Physiological Responses to Exercise — MCQs
Which of the following is a FALSE statement regarding hemodynamic changes occurring during exercise?
During exercise the cardiac output rises up to 5 times, but the rise in pulmonary vascular resistance is only a few mm Hg. Why?
Which of the following parameters is most critical for maintaining optimal oxygenation?
Least useful for a 800-m run in a competitive event would be
All of the following are increased in Acute stress except
When two different chemicals act on two different receptors and their responses are opposite to each other on the same cell, this phenomenon is called?
A patient on long-term high-dose steroid therapy (prednisolone 20 mg/day for 6 months) is scheduled for major abdominal surgery. What is the most essential perioperative requirement?
What is the recommended daily calcium intake for adult non-pregnant females?
What will be the level of the uterus on the second day post delivery?
What is the physiological dose of hydrocortisone (mg/m2/day)?
Physiological Responses to Exercise Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following is a FALSE statement regarding hemodynamic changes occurring during exercise?
- A. Venous return is augmented by the pumping action of skeletal muscles.
- B. End-diastolic volume increases in the failing heart during exercise.
- C. Venoconstriction in exercising muscles as well as increased cardiac output leads to marked increase in systemic blood pressure. (Correct Answer)
- D. The increased adrenergic nerve impulses to the heart as well as an increased concentration of circulating catecholamines help to augment the contractile state of the myocardium.
Explanation: ***Venoconstriction in exercising muscles as well as increased cardiac output leads to marked increase in systemic blood pressure.*** - This is the **FALSE statement**. During exercise, **vasodilation (not venoconstriction) occurs in exercising muscles** to increase blood flow to active tissues. Venoconstriction occurs in **non-exercising vascular beds** to redistribute blood. - While cardiac output increases significantly, **systemic vascular resistance (SVR) decreases** due to vasodilation in exercising muscles, which counteracts the rise in cardiac output. - The net effect is a **moderate increase in mean arterial pressure**, not a "marked increase." **Systolic BP rises** due to increased cardiac output, but **diastolic BP remains stable or slightly decreases** due to reduced SVR. - Therefore, this statement incorrectly describes both the vascular response in exercising muscles and the magnitude of systemic blood pressure change. *Venous return is augmented by the pumping action of skeletal muscles.* - **TRUE statement**. The **skeletal muscle pump** compresses veins during muscle contraction, pushing blood back toward the heart and increasing venous return. - This mechanism is crucial during exercise to maintain cardiac output and prevent blood pooling in lower extremities. *End-diastolic volume increases in the failing heart during exercise.* - **TRUE statement**. In a **failing heart**, the Frank-Starling mechanism operates on a flatter curve with reduced contractile reserve. - During exercise, increased venous return leads to **increased end-diastolic volume (preload)**, but the failing heart cannot adequately increase stroke volume proportionally, leading to volume accumulation and potential pulmonary congestion. *The increased adrenergic nerve impulses to the heart as well as an increased concentration of circulating catecholamines help to augment the contractile state of the myocardium.* - **TRUE statement**. During exercise, **sympathetic nervous system activation** increases, releasing **norepinephrine from adrenergic nerves** and **epinephrine from the adrenal medulla**. - These **catecholamines** bind to **beta-1 adrenergic receptors** on cardiomyocytes, increasing **heart rate (chronotropy)**, **contractility (inotropy)**, and **conduction velocity (dromotropy)**, thereby enhancing cardiac performance.
Question 2: During exercise the cardiac output rises up to 5 times, but the rise in pulmonary vascular resistance is only a few mm Hg. Why?
