Respiratory System — MCQs

A 9-year-old boy is brought to the emergency department by ambulance due to difficulty breathing. On presentation he is found to be straining to breathe. Physical exam reveals bilateral prolonged expiratory wheezing, difficulty speaking, and belly breathing. Radiographs also reveal hyperinflation of the lungs. He is given oxygen as well as albuterol, which begins to reverse the flow limitation in the airway segments of this patient. The airway segment that is most susceptible to this type of flow limitation has which of the following characteristics?

Q743

In which of the following conditions there is an increase in lung diffusion capacity?

Q744

Which of the following has prolonged inspiratory spasms that resemble breath holding?

Q745

Which of the following causes hypoxic hypoxia?

Q746

What is the ratio of lung weight to body weight after respiration?

Q747

A healthy, 37-year-old woman loses her job at the auto factory. She picks up her three young children from school and is involved in a road traffic accident. Her 5-year-old son sustains a severe head injury. The woman was not hurt in the accident but is hyperventilating as she sits in the waiting room at the hospital. She complains of feeling faint and has blurred vision. Which of the following is decreased in this woman?

Q748

Trendelenburg position produces decrease in all of the following except –

Q749

In which of the following conditions oxygen delivery is least to muscles?

Q750

Sibilant sounds are produced at:

Respiratory System Indian Medical PG Practice Questions and MCQs

Question 741: A histological examination of the carotid body reveals glomus cells containing dense-core vesicles. These cells function primarily as chemoreceptors for which of the following?

A. Partial pressure of oxygen (Correct Answer)
B. Blood pH
C. Temperature
D. Blood glucose levels

Explanation: ***Partial pressure of oxygen*** - Carotid body **glomus cells** are highly specialized **chemoreceptors** that primarily sense changes in the **partial pressure of oxygen (PO2)** in arterial blood. - When PO2 decreases (e.g., hypoxia), these cells are activated and stimulate the respiratory and cardiovascular systems to increase oxygen uptake. *Blood pH* - While carotid body chemoreceptors can sense large changes in blood pH, their primary and most sensitive role is in detecting changes in **PO2**. - Central chemoreceptors in the brainstem are more crucial for routine regulation of respiration in response to changes in **pH and PCO2**. *Temperature* - **Thermoreceptors** located in the skin, hypothalamus, and other internal organs are responsible for sensing body temperature, not the carotid body. - The carotid body's main function is related to blood gas homeostasis, not temperature regulation. *Blood glucose levels* - Blood glucose levels are regulated by specialized cells in the **pancreas** (islets of Langerhans) that secrete hormones like insulin and glucagon. - The carotid body is not directly involved in sensing or regulating glucose homeostasis.

Question 742: A 9-year-old boy is brought to the emergency department by ambulance due to difficulty breathing. On presentation he is found to be straining to breathe. Physical exam reveals bilateral prolonged expiratory wheezing, difficulty speaking, and belly breathing. Radiographs also reveal hyperinflation of the lungs. He is given oxygen as well as albuterol, which begins to reverse the flow limitation in the airway segments of this patient. The airway segment that is most susceptible to this type of flow limitation has which of the following characteristics?

A. Contains mucous producing goblet cells
B. Contains c-shaped hyaline cartilage rings
C. Distal most extent of smooth muscle (Correct Answer)
D. Lined by type I and type II pneumocytes

Explanation: ***Distal most extent of smooth muscle*** - The symptoms described (wheezing, difficulty breathing, hyperinflation) are characteristic of **asthma**, which primarily affects the **small airways** (bronchioles) where smooth muscle contraction causes significant narrowing. - The **terminal bronchioles** are the most susceptible to flow limitation in asthma because they are the smallest airways with significant amounts of smooth muscle, and their lack of cartilage makes them prone to collapse during spasm. - These airways represent the **distal-most extent of smooth muscle** in the respiratory tree, making them the primary site of bronchoconstriction in asthma. *Contains mucous producing goblet cells* - While **goblet cells** are present in the larger airways (trachea and bronchi) and contribute to mucus production in asthma, they are less prevalent or absent in the terminal bronchioles most affected by bronchoconstriction. - Mucus production is a contributing factor to airway obstruction but is not the primary characteristic defining the most susceptible airway segment for acute flow limitation. *Contains c-shaped hyaline cartilage rings* - **C-shaped cartilage rings** are characteristic of the **trachea** and large bronchi, which are rigid and less susceptible to the type of acute bronchoconstriction seen in asthma. - The lack of cartilage in the terminal bronchioles makes them more prone to collapse during smooth muscle contraction, highlighting them as the main site of flow limitation. *Lined by type I and type II pneumocytes* - **Type I and type II pneumocytes** line the **alveoli**, which are the gas exchange units and not the primary site of airway flow limitation and bronchoconstriction in asthma. - While hypoxemia can result from alveolar dysfunction due to poor ventilation, the initial pathology in asthma is in the conducting airways, specifically the terminal bronchioles.

