Cardiopulmonary examination shows a high-frequency, mid-to-late systolic murmur that is heard best at the apex. Her hemoglobin concentration is 11.9 g/dL. Which of the following is the most likely diagnosis?
- A. Heat exhaustion
- B. Hypertrophic obstructive cardiomyopathy
- C. Hypothyroidism
- D. Amphetamine use
- E. Anorexia nervosa (Correct Answer)
Exercise and thermoregulation Explanation: ***Anorexia nervosa***
- The patient's **low BMI** (16.9 kg/m^2), **bradycardia**, **hypotension**, **hypothermia**, and **dry, scaly skin** are classic signs of anorexia nervosa, exacerbated by intense exercise (marathon training).
- The **mid-to-late systolic murmur** heard best at the apex is likely due to **mitral valve prolapse**, a common cardiac finding in patients with severe anorexia nervosa due to decreased ventricular size and structural changes.
*Heat exhaustion*
- Although the patient was exercising, her **temperature is low (96°F)**, which contradicts the expected elevated temperature in heat exhaustion.
- Heat exhaustion typically presents with profuse sweating, not **dry mucous membranes** or **dry, scaly skin**.
*Hypertrophic obstructive cardiomyopathy*
- While it can cause a **systolic murmur** and exercise-induced syncope, it usually presents with a **loud S4**, and the patient's other symptoms like **hypothermia**, **bradycardia**, and severe **cachexia** are not typical.
- It would not explain the **low body weight**, **dry skin**, or **hypotension** as primary symptoms.
*Hypothyroidism*
- Hypothyroidism can cause **fatigue**, **bradycardia**, **hypothermia**, and **dry skin**, but it does not typically lead to such extreme **weight loss** or **hypotension** in a young, active individual.
- It doesn't explain the specific cardiac murmur described or the history of intense marathon training contributing to the presentation.
*Amphetamine use*
- Amphetamine use typically causes **tachycardia**, **hypertension**, **dilation of pupils**, and **hyperthermia**, which are opposite to this patient's presentation of bradycardia, hypotension, and hypothermia.
- The patient's **cachectic appearance** could be associated with stimulant use, but the vital signs and overall clinical picture strongly contradict it.
Exercise and thermoregulation US Medical PG Question 5: A 20-year-old woman reports to student health complaining of 5 days of viral symptoms including sneezing and a runny nose. She started coughing 2 days ago and is seeking cough medication. She additionally mentions that she developed a fever 2 days ago, but this has resolved. On exam, her temperature is 99.0°F (37.2°C), blood pressure is 118/76 mmHg, pulse is 86/min, and respirations are 12/min. Changes in the activity of warm-sensitive neurons in which part of her hypothalamus likely contributed to the development and resolution of her fever?
- A. Anterior hypothalamus (Correct Answer)
- B. Paraventricular nucleus
- C. Suprachiasmatic nucleus
- D. Lateral area
- E. Posterior hypothalamus
Exercise and thermoregulation Explanation: ***Anterior hypothalamus***
- The **anterior hypothalamus** contains warm-sensitive neurons that detect increases in body temperature and activate mechanisms for heat dissipation, such as sweating and vasodilation.
- In fever, **prostaglandins** increase the set point in the anterior hypothalamus, causing the body to retain heat and increase heat production until the new set point is reached; resolution of fever involves resetting this set point back to normal.
*Paraventricular nucleus*
- The **paraventricular nucleus** is primarily involved in neuroendocrine functions, stress response, and the regulation of appetite and autonomic nervous system.
- It plays a significant role in releasing hormones like **corticotropin-releasing hormone (CRH)** and **oxytocin**, not direct temperature regulation.
*Suprachiasmatic nucleus*
- The **suprachiasmatic nucleus (SCN)** is the body's main biological clock, regulating **circadian rhythms** including the sleep-wake cycle and daily fluctuations in body temperature.
- While it influences the normal diurnal variation in body temperature, it is not directly responsible for the acute regulation of fever.