- A. Sympathetic stimulation causing vasodilatation
- B. Pulmonary vasoconstriction
- C. Opening of parallel channels (Correct Answer)
- D. J receptors
Explanation: ***Opening of parallel channels*** - During exercise, increased cardiac output leads to increased pulmonary blood flow, which triggers the **recruitment** (opening) of previously closed pulmonary capillaries. - This recruitment of additional parallel vascular channels effectively **decreases total pulmonary vascular resistance**, preventing a significant rise in pulmonary arterial pressure despite the greatly increased flow. *Sympathetic stimulation causing vasodilatation* - While sympathetic stimulation is crucial during exercise, it generally causes **vasoconstriction in systemic circulation** to redistribute blood flow. - Pulmonary circulation is unique; its vessels have a relatively minor response to sympathetic stimulation and typically do not undergo significant **sympathetic-mediated vasodilatation** that would solely account for such a large reduction in resistance. *Pulmonary vasoconstriction* - Pulmonary vasoconstriction would **increase** pulmonary vascular resistance, which is the opposite of what is observed during exercise. - Local factors like **hypoxia** can cause pulmonary vasoconstriction, but during exercise, ventilation increases to maintain adequate oxygenation, making widespread hypoxia unlikely in healthy individuals. *J receptors* - **Juxtacapillary (J) receptors** are sensory nerve endings in the alveolar walls that respond to conditions like pulmonary edema or emboli, causing reflex responses such as rapid, shallow breathing and bradycardia. - They do not play a direct role in the regulation of **pulmonary vascular resistance** in response to increased cardiac output during exercise.
Question 3: Which of the following parameters is most critical for maintaining optimal oxygenation?
- A. FiO2
- B. Respiratory rate
- C. PEEP (Correct Answer)
- D. Tidal volume
Explanation: ***PEEP*** - **Positive End-Expiratory Pressure (PEEP)** is crucial for maintaining optimal oxygenation because it prevents **alveolar collapse** at the end of expiration, thereby increasing the **functional residual capacity** and improving gas exchange. - By keeping alveoli open, PEEP increases the number of available alveoli for ventilation, preventing **atelectasis** and optimizing the **venous admixture** from non-ventilated lung units. *FiO2* - While **Fraction of Inspired Oxygen (FiO2)** is essential for providing sufficient oxygen, simply increasing FiO2 without proper alveolar recruitment and patency (often achieved with PEEP) can be less effective and potentially harmful due to **oxygen toxicity**. - High FiO2 can improve oxygenation in cases of **hypoxemia**, but it doesn't address underlying problems like **alveolar collapse** or **ventilation-perfusion mismatch** as directly as PEEP does. *Respiratory rate* - **Respiratory rate** primarily affects **carbon dioxide elimination** (PaCO2) and, to some extent, alveolar ventilation. - While an adequate respiratory rate is necessary for overall gas exchange, it is not the most direct or critical parameter for optimizing **oxygenation** compared to PEEP's role in maintaining alveolar patency. *Tidal volume* - **Tidal volume** also primarily affects **carbon dioxide elimination** and plays a role in overall minute ventilation. - Excessive tidal volume can lead to **ventilator-induced lung injury (VILI)**, while insufficient tidal volume can reduce minute ventilation, but it does not directly optimize oxygenation by preventing **alveolar collapse** in the same way PEEP does.
Question 4: Least useful for a 800-m run in a competitive event would be
- A. Lohmann reaction (Correct Answer)
- B. Pale muscle fibres
- C. Muscle glycogen
- D. Oxidative phosphorylation
Explanation: ***Lohmann reaction*** - The **Lohmann reaction** (creatine kinase reaction) is primarily involved in rapid, **short-burst energy production** for activities lasting a few seconds (e.g., sprints). - An 800-meter run is a middle-distance event requiring sustained energy from both anaerobic and aerobic pathways, where the immediate **phosphocreatine** system (Lohmann reaction) is quickly depleted and less useful for the majority of the race. *Pale muscle fibres* - **Pale muscle fibers** (Type II or fast-twitch fibers) are characterized by a high capacity for **anaerobic metabolism** and rapid, powerful contractions. - While they are crucial for the initial burst and speed in an 800-m run, their high glycolytic capacity makes them essential for the sustained high-intensity effort required, even as the race progresses beyond pure sprint. *Muscle glycogen* - **Muscle glycogen** is the primary stored carbohydrate fuel for **anaerobic glycolysis**, which is a significant energy pathway during the high-intensity portions of an 800-m run. - Its breakdown provides quick ATP generation without oxygen, supporting the rapid pace required throughout much of the race. *Oxidative phosphorylation* - **Oxidative phosphorylation** (aerobic respiration) becomes increasingly important as an 800-m race progresses, contributing a substantial portion of the ATP required for sustained muscle contraction. - It allows for the efficient production of large amounts of ATP when oxygen is available, crucial for maintaining pace and minimizing fatigue over the middle distance.
