Respiratory System Practice Questions

Q: 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?

Partial pressure of oxygen. ***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.

Q: Which mechanism is primarily responsible for the increase in pulmonary diffusing capacity during exercise?

Pulmonary capillary recruitment. ***Pulmonary capillary recruitment*** - During exercise, more **pulmonary capillaries** that were previously unperfused or poorly perfused open up, increasing the **surface area available for gas exchange**. - This **recruitment** directly enhances the pulmonary diffusing capacity by providing more sites for oxygen to cross from the alveoli into the blood. *Decreased airway resistance* - While airway resistance can decrease during exercise due to **bronchodilation**, this primarily affects **airflow** and ventilation, not the efficiency of gas diffusion across the alveolar-capillary membrane. - Reduced airway resistance facilitates getting air into and out of the lungs but does not expand the surface area for diffusion or thin the membrane. *Reduced membrane thickness* - The thickness of the **alveolar-capillary membrane** is a structural characteristic that does not significantly change acutely during exercise. - While a thinner membrane would improve diffusion, this is not the primary mechanism behind the exercise-induced increase in diffusing capacity. *Increased alveolar ventilation* - Increased alveolar ventilation ensures a higher **partial pressure of oxygen** in the alveoli. - While essential for delivering oxygen, it primarily affects the **driving pressure for diffusion** rather than the physical capacity of the diffusion barrier itself.

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

Alveolar haemorrhage. ***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**.

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

Apneustic breathing. ***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.

Q: Which of the following causes hypoxic hypoxia?

Pneumonia. ***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.

Q: Decreased O2 carrying capacity and Normal PO2 is a feature of

Anemic hypoxia. ***Anemic hypoxia*** - This condition is characterized by a **reduced number of circulating red blood cells** or a **low hemoglobin concentration**, leading to a decreased capacity to transport oxygen to tissues. - While the overall oxygen-carrying capacity is diminished, the **partial pressure of oxygen (PO2)** in the arterial blood remains normal because the lungs are still efficiently oxygenating the existing hemoglobin. *Hypoxic hypoxia* - This type of hypoxia involves a **decreased partial pressure of oxygen (PO2)** in the arterial blood, often due to conditions affecting lung function or environmental factors (e.g., high altitude). - While there is a reduced amount of oxygen available for transport, the **oxygen-carrying capacity** of the blood itself is not inherently impaired. *Histotoxic hypoxia* - In histotoxic hypoxia, the **cellular machinery responsible for oxygen utilization is impaired**, typically due to toxins like cyanide. - Both the **PO2** and the **oxygen-carrying capacity** of the blood are usually normal, but the tissues cannot effectively use the delivered oxygen. *Stagnant hypoxia* - Also known as **ischemic hypoxia**, this occurs when there is inadequate blood flow to the tissues, leading to insufficient oxygen delivery despite normal **PO2** and **oxygen-carrying capacity**. - This is often seen in conditions like **heart failure** or **localized arterial obstruction**.

Q: During exercise the cardiac output rises up to 5 times, but the rise in pulmonary vascular resistance is only a few mm Hg. Why?

Opening of parallel channels. ***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.

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

Respiratory rate. ***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**.

Q: Maximum CO2 is seen in ?

Pulmonary artery. ***Pulmonary artery*** - The pulmonary artery carries **deoxygenated blood** from the right ventricle to the lungs. - This blood has picked up carbon dioxide from systemic circulation, making the pulmonary artery the vessel with the **highest CO2 concentration** leaving the heart. *Left ventricle* - The left ventricle pumps **oxygenated blood** to the systemic circulation. - This blood has recently returned from the lungs, where **CO2 was offloaded**, resulting in a very low CO2 concentration. *Left atrium* - The left atrium receives **oxygenated blood** from the pulmonary veins. - Similar to the left ventricle, this blood has a **low CO2 concentration** after gas exchange in the lungs. *Pulmonary vein* - Pulmonary veins carry **oxygenated blood** from the lungs to the left atrium. - During its passage through the lungs, CO2 is **exhaled**, leading to a low CO2 concentration in the pulmonary vein.

Question 1

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?

Accepted Answer

Partial pressure of oxygen

Answer

Blood pH

Answer

Temperature

Answer

Blood glucose levels

Question 2

Which mechanism is primarily responsible for the increase in pulmonary diffusing capacity during exercise?

Accepted Answer

Pulmonary capillary recruitment

Answer

Decreased airway resistance

Answer

Reduced membrane thickness

Answer

Increased alveolar ventilation

Question 3

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

Accepted Answer

Alveolar haemorrhage

Answer

Pulmonary oedema

Answer

Idiopathic pulmonary fibrosis

Answer

Emphysema

Question 4

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

Accepted Answer

Apneustic breathing

Answer

Kussmaul breathing

Answer

Biot breathing

Answer

Cheyne-Stokes breathing

Question 5

Which of the following causes hypoxic hypoxia?

Accepted Answer

Pneumonia

Answer

HCN poisoning

Answer

CO poisoning

Answer

Circulatory shock

Question 6

Decreased O2 carrying capacity and Normal PO2 is a feature of

Accepted Answer

Anemic hypoxia

Answer

Hypoxic hypoxia

Answer

Histotoxic hypoxia

Answer

Stagnant hypoxia

Question 7

During exercise the cardiac output rises up to 5 times, but the rise in pulmonary vascular resistance is only a few mm Hg. Why?

Accepted Answer

Opening of parallel channels

Answer

Sympathetic stimulation causing vasodilatation

Answer

Pulmonary vasoconstriction

Answer

J receptors

Question 8

Trendelenburg position produces decrease in all of the following except –

Accepted Answer

Respiratory rate

Answer

Compliance

Answer

Functional residual capacity

Answer

Vital capacity

Question 9

Maximum CO2 is seen in ?

Accepted Answer

Pulmonary artery

Answer

Left ventricle

Answer

Left atrium

Answer

Pulmonary vein

Question 10

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

Accepted Answer

Person with carbon monoxide poisoning

Answer

Marathon runner at sea level

Answer

Person inhaling 100 percent oxygen at the top of Mount Everest

Answer

Person with anemia at sea level

Respiratory System — MCQs

Respiratory System — MCQs

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