Respiratory System Practice Questions

Q: Damage to the pneumotaxic center will cause?

Apneusis. ***Apneusis*** - The **pneumotaxic center** (located in the upper pons) functions to **limit and terminate inspiration** by inhibiting the apneustic center in the lower pons. - When the pneumotaxic center is damaged, the **apneustic center becomes unopposed**, resulting in prolonged, sustained inspiratory gasps with brief expiratory phases. - This characteristic breathing pattern is called **apneusis**, which is the classic result of pneumotaxic center damage. - Reference: **Guyton and Hall Textbook of Medical Physiology** - the pneumotaxic center provides the "off-switch" for inspiration; without it, apneusis develops. *Apnea* - **Apnea** refers to complete cessation of breathing. - This would require damage to the **medullary respiratory centers** (dorsal and ventral respiratory groups), not the pneumotaxic center. - Pneumotaxic center damage alters the breathing pattern but does not stop breathing entirely. *Faster breathing with lesser tidal volume* - This would occur if inspiration were shortened and respiration rate increased. - Pneumotaxic center damage has the **opposite effect** - it prolongs inspiration rather than shortening it. *Slower breathing with greater tidal volume* - While prolonged inspiration in apneusis may result in increased tidal volume, this description is **incomplete and imprecise**. - The hallmark finding is **apneusis** (prolonged inspiratory gasps), not simply "slower, deeper breathing." - This option misses the characteristic pathological breathing pattern that defines pneumotaxic center damage.

Q: Which of the following factors increases the resistance of the airways?

Inhaling cigarette smoke. ***Inhaling cigarette smoke*** - **Cigarette smoke** causes irritation and inflammation of the airways, leading to **bronchoconstriction** and increased mucus production. These effects directly narrow the airway lumen, increasing resistance. - Exposure to irritants like cigarette smoke triggers reflex mechanisms that constrict **smooth muscle** in the bronchioles, reducing their diameter and thereby increasing the **resistance to airflow**. *Increasing lung volume* - As **lung volume** increases, the radial traction exerted on the airways by the surrounding parenchyma also increases. This traction tends to **widen the airways**, thereby decreasing resistance. - At higher lung volumes, the airways are stretched open, which reduces the **frictional forces** and improves airflow, leading to lower resistance. *Increased sympathetic stimulation* - **Sympathetic stimulation** (via beta-2 adrenergic receptors) causes **bronchodilation**, which involves the relaxation of smooth muscle in the airways. - This relaxation leads to a **widening of the airways**, thereby decreasing the resistance to airflow and facilitating easier breathing. *Going to high altitude* - Moving to **high altitude** primarily affects the **partial pressure of oxygen** and overall atmospheric pressure, but it does **not directly increase airway resistance**. - While high altitude can lead to changes in breathing patterns (e.g., hyperventilation), it does not directly cause narrowing of the airways or increased frictional forces within the respiratory tree.

Q: Which of the following does NOT cause hyperventilation?

CO poisoning. ***CO poisoning*** - **Carbon monoxide (CO)** binds to **hemoglobin** with a much higher affinity than oxygen, forming **carboxyhemoglobin**. This reduces the oxygen-carrying capacity of blood and shifts the **oxygen-hemoglobin dissociation curve to the left**, impairing oxygen release to tissues. - While it causes **tissue hypoxia**, CO poisoning does **not stimulate chemoreceptors** to induce hyperventilation because it does not significantly alter the **partial pressure of oxygen (PO2)** in the arterial blood, which is what peripheral chemoreceptors primarily respond to. Additionally, it does not directly increase **acidosis** that would stimulate central chemoreceptors. *Decreased pH in CSF* - A **decreased pH in the cerebrospinal fluid (CSF)** indicates an increase in **H+ ions**, which directly stimulates the **central chemoreceptors** located in the medulla oblongata. - This stimulation leads to an increased respiratory drive, resulting in **hyperventilation** to "blow off" more CO2 and thus normalize the CSF pH. *Increased adrenergic levels* - Elevated **adrenergic levels**, such as during stress, fear, or anxiety, stimulate the **respiratory center** in the brainstem. - This stimulation can lead to an increased rate and depth of breathing, causing **hyperventilation**. *Decreased plasma HCO3* - A **decrease in plasma bicarbonate (HCO3-)** is characteristic of **metabolic acidosis**. - To compensate for the metabolic acidosis, the body will **increase ventilation (hyperventilate)** to decrease the partial pressure of CO2 (PCO2), thereby raising the blood pH back towards normal.

