As the external carotid artery, the external carotid artery supplies blood to the thyroid gland, larynx, pharynx, cranial bones, dura mater, and soft tissues of the head. Its wall consists of three layers and contributes to the maintenance of vascular pressure through the activity of ring muscles.
What is the external carotid artery?
The external carotid artery is the external carotid artery and one of the larger blood vessels in the human body. It forms a branch from the common carotid artery and in turn branches into numerous branches. Behind it lies the internal carotid artery or arteria carotis interna, through which blood flows to the brain, among other places. Although the course of the blood vessels follows a certain pattern in all people, individual development may deviate from it. Such deviations do not necessarily represent a malformation or disease; instead, they are variants that need not lead to functional impairment. Some variants even occur frequently: Branches of the external carotid artery leading to the tongue and through the face (lingual and facial arteries) share a common outlet, the truncus linguofacialis, in 20% of the population.
Anatomy and structure
Stable but expandable walls surround the external carotid artery, allowing it to maintain constant blood pressure internally. The outermost layer (tunica externa or tunica adventitia) contains nerves responsible for controlling the artery. In addition, vessels run through it, which distribute nutrients in the tissues of the outer layers. However, mainly the structure of the tunica externa is composed of connective tissue. Under this layer lies the tunica media, which contains the muscles of the blood vessel. For the most part, these are ring-shaped muscles that wind in oblique paths around the artery. In addition to muscle fibers, the tunica media contains elastic and collagen fibers. The tunica intima lines the inner wall of the external carotid artery with its endothelium; the intima also includes a connective tissue layer overlying the endothelium, as well as the stratum subendotheliale and the membrana elastica interna, which forms the boundary with the tunica media.
Function and Tasks
In its function as an artery, the external carotid artery transports blood away from the heart, with its capacity accounting for 20% of the total volume of blood in the human body. To allow blood to flow, the heart pumps the fluid in a steady rhythm, thereby propelling it. The blood pressure in the arteries also contributes to this and is a frequently measured value in medicine as arterial vascular pressure. To reach the different parts of its supply area, the external carotid artery divides into different branches. The main branches are:
- The superior thyroid artery, which supplies blood to the thyroid gland;
- The lingual artery, which carries blood to the tongue;
- The facial artery, which covers the superficial parts of the face;
- The ascending pharyngeal artery, which passes over the pharyngeal sidewall to the pharyngeal muscles, tympanic cavity, and dura mater;
- The sternocleidomastoid ramus, which forms the branch leading to the sternocleidomastoid muscle;
- Occipital artery, which carries blood to the back of the head;
- The posterior auricular artery, which supplies the middle and inner ear, the pinna, and surrounding soft tissue;
- The superficial temporal artery, which covers the top of the head and runs along in front of the ear;
- The maxillary artery, which continues the path of the temporal artery and covers the deep parts of the face.
This order corresponds to the order in which the main branches branch off from the external carotid artery. In addition, the individual blood vessels sometimes split even further to reach fine tissue structures. Medical students often learn the sequence with the help of a mnemonic: “Theo Lingen makes fantastically strong oxtail soup from dead mice.”
Diseases
The external carotid artery pulse is easily measurable in two places. On the one hand, it is easily felt at the facial branch (arteria facialis) at the edge of the lower jaw, and on the other hand, at the temple. A strong pulse in particular may be visible through the skin with the naked eye at the temple.Injuries to the face and neck can cause damage to the common carotid artery and its branches. The extent of the consequences depends on the type, location, and extent of the lesion. Pain in the common carotid artery or both of its branches may indicate vascular problems. One condition that can cause pain in the carotid artery is arterial dissection, in which the walls of the vessel separate. Blood is often responsible, which can get between the other layers due to a tear in the tunica intima, causing them to separate. In some cases, the blood forms clots as it coagulates, which can obstruct blood flow as a thrombus. Depending on which organ is affected by the restricted blood supply and to what extent, stroke, heart attack and other events can occur and cause permanent damage. However, not all sufferers feel pain in the carotid artery, and such pain does not always have to indicate dissection. To make matters worse, the pain may radiate to areas other than the site of origin. Carotid stenosis also results in vasoconstriction; it is usually due to deposits within the artery (atherosclerosis) and can also lead to stroke and other complications.
