Respiratory System Practice Questions

Q: The normal value of P50 on the oxyhaemoglobin dissociation curve in an adult is:

3.6 kPa. **Explanation:** The **$P_{50}$** is a standard physiological index used to describe the affinity of hemoglobin for oxygen. It represents the partial pressure of oxygen ($PO_2$) at which hemoglobin is **50% saturated**. **1. Why 3.6 kPa is correct:** In a healthy adult, the normal $P_{50}$ value is approximately **26.6 mmHg**. To convert this value into kilopascals (kPa), we use the conversion factor: $1\text{ kPa} \approx 7.5\text{ mmHg}$. Calculation: $26.6 / 7.5 \approx \mathbf{3.6\text{ kPa}}$. This value indicates a normal affinity of hemoglobin for oxygen under standard physiological conditions (pH 7.4, Temp 37°C, $PCO_2$ 40 mmHg). **2. Analysis of Incorrect Options:** * **1.8 kPa (~13.5 mmHg):** This represents an abnormally high affinity (Left shift). This is seen in fetal hemoglobin (HbF) or carbon monoxide poisoning. * **2.7 kPa (~20 mmHg):** This is lower than the adult average, often seen in conditions that shift the curve to the left (e.g., alkalosis, hypothermia). * **4.5 kPa (~34 mmHg):** This represents a decreased affinity (Right shift), seen in conditions like high altitude, fever, or increased 2,3-BPG. **3. High-Yield Clinical Pearls for NEET-PG:** * **Right Shift (Increased $P_{50}$):** Occurs when oxygen affinity decreases, facilitating "unloading" to tissues. Causes: **CADET**, face Right! (**C**O2 increase, **A**cidosis/H+, **D**PG increase, **E**xercise, **T**emperature increase). * **Left Shift (Decreased $P_{50}$):** Occurs when oxygen affinity increases, meaning Hb "clings" to oxygen. Causes: HbF, CO poisoning, Methemoglobinemia, and the opposite of the CADET factors. * **HbF vs. HbA:** Fetal hemoglobin has a lower $P_{50}$ (approx. 19–20 mmHg) than adult hemoglobin, allowing the fetus to extract oxygen from maternal blood.

Q: Which of the following is NOT a cause of a rightward shift of the oxyhemoglobin dissociation curve?

Decreased CO2. The oxyhemoglobin dissociation curve (ODC) represents the relationship between the partial pressure of oxygen ($PO_2$) and the percentage saturation of hemoglobin. A **rightward shift** indicates a decreased affinity of hemoglobin for oxygen, facilitating oxygen unloading to the tissues. ### Why "Decreased $CO_2$" is the Correct Answer A rightward shift is caused by factors that signal high metabolic activity in tissues. **Decreased $CO_2$** (hypocapnia) actually increases hemoglobin's affinity for oxygen, causing a **leftward shift**. This prevents oxygen from being released easily. Conversely, increased $CO_2$ causes a rightward shift (the **Bohr Effect**). ### Analysis of Incorrect Options (Causes of Rightward Shift) * **Increased Hydrogen Ions (Decreased pH):** An acidic environment (acidosis) reduces hemoglobin's affinity for $O_2$, shifting the curve to the right to provide more oxygen to metabolically active (acidic) tissues. * **Increased Temperature:** Hyperthermia (e.g., during exercise or fever) weakens the bond between hemoglobin and oxygen, shifting the curve to the right. * **Increased 2,3-BPG:** This byproduct of glycolysis binds to the beta chains of deoxyhemoglobin, stabilizing the "T" (Tense) state and promoting oxygen release (Right shift). ### NEET-PG High-Yield Pearls * **Mnemonic for Right Shift:** "**CADET**, face Right!" (**C**-$CO_2$ increase, **A**-Acid/H+ increase, **D**-2,3-DPG/BPG increase, **E**-Exercise, **T**-Temperature increase). * **Fetal Hemoglobin (HbF):** Causes a **Left shift** because it does not bind 2,3-BPG effectively, allowing the fetus to "pull" oxygen from maternal blood. * **P50 Value:** The $PO_2$ at which 50% of hemoglobin is saturated. A right shift **increases** the P50 (normal is ~26.7 mmHg).

