THE PERICARDIUM

The pericardium is the sac that encloses the heart. It consists of an outer fibrous part known as the fibrous pericardium, and a double layered serous sac known as the serous pericardium.

The fibrous pericardium servers to limit the sudden distention of the heart, it is conical in shape and has an apex and a base, anterior and a posterior surface.

The apex fuses with the roots of the great vessels. It encloses the aorta, superior vena cava, and the pulmonary trunk. Its base fuses with the central tendon of the diaphragm and with some muscular fibres in the left side of the diaphragm. Anteriorly it lies posterior to the body of the sternum, between the 2^nd to 6^th costal cartilages. It is attached superiorly and inferiorly to the body of the sternum by the sterno-pericardial ligament. It is prevented from contact with the anterior thoracic wall by the lungs and pleura except at the lower left part of the sternum and at the sternal end of 4^th to 6^th costal cartilages. Posteriorly it lies anterior to the body of 5^th to 8^th thoracic vertebrae. It is prevented from contact with the vertebrae by the oesophagus, posterior surface of the mediastinal part of the lungs, and the descending thoracic aorta. Laterally it is bounded by the mediastinal pleura, here it is in contact with the phrenic nerves.

The serous pericardium is one of the serous membranes of the body and is similar in structure to the pleura and peritoneum. The serous pericardium has both a parietal layer and a visceral layer. The parietal layer lines the inside of the fibrous pericardium while the visceral layer lines the heart and the vessels entering it. This layer is also known as the epicardium of the heart.

The serous pericardium gives rise to two sheaths – A venous serous sheath and arterial serous sheath. The venous serous sheath encloses the inferior vena cava, the two right pulmonary veins, and the superior vena cava. It then deviates to enclose the two left pulmonary veins. In between the inferior vena cava and left pulmonary vein is a space referred to as the oblique sinus. It presents site for ligation of the veins during cardiac operations. The arterial serous sheath encloses the aorta and the pulmonary trunk. It also has a transverse sinus below it. A double layer of serous membrane separates the two sinuses.

BLOOD SUPPLY

Blood is supplied by branches from the internal thoracic artery, and musculophrenic artery and from the descending aorta. Its venous drainage is from tributaries that empty into the azygous system of veins.

NERVE SUPPLY

It is supplied by branches arising from the vagus, phrenic and sympathetic trunk.

APPLIED ANATOMY

1.                 Pericardiatis: This is a condition whereby the pericardium becomes inflamed. In severe cases it could lead to adhesion of the pericardium to the heart. And this could lead to hypertrophy of the heart since it will require more force or pressure to expand the pericardium.

2.                 Pericardial puncture is carried out close to the medial or sternal end of the 5^th to 6^th costal cartilage near the margin of the sternum to avoid puncture of the internal thoracic artery. It can also be made close to the xyphoid process i.e. left xiphicostal angle; the syringe is passed upwards and backwards to enter the pericardium.

CONTENTS OF THE PERICARDIUM

1.                 Pulmonary trunk

2.                 Ascending aorta

3.                 Terminal end of inferior vena cava and superior vena cava

4.                 Right and left pulmonary veins

5.                 The heart.

PULMONARY TRUNK

The pulmonary trunk is about 5cm in lenght. It begins  in front of the Aorta and passes (semi-spirally) upwards, backwards and to the left until it reaches the concavity  of the arch of Aorta where it bifurcates into the right and left pulmonary arteries.

ASCENDING AORTA

The ascending aorta begins behind the pulmonary trunk and passes obliquely upward, forward and to the right, to reach the right margin to the sternum within the pericardial sac.  Its right wall is dilated and is known as the bulb of the aorta.

AORTA VALUE & PULMONARY VALVE

Both values prevent backflow of blood into the ventricles and both have 3 semilunar values or cups, though the aortic cusps are stronger.

At the root of both arteries, there are 3 dilatations known as sinuses each lies external to each values to prevent it from sticking to the wall of prevent it from the vale is open.

The aorta orifice and the first 5mm to 10mm of the Aorticare filorous and not dilatable so the values remains  competent. The 3 values of the Arotic  value are the right and left, & posterior values. While the pulmonary trunk  has right, left & anternior values.