The Heart and It’s Working - 2

The veins walls are considerably thinner in comparison to arterial walls. The larger veins have a system of internal one-way valves which do not allow the blood from flowing downward under the pull of gravity when person stands up. When a human being makes movement, the veins get squeezed by the surrounding muscle that helps in moving more blood towards the heart. Without valves in the veins, blood would move in the legs, which would then be continuing to grow.

The Pulmonary Circulation

The most important function of the pulmonary circulation is to transfer oxygen to the blood and free it from carbon dioxide. This task is completed when the blood flows through the lungs. The pressure at this part of the system is only about one-sixth as great as in the systemic circulation, and the pulmonary arteries walls and veins are thinner in comparison to the walls of other vessels in the rest of the body. In the pulmonary circulation, the role of arteries and veins are the opposite of what they do in the systemic circulation. Blood in the arteries has lesser oxygen, while blood in the veins has higher oxygen. The circuit starts with the pulmonary artery, which extends from the right ventricle and brings blood with low level oxygen content to the lungs. In the lungs, it branches off into the two different arteries, one for each lung, and then into arterioles and capillaries. The gas exchange between the air we breathe in and the blood takes place in the pulmonary capillaries. Pulmonary Capillaries walls work like filters by permitting molecules of gas to pass through but not to molecules of fluid. The total surface area of the capillaries in the lungs ranges from around 500 to 1,000 square feet.

Blood Vascular function

Blood is a life-saving fluid which helps to maintain an optimum environment in the body by providing a regular supply of nutrients from the outer world and removing waste products from the tissues present in body. Its cells are produced in the bones marrow, primarily in the flat bones like the ribs and the breastbone. The volume of blood in an average adult human being amounts to around 10.5 pints.

Heart and its working

In an adult, the pacemaker makes almost 72 impulses in a minute in the rest condition; it means that in one minute the heart goes through a full cardiac cycle around 72 times. Normally, as good the physical fitness of an individual is, as slower the heart rate at rest will be. Some of the very good athletes are known to have a pulse rate of 35 beats per minute which is half the average figure for the general population. For them, the slow heart rate is enough and does not make any danger.
As the lungs are very close to the heart and the walls of the pulmonary vessels, which are thinner so offer less resistance, the right ventricle does not have to exert nearly as much energy to do its job of supplying blood to the lungs as the left ventricle does in supplying to the rest of the body, is known as the cardiac output. When there is a requirement for an increased blood supply, as during physical stress, the heart most increases its output by beating faster. This mechanism has its limits: Above a certain rate, the heart chambers do not have time to fill properly and fail to pump efficiently.

The cardiac output is examined by the heart rate as well as by the amount of blood that ventricles eject or pump out in each contraction. This amount is known as the stroke volume. Usually the ventricles force about half the blood they contain, which corresponds to about 3 ounces in an average person at his rest position. A decrement in the stroke volume is one of the first signs of a heart failing. When both ventricles pump out, the same amount of blood in each stroke, cardiologists usually measure only the stroke volume of the left ventricle.

Heart and Circulation

Blood Circulatory system in our body is a system of large and small elastic vessels which transports or conveys blood throughout the body parts. In one day, blood pumped through the heart of a normal healthy adult at rest reaches around 2,100 gallons.
Heart is the central organism of the cardiovascular system and it is located between the two lungs in the middle of the chest. Two-third part of the heart lies in the left of the breastbone and remaining one third in the right. Putting a hand on left side the chest, we can easily feel heartbeats on the left side of the rib cage because at that place, the bottom left corner part of the heart, that is somewhat tilted forward, comes nearest to the body surface. The heart of an adult is about the size of two clenched fists. Heart shape is conical and it weighs around 7 to 15 ounces, depends on the size and weight of the individual.
The human heart has four chambers:
• The right atrium and right ventricle.
• The left atrium and left ventricle.
The chamber walls are made of a special kind of muscle myocardium which contracts rhythmically under the stimulation of electrical currents. The left and right atria and the left and right ventricles are separated from each other by a muscle wall known as the septum. Blood returning from the body through the venous system enters into the heart through the right atrium, where it is collected and is then pumped to the right ventricle. Each time when the right ventricle contracts; it propels this collected blood, which is low in oxygen content, into the lungs; there it is enriched with oxygen. Pulmonary veins transfer the blood to the left atrium, which contracts and pass it to the left ventricle. The left ventricle, which is the main pumping chamber of the heart, ejects the blood.