Q: Which of the following stimulates peripheral chemoreceptors?

Hypoxia. ***Hypoxia*** - Peripheral chemoreceptors, particularly the **carotid and aortic bodies**, are most sensitive to decreases in arterial **partial pressure of oxygen (PaO2)**. - **Hypoxia is the PRIMARY and MOST POTENT stimulus** for peripheral chemoreceptors, causing a dramatic increase in ventilation when PaO2 falls below 60 mmHg. - Among all stimuli, hypoxia produces the strongest response from peripheral chemoreceptors. *Acidosis* - **Acidosis does stimulate peripheral chemoreceptors**, but its effect is **much weaker** compared to hypoxia. - Peripheral chemoreceptors respond to decreased pH (H+ ions), but this is a **secondary stimulus**. - The effect of acidosis is **potentiated in the presence of hypoxia** (synergistic effect), but alone it produces a modest response. - When both options are present, **hypoxia is the correct answer** as the primary stimulus. *Hypocapnia* - **Hypocapnia** (low CO2 levels) **inhibits peripheral chemoreceptor activity** and reduces their sensitivity to other stimuli. - This acts as a respiratory depressant rather than a stimulant. - Note: **Hypercapnia** (elevated CO2) does stimulate peripheral chemoreceptors, but hypocapnia does not. *Low perfusion pressure* - **Low perfusion pressure** (hypotension) does not directly stimulate peripheral chemoreceptors. - Chemoreceptors respond to chemical stimuli (O2, CO2, pH), not mechanical pressure changes. - While severe hypotension can lead to tissue hypoxia, it is the resulting **hypoxia** that stimulates the chemoreceptors, not the pressure change itself.

Q: The transport of CO2 in the blood is primarily influenced by which of the following factors?

Conversion to bicarbonate ions by carbonic anhydrase. ***Conversion to bicarbonate ions by carbonic anhydrase*** - This is the **primary mechanism** for CO2 transport, accounting for approximately **70%** of total CO2 transport in blood. - Inside red blood cells, CO2 combines with water to form carbonic acid (H2CO3), catalyzed by the enzyme **carbonic anhydrase**. - Carbonic acid **immediately dissociates** into hydrogen ions (H+) and **bicarbonate ions (HCO3-)**. - Bicarbonate ions then diffuse into plasma in exchange for chloride ions (chloride shift), making this the most quantitatively significant transport mechanism. - **Carbonic anhydrase** is the key enzyme that influences this process by accelerating the reaction by approximately **5000-fold**. *Binding to hemoglobin as carbaminohemoglobin* - Approximately **20-23%** of CO2 is transported by directly binding to amino groups on hemoglobin to form **carbaminohemoglobin**. - This is significant but less than bicarbonate transport. - Deoxygenated hemoglobin binds CO2 more readily than oxygenated hemoglobin (Haldane effect). *Transport as carbonic acid in red blood cells* - This is **not correct** because carbonic acid (H2CO3) is only a **transient intermediate** that exists momentarily. - It immediately dissociates into H+ and HCO3-, so CO2 is not actually transported "as carbonic acid" but rather as **bicarbonate ions**. - The carbonic acid step is part of the mechanism, but bicarbonate is the actual transport form. *Direct dissolution in blood plasma* - Only about **7-10%** of CO2 is transported dissolved directly in plasma. - CO2 has limited solubility in plasma, making this the least significant mechanism. - This dissolved CO2 contributes to the partial pressure of CO2 (PCO2) in blood.

Q: Which of the following lung volumes remains unchanged during pregnancy?

