Roots of Great Vessels

The roots of the great vessels refer to the proximal segments of the major arteries and veins that enter and leave the heart. These vessels are enclosed within the fibrous pericardium and are situated in the middle mediastinum. They form the major conduits of blood circulation to and from the heart, connecting it to the pulmonary and systemic circuits. Anatomically, they are tightly arranged around the superior aspect of the heart, near the base, and pass through the pericardial reflections.

Arterial Roots

The two main arteries emerging from the heart are the pulmonary trunk and the ascending aorta. Both arise from the ventricles and carry blood away from the heart.

Pulmonary Trunk

• Origin: Arises from the right ventricle at the level of the pulmonary valve
• Course: Ascends posteriorly and slightly to the left of the ascending aorta, and bifurcates into the right and left pulmonary arteries at the level of the T5 vertebra
• Enclosed in: Pericardium, forming part of the arterial root of the heart

The pulmonary trunk transports deoxygenated blood from the right ventricle to the lungs. It lies anterior to the ascending aorta in its initial course and is connected to the aortic arch via the ligamentum arteriosum (a remnant of the ductus arteriosus).

Ascending Aorta

• Origin: Arises from the left ventricle at the level of the aortic valve
• Course: Rises superiorly, anteriorly, and to the right before continuing as the arch of the aorta
• Length: Approximately 5–6 cm long
• Branches: Right and left coronary arteries arise from the aortic sinuses

The ascending aorta is completely enclosed within the pericardial sac and is located posterior to the pulmonary trunk in its distal portion. It is continuous with the aortic arch, which lies in the superior mediastinum.

Venous Roots

Venous blood returns to the heart via the superior vena cava, inferior vena cava, and the pulmonary veins. These vessels enter the atria and are also enclosed by the fibrous pericardium at their roots.

Superior Vena Cava (SVC)

• Formation: Formed by the union of the right and left brachiocephalic veins
• Entry: Drains into the superior aspect of the right atrium at the level of the third costal cartilage
• Course: Descends vertically through the superior and middle mediastinum

Only the terminal segment of the SVC (about 2–3 cm) is located within the pericardial sac. It is positioned to the right of the ascending aorta and anterior to the right pulmonary artery. The azygos vein drains into the SVC just before it enters the pericardium.

Inferior Vena Cava (IVC)

• Entry: Penetrates the diaphragm at the T8 vertebral level and enters the lower aspect of the right atrium
• Pericardial relation: The terminal 1–2 cm of the IVC is enclosed by pericardium

The IVC delivers deoxygenated blood from the lower limbs, abdomen, and pelvis. It ascends on the right side of the vertebral column and enters the heart almost vertically.

Pulmonary Veins

• Number: Four (two from each lung – superior and inferior)
• Entry: Drain into the posterior wall of the left atrium
• Pericardial relation: Enclosed by the serous pericardium at their roots

The pulmonary veins carry oxygenated blood from the lungs. They are located posterior to the other great vessels and enter the heart in close proximity to one another, forming a square-like arrangement on the posterior aspect of the left atrium.

Arrangement at the Heart Base

At the base of the heart, the roots of the great vessels are tightly clustered within the pericardial sac. From anterior to posterior, the general arrangement is:

• Pulmonary trunk (most anterior)
• Ascending aorta (posterior and to the right of pulmonary trunk)
• Superior vena cava (to the right of aorta)
• Pulmonary veins (posterior, entering left atrium)
• Inferior vena cava (inferior and posterior, entering right atrium)

This clustered configuration at the cardiac base is surrounded by the transverse and oblique pericardial sinuses, which allow surgical access and provide anatomical separation between arterial and venous vessels.

Pericardial Relationships

The fibrous pericardium encloses the proximal portions of all these vessels. The serous pericardium reflects off the surface of the heart to form tubular sheaths around each vessel root. These reflections create the pericardial sinuses mentioned earlier and mark the boundary between intrapericardial and extrapericardial segments of the vessels.