22.1
O Sistema Respiratório
O sistema respiratório é composto pelos órgãos que permitem a respiração. O ar entra pelas narinas e pela boca, seguindo para a faringe (garganta) e l…
O sistema respiratório consiste em uma série de passagens e dutos que trazem o ar da parte externa do corpo para os pulmões internos. O ar entra primeiro pelas narinas e na cavidade nasal onde o material particulado, potencialmente prejudicial para respirar como bactérias e sujeira, é filtrado por cabelos e muco e o ar mais limpo é aquecido e humidificado. O ar também pode fluir pela boca, alcançando a faringe e laringe antes de ser canalizado para a via aérea principal, a traqueia.
À medida que a traqueia leva para a cavidade torácica, as extremidades se bifurcam em dois brônquios, correspondendo para os pulmões esquerdo e direito, que estão rodeados por membranas pleurais e limitados inferiormente pelo diafragma. Dentro de cada pulmão, um brônquio se divide em ramos cada vez menores chamados bronquíolos. Nas pontas menores estão os dutos alveolares subdivididos em pequenos sacos de alvéolos, camadas finas de células parenquimatosas.
Essa organização fornece uma grande área de superfície para que ocorram as trocas gasosas com o sistema circulatório.
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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.