Biological Systems MCAT Practice Exam 2025 - Free Biological Systems Practice Questions and Study Guide.

The correct answer highlights the role of peripheral chemoreceptors, which are specialized sensory receptors primarily located in the carotid and aortic bodies. These receptors play a crucial role in monitoring the composition of blood, specifically focusing on the levels of pH, partial pressure of carbon dioxide (P_CO2), and partial pressure of oxygen (P_O2).

When changes in the levels of these gases occur, peripheral chemoreceptors are activated. For instance, an increase in carbon dioxide levels or a decrease in oxygen levels will stimulate these receptors, leading to a signal that can trigger respiratory changes through the central nervous system, enabling the body to effectively maintain homeostasis.

Central chemoreceptors are important as well, but they primarily respond to changes in carbon dioxide levels and pH in the cerebrospinal fluid rather than directly in the blood. Stretch receptors are associated with the mechanics of respiration and lung inflation, and irritant receptors are involved in reflex responses to harmful substances rather than monitoring blood gas levels. Therefore, peripheral chemoreceptors are the primary sensors for blood pH and gas concentrations.