Q: A pulmonary disorder causes the alveoli to break down and coalesce into large air spaces. The lungs also lose elasticity and compliance is increased. A person who suffers from this disease will have what characteristic?

Increased dead air space. The clinical scenario describes **Emphysema**, a type of Chronic Obstructive Pulmonary Disease (COPD). In emphysema, the destruction of alveolar septa leads to the formation of large, permanent air spaces (bullae), reducing the surface area for gas exchange and causing a loss of elastic recoil. ### Why Option A is Correct **Increased Dead Air Space:** The breakdown and coalescence of alveoli create large air sacs with a significantly reduced capillary interface. While these areas are still ventilated, they are poorly perfused (or the surface area is insufficient for exchange). This increases **physiological dead space** (wasted ventilation). Additionally, the loss of elastic recoil leads to air trapping and hyperinflation, further increasing the volume of air that does not participate in gas exchange. ### Why Other Options are Incorrect * **B. Increased Vital Capacity:** In emphysema, the Vital Capacity (VC) actually **decreases**. This is because air trapping increases the Residual Volume (RV), which "encroaches" upon the VC. * **C. Decreased PCO2:** Due to the loss of exchange surface and airway obstruction, patients typically experience hypoventilation and ventilation-perfusion (V/Q) mismatch, leading to **increased PCO2** (hypercapnia), not a decrease. * **D. Decreased Anteroposterior (AP) Diameter:** Loss of elasticity leads to hyperinflation of the lungs. To accommodate this, the chest wall expands, leading to an **increased AP diameter**, classically known as a **"Barrel Chest."** ### NEET-PG High-Yield Pearls * **Compliance:** Emphysema is the classic example of **increased lung compliance** due to the loss of elastic fibers (elastin). * **Flow-Volume Loop:** Shows a characteristic **"scooped-out"** appearance during expiration. * **Diffusion Capacity:** Emphysema is one of the few obstructive diseases where the **DLCO (Diffusion Capacity of Carbon Monoxide) is decreased** due to alveolar wall destruction.

Q: What diagnosis is suggested by these spirography findings?

Intrathoracic localized obstruction. ### Explanation The diagnosis of **Intrathoracic localized (variable) obstruction** is based on the characteristic morphology of the Flow-Volume loop. **1. Why the Correct Answer is Right:** In **variable intrathoracic obstructions** (e.g., tracheomalacia or a localized tumor in the lower trachea), the obstruction is influenced by changes in pleural pressure. During **expiration**, the positive intrapleural pressure compresses the airway, worsening the obstruction and resulting in a **flattening or "plateau" of the expiratory limb**. During inspiration, the negative pleural pressure helps pull the airway open, leaving the inspiratory limb relatively normal. **2. Why the Incorrect Options are Wrong:** * **Fixed inspiratory/expiratory obstruction:** This occurs in conditions like tracheal stenosis or goiter. It results in **flattening of both** the inspiratory and expiratory limbs (the loop looks like a "box"). * **Pneumothorax:** This is an acute clinical emergency. While it causes a restrictive pattern, it is not typically diagnosed via routine spirography. * **Restrictive lung disease:** Characterized by a "miniature" version of a normal loop. Both volumes (FVC) and flow rates are reduced, but the **shape remains preserved** (tall and narrow) without flattening of the limbs. **3. High-Yield Clinical Pearls for NEET-PG:** * **Extrathoracic Variable Obstruction:** (e.g., Vocal cord palsy) Flattening occurs during **Inspiration** (atmospheric pressure collapses the airway). * **Intrathoracic Variable Obstruction:** Flattening occurs during **Expiration**. * **Fixed Obstruction:** Flattening occurs in **Both** phases. * **Scooped-out appearance:** Classic for **Obstructive** diseases like Asthma and COPD (due to reduced effort-independent flow).

