Archive for the ‘Cardio & Blood-Cholesterol’ Category

A MATTER OF THE HEART: THE CIRCULATION

Saturday, February 26th, 2011
You begin to marvel at the way it continues to beat 100000 times a day, continuously pumping about 5 litres of blood per minute around the circulatory system, handling some 7000 litres of blood every 24 hours. That means that, in the average lifetime, nearly 200 million litres are circulated around the body.
The basic route of the blood’s remarkable journey is this. Fresh blood (i. e., blood saturated with oxygen (O2) and bright red in colour) is pushed from the left ventricle through the aortic valve into the aorta. It then flows through the arteries to all parts of the body, where it supplies the various tissues with essential oxygen and other nutrients. Once these life-giving nutrients have been expended, leaving in their stead carbon dioxide (CO2), water and other waste-products, the blood, now dark purplish-red (it is often called ‘blue’ or venous blood) flows through the veins back to the heart, entering the right atrium (or receiving area). It then passes through the tricuspid valve into the right ventricle; from here it is pumped through the pulmonary valve into the pulmonary artery, which leads to the lungs. In the lungs the blood is oxygenated and water and CO2 are extracted; it then flows through the pulmonary veins to the left atrium, ready to begin the cycle again.
There is, then, a strict route taken by the blood: from the body via the veins to the right side of the heart, from there to the lungs, from the lungs to the left side of the heart and from there back to the body via the arteries. This is where those one-way valves become important, ensuring that the blood does not seep back. And, of course, in order to maintain sufficient driving force the heart has to keep going – the body cannot wait for fresh supplies of oxygenated blood. The wastes soon become toxic unless they are removed and replaced by fresh oxygen.
The blood is carried by three kinds of vessels: arteries, which take blood from the heart to the body’s tissues and lungs; veins, which carry it on its return journey to the heart; and capillaries, which act as link roads, as it were, connecting the smaller arteries to the smaller veins. (Note that, while normally veins carry ‘blue’ blood and arteries carry oxygenated blood, the pulmonary vessels are the exception – the pulmonary vein carries red blood and the pulmonary artery carries ‘blue’.) Thus when an artery reaches a muscle, for example, it will branch out into tiny capillaries so that the blood can enter the muscle itself. After being deprived of its oxygen and loaded with waste products, the blood then leaves the muscle through a similar network of capillaries which then join up at a vein. Think of the capillaries as the smallest twigs of a tree, carrying nourishment from the main boughs and larger branches to all the leaves.
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A MATTER OF THE HEART: THE CIRCULATIONYou begin to marvel at the way it continues to beat 100000 times a day, continuously pumping about 5 litres of blood per minute around the circulatory system, handling some 7000 litres of blood every 24 hours. That means that, in the average lifetime, nearly 200 million litres are circulated around the body.The basic route of the blood’s remarkable journey is this. Fresh blood (i. e., blood saturated with oxygen (O2) and bright red in colour) is pushed from the left ventricle through the aortic valve into the aorta. It then flows through the arteries to all parts of the body, where it supplies the various tissues with essential oxygen and other nutrients. Once these life-giving nutrients have been expended, leaving in their stead carbon dioxide (CO2), water and other waste-products, the blood, now dark purplish-red (it is often called ‘blue’ or venous blood) flows through the veins back to the heart, entering the right atrium (or receiving area). It then passes through the tricuspid valve into the right ventricle; from here it is pumped through the pulmonary valve into the pulmonary artery, which leads to the lungs. In the lungs the blood is oxygenated and water and CO2 are extracted; it then flows through the pulmonary veins to the left atrium, ready to begin the cycle again.There is, then, a strict route taken by the blood: from the body via the veins to the right side of the heart, from there to the lungs, from the lungs to the left side of the heart and from there back to the body via the arteries. This is where those one-way valves become important, ensuring that the blood does not seep back. And, of course, in order to maintain sufficient driving force the heart has to keep going – the body cannot wait for fresh supplies of oxygenated blood. The wastes soon become toxic unless they are removed and replaced by fresh oxygen.The blood is carried by three kinds of vessels: arteries, which take blood from the heart to the body’s tissues and lungs; veins, which carry it on its return journey to the heart; and capillaries, which act as link roads, as it were, connecting the smaller arteries to the smaller veins. (Note that, while normally veins carry ‘blue’ blood and arteries carry oxygenated blood, the pulmonary vessels are the exception – the pulmonary vein carries red blood and the pulmonary artery carries ‘blue’.) Thus when an artery reaches a muscle, for example, it will branch out into tiny capillaries so that the blood can enter the muscle itself. After being deprived of its oxygen and loaded with waste products, the blood then leaves the muscle through a similar network of capillaries which then join up at a vein. Think of the capillaries as the smallest twigs of a tree, carrying nourishment from the main boughs and larger branches to all the leaves.*5/353/5*