Structure of the Heart
The heart weighs between 200 and 425 grams and is a little larger than the size of your fist. It has a volume capacity of 80-100mls. By the end of a long life a person’s heart may have beat more than 3.5 billion times. In fact, each day the average heart beats about 100,000 times, pumping around 7500 litres of blood.
Your heart is located between your lungs in the middle of your chest, behind and slightly to the left of your breastbone. A double layered membrane called the pericardium surrounds your heart like a sac. The outer layer of the pericardium surrounds the roots of your hearts major blood vessels and is attached by ligaments to your spinal column, diaphragm and other parts of your body. The inner layer of the pericardium is attached to the heart muscle. A coating of fluid separates the two layers of membrane, letting the heart move as it beats, yet still be attached to your body.
Chambers of the Heart
Your heart has 4 chambers. The upper chambers are called the left and right atria and the lower chambers are called the left and right ventricles. A wall of muscle called the septum separates the left and right atria and the left and right ventricles. These are referred to as the atrial and ventricular septum. You may have heard your doctor refer to a condition called a ‘hole in the heart’. This simply means a tiny hole in the atrial septum separating the atria (called a PFO– Patent Foramen ovale or ASD—Atrial Septal Defect) or in the ventricular septum separating the ventricles (called a VSD—Ventricular Septal Defect). The left ventricle is the largest and strongest chamber in your heart.The left ventricle’s chamber walls are only about 1.0 to 1.3cm, but they have enough force to push blood through the aortic valve and into your body.
Heart Valves
Four types of valve regulate blood flow through your heart:
- The tricuspid valve regulates blood flow between the right atrium and right ventricle.
- The pulmonary valve controls blood flow from the right ventricle into the pulmonary arteries, which carry blood to your lungs to pick up oxygen.
- The mitral valve lets oxygen rich blood from your lungs pass from the left atrium into the left ventricle.
- The aortic valve opens the way for oxygen rich blood to pass from the left ventricle into the aorta, your body’s largest artery, where it is delivered to the rest of your body.
A more detailed description of blood flow through the heart is seen below.
Flow of Blood Through the Heart
Blood enters the right atrium of the heart through the superior vena cava. The right atrium contracts and pushes the blood cells through the tricuspid valve into the right ventricle. The right ventricle then contracts and pushes the blood through the pulmonary valve into the pulmonary artery, which takes it to the lungs. In the lungs, the blood cells exchange carbon dioxide for oxygen. The oxygenated blood returns to the heart via the pulmonary veins and enters the left atrium. The left atrium contracts and pumps the blood through the mitral valve into the left ventricle. Finally, the left ventricle contracts and pushes the blood into the aorta. The aorta branches off into several different arteries that pump the oxygenated blood to various parts of the body.
