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Organs of the respiratory system

Anatomy and function of the main organs of the respiratory system.

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Hey everyone! This is Nicole from Kenhub, and in this tutorial, we're going to be looking at the organs of the respiratory system.

The respiratory system is comprised of several organs that facilitates the intake of oxygen which is needed for tissue function, and also the expulsion of carbon dioxide which is a by-product of respiration through exhalation. In this tutorial, we'll discuss the organs that make up the respiratory system and their function.

The respiratory system can be divided into the upper, middle and lower respiratory tracts. To begin with, let's look at the organs that make up the upper respiratory tract, most of which, except the parts of the pharynx that come in contact with the food bolus, are lined with ciliated pseudostratified columnar epithelium, also known as respiratory epithelium.

The first organ of the upper respiratory tracts that we see here is the nose, and it's the only part of the respiratory tract that's visible externally. The structure of the nose is comprised of a framework of hyaline cartilage such as the alar cartilages that form the external nares and the bone, for example, the nasal bones which form the bridge of the nose.

So, once the air is breathed in through the nose, it enters the nasal cavity. The nasal cavity is the space behind the nasal vestibule that is lined with respiratory epithelium and is divided into two equal chambers by the nasal septum. The piriform aperture is the anterior opening of the nasal cavity and it is bounded by the nasal bones and the maxilla.

There are three elevations found on the lateral walls of the nasal cavities that drain the paranasal sinuses, and they are the superior, middle and inferior nasal conchae. As we just saw, the nasal conchae found on the lateral walls of the nasal cavities drain the paranasal sinuses. There are four paired paranasal sinuses – the maxillary sinuses, and if we cut our skull here sagittally, we can see our frontal sinuses in green; the sphenoidal sinuses, and the ethmoidal sinuses which we can see here on this image of the superior view of the isolated ethmoid bone.

The paranasal sinuses are basically air-filled cavities situated around the nasal cavities that helps circulate the air that we breathe, produce mucus, lies in the skull, and also produce a resonance to amplify our vocalizations.

Running behind the nasal cavity and the oral cavity is a five-centimeter long tube that runs into the esophagus and the respiratory tract known as the pharynx. It connects the nasal cavity to the larynx, allowing air to move in and out of the lungs. It also connects the oral cavity to the esophagus, enabling food and fluids to be passed from the oral cavity to the stomach for further digestion. The pharynx can be divided anatomically into three regions, and these are the nasopharynx, the oropharynx, and the laryngopharynx.

The pharynx is the final organ of the upper respiratory tract.

Next, let's look at some of the organs of the middle respiratory tract, also known as the respiratory airways. The first organ we'll look at is the larynx, seen here highlighted in green. The larynx is attached to the hyoid bone superiorly and to the trachea inferiorly. It's comprised of many different soft and hard tissues that allow for the production of sound or speech as well as breathing.

The larynx can be divided into three regions – the vestibule, the ventricle, and the infraglottic area. The function of the larynx is to connect the pharynx and the trachea, to prevent foreign bodies from entering the airways, and phonation.

Next here we see the trachea, a cartilaginous tubular structure that begins just below the larynx. The trachea connects the larynx into the lower respiratory tract. It is comprised of approximately fifteen to twenty C-shaped hyaline cartilages and it bifurcates into the right and left main bronchi at approximately the level of the fifth thoracic vertebra, T5.

The main bronchi which are two branches of the trachea are also known as primary bronchi. The right main bronchus is shorter, wider, and more vertical than the left main bronchus. The two main bronchi enter the right and left lungs at the hilum, after which they further branch into secondary or lobar bronchi. The lobar bronchi go in to give smaller branches namely the segmental bronchi which then further branch to give the large subsegmental bronchi.

The large subsegmental bronchi then divide into the small subsegmental bronchi which in turn give off the bronchioles. The bronchioles are the smallest branches of the bronchi in the lungs and they give rise to the terminal bronchioles. The terminal bronchioles mark the end of the middle respiratory tract but they still divide further to give respiratory bronchioles that in turn give rise to the alveolar sacs. The respiratory bronchioles and the alveolar sacs are part of the lower respiratory tract which happens to be the next topic on our list.

The organs that make up the lower respiratory tract are the lungs and the tissue within the lungs. It's here in the lungs that gaseous exchange takes place. Inhaled oxygen diffuses into the blood and carbon dioxide produced as a result of cell metabolism is removed from blood and exhaled. The lungs are made of a light and soft elastic tissue.

Looking at the macroscopic structure of the lungs – the right lung and the left lung – we can see the differences in their structure. The right lung is larger than the left one and it has three lobes separated by two fissures. The left lung has only two lobes and one fissure separating the two lobes. The left lung is slightly smaller owing to the position of the heart.

The bases of both lungs rest on the diaphragm. Here we can see the lungs from a medial view. Each lung has a costal surface or the part of the lung found closer to the ribs, a mediastinal surface which is the part closer to the mediastinum, and the diaphragmatic part which is the part of the lung which lies on top of the diaphragm.

So, thanks for sticking with me throughout this tutorial. Now that we've reached the end, let's have a quick overview of what we've discussed about the respiratory tract so far.

You now know that the respiratory system is divided into the upper, middle and lower respiratory tracts. The organs of the upper respiratory tract include the nose, the nasal cavities, the nasal septum, the nasal conchae, the paranasal sinuses, and the pharynx. The organs of the middle respiratory tract include the larynx, the trachea, the bronchi, and the bronchioles. And, finally, the organs of the lower respiratory tract include the lungs, the respiratory bronchioles, and the alveolar ducts, the sacs and the terminal alveoli. So, for example, if you're looking at an infection of the lower respiratory tract, you know what organs are involved.

Thanks for watching, and happy studying!

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