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Biology 2nd Baccalaureate

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4.1.1. Airways


The nostrils are the two cavities that communicate with the outside through the nostrils. It is the entry point for air into the lungs.        

The inner wall is covered by a nasal mucosa that allows:

  • Heat the air, as it has abundant capillaries with blood at body temperature. They also have recesses that increase the path of the air and that it can be heated more.
  • Moisten the air.
  • Clean the air through mucus and nasal hairs.
  • Identify odors by smell (olfactory mucosa) .

Answer in your notebook

4.1.- Why do you think it is better to breathe through the nose than through the mouth?

Answer in your notebook

4.2.- Why do we cough when we are breathing in a place that has a lot of dust?


The pharynx is a common organ of the digestive and respiratory systems. It is a short muscular tube that connects the mouth, nostrilswindpipe, and esophagus.       

The pharynx is also connected to the ear through the Eustachian tube, whose function is to balance the air pressure between the ear and the mouth.

In the walls of the pharynx are the tonsils, glands with immune function, which produce white blood cells that defend us against infections.     

Aparato respiratorio

By Lord Akryl (original author); translated by Angelito7 (File:Illu conducting passages.svg) [Public domain or Public domain], via Wikimedia Commons


The larynx is made up of cartilage that allows the larynx to be always open. It is located between the pharynx and the trachea. Its entry is regulated by the epiglottis, the membrane that separates the respiratory tract from the digestive tract when swallowing occurs, preventing food from entering the lung.         

In the larynx there are also the vocal cords, made up of cartilage and muscles that allow phonation .

Curiosity: Why does helium make our voices change?

Surely you have ever tried with a helium balloon that was deflating, or surely you have seen on television, that inhaling the helium gas the voice becomes much higher-pitched producing a fun effect. This is because helium is much less dense than air, which is why the vocal cords vibrate more frequently and produce a higher pitch. The speed of sound in air is 344 m / s, while in helium it is 927 m / s.

You have to be very careful when playing with helium because there is a risk of suffocation, since we stop receiving oxygen, and this joke cannot last long.

Another curious fact about helium is that, despite being the second most abundant element in the universe, it is very scarce on Earth because it is in the form of gas and, due to its low density, it escapes into space.

Trachea or windpipe

It is a tube of about 13 cm that remains open due to 20 semicircular cartilaginous rings, open at the back, which allow air to pass through constantly.

Inside, its cells form mucus that trap foreign particles in the air, and clean it. These cells have cilia, filaments that vibrate, moving the mucus with impurities to the outside to be expelled.

If cilia and mucus are not enough to clear the airways, coughing and sneezing can clear them.

Tráquea ramificándose en dos bronquiosArtificial Trachea, by Chris Carr - OpenWetWare. (s. f.). Recuperado 11 de julio de 2013, a partir de,_by_Chris_Carr


The trachea divides into two bronchi, one leading to each lung.   

Its structure is similar to that of the trachea, formed by cartilaginous rings.  


The bronchi branch out to form the bronchioles, smaller diameter tubes.

The bronchioles branch, in turn, into smaller ones until they end up in small sacs, the pulmonary alveoli. The set of each bronchus and its branchioles into which it branches forms the bronchial tree.

Bronchial anatomy

By Patrick J. Lynch, medical illustrator (Patrick J. Lynch, medical illustrator) [CC BY 2.5], via Wikimedia Commons


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