*Lateral area*
- The **lateral hypothalamus** primarily functions as the "hunger center," stimulating foraging and feeding behavior.
- Damage to this area can lead to **anorexia** and reduced food intake, not impairments in fever response.
*Posterior hypothalamus*
- The **posterior hypothalamus** is primarily involved in heat conservation and production mechanisms, such as shivering and vasoconstriction, in response to cold.
- It contains cold-sensitive neurons and functions to raise body temperature if it falls below the set point, but it is not where the set point itself is regulated in response to pyrogens.
Exercise and thermoregulation US Medical PG Question 6: A 27-year-old man is running on the treadmill at his gym. His blood pressure prior to beginning his workout was 110/72. Which of the following changes in his cardiovascular system may be seen in this man now that he is exercising?
- A. Decreased blood pressure
- B. Decreased systemic vascular resistance (Correct Answer)
- C. Increased systemic vascular resistance
- D. Decreased stroke volume
- E. Decreased heart rate
Exercise and thermoregulation Explanation: ***Decreased systemic vascular resistance***
- During dynamic exercise, metabolic vasodilation in exercising muscles leads to a substantial **decrease in systemic vascular resistance (SVR)** to accommodate increased blood flow.
- This vasodilation overrides the systemic vasoconstriction driven by the sympathetic nervous system, resulting in a net decrease in overall SVR.
*Decreased blood pressure*
- While SVR decreases, **systolic blood pressure typically increases** during exercise due to increased cardiac output.
- **Diastolic blood pressure** usually remains stable or may slightly decrease, but overall blood pressure, specifically the mean arterial pressure, is generally maintained or elevated.
*Increased systemic vascular resistance*
- This is incorrect as **vasodilation in active muscles** causes a significant decrease in overall systemic vascular resistance.
- An increase in SVR would typically hinder blood flow to working muscles and is not a characteristic cardiovascular response to dynamic exercise.
*Decreased stroke volume*
- Stroke volume generally **increases significantly** during exercise due to enhanced venous return, increased contractility, and reduced afterload (from decreased SVR).
- A decreased stroke volume would limit cardiac output and exercise performance.
*Decreased heart rate*
- Heart rate **increases proportionally with exercise intensity** to boost cardiac output and oxygen delivery to active muscles.
- A decreased heart rate would counteract the body's physiological demand for increased blood flow during physical activity.
Exercise and thermoregulation US Medical PG Question 7: A previously healthy 44-year-old man is brought by his coworkers to the emergency department 45 minutes after he became light-headed and collapsed while working in the boiler room of a factory. He did not lose consciousness. His coworkers report that 30 minutes prior to collapsing, he told them he was nauseous and had a headache. The patient appears sweaty and lethargic. He is not oriented to time, place, or person. The patient’s vital signs are as follows: temperature 41°C (105.8°F); heart rate 133/min; respiratory rate 22/min; and blood pressure 90/52 mm Hg. Examination shows equal and reactive pupils. Deep tendon reflexes are 2+ bilaterally. His neck is supple. A 0.9% saline infusion is administered. A urinary catheter is inserted and dark brown urine is collected. The patient’s laboratory test results are as follows:
Laboratory test
Blood
Hemoglobin 15 g/dL
Leukocyte count 18,000/mm3
Platelet count 51,000/mm3
Serum
Na+ 149 mEq/L
K+ 5.0 mEq/L
Cl- 98 mEq/L
Urea nitrogen 42 mg/dL
Glucose 88 mg/dL
Creatinine 1.8 mg/dL
Aspartate aminotransferase (AST, GOT) 210
Alanine aminotransferase (ALT, GPT) 250
Creatine kinase 86,000 U/mL
Which of the following is the most appropriate next step in patient management?
- A. Dantrolene
- B. Acetaminophen therapy
- C. Hemodialysis
- D. Ice water immersion (Correct Answer)
- E. Evaporative cooling
Exercise and thermoregulation Explanation: ***Ice water immersion***
- This patient presents with signs and symptoms consistent with **heat stroke**, including high body temperature (41°C), altered mental status, and a history of working in a hot environment (boiler room). **Rapid aggressive cooling** is the most critical immediate intervention to prevent organ damage.
