NEET-PG 2015 Practice Questions

Q: Vitamin D absorption is decreased by ?

Fat malabsorption. ***Fat malabsorption*** - **Vitamin D** is a **fat-soluble vitamin**, meaning it requires dietary fat for proper absorption in the small intestine. - Conditions causing **fat malabsorption**, such as **cystic fibrosis**, **celiac disease**, or **pancreatic insufficiency**, significantly reduce the uptake of vitamin D. *Proteins* - **Proteins** do not directly decrease vitamin D absorption; in fact, some dietary proteins can enhance vitamin D binding and transport in the bloodstream. - Their primary role is in structural and enzymatic functions, not impeding fat-soluble vitamin uptake. *Acid* - **Gastric acid** is important for the absorption of some nutrients, but it generally does not directly hinder the absorption of **fat-soluble vitamins** like vitamin D. - Conditions like **achlorhydria** primarily affect the absorption of minerals and vitamin B12, rather than vitamin D. *Lactose* - **Lactose** is a sugar found in milk, and its malabsorption (lactose intolerance) primarily causes gastrointestinal symptoms like bloating and diarrhea. - It does not directly interfere with the absorption of **fat-soluble vitamins**; rather, it affects carbohydrate digestion.

Q: Which of the following statements about lung compliance is false?

Decreased in emphysema. ***Decreased in emphysema*** - This statement is **false** because **emphysema** is characterized by the destruction of elastic fibers in the lung parenchyma, which paradoxically leads to an **increase** in lung compliance. - The loss of elastic recoil makes the lungs more distensible and easier to inflate, but also impairs their ability to passively exhale. *Total compliance is 0.2 L/cm H2O* - This value represents the **normal total lung compliance** in a healthy adult (0.17 to 0.25 L/cm H2O), including both lung and chest wall compliance. - Lung compliance alone is typically around 0.2 L/cm H2O for healthy lungs. *A measure of lung distensibility* - **Compliance** is intrinsically defined as a measure of how easily the lungs or chest wall can be stretched or distended. - High compliance means the lungs are easy to inflate, while low compliance means they are stiff and difficult to inflate. *Change in volume per unit change in pressure* - This is the explicit **formula and definition of compliance** (C = ΔV/ΔP). - It quantifies the change in lung volume in response to a given change in transpulmonary pressure.

Q: In patients with emphysematous bullae, total lung volume is best determined by?

Plethysmography. ***Plethysmography*** - This method accurately measures **total lung capacity (TLC)**, functional residual capacity (FRC), and residual volume (RV) by determining the **volume of gas in the thorax**. - It is particularly useful in conditions like **emphysema** with air trapping and bullae, as it accounts for **non-communicating air spaces** that other methods miss. *Spirometry* - Spirometry measures volumes of air that can be **exhaled or inhaled forcibly**, such as FVC and FEV1. - It cannot measure residual volume (RV) or total lung capacity (TLC) directly, especially in cases of **air trapping** where trapped air cannot be exhaled. *Helium dilution method* - The helium dilution method measures **communicating lung volumes**, like functional residual capacity (FRC), by assessing the dilution of a known concentration of helium after rebreathing. - In conditions with **emphysematous bullae** and air trapping, it **underestimates total lung volume** because it cannot measure air in non-communicating or poorly communicating spaces. *Any of the above* - Only plethysmography can accurately measure total lung volume in the presence of **emphysematous bullae** due to its ability to measure both communicating and non-communicating air spaces. - Spirometry and helium dilution methods would provide **inaccurate or incomplete measurements** in this clinical scenario.

Q: Vital capacity is measured by:

Spirometer. ***Spirometer*** - A **spirometer** is a device used to measure lung volumes and capacities, including **vital capacity**. - It measures the volume of air inspired and expired by evaluating mechanical changes in the volume of air in the lungs. *Plethysmography* - **Plethysmography** is primarily used to measure **residual volume** and **total lung capacity**, not vital capacity directly. - This method measures changes in body volume to infer changes in lung volume. *Gas-dilution method* - The **gas-dilution method**, typically using helium, is used to measure the **functional residual capacity (FRC)** and subsequently calculate residual volume and total lung capacity. - It involves rebreathing a known concentration of gas to determine the volume of gas already in the lungs. *Nitrogen washout technique* - The **nitrogen washout technique** is also used to measure **functional residual capacity (FRC)** and detect uneven ventilation. - It involves breathing 100% oxygen to wash out all nitrogen from the lungs, allowing for calculation of lung volumes.

Q: Isocapnic buffering is?

