Major Upper Respiratory Tract Organs:
I think that you can picture this organ! Right? In my family, we all have quite prominent noses! When I was growing up and my Grandpa Sam would pull out his handkerchief at our dinner table, my sister and I would dive under the table!
The nose has two nostrils which serve as the first air passageways from our surroundings.
The air that enters our nostrils runs into a larger opening, called the nasal cavity posterior to the nose. You have learned a little about the nasal cavity before-- you learned about the superior, middle, and inferior nasal conchae the invade the nasal cavity from the sides, and you learned about the olfactory epithelium that lines this nasal cavity.
Well, the nasal cavity serves as a single air-collecting region. As air passes through here, it bangs around (because of the contortions of the conchae) against the olfactory epithelium. The olfactory epithelium is a mucous membrane, covered in mucus and ciliated at its apical edge. The mucus is actually a very helpful substance, although we tend to think of it as an annoyance when our nose is runny. (mucous is an adjective, and mucus is a noun). In the nasal cavity, the term "mucous membrane" is synonymous with "olfactory epithelium." But, as you progress farther into the respiratory system, the olfactory epithelium is no longer there (since we don't smell in our throats and lungs), and just a pseudostratified, ciliated mucous membrane is there.
Any material in the air, like dust and bacteria, that is not useful for our respiratory system tends to get stuck in the mucus. Therefore, by having mucus coating our olfactory epithelium, we are able to filter our air before taking it into the lungs. However, once materials begin to accumulate in the mucus, we have to clean the mucus out. That's where the cilia come in. All of the cilia on our mucous membrane sweep mucus toward our pharynx (throat). The mucus is thus moved along into the pharynx (where we swallow it), and new mucus is secreted to cover the mucus membrane.
I know... you are probably thinking, "gross, we swallow our filthy mucus." But, we don't taste it, and we have to deal with all the bacteria we breathe, right? You learned about chemical barriers as a nonspecific body defense against infection last week. This is just one way that we use that nonspecific defense-- by swallowing the bacteria, we force them into our digestive chemicals for destruction. So, the ability to trap bacteria in mucus and send this mucus on to the stomach is actually a handy way to deal with any pathogens in the air.
We have air-filled spaces within our skull called sinuses. The purposes of the sinuses are:
However, these sinuses are not only air-filled, but they are also connected to the nasal cavity. Therefore, they need a mucous membrane covering to get rid of any unwanted materials that get inside of them, just like the nasal cavity. Unfortunately, sometimes sinuses cannot remove their harmful materials fast enough, and a sinus infection ensues. During a sinus infection (sinusitis), the mucous membrane is extremely active in secreting mucus, and this mucus drains into the nasal cavity; that's why you tend to have a runny nose during a sinus infection. Also, during sinusitis, the opening that connects the sinus to the nasal cavity can get blocked-- yuck.
This image to the right is a sagittal section from the NPAC Visible Human Viewer, but then I labeled it so that you could tell what was what. I took this section because you can see two sinuses (the frontal and sphenoid sinuses), as well as the trachea, really nicely. The nasal cavity and the pharynx are hard to see, so I didn't label them. This section was near the midsagittal plane, so lungs are not visible, but the heart is.
There's a passageway in your throat where both air and food can travel. This passageway is the pharynx. We will spend quite a bit of time on this in lab. The reason that you can breathe through your mouth is because the oral cavity, just like the nasal cavity, runs into the pharynx. So any air that travels through the nose or the mouth will enter the pharynx, and continue on toward the lungs from there. In figure 19.2 of your book, there is nothing indicated as the "pharynx." That's because this figure is even more specific in describing the regions of the pharynx (as we will do in lab). There are three regions of the pharynx... you only have to worry about them in lab... but so that you can understand these figures, they are: 1) nasopharynx; 2) oropharynx; and 3) laryngopharynx.
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