A 3-year-old boy dies in an automobile accident. At autopsy the right lung is markedly shrunken. Dissection shows that the right main stem bronchus ends blindly in nondescript tissue composed of rudimentary ducts and connective tissue. This finding represents an example of which of the following errors of morphogenesis?

**Core Concept:** Morphogenesis is the process by which an organism develops its structure and organ systems. In humans, this includes the formation of organs and their proper connections, such as the development of the respiratory system and its components. Errors in morphogenesis can lead to abnormalities in organ development and function.

**Why the Correct Answer is Right:** The correct answer "D" refers to the agenesis of the lung. Agenesis is the complete absence of a normally formed organ or structure due to developmental abnormalities. In this case, the right lung is not formed, and the main stem bronchus ends blindly in non-descript tissue. This is an example of a developmental defect, which results in the absence of a functional lung.

**Why Each Wrong Option is Incorrect:**

A. **Aplasia:** Aplasia is the partial absence of an organ or structure. In contrast to agenesis, the affected part is present but underdeveloped. In this question, aplasia would not explain the complete absence of a lung.

B. **Dysplasia:** Dysplasia refers to abnormal development or growth of an organ or structure. It is not the same as agenesis, as dysplastic lungs are present but abnormally formed.

C. **Torsion:** Torsion is a rotation or twisting of an organ or structure, which is not relevant to the described situation of a missing lung.

E. **Hypertrophy:** Hypertrophy is an increase in size due to hyperplasia or hypertrophy, which is the opposite of the described situation of a missing lung.

**Clinical Pearl:** This clinical scenario illustrates the importance of understanding developmental disorders and their effects on organ systems. Agenesis of the lung is crucial to know for students studying developmental biology, embryology, and clinical medicine, as it can lead to severe respiratory compromise and requires lifelong respiratory support for affected individuals.

✓ Correct Answer: A. Aplasia