by Caroline Fynn

Created on: June 29, 2009   Last Updated: May 20, 2012

The heart is located in the space between the lungs referred to as the thoracic cavity within the mediastium. It lies slightly to the left and is approximately the size of the fist.

Anatomy of the Heart

The heart's interior is divided into four chambers, the two upper chambers are known as the atria, and the lower are the ventricles. A wall referred to as the septum divides the two sides of the heart.

Four valves control the one way blood flow in and out of the heart chambers, the tricuspid valve, also known as the right atrioventricular, and the pulmonary valve are located on the right side of the heart. The mitral valve, also known as the left atrioventricular, and the aortic valve are situated on the left.

Three layers of tissue make up the heart wall, and these are known as the pericardium, the myocardium, and the endocardium.

The Pericardium

This is the heart's outer layer and comprises of two sacs. The outer sac is made up of fibrous tissue that prevents over distension of the heart, and the inner sac is a double layer of serous membrane, made up of flattened epithelial cells, which determine smooth movement within the heart wall.

The Myocardium

This makes up the middle layer of the heart wall and comprises of specialised cardiac muscle tissue exclusive to the heart. When a contraction occurs the impulses spread across the cells over the entire layer of the myocardium.

The Endocardium

This is the inside layer that consists of flattened epithelial cells and is continuous with the heart's blood vessels.

The atrial walls are much thinner than those of the ventricles, and as we shall see, this is because the atria simply push the blood through the valves into the ventricles, but it is the task of the ventricles to send the blood out to the entire body, and it is the left ventricle that contains the thickest heart wall.

Physiology of the Heart

The function of the heart is to pump the blood around the body in order to deliver properties such as nutrients, oxygen and a variety of hormones. It does this by pumping oxygenated blood out to the body via the aorta; this is the largest blood vessel in the body. The blood being transported to the arms, the neck, and the head, travels from the heart by way of the aortic arch. Blood travelling to the lower body flows out from the descending aorta. Nutrients, oxygen and various hormones are delivered throughout the body and then the blood returns to the heart deoxygenated.

Blood returning from the upper body comes into

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