Normal pCO2 with increased CO2. ***Normal pCO2 with increased CO2*** - Isocapnic buffering refers to the process where the body buffers an **increase in lactic acid** or other metabolic acids without a significant change (maintaining it within a normal range) in **arterial partial pressure of carbon dioxide (pCO2)**. - This is achieved by an increase in **ventilation** stimulated by the acid, which expels more CO2 to compensate for the additional CO2 produced from the buffering reaction, thereby keeping pCO2 stable. *Increased pCO2 with increased CO2* - This scenario would indicate **hypoventilation** or a failure of the respiratory compensation mechanism to maintain pCO2 within normal limits during an increased metabolic CO2 load. - **Increased pCO2** would signify a state of **respiratory acidosis** or inadequate respiratory compensation, not isocapnic buffering. *Increased pCO2 with decreased CO2* - This statement is inherently contradictory; it is not possible to have an **increased pCO2** simultaneously with **decreased CO2** in the context of buffering. - **pCO2** is a measure of the partial pressure of carbon dioxide, directly related to the amount of CO2 present and dissolved in the blood. *None of the options* - This option is incorrect because "Normal pCO2 with increased CO2" accurately describes the physiological phenomenon of **isocapnic buffering**.

Q: What is the partial pressure for oxygen in the inspired air?

158 mm Hg. ***158 mm Hg*** - The partial pressure of oxygen in inspired air (PIO2) is calculated by multiplying the **fraction of inspired oxygen (FiO2)** by the total atmospheric pressure. - At sea level, atmospheric pressure is approximately **760 mm Hg** and FiO2 is 21% (0.21), so 0.21 × 760 mm Hg = **159.6 mm Hg**, which rounds to 158 mm Hg. - This represents **dry atmospheric air** before it enters the respiratory tract. *116 mm Hg* - This value does not correspond to a standard physiological measurement in respiratory physiology. - It is lower than inspired air PO2 but higher than alveolar PO2, making it an intermediate value used as a distractor. - **Humidified tracheal air** has PO2 of approximately 150 mm Hg: (760-47) × 0.21 = 149.7 mm Hg, where 47 mm Hg is water vapor pressure. *0.3 mm Hg* - This value is extremely low and represents the approximate **partial pressure of oxygen in mixed venous blood**, not inspired air. - Such a low value in inspired air would indicate **severe hypoxia** incompatible with life. - This is used as an unrealistic distractor. *100 mm Hg* - This value represents the approximate **partial pressure of oxygen in alveolar air (PAO2) and arterial blood (PaO2)**. - It is lower than inspired air due to humidification, mixing with residual air, and continuous oxygen uptake by blood. - It does not represent the partial pressure of oxygen in the inspired atmospheric air.

Q: What is the normal transpulmonary pressure during quiet breathing?

+5 to +8 cm H2O. ***+5 to +8 cm H2O*** - Transpulmonary pressure (P_tp) is the **difference between alveolar pressure and pleural pressure** (P_alv - P_pl). - During quiet breathing at **functional residual capacity (FRC)**, alveolar pressure is **0 cm H2O** (atmospheric) while pleural pressure is approximately **-5 cm H2O**, giving P_tp = **+5 cm H2O**. - At end-inspiration during quiet breathing, pleural pressure becomes more negative (**-8 cm H2O**) while alveolar pressure remains near atmospheric, resulting in P_tp ≈ **+8 cm H2O**. - This positive transpulmonary pressure gradient is essential to **keep the lungs inflated** against elastic recoil and prevent **atelectasis**. *0 to +1 cm H2O* - This pressure is far too low to maintain lung inflation against elastic recoil forces. - Normal transpulmonary pressure must be several cm H2O positive to counterbalance the lung's tendency to collapse. - This value would result in **near-complete lung collapse**. *0 to -1 cm H2O* - A negative or zero transpulmonary pressure would mean pleural pressure equals or exceeds alveolar pressure. - This condition would cause **immediate lung collapse (pneumothorax)** as there would be no pressure gradient to keep the lungs expanded. *-8 to -5 cm H2O* - This range represents **pleural pressure**, not transpulmonary pressure. - Pleural pressure is indeed -5 to -8 cm H2O during quiet breathing, but transpulmonary pressure is calculated as the difference between alveolar and pleural pressures. - Confusing pleural pressure with transpulmonary pressure is a common error.

Q: Damage to pneumotaxic center along with vagus nerve causes which type of respiration?

Apneustic breathing. ***Apneustic breathing*** - Damage to the **pneumotaxic center** prevents the normal inhibition of inspiration, leading to **prolonged inspiratory gasps**. - **Vagal nerve damage** further removes the inhibitory feedback from the lungs, exacerbating the inspiratory "holds" characteristic of apneustic breathing. *Cheyne-Stokes breathing* - This pattern is characterized by a **crescendo-decrescendo pattern** of breathing, interspersed with periods of **apnea**. - It is often associated with conditions like **heart failure**, stroke, or severe neurological damage, not specifically the pneumotaxic center and vagus nerve. *Deep and slow breathing* - This pattern can be seen in conditions like **Kussmaul breathing** (due to metabolic acidosis) or as a compensatory mechanism. - It does not directly result from the combined damage of the **pneumotaxic center** and the **vagus nerve**. *Shallow and rapid breathing* - This pattern is commonly seen in restrictive lung diseases, anxiety, or pain, where tidal volume is decreased and respiratory rate increased. - It does not reflect the **prolonged inspiration** that would result from a compromised pneumotaxic center and vagal input.

