The approximate amount of air left in the lungs after maximal forced expiration in a normal woman is
**Core Concept**
The residual volume (RV) is the amount of air remaining in the lungs after a maximal forced expiration. It is an essential component of lung function and is influenced by the elastic recoil of the lungs, the tone of the airway smooth muscles, and the pressure of the abdominal contents on the diaphragm.
**Why the Correct Answer is Right**
The residual volume is approximately 1.2 liters in a normal adult woman. This is because the diaphragm and intercostal muscles relax after a maximal forced expiration, allowing the lungs to recoil and return to their resting volume. The airway smooth muscles also relax, reducing airway resistance and allowing the lungs to deflate further. The residual volume is an important measure of lung function, as it reflects the ability of the lungs to deflate and empty.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the residual volume is not typically measured in milliliters. While milliliters are a common unit of measurement for blood volumes, lung volumes are typically expressed in liters.
* **Option B:** This option is incorrect because the residual volume is not typically measured in deciliters. Deciliters are a unit of measurement used for small volumes, such as medication dosages, but are not commonly used for lung volumes.
* **Option C:** This option is incorrect because the residual volume is not typically measured in fractions of a liter. While fractions of a liter may be used for small volumes, the residual volume is typically expressed as a whole number of liters.
**Clinical Pearl / High-Yield Fact**
The residual volume is an important measure of lung function, as it reflects the ability of the lungs to deflate and empty. A normal residual volume is essential for maintaining adequate oxygenation and carbon dioxide removal.
**Correct Answer: C. 1.2 L**