Total Lung Capacity. ***Total Lung Capacity*** - The **total lung capacity (TLC)** represents the total volume of air the lungs can hold after a maximum inspiration and remains largely **unchanged** during pregnancy due to opposing physiological shifts. - While other lung volumes are affected by mechanical compression from the gravid uterus and hormonal changes, the **increase in inspiratory capacity** often balances the **decrease in functional residual capacity**, leading to a relatively stable TLC. *Functional Residual Capacity* - **Functional Residual Capacity (FRC)**, the volume of air remaining in the lungs after a normal expiration, **decreases significantly** during pregnancy due to the upward displacement of the diaphragm by the enlarging uterus. - This **reduction in FRC** makes pregnant individuals more susceptible to hypoxemia during periods of apnea or hypoventilation. *Inspiratory Capacity* - **Inspiratory Capacity (IC)**, the maximum volume of air that can be inhaled from the end-expiratory position, typically **increases during pregnancy**. - This increase is primarily due to a **higher tidal volume** and an enhanced ability to expand the chest wall. *Tidal Volume* - **Tidal Volume (TV)**, the amount of air inhaled or exhaled during normal breathing, **increases progressively** throughout pregnancy. - This increase is driven by **progesterone-mediated stimulation** of the respiratory center, leading to increased minute ventilation despite a relatively constant respiratory rate.

Q: Which of the following statements about the Hering-Breuer inflation reflex is false?

Protects against underinflation of the lungs.. ***Protects against underinflation of the lungs.*** - The **Hering-Breuer inflation reflex** is activated by **stretch receptors** in the lungs during excessive inspiration, preventing overinflation. - Its primary role is to protect against **overinflation**, not underinflation, by terminating inspiration prematurely when lungs are excessively inflated. *Is mediated by vagal afferents from pulmonary stretch receptors.* - This statement is **true** and correctly describes the neural pathway of the reflex. - **Pulmonary stretch receptors** detect lung inflation and send signals via **vagal afferents** (vagus nerve) to the respiratory centers in the medulla oblongata. *Involves stimulation of the inspiratory center.* - The Hering-Breuer reflex is a **protective reflex** that is *inhibitory* to the inspiratory center, not stimulatory. - It works by sending signals via the **vagus nerve** to *inhibit* inspiratory neurons in the **medulla oblongata** when stretch receptors in the lungs are activated during excessive inflation. *Inhibits further inspiration when lung inflation is excessive.* - This statement is **true** and describes the key function of the reflex, which is to prevent overexpansion of the lungs. - When lung volume increases significantly, **stretch receptors** are activated, sending signals that *inhibit* the inspiratory effort and promote expiration.

Q: In inspiration, the intrapleural pressure becomes:

More negative. ***More negative*** - During inspiration, the **diaphragm contracts** and moves downwards, and the **external intercostal muscles contract**, pulling the rib cage upwards and outwards. - This increases the volume of the thoracic cavity, causing the intrapleural pressure to become **more negative** (i.e., further below atmospheric pressure), which in turn pulls the lungs outward and causes air to flow in. *More positive* - An increase in intrapleural pressure beyond atmospheric pressure (**positive**) would lead to lung collapse or prevent air from entering the lungs. - Positive intrapleural pressure is typically observed during **forced expiration** or in pathological conditions like **pneumothorax**. *Same as expiratory level* - Intrapleural pressure **changes dynamically** throughout the respiratory cycle, becoming more negative during inspiration and less negative (closer to atmospheric pressure) during expiration. - Maintaining the same pressure level would imply no change in lung volume, which is inconsistent with the process of breathing. *Initially positive then negative* - The intrapleural pressure is always **subatmospheric** (negative) during normal breathing due to the elastic recoil of the lungs pulling inward and the chest wall pulling outward. - A transient positive pressure followed by negative pressure is not characteristic of normal inspiration.

Q: What does the plateau of oxygen-hemoglobin dissociation curve signify?

Hb is almost fully saturated with O₂. ***Hb is almost fully saturated with O₂*** - The **plateau phase** of the oxygen-hemoglobin dissociation curve represents the region where hemoglobin is nearly fully saturated with oxygen (typically **97-100% saturation**). - At this stage, nearly all available **hemoglobin binding sites** are occupied by oxygen molecules, even with only moderate increases in partial pressure of oxygen (PO₂). - This plateau occurs at **PO₂ above 60-70 mmHg**, providing a **safety margin** for oxygen loading in the lungs despite variations in alveolar PO₂. - The flat plateau ensures stable oxygen saturation even with minor fluctuations in inspired oxygen or at moderate altitudes. *No oxygen is available for binding to Hb* - This is incorrect as the plateau region occurs at **high partial pressures of oxygen**, meaning plenty of oxygen is available in the environment. - If no oxygen were available, hemoglobin saturation would be minimal, corresponding to the **lowest point on the curve**, not the plateau. *All oxygen is released to tissues* - The plateau shows **high oxygen saturation**, meaning oxygen is tightly bound to hemoglobin, not released. - Oxygen release to tissues primarily occurs in the **steep portion of the curve** at lower PO₂ values (20-40 mmHg), typical of metabolically active tissues. - The steep part allows for **efficient oxygen unloading** in response to small changes in tissue PO₂. *None of the above* - This is incorrect because the first option accurately describes the physiological significance of the plateau phase as representing near-maximal hemoglobin saturation.