Question 743: In which of the following conditions there is an increase in lung diffusion capacity?

A. Alveolar haemorrhage (Correct Answer)
B. Pulmonary oedema
C. Idiopathic pulmonary fibrosis
D. Emphysema

Explanation: ***Alveolar haemorrhage*** - The presence of **red blood cells within the alveoli** provides an additional source of **hemoglobin**, which can bind to carbon monoxide (CO) and therefore **increase the measured CO diffusion capacity (DLCO)**. - This is often seen in conditions like **Goodpasture's syndrome** or **pulmonary capillaritis**. *Pulmonary oedema* - Characterized by an **accumulation of fluid in the interstitial and alveolar spaces**, which **increases the diffusion barrier** for gases. - This fluid buildup **impairs gas exchange**, leading to a **decrease in DLCO**. *Idiopathic pulmonary fibrosis* - This condition involves **thickening and scarring of the alveolar-capillary membrane**, which significantly **increases the diffusion distance** for gases. - The resultant **fibrosis and destruction of capillaries** lead to a **marked decrease in DLCO**. *Emphysema* - Emphysema causes **destruction of alveolar walls** and the **pulmonary capillary bed**, leading to a **reduction in the surface area available for gas exchange**. - This loss of functional alveolar-capillary units results in a **decreased DLCO**.

Question 744: Which of the following has prolonged inspiratory spasms that resemble breath holding?

A. Kussmaul breathing
B. Biot breathing
C. Apneustic breathing (Correct Answer)
D. Cheyne-Stokes breathing

Explanation: ***Apneustic breathing*** - This pattern is characterized by **prolonged inspiratory pauses**, resembling breath-holding, followed by a short, insufficient expiratory phase. - It is caused by damage to the **pons** in the brainstem, often due to stroke or trauma, which disrupts the normal rhythm of breathing. *Kussmaul breathing* - Characterized by **deep**, **rapid**, and labored breathing, typically seen in metabolic acidosis like **diabetic ketoacidosis**. - It is a compensatory mechanism to increase CO2 elimination and raise blood pH. *Biot's breathing* - Involves irregular breathing with **periods of apnea** interspersed with shallow breaths. - This pattern is associated with damage to the **medulla oblongata** or severe intracranial pressure. *Cheyne-Stokes breathing* - Characterized by a **crescendo-decrescendo pattern** of respiration, where breathing gradually increases in depth and rate, then decreases, followed by a period of **apnea**. - It is often observed in **heart failure**, stroke, or severe neurological conditions, indicating brainstem or cerebral dysfunction.

Question 745: Which of the following causes hypoxic hypoxia?

A. Pneumonia (Correct Answer)
B. HCN poisoning
C. CO poisoning
D. Circulatory shock

Explanation: ***Pneumonia*** - Pneumonia causes **hypoxic hypoxia** by impairing **gas exchange** in the lungs due to inflammation and fluid accumulation in the alveoli, leading to reduced oxygen uptake. - This results in a **low partial pressure of oxygen (PaO2)** in the arterial blood, even with normal oxygen-carrying capacity and tissue perfusion. *HCN poisoning* - **Hydrogen cyanide (HCN) poisoning** causes **histotoxic hypoxia**, where cells are unable to utilize oxygen despite adequate delivery, by inhibiting **cytochrome c oxidase** in the electron transport chain. - It does not directly reduce the amount of oxygen in the blood or its delivery to tissues. *CO poisoning* - **Carbon monoxide (CO) poisoning** causes **anemic hypoxia** by binding to hemoglobin with a much higher affinity than oxygen, forming **carboxyhemoglobin (COHb)**. - This reduces the **oxygen-carrying capacity** of the blood and shifts the oxygen-hemoglobin dissociation curve to the left, but it is not a direct problem with alveolar gas exchange or oxygen partial pressure. *Circulatory shock* - **Circulatory shock** causes **stagnant or ischemic hypoxia**, characterized by reduced blood flow and oxygen delivery to tissues due to systemic circulatory failure. - While it results in tissue oxygen deprivation, the primary issue is impaired perfusion rather than a defect in the initial oxygenation of blood in the lungs or the blood's capacity to carry oxygen.