Question 5: All of the following are increased in Acute stress except
- A. Growth hormone
- B. Epinephrine
- C. Glucagon
- D. Insulin (Correct Answer)
Explanation: ***Insulin*** - During acute stress, **insulin secretion is actively suppressed** by catecholamines (epinephrine and norepinephrine) acting on **alpha-2 adrenergic receptors** on pancreatic beta cells. - This suppression is crucial for the stress response, as it allows **unopposed action of counter-regulatory hormones** to mobilize glucose and raise blood glucose levels. - The body prioritizes **immediate energy availability** (high blood glucose) over storage, making insulin the hormone that is **decreased, not increased**, during acute stress. *Growth hormone* - **Growth hormone** is a counter-regulatory hormone that **increases during acute stress** to mobilize energy stores, particularly by promoting lipolysis and gluconeogenesis. - Its actions contribute to the stress-induced elevation of **blood glucose levels**. *Epinephrine* - **Epinephrine** (adrenaline) is a primary catecholamine released during acute stress, leading to a rapid **fight or flight response**. - It significantly **increases heart rate**, blood pressure, and **glucose mobilization** through glycogenolysis and gluconeogenesis. *Glucagon* - **Glucagon** is a key hormone involved in **maintaining glucose homeostasis** and is significantly **increased during acute stress**. - It primarily acts on the liver to **stimulate glycogenolysis** and **gluconeogenesis**, thereby raising blood glucose levels to provide energy.
Question 6: When two different chemicals act on two different receptors and their responses are opposite to each other on the same cell, this phenomenon is called?
- A. Physiological antagonism (Correct Answer)
- B. Chemical antagonism
- C. Reversible antagonism
- D. Competitive antagonism
Explanation: ***Physiological antagonism*** - This occurs when two drugs act on **different receptors** to produce **opposite physiological effects** within the same system or cell, effectively canceling each other out [1]. - A classic example is the opposing actions of **histamine** (causing bronchoconstriction) and **adrenaline** (causing bronchodilation) on the bronchi [1]. *Chemical antagonism* - This involves a direct **chemical interaction** between two drugs that results in the **inactivation of one or both** of them. - An example is the binding of **chelating agents** to heavy metals, forming an inert complex. *Reversible antagonism* - This describes antagonism where the antagonist binds to the receptor and can be **displaced by a higher concentration of the agonist**. - It does not specifically describe antagonists acting on different receptors or producing opposing physiological effects. *Competitive antagonism* - This occurs when an antagonist directly **competes with an agonist for the same binding site** on a receptor [1]. - The antagonist, while not producing a response itself, prevents the agonist from binding and activating the receptor.
Question 7: A patient on long-term high-dose steroid therapy (prednisolone 20 mg/day for 6 months) is scheduled for major abdominal surgery. What is the most essential perioperative requirement?
- A. Insulin only
- B. Hydrocortisone only (Correct Answer)
- C. Both
- D. None of the options
Explanation: ***Hydrocortisone only*** - Patients on chronic **high-dose steroid therapy** (>5 mg prednisolone daily for >3 weeks) are at risk of **adrenal insufficiency** during surgical stress due to suppression of the hypothalamic-pituitary-adrenal (HPA) axis. - **Hydrocortisone stress dose** (100 mg IV at induction, followed by 50 mg every 8 hours) is the **most essential and immediate requirement** to prevent **adrenal crisis** during major surgery. - Hydrocortisone has both glucocorticoid and mineralocorticoid activity, mimicking the body's natural cortisol response to surgical stress. *Insulin only* - While steroids can cause **hyperglycemia** requiring insulin management, this is a **secondary concern** compared to preventing life-threatening **adrenal crisis**. - Insulin addresses a metabolic complication but does not protect against **inadequate cortisol response** to surgical stress. - **Without stress-dose steroids**, the patient risks hemodynamic collapse regardless of glucose control. *Both* - Although **both** medications might eventually be needed if hyperglycemia develops, the question asks for the **most essential** requirement. - **Hydrocortisone is non-negotiable** and must be given prophylactically; insulin is only needed if blood glucose is elevated. - Prioritizing both equally misses the critical time-sensitive need for **adrenal axis support**. *None of the options* - This is incorrect because patients on chronic high-dose steroids undergoing major surgery **absolutely require stress-dose steroid coverage**. - Failure to administer hydrocortisone can result in **acute adrenal crisis** with severe hypotension, shock, and potential mortality. - Modern guidelines confirm the need for perioperative steroid supplementation in high-risk patients.
