Example of direct chemoreceptors are:
**Core Concept**
The question is testing the concept of chemoreceptors, which are specialized sensory receptors responsible for detecting changes in the chemical composition of the blood, particularly in the regulation of respiration. Direct chemoreceptors are a type of chemoreceptor that directly senses the changes in the chemical environment and responds accordingly.
**Why the Correct Answer is Right**
The correct answer is the carotid body. The carotid body is a pair of small organs located at the bifurcation of the common carotid artery, and it contains specialized glomus cells that are sensitive to changes in the levels of oxygen, carbon dioxide, and pH in the blood. When the levels of these chemicals change, the glomus cells depolarize and send signals to the brainstem, which responds by adjusting the rate and depth of breathing accordingly. The carotid body is an example of a direct chemoreceptor because it directly senses the changes in the chemical composition of the blood and responds without the need for a secondary messenger.
**Why Each Wrong Option is Incorrect**
**Option A:** Jugular bulb chemoreceptors are not a recognized type of chemoreceptor.
**Option B:** Cerebral cortex is not a chemoreceptor; it is the site of integration of sensory information from various sources.
**Option C:** Pulmonary chemoreceptors are located in the lungs and are involved in detecting changes in oxygen and carbon dioxide levels in the blood, but they are not considered direct chemoreceptors.
**Clinical Pearl / High-Yield Fact**
The carotid body is also sensitive to changes in blood pressure and can detect the presence of certain gases, such as hydrogen sulfide and carbon monoxide, which can be toxic to the body.
**Correct Answer:** C. Pulmonary chemoreceptors are located in the lungs and are involved in detecting changes in oxygen and carbon dioxide levels in the blood, but they are not considered direct chemoreceptors.