Category Archives: Function Of the Heart And Blood Circulation
What Are Blood Vessels
The network of blood vessels in the human body consists of arterioles, arteries, capillaries, veins and venules. All the blood flowing through the human body is carried through these blood vessels. The arteries are flexible, strong as well as resilient and carry away the blood from the heart. The arteries bear the highest blood pressures among all the blood vessels present in the human body. The arteries can handle the highest blood pressures because they are elastic and they can also recoil passively when the heart is relaxing two heartbeats. The arteries narrow down passively so that they can maintain the blood pressure in the human body. When the arteries branch out into smaller blood vessels they are known as arterioles. The arterioles and arteries have adjustable muscular walls and hence can adjust their diameter to accommodate the increasing or decreasing flow of blood to different parts of the body.
The capillaries are one of the smallest blood vessels in the human body and are also among the most thin-walled blood vessels. The capillaries typically act as bridges between the arteries which are carrying blood away from the heart. The capillaries also act as bridges between the veins which are carrying blood back into the heart. The capillaries have thin walls so that nutrients and oxygen can pass from the blood passing through the capillaries into the tissues. Similarly the waste products can also pass from the tissues into the blood being carried through the capillaries.
The blood flows into small veins commonly known as venules (arising from the capillaries) and subsequently the blood flows back into the veins which lead the blood back into the heart. The veins have much thinner walls in comparison to the arteries mostly because the blood pressure exerted on the veins is much lower than that exerted on the arteries. In case the amount of fluid passing through the veins increases the veins can dilate or widen in diameter to accommodate the increase in flow. The larger veins in the human body such as the veins in the legs have valves in them so that the blood in his veins does not flow backwards. In case the valves in such veins are leaking the backflow of the blood in his veins can cause them to stretch as well as become convoluted and elongated. When the veins become convoluted and elongated near the surface of the body they are known as varicose veins.
In case a blood vessel tears, breaks or is cut then the blood passing through the blood vessel starts to leak out and causes bleeding. Often the blood may flow out of the body which is known as external bleeding and it can also flow into cavities in the human body such as into spaces around the organs. The blood can also flow directly into the organs and it is known as internal bleeding.
Aging Blood Vessels
With age the walls of the arterioles and that of the arteries become thicker and the space within the arteries also begins to expand slightly. The elastic tissue contained in the walls of the arterioles and arteries is also lost with age. When combined, these changes can make the blood vessels less resilient and much stiffer.
Since the blood vessels like the arterioles and arteries become less elastic with age older people cannot relax fast during the rhythmic pumping of their heart. It is because of this reason that the blood pressures increases during the contraction cycle of the heart that is during systole. The blood pressure often increases above normal in comparison to the younger people who can relax quickly even during the rhythmic pumping of the heart. It is thus very common to observe high blood pressure during systole in older people. It is also quite common to observe normal blood pressure during diastole in older people. Abnormally high blood pressure during systole and normal blood pressure during diastole is known as isolated systolic hypertension.
These effects of aging on blood vessels and the heart can be reduced by regular exercise since the exercise helps maintain fitness of the cardiovascular system in human beings. Exercise can also help maintain the muscular fitness of people as they begin to age. Exercise is thus considered to be extremely beneficial irrespective of their age at which it started.
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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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How The Heart Works
Do you know that your Heart is the strongest muscle of your body? The heart is formed of special type of muscles called the cardiac muscle that is present in your heart only and it is not found elsewhere in your body. This special strong muscle can easily explain how the heart works since you were in the uterus of your mother. The heart size is quite similar to the size of your fist. it is located in the middle of your chest cavity slightly to the left. The heart muscle functions as a pump which pumps blood to your body. The heart consists of four chambers. The two upper chambers are called the right and left atria and they function as reservoirs and the two lower chambers are called the right and left ventricles and they function as pumps. Flow of blood inside your heart is guarded by four heart valves which ensures flow of blood in one direction. The heart receives blood supply through small blood vessels called coronary arteries.
How The Heart Works As a Pump
When your body uses the blood to produce energy and to do its functions, it consumes a big portion of oxygen in your blood. This oxygen has to be renewed or “refilled”. The body returns this blood to the heart through the superior vena cava and inferior vena cava. These 2 big veins drain venous blood and bring it to the right atrium “See Image”. This venous (blue) blood passes from the right atrium through the tricuspid valve to the right ventricle. The right ventricle then pumps this blood through the pulmonary valve to the pulmonary artery. The pulmonary artery takes this blood all the way to your lungs. In the lungs your blood gets its “Refill” of oxygen and becomes oxygenated (red) blood. This oxygen rich blood is returned through the pulmonary veins to your left atrium and then through the mitral valve to your left ventricle. The left ventricle will pump this blood through the aortic valve to the aorta (biggest artery in the body). The aorta carries this oxygen rich blood to the body which uses it to do its function. This cycle is called the cardiac cycle or blood circulation and explains how the heart works physiologically.
How The Heart works Abnormally
As any pump, the heart can be damaged. When the heart is affected by disease, it functions abnormally. Disease which affect the heart muscle will impair the ability of this muscle to contract well. Heart failure will happen. The patient may then start to develop symptoms of heart failure such as shortness of breath. Other diseases can affect the heart valves. These diseases will affect the flow of blood inside the heart chambers. Blood will flow in directions that is different from normal. This can result in enlargement of heart, development of irregular heart beats and sometimes heart failure. Diseases of the coronary arteries will decrease the blood reaching the heart. This can result in chest pain. Sometimes coronary arteries are blocked suddenly and this will lead to a heart attack. Heart attacks or acute coronary syndromes can be life threatening and require immediate medical attention.