- **Ice water immersion** is the fastest and most effective cooling method for heat stroke, aiming to reduce core body temperature to less than 39°C (102.2°F) within 30 minutes.
*Dantrolene*
- **Dantrolene** is primarily used to treat **malignant hyperthermia** and **neuroleptic malignant syndrome**, conditions caused by abnormal calcium release in muscle cells, not environmental heat exposure.
- While both conditions involve hyperthermia, the underlying pathophysiology and triggers are different from heat stroke.
*Acetaminophen therapy*
- **Acetaminophen** is an antipyretic that works by inhibiting prostaglandin synthesis in the central nervous system, affecting the hypothalamic thermoregulatory center.
- It is **ineffective** for the hyperthermia seen in heat stroke, which is due to a failure of thermoregulation rather than an altered hypothalamic set point, and could potentially worsen liver injury.
*Hemodialysis*
- **Hemodialysis** is indicated for severe **renal failure**, drug overdose, or certain electrolyte imbalances. Although this patient has acute kidney injury (elevated BUN and creatinine, dark urine suggestive of rhabdomyolysis), aggressive cooling is the immediate life-saving intervention for heat stroke.
- While renal support might be necessary later if kidney injury progresses, it is not the most appropriate *initial* next step for hyperthermia and altered mental status.
*Evaporative cooling*
- **Evaporative cooling** (e.g., spraying with lukewarm water and using fans) is a cooling method that can be effective, particularly in environments with low humidity.
- However, for severe heat stroke with a temperature as high as 41°C, **ice water immersion** provides a more rapid and aggressive temperature reduction, which is crucial for improving outcomes.
Exercise and thermoregulation US Medical PG Question 8: A group of investigators is studying thermoregulatory adaptations of the human body. A subject is seated in a thermally insulated isolation chamber with an internal temperature of 48°C (118°F), a pressure of 1 atmosphere, and a relative humidity of 10%. Which of the following is the primary mechanism of heat loss in this subject?
- A. Convection
- B. Evaporation (Correct Answer)
- C. Conduction
- D. Piloerection
- E. Radiation
Exercise and thermoregulation Explanation: ***Evaporation***
- In an environment where the ambient temperature (48°C) is **higher than body temperature**, heat gain by convection, conduction, and radiation occurs. Therefore, **evaporation** of sweat is the only significant mechanism for heat loss.
- The relatively low humidity (10%) at this high temperature facilitates efficient sweat **evaporation**, which cools the body as it converts liquid sweat into water vapor.
*Convection*
- **Convection** involves heat transfer through the movement of air or fluid over the body surface.
- Since the ambient temperature (48°C) is significantly **above body temperature**, the body would gain heat via convection, not lose it.
*Conduction*
- **Conduction** is direct heat transfer between objects in contact.
- As the ambient temperature (48°C) is much **higher than the skin temperature**, the body would actually **gain heat** through conduction from any surfaces it touched if they were at ambient temperature.
*Piloerection*
- **Piloerection** (goosebumps) is a mechanism for minimizing heat loss by trapping a layer of warm air close to the skin.
- This response is activated in **cold environments** to conserve heat, not in hot environments to dissipate it.
*Radiation*
- **Radiation** is heat transfer via electromagnetic waves without direct contact.
- Since the ambient temperature (48°C) is **higher than body surface temperature**, the body would **gain heat** by radiation, not lose it efficiently, from the surrounding environment.
Exercise and thermoregulation US Medical PG Question 9: An 18-year-old man presents to his primary care physician with a complaint of excessive daytime sleepiness. He denies any substance abuse or major changes in his sleep schedule. He reports frequently dozing off during his regular daily activities. On further review of systems, he endorses falling asleep frequently with the uncomfortable sensation that there is someone in the room, even though he is alone. He also describes that from time to time, he has transient episodes of slurred speech when experiencing heartfelt laughter. Vital signs are stable, and his physical exam is unremarkable. This patient is likely deficient in a neurotransmitter produced in which part of the brain?
