Physiology of the Respiratory System

Describe how to calculate the inspiratory reserve volume.

As stated earlier, vital capacity is the sum of inspiratory reserve volume, tidal volume and expiratory reserve volume (VC = IRV + TV + ERV). Therefore, IRV can be calculated by subtracting tidal volume and expiratory reserve volume from vital capacity (IRV = VC - TV - ERV).

Use Boyle's law to explain the process of pulmonary ventilation.

Boyle's law state that there is an inverse relationship between volume and pressure. As the volume of a container increases, the pressure of gas inside the container decreases. As the volume of a container decreases, the pressure of gas inside the container increases. During inhalation in pulmonary ventilation, the lungs expand causing an increase in lung volume; thus, the pressure in the lungs decreases. Because the pressure inside the lungs is less than the pressure in the atmosphere, air rushes into the lungs (movement of gas is from an area of higher pressure to area of lower pressure). During exhalation in pulmonary ventilation, the lungs' volume is decreased causing the pressure inside the lungs to increase. Because the pressure inside the lungs is greater than the pressure in the atmosphere, air rushes out of the lungs and into the atmosphere.

How do external and internal respiration differ?

External respiration is the exchange of gases between the lungs and the blood. Oxygen rich air diffuses through the alveolar wall of the lungs, and moves into the capillaries. Concurrently, carbon dioxide moves into the lungs and it is expelled during exhalation. Internal respiration is the exchange of gases between the blood and surrounding tissues. Oxygenated blood travels to the circulatory system, where the oxygen is unloaded and the carbon dioxide is taken up from the cells. Oxygen is needed for cellular respiration to produce ATP, carbon dioxide and water.

expiration

It is also known as exhalation. The diaphragm relaxes and returns to its dome-shaped. The internal intercostal contracts, while the external intercostal relaxes causing the depression of the rib cage. As a result, thoracic volume is decreased and the thoracic pressure is increased, which forces the air out of the lungs.

inspiration

It is also known as inhalation. The diaphragm flattens on the floor of the thoracic cavity as it contracts. The external intercostal also contracts increasing the volume of the thoracic cavity. As a result, thoracic volume is increased and thoracic pressure is decreased causes the expansion of the lungs and a reduction in lung pressure leading to the movement of oxygen rich air into the lungs.

tidal volume

It is the amount of air during a normal breathing (inhalation and exhalation). The average TV of is approximately 500 ml per inspiration.

expiratory reserve volume

It is the amount of air that can be forced out of exhalation after a normal inhalation. The average ERV is approximately 1,000 ml.

minute volume

It is the amount of air that is exchanged between the lungs and the environment. It is the product of tidal volume and respiratory rate (MV = TV x RR). The normal MV is 6,000-10,000 ml/min.

residual volume

It is the amount of air that is left in the lungs that cannot be forcefully exhaled. Residual volume averages at 1,200ml.

respiratory rate

It is the amount of breaths taken in a minute. The normal RR of a resting adult is 12-20 per minute.

intrapulmonary pressure

The pressure in the lungs that allows the exchange of carbon dioxide and oxygen gases. During inhalation, the pressure in the lungs is less than the atmospheric pressure (volume increases due to lung expansion resulting in reduction in pressure); thus, air moves in the lungs. During exhalation, the pressure in the lungs is greater than the atmospheric pressure (lung volume decrease and pressure increases); thus, air moves out of the lungs.

pulmonary ventilation

This is also known as breathing. It is the movement of air into the lungs during inhalation, and out of the lungs during exhalation that requires the relaxation or contraction of the diaphragm, intercostal and abdominal muscles.

vital capacity

This is the maximum amount of air that can be exhaled after a maximum inhalation. The average VS is about 4,500-5,000 ml. In addition, vital pressure is the sum of inspiratory reserve volume, tidal volume and expiratory reserve volume.

spirometer

instrument used to measure respiratory volumes

total lung capacity

vital capacity + residual volume averages 5,900 ml