Structure And Function Of The Human Heart
Structure Of The Heart
The Human heart is located in the centre of the chest and is a muscular and hollow organ. The heart consists of left and right sides each which consist of an upper chamber or atrium and a lower chamber or ventricle which collect the blood and pump the blood out respectively. The atrium collects the blood and then pumps it into the ventricle which subsequently pumps the blood out into the rest of the body.
Each ventricle consists of an inlet valve as well as an outlet valve to ensure that the blood flows in only one direction. The inlet valve in the left ventricle is known as the mitral valve while the outlet valve in the ventricle is known as the aortic valve. The inlet valve in the right ventricle is known as the tricuspid valve while the outlet valve in the right ventricle is known as the pulmonic or pulmonary valve. The valves consist of flaps which are also known as leaflets or cusps that open and close in a way similar to one way swinging doors to let in the blood and let out the blood. The mitral valve consists of two flaps while the remaining valves consist of three flaps each. The inlet valves consist of leaflets which have cords of tissue as well as papillary muscles that help prevent the valves from breaking and swinging inward into the heart chamber or the atria.
In heart conditions such as in a heart attack the papillary muscle is often damaged and in such a situation the valve swings backward and begins leaking. The blood flow through the valve is often reduced when the opening of the valve is narrowed and often a valve may be affected by both problems.
The evidence that your heart is pumping is the heartbeats and the first sound produced by the heart is the sound of the tricuspid and mitral valves closing. The second sound produced by the pumping of the heart is the sound of the pulmonary and aortic valves closing. Every heartbeat consists of two different parts which are known as the diastole and systole. The ventricles relax and are filled with blood during the diastole and subsequently the atria contract which force the blood into the ventricles. The ventricles contract and pump the blood during systole and subsequently the atria relax and begin filling up with blood once again.
Function of the Heart
The only function of the heart is to pump blood and hence the right side of the heart functions by pumping blood into the lungs where oxygen is added to the blood while carbon dioxide is removed from the blood. The left side of the heart pumps blood to the remaining parts of the body after the oxygen and nutrients have been added to the blood and are delivered to the tissues and the waste products such as carbon dioxide are transferred into the blood for removal from different organs such as the kidneys and the brain.
The blood in the human body travels by following a given circuit known as the cardiac cycle. The blood in the body which has been depleted of oxygen and is full of carbon dioxide flows through the two largest veins in the human body into the right atrium of the heart. Subsequently the right ventricle relaxes and the blood collected in the right atrium moves through the tricuspid valve into the right ventricle of the heart. Once the right ventricle is almost full it starts to contract. This contraction of the right ventricle propels blood into the pulmonary arteries through the pulmonary valve and the blood is subsequently supplied to the lungs. The blood in the lungs flows through numerous tiny capillaries that surround the numerous air sacs contained in the lungs. In the tiny capillaries the blood gives up its carbon dioxide content and absorbs oxygen and subsequently the carbon dioxide removed from the blood is exhaled.
The oxygen rich blood from the lungs now flows into the left atrium through the pulmonary veins. The blood on the left atrium is subsequently forced through the mitral valve when the left ventricle relaxes and the blood is poured into the left ventricle. The left atrium contracts when the left ventricle is almost filled with blood. The contraction of the left atrium propels additional blood into the left ventricle which subsequently contracts. In many older people the left ventricle is not filled up to the level it used to fill up before, prior to the contraction of the left atrium and hence in older people contraction of the left atrium is very important. Blood is propelled into the aorta through the aortic valve by the contraction of the left ventricle. The aorta is the largest artery in the body and carries the oxygen infused blood to all parts of the body except the lungs.
The circulation of blood flow is divided into two parts which are known as pulmonary circulation and systemic circulation. Pulmonary circulation is a circuit of blood flow through the right side of the heart, the left atrium and the lungs. While the systemic circulation is a circuit of blood flow through the left side of the heart, the right atrium and the remaining parts of the body except the lungs.
Coronary arteries (Heart Blood Supply)
The heart like most of the organs contained in the human body requires a constant supply of blood that is rich in oxygen. Hence a system of veins and arteries which is collectively known as the coronary circulation supplies the heart muscles or myocardium with blood that is rich in oxygen. The coronary circulation also returns the blood depleted of oxygen to the right atrium of the heart. The left coronary artery and the right coronary artery branch off from the aorta after the aorta leaves the heart to deliver the blood rich in oxygen to the muscles of the heart. The left and right coronary arteries subsequently branch out into other arteries that supply blood to the heart including the circumflex artery, left anterior descending artery and posterior descending artery.
Blood is collected from the heart muscle by the cardiac veins and the blood is emptied out into a large vein located on the back surface of the heart which is known as the coronary sinus. The coronary sinus subsequently returns the blood into the right atrium of the heart. Since great amounts of pressure is exerted on the heart during contraction, maximum amount of the blood flows through the coronary circulation only when the heart is relaxing in between heartbeats or during diastole.
Normal Heart Rhythm
The system of contraction of the muscle fibers in the heart is an extremely controlled and organized process. The rhythmic electrical impulses or discharges usually flow through the heart and are controlled in speed and also flow along distinct pathways in the most precise manner. The impulses originate in the sinoatrial node or sinus of the heart which is commonly known as the pacemaker of the heart that generates tiny amounts of electrical current. The sinoatrial node is essentially a small mass of tissue that is located on the wall of the right atrium.
The heart rate is governed by the rate at which the sinoatrial node or the pacemaker gives out the impulses. The rate at which the impulses are given out is determined by two opposing systems. The systems include one system to speed up the heart rate and the other system is which slows the heart rate down. The system that speeds up the heart rate involves the sympathetic division of the central nervous system while the system which slows down the heart rate consists of the parasympathetic division of the central nervous system. The sympathetic division of the central nervous system usually works through a network of nerves which are known as the sympathetic plexus and also works through different hormones such as adrenaline (epinephrine). These hormones are released by the nerve endings and adrenal glands. The parasympathetic division of the central nervous system on the other hand works through only a single nerve which is known as the vagus nerve. The vagus nerve releases a neurotransmitter called acetylcholine that slows down your heart.
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Yasser Elnahas
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