In a gas, pressure increases as volume decreases. If the two- and one-litre containers were connected by a tube and the volume of one of the containers were changed, then the gases would move from higher pressure (lower volume) to lower pressure (higher volume). In this formula, P1 represents the initial pressure and V1 represents the initial volume, whereas the final pressure and volume are represented by P2 and V2, respectively. Boyle’s law is expressed by the following formula: Therefore, the pressure in the one-litre container (one-half the volume of the two-litre container) would be twice the pressure in the two-litre container. Pressure and volume are inversely related ( P = k/ V). Likewise, if volume decreases, pressure increases. Boyle discovered that the pressure of a gas is inversely proportional to its volume: If volume increases, pressure decreases. Boyle’s law describes the relationship between volume and pressure in a gas at a constant temperature. At a constant temperature, changing the volume occupied by the gas changes the pressure, as does changing the number of gas molecules. Therefore, the pressure is lower in the two-litre container and higher in the one-litre container. In this case, the force exerted by the movement of the gas molecules against the walls of the two-litre container is lower than the force exerted by the gas molecules in the one-litre container. For example, a certain number of gas molecules in a two-litre container has more room than the same number of gas molecules in a one-litre container (Figure 8.3.1). In a gas, pressure is a force created by the movement of gas molecules that are confined. Inspiration (or inhalation) and expiration (or exhalation) are dependent on the differences in pressure between the atmosphere and the lungs. However, the ability to breathe-to have air enter the lungs during inspiration and air leave the lungs during expiration-is dependent on the air pressure of the atmosphere and the air pressure within the lungs. The alveolar and intrapleural pressures are dependent on certain physical features of the lung. The major mechanisms that drive pulmonary ventilation are atmospheric pressure ( Patm) the air pressure within the alveoli, called alveolar pressure ( Palv) and the pressure within the pleural cavity, called intrapleural pressure ( Pip). Pulmonary ventilation is the act of breathing, which can be described as the movement of air into and out of the lungs. Discuss factors that can influence the respiratory rate.
Describe the respiratory centres of the pons.Describe the respiratory centres of the medulla oblongata.Outline the mechanisms behind the control of breathing.Discuss the meaning of respiratory volume and capacities.Discuss the physical factors related to breathing.List the steps involved in pulmonary ventilation.Discuss how pressure, volume, and resistance are related.Describe the mechanisms that drive breathing.By the end of this section, you will be able to:
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