Q: What is the total surface area of the respiratory membrane in a healthy adult human?

75 m2. ***75 m²*** - The **total surface area** of the respiratory membrane in a healthy adult human is approximately **70-80 m²**, with 75 m² being the most accurate estimate among the given options. - This large surface area is primarily attributed to the presence of approximately **300-500 million alveoli**, which are crucial for efficient gas exchange. - Modern measurements using **stereological techniques** have refined earlier estimates and established this range as the current standard. *100 m²* - This value represents an **older estimate** that has been revised downward with more accurate measurement techniques. - While historically cited in older textbooks, current physiological data supports a **smaller surface area** of approximately 70-80 m². *30 m²* - This value is significantly **underestimated** for the total respiratory membrane surface area. - Such a small surface area would result in highly **inefficient gas exchange**, leading to severe respiratory compromise and inability to meet metabolic demands. *50 m²* - While larger than 30 m², this is still an **underestimation** of the full respiratory membrane surface area. - It does not adequately account for the extensive and intricate branching of the **respiratory bronchioles** and the vast number of alveolar sacs.

Q: What is the Haldane Effect?

CO2 delivery by increased O2. ***CO2 delivery by increased O2*** - The **Haldane effect** describes how **oxygenation of hemoglobin** decreases its affinity for **carbon dioxide (CO2)**, leading to the release of CO2 from the blood. - This is crucial in the lungs, where high oxygen levels promote CO2 unloading for exhalation. *O2 delivery by increased CO2* - This describes the **Bohr effect**, where an increase in **carbon dioxide (CO2)** or acidity in the tissues causes hemoglobin to release **oxygen (O2)**. - The Haldane effect is the converse, relating oxygen binding to CO2 release, not the other way around. *CO2 delivery by increased CO2* - This statement is inherently circular and does not describe a physiological effect. - It confuses the mechanism with the substance being transported. *O2 delivery by increased CO* - **Carbon monoxide (CO)** has a much higher affinity for hemoglobin than oxygen, forming **carboxyhemoglobin** and impairing oxygen delivery. - This is related to **carbon monoxide poisoning**, not a physiological regulatory effect like the Haldane or Bohr effects.

Question 1

Vitamin D absorption is decreased by ?

Accepted Answer

Fat malabsorption

Answer

Proteins

Answer

Acid

Answer

Lactose

Question 2

Which of the following statements about lung compliance is false?

Accepted Answer

Decreased in emphysema

Answer

Total compliance is 0.2 L/cm H2O

Answer

A measure of lung distensibility

Answer

Change in volume per unit change in pressure

Question 3

In patients with emphysematous bullae, total lung volume is best determined by?

Accepted Answer

Plethysmography

Answer

Spirometry

Answer

Any of the above

Answer

Helium dilution method

Question 4

Vital capacity is measured by:

Accepted Answer

Spirometer

Answer

Plethysmography

Answer

Nitrogen washout technique

Answer

Gas-dilution method

Question 5

Isocapnic buffering is?

Accepted Answer

Normal pCO2 with increased CO2

Answer

None of the options

Answer

Increased pCO2 with increased CO2

Answer

Increased pCO2 with decreased CO2

Question 6

What is the partial pressure for oxygen in the inspired air?

Accepted Answer

158 mm Hg

Answer

116 mm Hg

Answer

0.3 mm Hg

Answer

100 mm Hg

Question 7

What is the normal transpulmonary pressure during quiet breathing?

Accepted Answer

+5 to +8 cm H2O

Answer

0 to + 1 cm H2O

Answer

0 to -1 cm H2O

Answer

- 8 to - 5 cm H2O

Question 8

Damage to pneumotaxic center along with vagus nerve causes which type of respiration?

Accepted Answer

Apneustic breathing

Answer

Cheyne-Stokes breathing

Answer

Deep and slow breathing

Answer

Shallow and rapid breathing

Question 9

What is the total surface area of the respiratory membrane in a healthy adult human?

Accepted Answer

75 m2

Answer

30 m2

Answer

50 m2

Answer

100 m2

Question 10

What is the Haldane Effect?

Accepted Answer

CO2 delivery by increased O2

Answer

O2 delivery by increased CO2

Answer

CO2 delivery by increased CO2

Answer

O2 delivery by increased CO

NEET-PG 2015

Biochemistry

Physiology