A 17-year-old college-bound student receives a vaccine against an organism that causes meningitis. This is an example of:

Choice A Reason:

Hyperplasia refers to an increase in the number of cells in an organ or tissue, usually resulting in an increase in the size of the organ or tissue. This process is often a response to a stimulus and can be physiological or pathological. However, hyperplasia does not involve the replacement of one cell type with another, as seen in this case.

Choice B Reason:

Dysplasia is characterized by abnormal growth and development of cells within tissues or organs. It often indicates a precancerous condition and involves changes in cell size, shape, and organization. While dysplasia can occur in the respiratory tract, it does not describe the replacement of one type of epithelial cell with another.

Choice C Reason:

This is the correct answer. Metaplasia is the process by which one type of adult cell is replaced by another type of adult cell that is not typical for that tissue. In this case, the normal columnar ciliated cells in the bronchial airway have been replaced by stratified squamous epithelial cells, a common adaptation in response to chronic irritation from smoking.

Choice D Reason:

Hypertrophy refers to an increase in the size of cells, leading to an increase in the size of the affected organ or tissue. This process does not involve a change in cell type, making it an incorrect choice for this scenario.

Choice A: Alkalosis

Alkalosis refers to a condition where the blood pH is higher than the normal range (above 7.45). In this case, the pH is 7.25, which indicates an acidic environment rather than an alkaline one. Therefore, alkalosis is not the correct answer.

Choice B: Respiratory

Respiratory acidosis or alkalosis is determined by the levels of PaCO2. In respiratory acidosis, PaCO2 is elevated, while in respiratory alkalosis, PaCO2 is decreased. Here, the PaCO2 is 20 mm Hg, which is below the normal range, indicating a respiratory component. However, the primary issue is not respiratory because the HCO3- is also significantly low, pointing towards a metabolic cause.

Choice C: Metabolic

Metabolic acidosis is characterized by a low pH and a low HCO3- level. In this case, the pH is 7.25, and the HCO3- is 10 mEq/L, both of which are below the normal ranges. This indicates that the primary acid-base imbalance is metabolic acidosis.

Choice D: Acidosis

Acidosis refers to a condition where the blood pH is lower than the normal range (below 7.35). The given pH of 7.25 confirms that the patient is experiencing acidosis. However, this choice alone does not specify whether it is metabolic or respiratory acidosis.

Choice E: With Compensation (Being Compensated)

Compensation refers to the body’s attempt to return the pH to normal by adjusting the levels of PaCO2 or HCO3-. In this case, the low PaCO2 suggests that there is a respiratory compensation for the metabolic acidosis. However, the primary imbalance remains metabolic acidosis.