Question 746: What is the ratio of lung weight to body weight after respiration?

A. 1:25
B. 1:30
C. 1:35 (Correct Answer)
D. 1:60

Explanation: ***1:35*** - This ratio of lung weight to body weight, approximately **1:35** (or 0.028), is generally observed in healthy adults after respiration, reflecting the proportion of the lungs' mass relative to the total body mass. - The lungs are relatively light organs due to their **spongy, air-filled structure**, which allows for efficient gas exchange without adding excessive weight to the thoracic cavity. *1:25* - A ratio of 1:25 would imply that the **lungs are heavier** relative to body weight than typically observed in healthy adults. - Such a ratio might be seen in conditions involving **pulmonary edema** or other forms of lung congestion, where increased fluid or tissue mass elevates lung weight. *1:30* - A ratio of 1:30 also suggests a **slightly higher lung weight** relative to body weight compared to the average healthy adult. - While closer to the normal range, it still generally indicates a greater proportion of the body's mass being attributed to the lungs than is typical in normal physiological states. *1:60* - A ratio of 1:60 would indicate that the **lungs are significantly lighter** relative to overall body weight. - This extreme ratio is not physiologically typical and could suggest **severe lung hypoplasia** or other developmental abnormalities affecting lung mass.

Question 747: A healthy, 37-year-old woman loses her job at the auto factory. She picks up her three young children from school and is involved in a road traffic accident. Her 5-year-old son sustains a severe head injury. The woman was not hurt in the accident but is hyperventilating as she sits in the waiting room at the hospital. She complains of feeling faint and has blurred vision. Which of the following is decreased in this woman?

A. Arterial pH
B. Cerebral blood flow (Correct Answer)
C. Arterial oxygen content
D. Arterial oxygen tension (PO2)

Explanation: ***Cerebral blood flow*** - **Hyperventilation** leads to a decrease in arterial **pCO2**, causing **vasoconstriction** of cerebral blood vessels. - Reduced cerebral blood flow results in symptoms like **dizziness**, **lightheadedness**, and **blurred vision** due to decreased oxygen delivery to the brain. *Arterial pH* - **Hyperventilation** causes a decrease in arterial pCO2, leading to **respiratory alkalosis** (increased arterial pH). - A decreased arterial pH would be characteristic of acidosis, which is the opposite of what occurs during hyperventilation. *Arterial oxygen content* - While hyperventilation increases the amount of oxygen in the blood, the **arterial oxygen content** (total oxygen bound to hemoglobin plus dissolved oxygen) is not significantly decreased in a healthy individual. - The primary effect of hyperventilation is on CO2 levels and pH, not a reduction in overall oxygen-carrying capacity. *Arterial oxygen tension (PO2)* - **Hyperventilation** actually leads to an **increase** in arterial PO2 due to increased alveolar ventilation. - A decreased arterial PO2 would indicate hypoxemia, which is not caused by hyperventilation and is generally associated with conditions causing impaired gas exchange.

