A. Air pressure in the lungs is higher than atmospheric pressure, and the diaphragm relaxes. B. Thoracic pressure decreases. C. The diaphragm contracts, enlarging the thoracic cavity. D. The intercostal muscles raise the ribs.
The correct answer is option A - Air pressure in the lungs is higher than atmospheric pressure, and the diaphragm relaxes. During expiration, the diaphragm relaxes, it does not contract (option C is incorrect). The diaphragm contracts and expands the thoracic cavity during inspiration. The volume in the thoracic cavity decreases these causes an increase in thoracic pressure.
A decrease in thoracic pressure is seen during inspiration (option B is incorrect). Intercostal muscles are muscles found between the ribs. They cause depression of the ribs and also decrease the pressure in the chest wall to force air out of the lungs. Intercostal muscles do not raise the ribs during expiration (option D is incorrect).
People breathe every second without even knowing it. Breathing is an automatic reaction that takes place all the time. When someone breathes air into their lungs, it is important that carbon dioxide is released. Since the pressure is greater outside of the lungs that forced the diaphragm to relax and forces the carbon dioxide out of the person’s mouth.
The diaphragm is an organ in the body that is located below the lungs. Once the diaphragm relaxes, the air can escape back up through pathways it came from. Sometimes, problems may occur. If someone is in water, they can’t take in air but they can release the air that is already in their lungs. The diaphragm still functions even though the person can’t breathe in air.