22.1
呼吸器系
呼吸器系は、呼吸をするための器官で構成されています。空気は鼻孔と口から入り、咽頭（のど）、喉頭（声帯）を経て、気管（風の通り道）へとつながます。胸腔内では、気管は2本の気管支に分かれ、空気は肺に入ります。気管支は徐々に小さな気管支に分かれ、肺胞と呼ばれる肺の中の小さな袋のグループで終わり、そこでガス…
呼吸器系は 一連の通路と管で構成されており 外から空気を体内に取り込み、肺まで届けます。空気はまず、鼻孔から入り 次に鼻腔へと送られ バクテリアやほこりなどといった 害を及ぼす可能性がある微粒子状物質を 毛や粘液で除去し、きれいな空気を温め湿らせます。空気は口からも入り 咽頭と喉頭を通った後 主な気道である気管に入ります。軟骨性の管である気管は平滑筋でできており 呼吸に必要な収縮と弛緩をもたらします。気管は胸腔に通じており そこから2つの気管支に別れ 左と右の肺へと繋がっています。肺は側膜で囲まれており 下方は横隔膜と結合しています。各肺では気管支が徐々に細かく枝分かれした 細気管支へと続いています。最小の先端である肺胞管では 薄層の実質細胞である 肺胞という小さな嚢に細分されています。こうした組織は、循環系で生じるガス交換において 広い表面積をもたらします。
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Q1: How does air travel through the respiratory system from the nostrils to the lungs?
Air enters through the nostrils into the nasal cavity where hairs and mucus filter out harmful particles like bacteria and dirt. The air is then warmed and humidified before traveling through the pharynx and larynx into the trachea. The trachea bifurcates into two bronchi that lead to the left and right lungs, where air continues through progressively smaller bronchioles to reach the alveoli for gas exchange.
Q2: What role do cilia and mucus play in keeping the lungs clean?
The bronchi and bronchioles are lined with cilia that beat upward to move mucus and trapped debris toward the throat for disposal through swallowing. This mucus traps foreign particles that pass through the nasal cavity defenses or enter via the mouth. Smoking damages cilia, making mucus removal difficult and increasing susceptibility to respiratory infections.
Q3: Why is the structure of alveoli important for lung function?
Alveoli are tiny sacs where gas exchange occurs between the lungs and the circulatory system. Each alveolar duct divides into approximately 100 alveolar sacs, each containing 20-30 alveoli. This grape-like structure maximizes surface area—the lungs contain 75 square meters of alveoli surface area, equivalent to a small apartment, enabling efficient oxygen uptake and carbon dioxide removal.
Q4: What is the function of the trachea and how does its structure support breathing?
The trachea is a 10-12 centimeter tube located in front of the esophagus that allows air to enter and exit the lungs. Its C-shaped hyaline cartilage keeps the trachea open during breathing. When smooth muscle in the trachea contracts, the diameter decreases and exhaled air is pushed out forcefully, as occurs during coughing.
Q5: How do the bronchi and bronchioles organize air distribution in the lungs?
As the trachea enters the thoracic cavity, it bifurcates into two bronchi corresponding to the left and right lungs. Each bronchus then splits into increasingly smaller branches called bronchioles. This branching pattern creates a tree-like structure that distributes air throughout the lungs while maximizing surface area for gas exchange.
Q6: What happens if the throat or mouth is blocked and breathing is obstructed?
In cases of damage to the throat or mouth that blocks breathing, a tracheostomy—a surgically-created hole in the trachea—can allow air to enter and exit the lungs, bypassing the obstruction. This procedure provides an alternative airway when normal breathing passages are compromised.
Q7: How does the nasal cavity prepare air before it reaches the lungs?
The nasal cavity filters, warms, and humidifies incoming air. Hairs and mucus in the nasal cavity trap particulate matter such as bacteria and dirt that could be harmful if inhaled. This initial processing ensures that cleaner, conditioned air reaches the lower respiratory tract and lungs.