Human Heart Structure And Function

The human heart is an organ that provides a continuous blood circulation through the cardiac cycle and is a vital organ in the human body.The heart is divided into four main chambers: the two upper chambers are called the left atrium and the right atrium (plural atria) and the two lower chambers are called the right and the left ventricle.There is a thick wall of muscle separating the right side and the left side of the heart called theseptum. Normally with each heartbeat, the right ventricle pumps the same amount of blood into the lungs that the left ventricle pumps out into the body. Physicians commonly refer to the right atrium and right ventricle together as the right heart and to the left atrium and left ventricle as the left heart.

Structure:

The human heart has a mass of between 250 and 350 grams and is about the size of a large fist.

It is enclosed in a double-walled protective sac called the pericardium. The superficial part of this sac is called the parietal pericardium. The inner pericardium layer is called the visceral pericardium. Together they are usually called the serous pericardium because they contain the pericardial fluid. Outside the parietal pericardium there is a fibrous layer which depends from the mediastinal fascia and is called the fibrous pericardium. The pericardium protects the heart, from physical knocks and shocks, and from infection. It anchors its surrounding structures, but has no effect over the heart function in normal individuals.

The double membrane of the pericardium contains the pericardial fluid which provides a smooth lubricated sliding surface within which the heart organ can move in response to its own contractions and to movement of adjacent structures such as the diaphragm and lungs.At 21 days after conception, the human heart begins beating at 70 to 80 beats per minute and accelerates linearly for the first month of beating.

The outer wall of the human heart is composed of three layers. The outer layer is called the epicardium, or visceral pericardium since it is also the inner wall of the (serous) pericardium. The middle layer of the heart is called the myocardium and is composed of muscle which contracts. The inner layer is called the endocardium and is in contact with the blood that the heart pumps. Also, it merges with the inner lining (endothelium) of blood vessels and covers heart valves.

The human heart has four chambers, two superior atria and two inferior ventricles. The atria are the receiving chambers and the ventricles are the discharging chambers.

The pathways of blood through the human heart are part of the pulmonary and systemic circuits. These pathways include the tricuspid valve, the mitral valve, the aortic valve, and the pulmonary valve. The mitral and tricuspid valves are classified as the atrioventricular (AV) valves. This is because they are found between the atria and ventricles. The aortic and pulmonary semi-lunar valves separate the left and right ventricle from the aorta and the pulmonary arterty respectively. These valves are attached to the chordae tendinae (literally the heartstrings), which anchors the valves to the papilla muscles of the heart.

The interatrioventricular septum separates the left atrium and ventricle from the right atrium and ventricle, dividing the heart into two functionally separate and anatomically distinct units.

How does my heart work?

Your heart is located under the ribcage in the centre of your chest between your right and left lungs.

Its muscular walls beat, or contract, pumping blood continuously to all parts of your body.

The size of your heart can vary depending on your age, size and the condition of your heart.

A normal, healthy adult heart is generally the size of a clenched adult fist. However, some diseases of the heart can cause it to become larger.

How does my heart pump blood?

There are two sides to the heart (left and right) and both sides act as pumps.

The two sides are further divided into two chambers - so four chambers in total.

The upper chambers are called ATRIA: they collect blood.

The lower chambers are called VENTRICLES: they contract to pump the blood out.

Why does it pump blood?

The left side of the heart is larger than the right and pumps blood, rich in oxygen and nutrients, out through blood vessels (arteries) to the head and body.

The oxygen is used by the body and then your veins carry the blood, which is now low in oxygen, back to the right side of the heart.

The right side of the heart then pumps this blood to the lungs where it receives more oxygen.

This blood returns to the left side of the heart and is pumped around the body again.

Blood is pumped at high pressure so it can reach all the body's parts. For this to happen, the heart has to be very strong and needs a very good blood supply. This is provided by the coronary arteries.