- A. Hippocampus
- B. Midbrain
- C. Pons nucleus
- D. Hypothalamus (Correct Answer)
- E. Thalamus
Exercise and thermoregulation Explanation: ***Hypothalamus***
- The patient's symptoms of excessive daytime sleepiness, cataplexy (falling asleep with strong emotions like laughter), and hypnagogic hallucinations (sensing someone in the room upon falling asleep) are classic for **narcolepsy**.
- Narcolepsy type 1 is characterized by a significant loss of **orexin (hypocretin)** neurons, a neuropeptide primarily produced in the **lateral hypothalamus** (specifically the lateral and perifornical areas), which plays a crucial role in maintaining wakefulness.
*Hippocampus*
- The **hippocampus** is primarily involved in **memory formation** and spatial navigation.
- Deficiencies in neurotransmitters produced or acting in the hippocampus are typically associated with memory disorders, not narcolepsy.
*Midbrain*
- The **midbrain** contains nuclei involved in dopamine, serotonin, and norepinephrine pathways, which are critical for mood, reward, and sleep-wake regulation.
- While these neurotransmitters influence the sleep-wake cycle, the primary deficiency in narcolepsy type 1 is specifically orexin, which originates from the hypothalamus, not the midbrain.
*Pons nucleus*
- The **pons** is essential for regulating sleep stages, particularly **REM sleep**, and contains nuclei involved in breathing and motor control.
- While it contributes to sleep architecture, the core pathology of narcolepsy type 1, the loss of orexin-producing neurons, is located higher in the brain, in the hypothalamus.
*Thalamus*
- The **thalamus** acts as a crucial relay station for sensory and motor signals to the cerebral cortex and is involved in regulating consciousness and alertness.
- While it is involved in arousal regulation, it is not the primary site of orexin production, nor is a neurotransmitter deficiency directly from the thalamus the primary cause of narcolepsy.
Exercise and thermoregulation US Medical PG Question 10: A 34-year-old woman comes to a physician for a routine health maintenance examination. She moved to Denver 1 week ago after having lived in New York City all her life. She has no history of serious illness and takes no medications. Which of the following sets of changes is most likely on analysis of a blood sample obtained now compared to prior to her move?
Erythropoietin level | O2 saturation | Plasma volume
- A. ↑ unchanged unchanged
- B. ↑ ↓ ↓ (Correct Answer)
- C. Unchanged ↓ unchanged
- D. ↓ unchanged ↑
- E. Unchanged unchanged ↓
Exercise and thermoregulation Explanation: ***↑ ↓ ↓***
- Moving to a high altitude like Denver (from sea level NYC) leads to **hypoxia**, which triggers increased **erythropoietin (EPO)** production to stimulate red blood cell formation.
- The immediate physiological response to high altitude is a **decrease in arterial PO2** and thus **oxygen saturation**, along with a **reduction in plasma volume** due to increased diuresis and fluid shifts.
*↑ unchanged unchanged*
- While **erythropoietin** would increase due to hypoxia at higher altitudes, **oxygen saturation** would decrease, not remain unchanged.
- **Plasma volume** also tends to decrease acutely at high altitudes, rather than staying unchanged.
*Unchanged ↓ unchanged*
- **Erythropoietin** would be expected to increase, not remain unchanged, as a compensatory mechanism to hypoxia.
- While **oxygen saturation** would decrease, **plasma volume** typically decreases acutely, not remaining unchanged.
*↓ unchanged ↑*
- **Erythropoietin** would increase, not decrease, in response to the lower atmospheric oxygen.
- Both **oxygen saturation** and **plasma volume** would decrease, not remain unchanged or increase, respectively.
*Unchanged unchanged ↓*
- **Erythropoietin** would increase, not remain unchanged, to stimulate red blood cell production in response to hypoxia.
- **Oxygen saturation** would decrease, not remain unchanged, at higher altitudes.
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