In restrictive lung diseases like fibrosis, which of the following is typically decreased the most?

 # In restrictive lung diseases like fibrosis, which of the following is typically decreased the most?

 A. Tidal Volume (TV)

B. Vital Capacity (VC)

C. Forced Expiratory Volume in 1 second (FEV1)

D. Residual Volume (RV)

The correct answer is B. Vital Capacity (VC).

In restrictive lung diseases, such as pulmonary fibrosis, the lungs become stiff and less compliant, making it difficult to fully expand them during inspiration. This primarily results in a significant reduction in Vital Capacity (VC), which is the maximum amount of air a person can exhale after a maximum inhalation. VC includes tidal volume, inspiratory reserve volume, and expiratory reserve volume, and it is typically the most affected parameter because the restricted lung expansion limits the total volume of air the lungs can hold.

• A. Tidal Volume (TV): This is the volume of air moved during normal, quiet breathing and may be reduced in restrictive lung diseases, but the reduction is less pronounced than VC.
• C. Forced Expiratory Volume in 1 second (FEV1): FEV1 is reduced in restrictive lung diseases, but the reduction is proportional to the decrease in VC, and the FEV1/FVC ratio is typically normal or increased, unlike in obstructive diseases.
• D. Residual Volume (RV): RV, the volume of air remaining in the lungs after maximal exhalation, may be normal or slightly reduced but is not the most affected parameter in restrictive lung diseases.

The majority of carbon dioxide is transported in the blood as:

 # The majority of carbon dioxide is transported in the blood as:

A. Carbaminohemoglobin

B. Dissolved CO2 in plasma

C. Bicarbonate ions (HCO3−)

 D. Carbonic acid (H2CO3​)

The correct answer is C. Bicarbonate ions (HCO3−).

The majority of carbon dioxide (CO₂) in the blood, approximately 70–80%, is transported as bicarbonate ions (HCO3−). CO₂ produced in tissues diffuses into the blood, where it reacts with water in red blood cells, catalyzed by the enzyme carbonic anhydrase, to form carbonic acid (H2CO3). This quickly dissociates into bicarbonate ions (HCO3−) and hydrogen ions (H+). The bicarbonate ions are then transported in the plasma to the lungs, where they are converted back to CO₂ for exhalation.

• A. Carbaminohemoglobin: Accounts for about 10–20% of CO₂ transport, where CO₂ binds to hemoglobin.
• B. Dissolved CO2 in plasma: Only about 5–10% of CO₂ is transported as dissolved gas in plasma.
• D. Carbonic acid (H2CO3): Exists briefly as an intermediate but is not a major transport form due to its rapid dissociation.

What is the primary muscle of quiet inspiration?

 # What is the primary muscle of quiet inspiration?

 A. Internal intercostals

 B. Diaphragm

 C. Abdominal muscles

D. External intercostals

The correct answer is B. Diaphragm.

The diaphragm is the primary muscle responsible for quiet inspiration (normal, resting breathing). During quiet inspiration, the diaphragm contracts, flattens, and moves downward, increasing the volume of the thoracic cavity and creating negative pressure that draws air into the lungs. The external intercostals (D) assist in inspiration by elevating the ribs, but they play a secondary role. The internal intercostals (A) are primarily involved in forced expiration, and the abdominal muscles (C) aid in forced expiration or active breathing, not quiet inspiration.