10.5.1. Working with texts. The heart and circulation
Read the text and complete the gaps with the words given.
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This text was adapted from Biology. Concepts and Connections. by Neil A. Campbell, Lawrence G. Mitchell, and Jane B. Reece. 1994. The Benjamin/Cummings Publishing Company, Inc. (p.415)
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aorta, arteries, atria, atrium, blood vessels, capillaries, cardiac muscle tissue, circulatory system, pulmonary circuit, veins, ventricles, venules
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Let’s see what happens to the O2 after it enters the body and the blood vessels through the lungs. O2 has to reach every single cell of the body, it reaches the cells of the body through the circulatory system. The engine driving the circulatory system is the heart.
The heart is a relatively small organ located in the chest and is made up of cardiac muscle tissue. It has four chambers: two ventricles and two atria. The two ventricles have thick walls and they pump blood to the body organs through the arteries. The two atria (sing. atrium) have thin walls and they receive blood returning to the heart via the veins.
This is how the circulatory system works.
The circulatory system comprises of two cycles, there is one cycle to the lungs called the pulmonary circuit, and another one to the body organs, called the systemic cycle.
Blood with high CO2 level is pumped from the right ventricle through the pulmonary arteries to the lung. As you have seen in 8.4.2., in the alveoli of the lung the blood gets rid of CO2 and takes up O2. Blood rich in O2 from the lungs flows back to the heart through the pulmonary veins to the left atrium. The first cycle is now completed. The next step is to make sure that blood rich in O2 reaches the organs of the body. This happens through the second cycle, the systemic cycle. Blood rich in O2 is pumped from the left atrium to the left ventricle of the heart. The blood from the left ventricle flows through the aorta, which is the largest blood vessel in the body. Many arteries branch from the aorta, they carry blood to different body organs. O2 is taken to the body organs through capillaries, and blood loaded with CO2 from the organs is collected by the venules. Venules carry blood back to the veins. Blood from the veins flows into the right atrium, then to the right ventricle, and then the cycle is completed.