Q: All of the following factors increase the level of respiratory neuron activity in the medulla, EXCEPT:

Rise in PO2. The respiratory center in the medulla is responsible for the rhythmic generation of breathing. Its activity is primarily regulated by chemical stimuli sensed by central and peripheral chemoreceptors. **Why "Rise in PO2" is the correct answer:** A **Rise in PO2 (Hyperoxia)** actually **decreases** respiratory drive. When arterial oxygen levels are high, the peripheral chemoreceptors (carotid and aortic bodies) decrease their firing rate to the medulla. This leads to a reduction in the activity of respiratory neurons. Therefore, it is the only factor among the options that does not increase medullary activity. **Explanation of incorrect options:** * **Rise in PCO2 (Hypercapnia):** This is the most potent stimulus for respiration. CO2 diffuses across the blood-brain barrier, forming H+ ions in the CSF that directly stimulate **central chemoreceptors**, significantly increasing medullary activity. * **Rise in H+ concentration (Acidosis):** Increased arterial H+ stimulates **peripheral chemoreceptors**. Although H+ does not cross the blood-brain barrier easily, the peripheral signal strongly increases medullary respiratory output to blow off CO2 (Kussmaul breathing). * **Drop in PO2 (Hypoxia):** A decrease in arterial PO2 (specifically below 60 mmHg) is sensed by peripheral chemoreceptors, which send excitatory signals via the glossopharyngeal and vagus nerves to the medulla to increase ventilation. **High-Yield NEET-PG Pearls:** * **Central Chemoreceptors:** Located in the ventral medulla; sensitive to **H+ changes in CSF** (driven by arterial CO2). They do NOT respond to hypoxia. * **Peripheral Chemoreceptors:** Located in carotid and aortic bodies; primarily sensitive to **low PO2**, high PCO2, and low pH. * **Breaking Point:** The urge to breathe during breath-holding is primarily due to the **rise in PCO2**, not the fall in PO2.

Q: What is the normal expiratory reserve volume of an adult?

1200 ml. **Explanation:** **Expiratory Reserve Volume (ERV)** is defined as the maximum volume of air that can be exhaled from the lungs by forceful expiration after the end of a normal tidal expiration. In a healthy adult male, the average value of ERV is approximately **1100 ml to 1200 ml**. **Analysis of Options:** * **Option C (1200 ml):** This is the correct physiological average for ERV. It represents the additional air available for expiration beyond the resting expiratory level. * **Option A (500 ml):** This represents the **Tidal Volume (TV)**, which is the volume of air inspired or expired during a single normal, quiet breath. * **Option B (3000 ml):** This corresponds to the **Inspiratory Reserve Volume (IRV)**, the maximum volume of air that can be inspired over and above the normal tidal volume. * **Option D (4500 ml):** This value represents the average **Vital Capacity (VC)**, which is the sum of IRV + TV + ERV. It is the maximum amount of air a person can expel from the lungs after a maximum inspiration. **High-Yield NEET-PG Clinical Pearls:** 1. **Functional Residual Capacity (FRC):** This is the sum of **ERV + Residual Volume (RV)**. It is the volume of air remaining in the lungs at the end of a normal expiration. 2. **Clinical Significance:** ERV is significantly reduced in **obstructive lung diseases** (due to air trapping) and **obesity**, where the chest wall compliance is decreased. 3. **Measurement:** Lung volumes like ERV and TV can be measured via simple **Spirometry**, whereas Residual Volume (RV), FRC, and Total Lung Capacity (TLC) require helium dilution or body plethysmography.

Q: Which of the following relaxes bronchial smooth muscles?

