23.3: Oxygenation and Gas Exchange
By the end of this section, you should be able to:
- 23.3.1 Describe the process of oxygenation.
- 23.3.2 Discuss the phases of gas exchange.
Two main functions of the lungs are oxygenation and gas exchange. Without these processes, the body would not get the oxygen that tissues and organs need and would not be able to expel waste gases from the body.
Oxygenation
Oxygenation is the process of supplying oxygen to body cells. When a person breathes in, oxygen diffuses and is picked up by the hemoglobin of the red blood cells. It is then transported and distributed to the organs and tissues of the body. All organs and tissues rely on oxygen to function properly.
The amount of oxygen bound to hemoglobin can be measured using oxygen saturation. This describes the percentage of hemoglobin currently bound to oxygen. Normal oxygen saturation is between 95% and 100% for a client breathing only room air.
When the tissues and organs lack oxygen, a condition called hypoxemia can result. Hypoxemia is lower-than-normal oxygen levels in the blood and often requires the client to receive concentrated oxygen. This condition can be fatal if not treated (Landry, 2022).
Gas Exchange
Gas exchange , shown in Figure 23.5, occurs when oxygen moves from the lungs to the bloodstream. For gas exchange to happen, the alveoli must be ventilated, gases must be diffused, and perfusion must take place. The pulmonary arteries bring venous blood from the right side of the heart to be oxygenated, and the gas exchange occurs in the pulmonary capillaries. The pulmonary veins then return the oxygenated blood to the left side of the heart, which pumps it out into the systemic circulation (Landry, 2022).
Ventilation
Ventilation is the process of moving air into and out of the lungs. It helps ensure that oxygen-rich air is brought into the lungs and carbon dioxide is expelled. The ventilation process also helps to maintain blood pH in the normal range by regulating the amount of carbon dioxide in the body.
Ventilation consists of inspiration and expiration. With inspiration, air flows into the body and travels through the respiratory system, down the airways, and into the alveoli. Upon normal expiration, the diaphragm and intercostal muscles relax, and air flows out of the alveoli and back through the respiratory system to the atmosphere (Landry, 2022).
Respiratory control is significantly influenced by chemical factors. Chemoreceptors sense changes in the levels of carbon dioxide, hydrogen ions, and oxygen in the blood. These receptors adjust the rate of ventilation in response to the amount of carbon dioxide in the blood. When carbon dioxide levels are too high, the respiratory rate increases to “blow off” the excess carbon dioxide. This, in turn, raises the pH level of blood because carbon dioxide is acidic. On the other hand, if carbon dioxide levels are too low, the respiratory rate will decrease to “hold on to” the carbon dioxide, thereby lowering the pH level (Landry, 2022).
Diffusion
Diffusion is the spontaneous movement of gases between the alveoli and capillaries in the lungs. This process does not require any use of energy or effort by the body. Diffusion of oxygen and carbon dioxide depends on the concentration or partial pressure of gases. The movement of gases always occurs from a high-pressure area to a low-pressure area. Diffusion can also be affected by the thickness of respiratory membranes and the thickness of the alveolar membrane (Dezube, 2023).
Perfusion
Perfusion is the process of blood flowing to tissues and organs, which is crucial for delivering oxygen and nutrients and removing waste products. Blood carries needed oxygen throughout the body, where it is used for various metabolic processes (Dezube, 2023).
In the lungs, perfusion takes place through the capillaries that surround the alveoli. This allows for the exchange of oxygen and carbon dioxide between the air in the lungs and the blood in the capillaries (Landry, 2022).
Perfusion can be affected by poor circulation, which reduces the amount of oxygen that is transported to the tissues and organs. Other factors that can affect perfusion are low circulating volume, the pumping ability of the heart, and low blood pressure (Dezube, 2023).