How do carotid bodies respond when oxygen levels in arterial blood fall?

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A pine grosbeak with pink and gray plumage perches on a branch, eating red berries among autumn foliage. — Chemoreception Animals, such as this pine grosbeak, use chemoreception to respond to chemicals that can be tasted and smelled in their environments. Many of these chemicals affect behaviors such as food preference and defense.

When oxygen levels in arterial blood fall, a condition known as hypoxia, the carotid bodies act as primary sensors to initiate a physiological response.1

These small organs, located at the bifurcation of the carotid arteries, respond specifically to the partial pressure of oxygen in the blood rather than the total oxygen content. As the partial pressure of oxygen decreases, the sensory nerve fibers associated with the carotid body increase their firing rate in a hyperbolic fashion.1

Microscopically, this process involves type I cells, which contain vesicles filled with neuroactive substances such as acetylcholine and catecholamines. It is believed that hypoxia triggers the release of these substances from type I cells, which then stimulate the sensory nerves. These signals travel via the carotid sinus nerve to the medullary respiratory neurons in the brain, allowing the body to adjust its ventilation in response to the detected oxygen deficit.1