How Your Lungs Work

Your lungs are located within your chest cavity inside the rib cage (see illustration below). They are made of spongy, elastic tissue that stretches and constricts as you breathe. The airways that bring air into the lungs (thetrachea和支气管）由平滑的肌肉和软骨制成，使气道可以收缩和膨胀。肺部和气道带来了新鲜的氧气富含空气，并摆脱了细胞制造的废物二氧化碳。它们还有助于调节血液中氢离子（pH）的浓度。

当您吸气时diaphragm和intercostal muscles(those are the muscles between your ribs) contract and expand the chest cavity. This expansion lowers the pressure in the chest cavity below the outside air pressure. Air then flows in through the airways (from high pressure to low pressure) and inflates the lungs. When you exhale, the diaphragm and intercostal muscles relax and the chest cavity gets smaller. The decrease in volume of the cavity increases the pressure in the chest cavity above the outside air pressure. Air from the lungs (high pressure) then flows out of the airways to the outside air (low pressure). The cycle then repeats with each breath.

As you breathe air in through your鼻子or mouth, it goes past theepiglottis并进入trachea. It continues down the trachea through your vocal cords in thelarynxuntil it reaches the支气管. From the bronchi, air passes into each lung. The air then follows narrower and narrower细支气管until it reaches the肺泡.

在每个空气囊中，氧气浓度很高，因此氧气通过牙槽膜进入或扩散pulmonary capillary. At the beginning of the pulmonary capillary, the血红蛋白in the red blood cells has carbon dioxide bound to it and very little oxygen (see illustration above). The oxygen binds to hemoglobin and the carbon dioxide is released. Carbon dioxide is also released from sodium bicarbonate dissolved in the blood of the pulmonary capillary. The concentration of carbon dioxide is high in the pulmonary capillary, so carbon dioxide leaves the blood and passes across the alveolar membrane into the air sac. This exchange of gases occurs rapidly (fractions of a second). The carbon dioxide then leaves the alveolus when you exhale and the oxygen-enriched blood returns to the heart. Thus, the purpose of breathing is to keep the oxygen concentration high and the carbon dioxide concentration low in the alveoli so this gas exchange can occur!

肺解剖学

You don't have to think about breathing because your body's autonomic nervous system controls it, as it does many other functions in your body. If you try to hold your breath, your body will override your action and force you to let out that breath and start breathing again. The respiratory centers that control your rate of breathing are in the brainstem ormedulla. The nerve cells that live within these centers automatically send signals to the diaphragm and intercostal muscles to contract and relax at regular intervals. However, the activity of the respiratory centers can be influenced by these factors:

在这些因素中，最大的影响是您的血液和CSF中的二氧化碳浓度，然后是氧气浓度。

有时，呼吸中心会暂时出差，并向隔膜发送额外的冲动。这些冲动会导致不必要的收缩（hiccups). The same thing happens in unborn children; many pregnant women often feel their babies hiccup. This happens because the respiratory centers of the developing child's brain are working just like those of an adult even though they are not yet breathing air.

There are many common conditions that can affect your lungs. Diseases or conditions of the lung fall mainly into two classes — those that make breathing harder and those that damage the lungs' ability to exchange carbon dioxide for oxygen.

影响呼吸机制的疾病或状况：

Diseases or conditions that minimize or prevent gas exchange:

Originally Published: Oct 6, 2000