Where is the carotid body located?
The carotid body is located at the base of the division of the common carotid artery into the external and internal carotid arteries. The division of the common carotid artery is at the level of the upper border of the thyroid cartilage (cartilago thyroidea), which corresponds approximately to the level of the fourth cervical vertebra (C4).
The glomus lies at the base of the carotid bifurcation (bifurcatio carotidis) — the site where the common carotid artery divides into the external (a. carotis externa) and internal (a. carotis interna) carotid arteries. Most often, it adheres to the posterior or medial surface of the artery and is connected to its wall by connective tissue.
Near the glomus, in the area of the bifurcation, is the carotid sinus (sinus caroticus) — an arterial dilation containing baroreceptors.
Structure and tissue origin
The carotid body is about the size of a grain of rice. Its length is 5–8 mm, width is 1.5–5 mm, and thickness reaches 1.5 mm. The tissue color varies from grayish-pink to yellowish-red.
Anatomically, the glomus belongs to the paraganglia (paraganglia) — remnants of the chromaffin (adrenal) system. This tissue is genetically related to the sympathetic ganglia of the autonomic nervous system. Chromaffin cells got their name due to their affinity for chromium salts: after appropriate staining, they turn yellow or dark brown. In their function, paraganglion cells resemble the adrenal medulla.
Innervation and central connections
The carotid body receives enteroceptive innervation: this is visceral and special sensory innervation, including impulses from internal organs and reflexogenic zones.
- Peripheral nerves: sensory fibers run as part of the branches of the glossopharyngeal nerve (n. glossopharyngeus, cranial nerve IX) and the vagus nerve (n. vagus, cranial nerve X). Branches to the carotid sinus and glomus run alongside the carotid artery.
- Central pathways: afferent impulses from the carotid body are received by the nucleus of the solitary tract (nucleus tractus solitarii). Along the course of the IX and X nerves are the superior (ganglion superius) and inferior (ganglion inferius) ganglia, containing the cell bodies of the first sensory neurons.
What is the function of the carotid body?
The carotid body functions as a chemoreceptor. Unlike the adjacent carotid sinus, which contains baroreceptors, the glomus is sensitive to the chemical composition of the blood: levels of oxygen ($O_2$), carbon dioxide ($CO_2$), and pH. The carotid body participates in the regulation of blood pressure and respiration.
Clinical significance: glomectomy
In surgical practice, there is a procedure for removing the carotid body — glomectomy.
- Indications: bronchial asthma refractory to conservative treatment.
- Approach: collar incision in the area of the right carotid triangle at the level of the upper border of the thyroid cartilage.
- Surgical procedure: the surgeon opens the fascial sheath over the bifurcation of the common carotid artery, locates the glomus caroticum on the posterior wall of the bifurcation, ligates the vessels running to the glomus from the bifurcation, and excises the glomus with scissors.
- Desympathectomy: some surgeons additionally remove the adventitia of the common, external, and internal carotid arteries over a length of 1 cm.
Class and exam questions
To which organ system does the carotid body belong?
It belongs to the endocrine system as a paraganglion — a structure associated with the chromaffin (adrenal) system and the autonomic nervous system.
What is the difference between the carotid body and the carotid sinus?
The carotid body is a chemoreceptor body that reacts to the chemical composition of blood (O₂, CO₂, pH). The carotid sinus is a dilation of the carotid artery containing baroreceptors sensitive to pressure.
Which nerves provide sensation to the carotid body?
Enteroceptive innervation is provided by the sensory branches of the glossopharyngeal (cranial nerve IX) and vagus (cranial nerve X) nerves. Impulses from the carotid body are received by the nucleus of the solitary tract.
What else to study on this topic
- Carotid bifurcation (bifurcatio carotidis)
- Carotid sinus (sinus caroticus)
- Glossopharyngeal nerve (n. glossopharyngeus)
- Paraganglia (paraganglia)
- Nucleus of the solitary tract (nucleus tractus solitarii)
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