Which of the following instruments is specifically used to examine the respiratory tract?

The bronchoscope is specifically designed for examining the respiratory tract, which includes the trachea and bronchi. This instrument allows for direct visualization of the airways, enabling healthcare professionals to diagnose conditions such as infections, blockages, or tumors within the lungs. The bronchoscope can also be used for various procedures, such as obtaining biopsies or removing foreign bodies.

Other instruments mentioned serve distinctly different purposes. The colonoscope is used for examining the large intestine, the gastroscope is designed for viewing the stomach and upper part of the small intestine, and the proctoscope is intended for inspecting the rectum and lower part of the colon. Therefore, these instruments do not provide access or visualization of the respiratory tract, which is a vital distinction that makes the bronchoscope the appropriate choice.