The central organ of the cardiovascular system is the heart. This is a hollow, muscular organ that contracts at regular intervals, forcing blood through the circulatory system.
2. The heart is cone-shaped, about the size of a fist, and is located in the centre of the thorax, between the lungs, directly behind the sternum (breastbone). The heart is tilted so that the base is tilted to the left.
3. The walls of the heart are made up of three layers of tissue:
a) The outer and inner layers are epithelial tissue.
b) The middle layer, comprising the cardiac muscle of
the heart itself, is called the myocardium.
4. For obvious reasons, the cardiac muscle is not under the conscious control of the nervous system, and can generate its own electrical rhythm (myogenic). For the same reasons, cardiac muscle cannot respire anaerobically and so the muscle cannot get tired (or develop cramp!)
5. Cardiac muscle has a rich supply of blood, which ensures
that it gets plenty of oxygen. This is brought to the heart
through the coronary artery. Since the heart relies on
aerobic respiration to supply its energy needs, cardiac muscle cells are richly supplied with
mitochondria.
. The heart can be thought of as two pumps sitting side by side – each of which has an upper atrium and a lower ventricle – a total of 4 chambers. It functions as two pumps inside one.
2. The right side of the heart pumps ‘deoxygenated blood’ (actually, blood low in oxygen) from the body into the lungs, where gas exchange takes place. In that process, carbon dioxide is lost to the air and oxygen is absorbed. This oxygen is almost all carried by the Red Blood Cells (RBC’s).
3. The left side of the heart pumps oxygenated blood from the lungs to the rest of the body.
4. The heart is enclosed in a protective membrane-like sac called the pericardium, which surrounds
the heart and secretes a fluid that reduces friction as the heart beats.
5. The atria (upper chambers) of the heart receive blood coming into the heart. Then have thin walls, so allowing them to be filled easily. They pump the blood into the ventricles (lower chambers), thus filling them.
6. The ventricles pump blood out of the heart and the left ventricle has the thickest walls of the heart because it has to do most of the work to pump blood to all parts of the body. This is where the blood has the highest pressure.
7. Vertically dividing the two sides of the heart is a wall, known as the septum. The septum prevents the mixing of oxygenated (left side) and deoxygenated (right side) blood.
8. It also carries electrical signals instructing the ventricles when to contract. These impulses pass down specially-modified muscle cells (Purkinje fibres), collectively known as the Bundle of His.
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