Page 138 - 84 human physiolofy part-1

Chapter 8

Pericardium

The pericardium is the thick, membranous sac that surrounds the heart. It protects and lubricates
the heart. There are two layers to the pericardium: the fibrous pericardium and the serous pericardium.
The serous pericardium is divided into two layers; in between these two layers there is a space called
the pericardial cavity.

Epicardium

The layer next to the heart is the visceral layer, also known as the Epicardium. This is the inner
most layer and consists of connective tissue.

Heart Chambers

The heart has four chambers, two atrium and two ventricles. The atriums are smaller with thin
walls, while the ventricles are larger and much stronger.

Atrium

There are two atria on either side of the heart. On the right side is the atrium that holds blood that
needs oxygen. The left atrium holds that blood that has been oxygenated and is ready to be sent to the
body. The right atrium receives de-oxygenated blood from the superior vena cava and inferior vena
cava. The left atrium receives oxygenated blood from the left and right pulmonary veins.

Ventricles

The ventricle is a heart chamber which collects blood from an atrium and pumps it out of the heart.
There are two ventricles: the right ventricle pumps blood into the pulmonary circulation for the lungs,
and the left ventricle pumps blood into the systemic circulation for the rest of the body. Ventricles have
thicker walls than the atria, and thus can create the higher blood pressure. Comparing the left and right
ventricle, the left ventricle have thicker walls because it needs to pump blood to the whole body. This
leads to the common misconception that the heart lies on the left side of the body.

Septum

The interventricular septum (ventricular septum, or during development septum inferious) is the
stout wall separating the lower chambers (the ventricles) of the heart from one another. The ventricular
septum is directed backward and to the right, and is curved toward the right ventricle. The greater
portion of it is thick and muscular and constitutes the muscular ventricular septum. Its upper and
posterior part, which separates the aortic vestibule from the lower part of the right atrium and upper
part of the right ventricle, is thin and fibrous, and is termed the membranous ventricular septum.

Valves

The two atrioventricular (AV) valves are a one-way valve that ensures blood flows from the atria

138 | Human Physiology