Breathing+HW2+MC

Breathing SCI Human Biology - 1 Assigned: 9/29 Due: 10/1 Mechanism of Breathing pp. 174-176

1. Define inspiration, expiration. Inspiration is the active phase of ventilation because this is the phase in which the diaphragm and the external intercostal muscles contract. It’s also called inhalation, moving air into the lungs. Expiration is the passive phase of breathing, and no effort required to bring it about. It’s also called exhalation, moving air out of the lungs. 2. Where are the intercostal muscles? The intercostal muscles lie between the ribs. 3. Where is the diaphragm muscle? The diaphragm muscle is located below the lungs, which is the large dome-shaped muscle that contracts rhythmically and forms the floor of the thoracic cavity. 4. The lungs are in a "sealed" off thoracic cavity. Describe this cavity. Why is it considered "sealed"? The lungs lie within the sealed off cavity. That is exactly why it is considered “sealed” off, because it seals off the lungs, it protects the lungs, and it provides a cover over the lungs. The rib cage, consisting of the ribs joined to the vertebral column posteriorly and to the sternum anteriorly, forms the top and sides of the thoracic cavity. The diaphragm and the connective tissue form the floor of the thoracic cavity. 5. Describe the diaphragm and intercostal muscles during inspiration. During inspiration, the diaphragm contracts and becomes a flattened sheet of muscle. Also, the external intercostal muscles contract, and the rib cage moves upward and outward 6. Air does NOT force open the lungs. So why does air enter the lungs? The air enters the lungs because the thoracic cavity and lungs expand and because a continuous column of air reaches into the lungs. Air will naturally flow from outside the body into the respiratory passages and into the alveoli. 7. Passive Recoil occurs during expiration. What does that mean? The lungs recoil because the surface tension of the fluid lining the alveoli tends to draw them closed. The elastic properties of the thoracic wall and lungs cause them to recoil. 8. Why is air pushed out during expiration? During expiration, air is pushed out because the thoracic cavity and lungs resume their original positions and pressures. The pressure in lungs increases. We liken this phase of breathing to pushing the handles of bellows together, increasing the pressure inside and causing air to flow out, as the lung collapses. 9. How can you achieve maximum inspiratory effort? You have to involve muscles of the back, chest, and neck, which increases the size of the thoracic cavity larger than normal, thus allowing maximum expansion of the lungs. 10. How can you force expiration, which is usually passive? It accompanies the maximum inspiratory efforts of heavy exercise, and is also necessary to sing, blow air into a trumpet, or blow out birthday candles. Contraction of the internal intercostal muscles can force the rib cage to move downward and inward. 11. Do you use your total lung capacity when you breathe? What do you use? No we do not use our total lung capacity when we breathe. We use about a quarter of air when we breathe. 12. Why are the nasal cavities, trachea, bronchi, and bronchioles considered "dead air space"? They are considered dead space because some of the air inhaled never reaches the lungs; instead it fills the nasal cavities, trachea, bronchi, and bronchioles. These passages are not used for gas exchange, and therefore they are said to be dead air spaces. 13. How should you breathe to get the most fresh air to your alveoli? Why? It’s better to breathe slowly and deeply to ensure that newly inhaled air reaches the lungs.