Wednesday, August 1, 2012

Science Form 3 (Chapter 2) Blood Circulation and Transport


Introduction to function of Heart

The role of the heart is to pump oxygen-rich blood to every living cell in the body. In order to achieve its goal, it must continuously beat for a person’s entire lifespan. Because of its vital role, a non-beating heart always results in death. The human heart beats approximately 80,000 to 100,000 a day and pumps almost 2,000 gallons of blood. This means that in a person’s life lasting 70 to 90 years, the heart beats approximately two to three billion times and pumps 50 to 65 million gallons of blood. Because the heart is so essential for human sustenance, it is made up of a muscle different from skeletal muscle that allows it to constantly beat.

In order for the heart to deliver oxygenated blood to all cells, blood is pumped through arteries. Veins bring deoxygenated blood cells to the lungs, which then are oxygenated, and then sent back to heart. In this way, a continuous cycle is formed of the heart pumping oxygenated blood and deoxygenated blood out to their designated destinations, and therefore the heart maintains the circulatory system.

Systole: Stage when the ventricles of heart are contracting resulting in blood being pumped out to the lungs and the rest of the body.
- Thick, muscular walls of both ventricles contract.
- Pressure rises in both ventricles, causing the bicuspid and tricuspid valves to close. Therefore, blood is forced up the aorta and the pulmonary artery.
- The atria relax during this time. The left atrium receives blood from the pulmonary vein, and the right atrium from the vena cava.

Diastole: Stage when the ventricles of the heart are relaxed and not contracting. During this stage, the atria are filled with blood and pump blood into the ventricles.
- Thick, muscular walls of both ventricles relax.
- Pressure in both ventricles falls low enough for bicuspid valves to open.
- The atria contract, and blood is forced into the ventricles, expanding them. The blood pressure in the aorta is decreased, therefore the semi-lunar valves close.