Heart - Great Vessels Flashcards
Which part of the mediastinum of the great vessels generally located?
Middle.
What are the four great vessels?
1) Aorta
2) Pulmonary arteries
3) Pulmonary veins
4) Superior and inferior vena cava
Aorta?
This is the largest artery in the body. It carries oxygenated blood from the heart to the rest of the body.
The aorta arises from the aortic orifice at the base of the left ventricle, with inflow via the aortic valve. Its first segment is known as the ascending aorta, which lies within the pericardium (covered by the visceral layer). From it branches the coronary arteries. The second continuous segment is the arch of the aorta, from which branch the major arteries to the head, neck and upper limbs. These are:
1) Brachocephalic trunk
2) Left common carotid artery
3) Left subclavian artery
After the arch of the aorta, the aorta then becomes the descending aorta which continues down through the diaphragm into the abdomen.
Clinical relevance - disorders of the aorta?
Aortic dissection
Aortic dissection refers to a tear in the inner wall of the aorta. The tear creates two channels for blood to flow; one is the normal lumen of the aorta, another is into the wall, where the blood becomes stationary.
Blood entering the wall can constrict the aortic lumen, reducing blood flow to the rest of the body. It can also cause further weakness and dilation of the wall, potentially leading to an aortic aneurysm.
Aortic aneurysm
An aortic aneurysm is due to an underlying weakness of the walls (such as Marfan’s syndrome), or a pathological process (such as aortic dissection).
The main concern with an aortic aneurysm is rupture of the aorta, which if not treated, will lead to death.
Pulmonary arteries?
The pulmonary arteries receive dexoygenated blood from the right ventricle and deliver it to the lungs for gas exchange to take place.
The arteries begin as the pulmonary trunk, a thick and short vessel, which is separated from the right ventricle by the pulmonary valve. The trunk is located anteriorly and medially to the right atrium, sharing a common layer of pericardium with the ascending aorta. It continues upwards, overlapping the root of the aorta and passing posteriorly.
At around the level T5-T6, the pulmonary trunk splits into righ and left pulmonary arteries. The left pulmonary artery supplies blood to the left lung, bifurcating into two branches to supply each lobe of the lung. Thr right pulmonary artery is the thicker and longer artery of the two, supplying blood to the right lung. It also further divides into two branches.
Pulmonary veins?
These receive oxygenated blood from the lungs, delivering it to the left atrium.
There are four pulmonary veins, with one superior and one inferior for each of the lungs. THey enter the pericardium to drain into the superior left atrium, on the posterior surface. The oblique pericardial sinus can be found within the pericardium, between the left and right veins.
The superior pulmonary veins return blood from the upper lobes of the lung, with the inferior veins returning blood from the lower lobes. The inferior left pulmonary vein is found at the hilum of the lung, while the right inferior pulmonary vein runs posteriorly to the SVC and the right atrium.
Superior vena cava?
The SVC receives deoxygenated blood from the upper body (superior to the diaphragm, exluding the lungs and heart), delivering it to the right atrium.
It is formed by merging of the brachiocephalic veins, travelling inferiorly through the thoracic region until draining into the superior portion of the right atrium at the level of the 3rd rib.
As the SVC makes its descent it is located in the right side of the superior mediastinum, before entering the middle mediastinum to lies beside the ascending aorta.
Inferior vena cava?
The IVC receives deoxygenated blood from the lower body (all structures inferior to the diaphragm), delivering it back to the heart.
It is initially formed in the pelvis by the common iliac veins joining together (at T5). It travels through the abdomen, collecting blood from the hepatic, lumbar, gonadal, renal and phrenic veins. The IVC then passes through the diaphragm, entering the pericardium at the level of T8. It drains into the inferior portion of the right atrium.