Question 8: What is the recommended daily calcium intake for adult non-pregnant females?
- A. 1000 mg (Correct Answer)
- B. 1200 mg
- C. 600 mg
- D. 800 mg
Explanation: ***1000 mg*** - The recommended daily calcium intake for adult non-pregnant females (ages 19-50) is **1000 mg** according to **WHO and international guidelines** (US RDA/NIH) to maintain bone health and prevent osteoporosis. - This is the **standard recommendation** used in most medical textbooks and international nutritional guidelines. - Adequate calcium intake supports various bodily functions, including **nerve transmission**, **muscle contraction**, and **hormone secretion**. *1200 mg* - While 1200 mg is the recommended intake for **older women (above 50-70 years)** or during **pregnancy/lactation** per some guidelines, it is generally higher than necessary for non-pregnant adult females aged 19-50. - While not harmful, this higher dose is not specifically indicated for the general non-pregnant adult female population. *600 mg* - This amount of calcium is **lower than the internationally recommended daily allowance** for adult women (though it aligns with some regional guidelines like ICMR for sedentary women). - For optimal bone health and prevention of osteoporosis, **1000 mg is the widely accepted standard** in medical education. *800 mg* - This value is **below the internationally recommended daily intake** for adult non-pregnant females, which could lead to long-term calcium deficiency. - Insufficient calcium intake can increase the risk of conditions like **osteopenia** and **osteoporosis**.
Question 9: What will be the level of the uterus on the second day post delivery?
- A. One finger breadth below umbilicus (Correct Answer)
- B. Two finger breadths below umbilicus
- C. Three finger breadths below umbilicus
- D. Four finger breadths below umbilicus
Explanation: ***One finger breadth below umbilicus*** - On the second day postpartum, the **fundus** is typically located approximately **one finger breadth below the umbilicus**. - This reflects the ongoing process of **involution**, where the uterus contracts and descends back into the pelvis. *Two finger breadths below umbilicus* - This level is usually observed around **day 3 or 4 postpartum**, as the uterus continues to involute. - The descent is gradual, making it less likely to be at this level on just the second day. *Three finger breadths below umbilicus* - This position is generally reached around **day 5 or 6 postpartum** as uterine involution progresses. - A uterus at this level on day 2 would suggest a more rapid than usual involution. *Four finger breadths below umbilicus* - This level is more consistent with the uterine position around **day 7 or 8 postpartum**. - On the second day, the uterus would still be considerably higher than this.
Question 10: What is the physiological dose of hydrocortisone (mg/m2/day)?
- A. 20-25 mg/m²/day
- B. 15-18 mg/m²/day
- C. 10-12 mg/m²/day (Correct Answer)
- D. 8-10 mg/m²/day
Explanation: ***10-12 mg/m²/day*** - This range represents the typical **physiological replacement dose** of hydrocortisone, mimicking the body's natural cortisol production. - This dose is used for patients with **adrenal insufficiency** to maintain normal metabolic functions without causing significant side effects. *8-10 mg/m²/day* - This dose is slightly on the lower side of the accepted physiological range and might not be sufficient for complete replacement in all individuals. - While close, it is not the most commonly cited optimal physiological dose for hydrocortisone replacement. *15-18 mg/m²/day* - This dose is typically considered above the physiological replacement level and may begin to cause **mild corticosteroid side effects** with prolonged use. - It might be used for short periods or in specific conditions, but not as a standard physiological replacement. *20-25 mg/m²/day* - This dose is well above the physiological range and would be considered a **pharmacological dose** often used for its anti-inflammatory or immunosuppressive effects. - Prolonged use at this dose would likely lead to significant **corticosteroid side effects** such as Cushingoid features, osteoporosis, and hyperglycemia.
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