Vasoactive intestinal peptide. **Explanation:** The tone of bronchial smooth muscle is regulated by the autonomic nervous system and various local mediators. Bronchodilation is primarily mediated by the sympathetic nervous system (via $\beta_2$ receptors) and the **Non-Adrenergic Non-Cholinergic (NANC)** inhibitory system. **Why Vasoactive Intestinal Peptide (VIP) is Correct:** VIP is the primary neurotransmitter of the **inhibitory NANC system** in the airways. It is co-released with Nitric Oxide (NO) from parasympathetic postganglionic neurons. VIP acts on specific receptors to increase intracellular cAMP and decrease calcium levels, leading to the **relaxation of bronchial smooth muscle**. It is considered one of the most potent endogenous bronchodilators. **Analysis of Incorrect Options:** * **Cold Air:** Acts as a physical trigger that induces bronchoconstriction, often via a reflex arc or by causing mast cell degranulation. This is a classic trigger for Exercise-Induced Bronchospasm (EIB). * **Leukotrienes (LTC4, LTD4, LTE4):** These are potent bronchoconstrictors produced via the lipoxygenase pathway of arachidonic acid metabolism. They are significantly more potent than histamine in inducing airway narrowing in asthma. * **Acetylcholine (ACh):** This is the primary neurotransmitter of the parasympathetic nervous system. It acts on **M3 muscarinic receptors** in the airways to cause bronchoconstriction and increased mucus secretion. **NEET-PG High-Yield Pearls:** * **Mnemonic for Bronchoconstrictors:** "HALT" (Histamine, Acetylcholine, Leukotrienes, Thromboxane A2). * **NANC System:** The excitatory NANC system uses Substance P and Neurokinin A to cause constriction; the inhibitory NANC system uses **VIP and NO** to cause relaxation. * **Clinical Correlation:** Anticholinergics (e.g., Ipratropium bromide) work by blocking the bronchoconstrictor effect of Acetylcholine.

Question 1

The normal value of P50 on the oxyhaemoglobin dissociation curve in an adult is:

Accepted Answer

3.6 kPa

Answer

1.8 kPa

Answer

2.7 kPa

Answer

4.5 kPa

Question 2

Which of the following is NOT a cause of a rightward shift of the oxyhemoglobin dissociation curve?

Accepted Answer

Decreased CO2

Answer

Increased hydrogen ions

Answer

Increased temperature

Answer

Increased 2,3-bisphosphoglycerate (BPG)

Question 3

Cyanosis is not seen in which of the following conditions?

Accepted Answer

Carbon Monoxide (CO) poisoning

Answer

Congestive Heart Failure (CHF)

Answer

Chronic Obstructive Pulmonary Disease (COPD)

Answer

High altitude

Question 4

A pulmonary disorder causes the alveoli to break down and coalesce into large air spaces. The lungs also lose elasticity and compliance is increased. A person who suffers from this disease will have what characteristic?

Accepted Answer

Increased dead air space

Answer

Increased vital capacity

Answer

Decreased PCO2 in the blood

Answer

Decreased anteroposterior diameter

Question 5

What diagnosis is suggested by these spirography findings?

Accepted Answer

Intrathoracic localized obstruction

Answer

Fixed inspiratory obstruction

Answer

Pneumothorax

Answer

Restrictive lung disease

Question 6

All of the following factors increase the level of respiratory neuron activity in the medulla, EXCEPT:

Accepted Answer

Rise in PO2

Answer

Rise in the PCO2

Answer

Rise in H+ concentration of arterial blood

Answer

Drop in PO2

Question 7

What is the normal expiratory reserve volume of an adult?

Accepted Answer

1200 ml

Answer

500 ml

Answer

3000 ml

Answer

4500 ml

Question 8

Which of the following relaxes bronchial smooth muscles?

Accepted Answer

Vasoactive intestinal peptide

Answer

Cold air

Answer

Leukotriene

Answer

Acetylcholine

Question 9

Which of the following is true about the main respiratory control neurons?

Accepted Answer

They are located in the medulla oblongata.

Answer

The neurons are located in the pons.

Answer

They are primarily responsible for inspiratory muscle contraction.

Answer

They respond to changes in arterial oxygen levels.

Question 10

Residual lung volume is increased in which of the following conditions?

Accepted Answer

Emphysema

Answer

Obesity

Answer

Bacterial pneumonia

Answer

Idiopathic pulmonary fibrosis

Respiratory System — MCQs

Respiratory System — MCQs

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