Question 748: Trendelenburg position produces decrease in all of the following except –

A. Compliance
B. Functional residual capacity
C. Respiratory rate (Correct Answer)
D. Vital capacity

Explanation: ***Respiratory rate*** - Trendelenburg position (head down, feet elevated) increases **venous return** to the heart and **intrathoracic blood volume**. - This position does not directly or consistently decrease the respiratory rate; instead, it might even slightly increase it due to **increased intrathoracic pressure** and reduced lung compliance. *Compliance* - The Trendelenburg position causes **abdominal contents** to shift towards the diaphragm, increasing **intra-abdominal pressure**. - This upward pressure on the diaphragm restricts its movement and reduces the **compliance** of the respiratory system, making it harder to inflate the lungs. *Functional residual capacity* - The cephalad displacement of the diaphragm by abdominal contents in the Trendelenburg position significantly reduces the **volume of air remaining in the lungs** after a normal exhalation. - This leads to a decrease in **functional residual capacity (FRC)**. *Vital capacity* - The decreased lung compliance and reduced FRC due to the elevated diaphragm in the Trendelenburg position make it more difficult for the lungs to fully expand. - This restriction can lead to a decrease in the **maximum amount of air** a person can exhale after a maximal inhalation, thus reducing **vital capacity**.

Question 749: In which of the following conditions oxygen delivery is least to muscles?

A. Marathon runner at sea level
B. Person with carbon monoxide poisoning (Correct Answer)
C. Person inhaling 100 percent oxygen at the top of Mount Everest
D. Person with anemia at sea level

Explanation: ***Person with carbon monoxide poisoning*** - **Carbon monoxide (CO)** binds to **hemoglobin** with an affinity 200-250 times greater than oxygen, forming **carboxyhemoglobin (COHb)**. This significantly reduces the **oxygen-carrying capacity** of the blood. - CO poisoning also shifts the **oxygen-hemoglobin dissociation curve** to the left, meaning that even the oxygen that *is* bound to hemoglobin is less readily released to the tissues, leading to severe **tissue hypoxia**. - **Dual mechanism** of impairment (reduced carrying capacity + impaired unloading) makes CO poisoning the most severe condition for oxygen delivery. *Marathon runner at sea level* - While a marathon runner at sea level experiences high oxygen demand, their **cardiovascular system** is highly adapted to deliver oxygen efficiently to the muscles. - The **partial pressure of oxygen** in the atmosphere is optimal, allowing for maximum oxygen saturation of hemoglobin and effective delivery. - Increased cardiac output and enhanced oxygen extraction compensate for high metabolic demands. *Person inhaling 100 percent oxygen at the top of Mount Everest* - Although the **atmospheric pressure** at the top of Mount Everest is very low, inhaling 100% oxygen significantly increases the **partial pressure of oxygen** in the inspired air. - This allows for a greater **driving pressure** for oxygen to enter the bloodstream and maintain higher oxygen saturation compared to breathing ambient air at altitude, mitigating the effects of hypoxia. - While not optimal, supplemental 100% O₂ can maintain adequate oxygen delivery despite low barometric pressure. *Person with anemia at sea level* - In anemia, there is a reduced **hemoglobin concentration**, which decreases the **oxygen-carrying capacity** of the blood. - However, unlike CO poisoning, the **oxygen-hemoglobin dissociation curve** remains normal, allowing for normal oxygen unloading to tissues. - Compensatory mechanisms include increased cardiac output and increased oxygen extraction, making it less severe than CO poisoning.

Question 750: Sibilant sounds are produced at:

A. Tongue blade against hard palate
B. Lips pressed together with airflow blockage
C. Tongue back against soft palate
D. Tongue tip against alveolar ridge with narrow constriction (Correct Answer)

Explanation: ***Tongue tip against alveolar ridge with narrow constriction*** - Sibilant sounds, such as /s/ and /z/, are characterized by a **high-frequency turbulent airflow** created by channeling air through a narrow constriction. - This constriction is typically formed between the **tongue tip or blade** and the **alveolar ridge**, producing a hissing or whistling sound. *Tongue blade against hard palate* - This articulation typically produces **palatal fricatives** or affricates, which may have some sibilant quality but are not the primary mechanism for the most common sibilants. - The resulting sound would be more spread out in the palatal region rather than focused at the alveolar ridge. *Lips pressed together with airflow blockage* - This articulation describes the production of **bilabial stop consonants** like /p/ and /b/, where airflow is completely blocked and then released. - Sibilant sounds require a **narrow opening** for turbulent airflow, not a complete blockage by the lips. *Tongue back against soft palate* - This describes the articulation of **velar consonants** such as /k/ and /g/, which are typically stop consonants or velar fricatives. - Velar sounds do not produce the characteristic **high-pitched, turbulent hiss** associated with sibilants.

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