Blood flows from right heart to lungs to left heart to body

Let's follow the circulation of the blood through the heart, starting in the right heart. The right atrium receives deoxy-genated blood from the superior (upper) vena cava and the inferior (lower) vena cava (see Figure 49.3), large veins that collect blood from the upper and lower body, respectively.

M "Lub": The ventricles contract, the atrioventricular valves close, and pressure in the ventricles builds up until the aortic and pulmonary valves open.

3} Blood is pumped out of the ventricles and into the aorta and pulmonary artery.

The veins of the heart itself also drain into the right atrium. From the right atrium, the blood flows into the right ventricle. Most of the filling of the ventricle results from passive flow while the heart is relaxed between beats. Just at the end of this period of ventricular filling, the atrium contracts and adds a little more blood to the ventricular volume. The right ventricle then contracts, pumping the blood into the pulmonary artery, which transports it to the lungs.

After gas exchange occurs in the lungs, the pulmonary veins return the oxygenated blood from the lungs to the left atrium, from which the blood enters the left ventricle. As with the right side of the heart, most left ventricular filling is passive, but the ventricle is topped off by contraction of the atrium just at the end of the period of passive filling.

The walls of the left ventricle are powerful muscles that contract around the blood with a wringing motion starting from the bottom. When pressure in the left ventricle is high

49.4 The Cardiac Cycle The rhythmic contraction (systole) and relaxation (diastole) of the ventricles is called the cardiac cycle.The graphical representation below shows pressure and volume changes during the cardiac cycle for the left ventricle only.

4} "Dub": The ventricles relax; pressure in the ventricles falls at the end of systole, and since pressure is now greater in the aorta, the aortic and pulmonary valves slam shut.

I The ventricles fill with blood.

Right atrium

Right ventricle

Left ventricle

3} Blood is pumped out of the ventricles and into the aorta and pulmonary artery.

I The ventricles fill with blood.

Heart Pressure Left Right Ventricle

Volume in left ventricle, ml ( )

Right atrium

Right ventricle

Left ventricle

Pressure in left ventricle, mm Hg

Pressure in aorta, mmHg ( )

Time (seconds)

Pressure in left ventricle, mm Hg

Pressure in aorta, mmHg ( )

Volume in left ventricle, ml ( )

Time (seconds)

enough to push open the aortic valve, the blood rushes into the aorta to begin its circulation throughout the body. In Figure 49.3, observe that the left ventricle is more massive than the right ventricle. The left ventricle has to propel the blood through many more kilometers of blood vessels than does the right ventricle and must therefore push against more resistance, even though both pump the same volume of blood.

Both sides of the heart contract at the same time. The contraction of the two atria, followed by the contraction of the two ventricles and then relaxation, is called the cardiac cycle. Contraction of the ventricles is called ventricular systole, and relaxation of the ventricles called ventricular diastole (Figure 49.4). Just at the end of diastole, the atria contract and top off the volume of blood in the ventricles. The sounds of the cardiac cycle, the "lub-dub" heard through a stethoscope placed on the chest, are created by the slamming shut of the heart valves. The closing and opening of these valves are simple mechanical events resulting from pressure differences on the two sides of the valves. As the ventricles begin to contract, the pressure in the ventricles rises above the pressure in the atria, blood starts flowing back into the atria, and the atrioventricular valves close ("lub"). When the ventricles begin to relax, the high pressure in the aorta and pulmonary artery causes blood to start to flow back into the ventricles, and this flow of blood closes the aortic and pulmonary valves ("dub"). Defective valves produce turbulent blood flow and produce the sounds known as heart murmurs. For example, if an atrioventricular valve is defective, blood will flow back into the atrium with a "whoosh" sound following the "lub."

The cardiac cycle can be felt in the pulsation of arteries such as the one that supplies blood to your hand. You can feel your pulse by placing two fingers from one hand lightly over the wrist of the other hand just below the thumb. During systole, blood surges through the arteries of your arm and hand, and you can feel the surge as a pulsing of the artery in your wrist.

Blood pressure changes associated with the cardiac cycle can be measured in the large artery in your arm by using an inflatable pressure cuff and a pressure gauge, together called a sphygmomanometer, and a stethoscope (Figure 49.5). This method measures the minimum pressure necessary to compress an artery so that blood does not flow through it at all (the systolic value) and the minimum pressure that permits intermittent flow through the artery (the diastolic value). In a conventional blood pressure reading, the systolic value is placed over the diastolic value. Normal values for a young adult might be 120 mm of mercury (Hg) during systole and 80 mm Hg during diastole, or 120/80.

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Responses

  • j
    Why is left ventricle more massive than right ventricle?
    7 years ago
  • tanja
    How the blood flows through the heart steps?
    6 years ago
  • roderic lothran
    When the left ventricle contracts blood push out the body.this surge in blood causes?
    3 years ago
  • annie
    Did ventricle pushes all the blood to lungs and aorta?
    2 years ago
  • luca
    Why not blood flow from atrium to ventrium?
    1 year ago
  • blair maclean
    Where does blood pushes out in heart?
    1 year ago

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