The Respiratory Cycle
The respiratory and circulatory systems have closely related jobs. The work of these two systems is sometimes referred to together as the cardiorespiratory system. The respiratory system is responsible for taking in oxygen and expelling carbon dioxide. However, it is dependent on the circulatory system to distribute the oxygen that has been taken in by the lungs to the body tissues. Similarly, the circulatory system picks up carbon dioxide from the tissues and delivers it to the lungs where it is exhaled. Every cell of the body requires oxygen to perform its jobs. Carbon dioxide is released as these jobs are performed and must be eliminated to prevent excess amounts from accumulating in the tissues. Continuous removal of carbon dioxide from the body is just as important for health as is a constant supply of oxygen. In the respiratory cycle, oxygen is picked up by the capillaries surrounding the alveoli (see Figure 1). The oxygen-rich blood is carried to the heart, which pumps the blood into arteries that carry it to the tissues of the body. In the tissues, capillaries release oxygen and pick up carbon dioxide. This carbon dioxide-rich blood is carried by veins back to the heart, which pumps it to the lungs. Carbon dioxide is released from the blood into the alveoli and new oxygen is picked up, beginning the cycle again. A more detailed discussion of the circulatory system is presented in the next section, The Circulatory System.
The success of the respiratory cycle is dependent on the very thin walls of the alveoli. These walls normally allow for a quick and easy exchange of oxygen and carbon dioxide. Lung diseases like emphysema and cancer can damage the delicate alveoli and interfere with the vital exchange of gases resulting in abnormal levels of oxygen and carbon dioxide in the blood.
The Circulatory System
Similar to the bronchial tree, the circulatory system is a branching network of blood vessels. The heart is at the center of the circulatory system. Its pumping action moves blood through the body. The heart has four compartments called chambers, two on the right and two on the left. The two chambers on the right work together as do the two chambers on the left. The top chambers of the heart are called the right atrium and left atrium. The bottom chambers are called the right ventricle and left ventricle (see Figure 2).
Blood passes through the alveolar capillaries releasing carbon dioxide and picking up oxygen. The oxygen-rich blood is delivered to the left atrium by the pulmonary veins (see Figure 3). Blood passes from the left atrium into the left ventricle, and is pumped out through the aorta to be distributed by a branching system of arteries, arterioles, and capillaries throughout the body. Lung diseases, including lung cancers, can affect the function of the right side of the heart since blood is pumped from the right side of the heart to the lungs. Although right heart abnormalities are not a common complication of lung cancer, they can occur. The left side of the heart is usually not affected by diseases of the lung. However, if the blood pressure in the lungs becomes very high, the left side of the heart can be affected.
The respiratory and circulatory systems have closely related jobs. The work of these two systems is sometimes referred to together as the cardiorespiratory system. The respiratory system is responsible for taking in oxygen and expelling carbon dioxide. However, it is dependent on the circulatory system to distribute the oxygen that has been taken in by the lungs to the body tissues. Similarly, the circulatory system picks up carbon dioxide from the tissues and delivers it to the lungs where it is exhaled. Every cell of the body requires oxygen to perform its jobs. Carbon dioxide is released as these jobs are performed and must be eliminated to prevent excess amounts from accumulating in the tissues. Continuous removal of carbon dioxide from the body is just as important for health as is a constant supply of oxygen. In the respiratory cycle, oxygen is picked up by the capillaries surrounding the alveoli (see Figure 1). The oxygen-rich blood is carried to the heart, which pumps the blood into arteries that carry it to the tissues of the body. In the tissues, capillaries release oxygen and pick up carbon dioxide. This carbon dioxide-rich blood is carried by veins back to the heart, which pumps it to the lungs. Carbon dioxide is released from the blood into the alveoli and new oxygen is picked up, beginning the cycle again. A more detailed discussion of the circulatory system is presented in the next section, The Circulatory System.
The success of the respiratory cycle is dependent on the very thin walls of the alveoli. These walls normally allow for a quick and easy exchange of oxygen and carbon dioxide. Lung diseases like emphysema and cancer can damage the delicate alveoli and interfere with the vital exchange of gases resulting in abnormal levels of oxygen and carbon dioxide in the blood.
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| Figure 1: The Respiratory Cycle. |
The Circulatory System
Similar to the bronchial tree, the circulatory system is a branching network of blood vessels. The heart is at the center of the circulatory system. Its pumping action moves blood through the body. The heart has four compartments called chambers, two on the right and two on the left. The two chambers on the right work together as do the two chambers on the left. The top chambers of the heart are called the right atrium and left atrium. The bottom chambers are called the right ventricle and left ventricle (see Figure 2).
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| Figure 2: Chambers of the Heart* Arrows show the direction of blood flow through the heart. |
Carbon dioxide-rich, oxygen-poor blood is delivered from the tissues of the body by the veins to the right atrium of the heart. Blood flows from the right atrium to the right ventricle, and then leaves the heart through the pulmonary artery (PA). Before reaching the lungs, the PA divides into a right and left branch, one for each lung. Once in the lungs, the PA branches several times into smaller blood vessels called arterioles. These arterioles run in the walls of the airway system’s bronchioles. The arterioles continue to branch and become progressively smaller until they reach the level of the alveoli. At the alveoli, the blood vessels have become the tiny, microscopic capillaries that are capable of gas exchange.
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| Figure3: Blood Flow through the Heart |
Blood passes through the alveolar capillaries releasing carbon dioxide and picking up oxygen. The oxygen-rich blood is delivered to the left atrium by the pulmonary veins (see Figure 3). Blood passes from the left atrium into the left ventricle, and is pumped out through the aorta to be distributed by a branching system of arteries, arterioles, and capillaries throughout the body. Lung diseases, including lung cancers, can affect the function of the right side of the heart since blood is pumped from the right side of the heart to the lungs. Although right heart abnormalities are not a common complication of lung cancer, they can occur. The left side of the heart is usually not affected by diseases of the lung. However, if the blood pressure in the lungs becomes very high, the left side of the heart can be affected.
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