Vasculature - Arterial Supply Flashcards
What are the main arteries that supply the head and neck?
1) Internal carotids
2) Vertebral arteries
What is the origin of the carotid arteries?
Right common carotid - bifurcation of the brachiocephalic trunk (right subclavian is the other branch). Bifurcation occurs at the level of the sternoclavicular joint.
Left common carotid - branches directly off of the arch of the aorta.
The left and right common carotid ascend up the neck, lateral to the oesophagus and trachea. They do not give off any branches in the neck.
Bifurcation of the common carotid?
The common carotid bifurcates into the internal carotid and external carotid at the level of the thyroid cartilage (C4). This occurs in an area called the carotid triangle.
The common caortid and internal carotid artery are slightly dilated here - this is called the carotid sinus. This is important in detecting and regulating blood pressure.
Clinical relevance - carotid hypersensitivity
The carotid sinus is a dilated portion of the common carotid and proximal internal carotid artery.
It contains baroreceptors that detect blood pressure. The glosspharyngeal nerve feeds this information to the brain, and is used to regulate blood pressure.
In some individuals, baroreceptors are hypersensitive to stretch. External pressure on the carotid sinus can cause slowing of the heart rate and a decrease in blood pressure. The brain becomes under-perfused and syncope results. In these patients, checking the carotid pulse is not advised.
External to the carotid sinus is a cluster of nervous cells knowns as the carotid body. These cells act as peripheral chemoreceptors; detecting the O2 content of the blood and it relays this information in the brain to determine respiratory rate.
External carotid artery
Location?
Branches?
Supplies areas to the head and neck external to the cranium. After arising from the common carotid, it travels up the neck, passing posteriorly to the mandibular neck and anteriorly to the lobule of the ear.
It ends within the parotid gland, by dividing into the superficial temporal artery, and the maxillary artery.(these supply superficial structures of the face). It gives rise to six branches in total:
1) Superior thyroid
2) Lingual artery
3) Facial artery - supplies deep structures of the face
4) Ascending pharyngeal artery
5) Occipital artery
6) Posterior auricular artery
Clinical relevance - blood supply to the scalp
There are five arteries that supply blood to the scalp:
1) Occipital
2) Posterior auricular
3) Superficial temporal
4) Supra-orbital (a branch of the ICA)
5) Supra-trochlear (a branch of the ICA)
Injury to the scalp can produce excessive bleeding for three reasons:
1) The walls of the arteries are close to the underlying connective tissue of the scalp, preventing them from constricting to limit blood loss following injury or laceration.
2) Numerous anastomoses formed by arteries produce a very densely highly vascularised area.
3) Deep lacerations are worsened by the epicranial aponeurosis, which is worsened by the opposing actions of the occipital and frontalis muscles.
Note that the bony skull itself will receive its blood supply from the middle meningeal artery, hence it will not undergo avascular necrosis.
Clinical relevance - extradural haematoma
The middle meningeal artery is a branch of the maxillary artery. It is unique as it suppllies some intracranial structures (whereas other branches of the ECA supply structures outside of the cranium).
The middle meningeal artery supply the skull and dura mater. A fracture at the pterion (weakest point of the skulll) can rupture this artery, causing blood to pool between the dura mater and the skull, consequently increasing intracranial pressure.
Increase in intra-cranial pressure can produce a variety of symptoms: nausea, vomiting seizures, bradycardia, and limb weakness. It is treated by diuretics in minor cases, and drilling burr holes into the skull for more extreme haemorrhages.
Internal carotid artery
It does not supply any structures in the neck, entering the cranial cavity, via the carotid canal, in the petrous part of the temporal bone. Within the cranial cavity, it supplies the brain, eyes and the forehead.
Clinical relevance - atherosclerosis of the carotid arteries
The swelling at the bifurcation of the common carotid arteries, the carotid sinus, produces turbulent blood flow. This increases the risk of atheroma formation in this area, with the ICA the most susceptible.
Atherosclerotic thickening of the tunica intima of these arteries will reduce blood flow to the brain resulting in various neurological symptoms: headache, dizziness, muscular weakness. If the blood vessel is completely occluded, a cerebral ischaemia (stroke) results.
Diagnosis - doppler study to assess the severity of the thickening. In severe cases, the artery can be opened, and the atheramatous tunica intima removed. This procedure is called a carotid endarterectomy.
Vertebral arteries
Paired arteries that arise from the subclavian arteries, medial to the anterior scalenes.
They ascend the posterior neck and travel through the transverse foramina of the cervical vertebrae.
They then enter the foramen magnum where they converge to form the basilar artery.
The vertebral arteries do not supply any structures in the neck or any other extra-cranial structures.
Other arteries in the neck?
1) Thyrocervical trunk - arises from the right and left subclavian arteries. From this trunk, several branches arise:
i) Inferior thyroid artery - thyroid gland
- Ascending cervical artery - arises from the inferior thyroid artery, as it turns medially into the neck - it supplies the posterior prevertebral muscles.
ii) Transverse cervical artery - crosses the base of the carotid triangle - supplies the trapezius and rhomboid muscles.
iii) Suprascapular artery - supplies the posterior shoulder area.