Q: All are accessory muscles of inspiration except

Latissimus dorsi. ***Latissimus dorsi*** - The **latissimus dorsi** is primarily an **accessory muscle of forced EXPIRATION**, not inspiration. - When it contracts with the arms fixed, it **depresses the lower ribs** and **compresses the thorax**, aiding in forceful exhalation. - Its primary actions involve **extension, adduction, and internal rotation of the humerus**, and it has **no role in elevating ribs or expanding the thoracic cavity** during inspiration. *Serratus anterior* - The **serratus anterior** muscle helps in **protracting the scapula** and also plays a role in respiration by **elevating the ribs** when the shoulder girdle is fixed, thus aiding inspiration. - Its action helps to increase the **anteroposterior and transverse diameters of the thoracic cavity**. *Serratus posterior superior* - The **serratus posterior superior** muscles are directly attached to the ribs (2-5) and are considered **accessory muscles of inspiration**. - They **elevate the upper ribs**, thereby increasing the volume of the thoracic cavity during inhalation. *Scaleni* - The **scalene muscles** (anterior, middle, and posterior) elevate the first two ribs, significantly contributing to the **expansion of the thoracic cage** during inspiration. - They are considered important **accessory muscles of inspiration**, especially during forceful breathing.

Question 1

Damage to the pneumotaxic center will cause?

Accepted Answer

Apneusis

Answer

Apnea

Answer

Faster breathing with lesser tidal volume

Answer

Slower breathing with greater tidal volume

Question 2

Which of the following factors increases the resistance of the airways?

Accepted Answer

Inhaling cigarette smoke

Answer

Increasing lung volume

Answer

Increased sympathetic stimulation

Answer

Going to high altitude

Question 3

Which of the following does NOT cause hyperventilation?

Accepted Answer

CO poisoning

Answer

Decreased pH in CSF

Answer

Increased adrenergic levels

Answer

Decreased plasma HCO3

Question 4

Which of the following stimulates peripheral chemoreceptors?

Accepted Answer

Hypoxia

Answer

Acidosis

Answer

Low perfusion pressure

Answer

Hypocapnia

Question 5

The transport of CO2 in the blood is primarily influenced by which of the following factors?

Accepted Answer

Conversion to bicarbonate ions by carbonic anhydrase

Answer

Binding to hemoglobin as carbaminohemoglobin

Answer

Transport as carbonic acid in red blood cells

Answer

Direct dissolution in blood plasma

Question 6

Which of the following lung volumes remains unchanged during pregnancy?

Accepted Answer

Total Lung Capacity

Answer

Tidal Volume

Answer

Functional Residual Capacity

Answer

Inspiratory Capacity

Question 7

Which of the following statements about the Hering-Breuer inflation reflex is false?

Accepted Answer

Protects against underinflation of the lungs.

Answer

Is mediated by vagal afferents from pulmonary stretch receptors.

Answer

Involves stimulation of the inspiratory center.

Answer

Inhibits further inspiration when lung inflation is excessive.

Question 8

In inspiration, the intrapleural pressure becomes:

Accepted Answer

More negative

Answer

More positive

Answer

Same as expiratory level

Answer

Initially positive then negative

Question 9

What does the plateau of oxygen-hemoglobin dissociation curve signify?

Accepted Answer

Hb is almost fully saturated with O₂

Answer

All oxygen is released to tissues

Answer

No oxygen is available for binding to Hb

Answer

None of the above

Question 10

All are accessory muscles of inspiration except

Accepted Answer

Latissimus dorsi

Answer

Serratus anterior

Answer

Serratus posterior superior

Answer

Scaleni

Respiratory System — MCQs

Respiratory System — MCQs

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