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Health & PE10 Human Movement (2015): Heart

Heart

 

The heart, a hollow muscular organ, is located in the centre of the chest. The right and left sides of the heart each have an upper chamber (atrium), which collects blood and pumps it into a lower chamber (ventricle), which pumps blood out.

To ensure that blood flows in only one direction, each ventricle has an "in" (inlet) valve and an "out" (outlet) valve. In the left ventricle, the inlet valve is the mitral valve, and the outlet valve is the aortic valve. In the right ventricle, the inlet valve is the tricuspid valve, and the outlet valve is the pulmonary (pulmonic) valve. Each valve consists of flaps (cusps or leaflets), which open and close like one-way swinging doors. The mitral valve has two cusps. The other valves (tricuspid, aortic, and pulmonary) have three. The large inlet valves (mitral and tricuspid) have tethers—consisting of the papillary muscles and cords of tissue—which prevent the valves from swinging backward into the atria. If a papillary muscle is damaged (for example, by a heart attack), the valve may then swing backward and start leaking. If a valve opening is narrowed (often present at birth or caused by an infection), blood flow through the valve is reduced. Both leaking and reduced blood flow may occur in the same valve.

The heartbeats are evidence that the heart is pumping. The first sound (the lub of lub-dub) is the sound of the mitral and tricuspid valves closing. The second sound (the dub) is the sound of the aortic and pulmonary valves closing. Each heartbeat has two parts: diastole and systole. During diastole, the ventricles relax and fill with blood. Then the atria contract, forcing more blood into the ventricles. During systole, the ventricles contract and pump blood, and the atria relax and begin filling with blood again.

 

Blood Vessels

The blood vessels consist of arteries, arterioles, capillaries, venules, and veins. All blood is carried in these vessels. The arteries, which are strong, flexible, and resilient, carry blood away from the heart and bear the highest blood pressures. Because arteries are elastic, they narrow (recoil) passively when the heart is relaxing between beats and thus help maintain blood pressure. The arteries branch into smaller and smaller vessels, eventually becoming very small vessels called arterioles. Arteries and arterioles have muscular walls that can adjust their diameter to increase or decrease blood flow to a particular part of the body.

Capillaries are tiny, extremely thin-walled vessels that act as a bridge between arteries (which carry blood away from the heart) and veins (which carry blood back to the heart). The thin walls of the capillaries allow oxygen and nutrients to pass from the blood into tissues and allow waste products to pass from tissues into the blood.

Blood flows from the capillaries into very small veins called venules, then into the veins that lead back to the heart. Veins have much thinner walls than do arteries, largely because the pressure in veins is so much lower. Veins can widen (dilate) as the amount of fluid in them increases. Some veins, particularly veins in the legs, have valves in them, to prevent blood from flowing backward. When these valves leak, the backflow of blood can cause the veins to stretch and become elongated and convoluted (tortuous). Stretched, tortuous veins near the body's surface are called varicose veins 

Blood travels from the heart in arteries, which branch into smaller and smaller vessels, eventually becoming arterioles. Arterioles connect with even smaller blood vessels called capillaries. Through the thin walls of the capillaries, oxygen and nutrients pass from blood into tissues, and waste products pass from tissues into blood. From the capillaries, blood passes into venules, then into veins to return to the heart.

Arteries and arterioles have relatively thick muscular walls because blood pressure in them is high and because they must adjust their diameter to maintain blood pressure and to control blood flow. Veins and venules have much thinner, less muscular walls than arteries and arterioles, largely because the pressure in veins and venules is much lower. Veins may dilate to accommodate increased blood volume.

HOW WELL DO YOU KNOW YOUR HEART?

 

 

Click on the heart and answer some questions