carotid body

The carotid body is a tiny organ, about the size of a grain of rice, tucked into the fork where the carotid artery splits in the neck. Despite its small size it is one of the most blood-hungry tissues in the body, perfectly placed to taste the arterial blood heading to the brain.

It is the most important peripheral chemoreceptor for breathing. Specialized glomus cells inside it detect a fall in arterial oxygen, a rise in carbon dioxide, and increasing acidity, then signal the brainstem through the glossopharyngeal nerve to increase ventilation. Its rich blood flow lets it report on blood composition almost in real time.

Beyond minute-to-minute control, the carotid body adapts at high altitude to support acclimatization, and it can become overactive in some heart and lung diseases, contributing to breathlessness. Rarely it gives rise to a tumor called a carotid body paraganglioma, presenting as a slow-growing neck mass.