The Heart and How It Works
A normal heart is a powerful, muscular pump about the size of a fist. It continually circulates blood through the circulatory system. Each day the average heart "beats" (expands and contracts) 100,000 times and pumps about 2,000 gallons of blood. A typical human heart beats more than 2.5 billion times in a 70-year lifetime.
The circulatory system is a system of flexible tubes that transports blood throughout the body. The heart, lungs, arteries, arterioles (small arteries), and capillaries are all part of it (very tiny blood vessels). All regions of the body receive oxygen- and nutrient-rich blood through these blood arteries. Venules (small veins) and veins are also part of the circulatory system. These are the blood arteries that return low in oxygen and nutrients blood to the heart and lungs. If all of these ships were put end-to-end, the total length would be around 60,000 miles. That's enough to encircle the globe twice over.
All of the body's organs and tissues, including the heart, receive oxygen and nourishment from the circulating blood. It also collects waste products from the cells of the body. These waste products are filtered out of the body via the kidneys, liver, and lungs.
What is the heart's structure?
The heart has four chambers through which blood is pumped. The right and left atria are the upper two. The right and left ventricles are the lower two. When the heartbeats, four valves open and close, allowing blood to flow in just one direction:
- Between the right atrium and the right ventricle is the tricuspid valve.
- Between the right ventricle and the pulmonary artery is the pulmonary or pulmonic valve.
- Between the left atrium and the left ventricle is the mitral valve.
- The aortic valve is located between the left ventricle and the aorta.
There are flaps on each valve (also called leaflets or cusps). The mitral valve has two flaps. The others have three. The valves only allow blood to flow in one way under typical circumstances. Only when there is a pressure difference across the valves that causes them to open does blood flow occur.
How does the heart pump blood?
The four chambers of the heart contract in a highly structured sequence to pump blood. The heart works as follows:
The right atrium receives blood from the veins. This blood has a low oxygen content and a high carbon dioxide content. This is due to the fact that it is returning from the body's tissues, where much of the oxygen has been withdrawn and carbon dioxide has been added. Because of the difference in dissolved gases, venous blood is darker than arterial blood. The open tricuspid valve allows venous blood to flow into the right ventricle while the heart is resting. The atria contract in response to an electrical impulse, which starts the heartbeat. This contraction "finishes" the ventricle's filling. The right ventricle contracts shortly after the atrium contracts. The tricuspid valve closes at this point, and partially deoxygenated blood is forced via the pulmonary valve, into the pulmonary artery, and into the lungs. Before returning to the left atrium, blood exchanges carbon dioxide for oxygen in the lungs. This freshly oxygenated blood is a vibrant red color.
The left atrium contracts simultaneously with the right atrium, topping off the flow of oxygenated blood through the mitral valve and into the left ventricle. The left ventricle then contracts for a fraction of a second, pouring blood past the aortic valve, into the aorta, and onto the body's tissues.
The four chambers of the heart must pulse in a coordinated manner. The electrical impulse is in charge of this. When an electrical impulse passes through a chamber of the heart, it contracts. The sinoatrial node (SA node), also known as the sinus node, is a small bundle of highly specialized cells in the right atrium that initiates such a signal. The heartbeats as a result of a discharge from this natural "pacemaker." Although this pacemaker produces electrical impulses at a set rate, emotional reactions and hormonal factors can influence the rate at which they are discharged. This enables the heart rate to adjust to changing demands.
The SA node sends electrical impulses across the right and left atrium, causing the muscle cells to contract. The electrical signal passes down specialized fibers throughout the ventricles shortly after both atria have contracted. The course of the signal leads the ventricles to wring together in a wringing motion, sucking the blood out. This electrical impulse takes a precise path, resulting in the synchronized, sequential contraction of the heart's four chambers, which is required for the heart to function effectively.
Talk to Best Heart Doctor in Coimbatore for more information on the heart.
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