Respiratory System Anatomy

The models provide good detail for the upper respiratory tract.  To get a sense of the anatomy of the lower respiratory tract, we will look at two videos from Acland's Video Atlas of Anatomy.

Recommended Reading

Read pages 534-38 in Silverthorn, focussing on figure 17.2.

Upper Respiratory Tract: Head Model

On the lateral surface of the nasal cavity, there are three ridges known as the nasal conchae (plural; singular:  nasal concha; also known as the turbinates).  These are formed by shelves of bone that protrude into the nasal cavity.  There are three conchae:  the superior concha, middle concha, and inferior concha.  Underneath each concha is a passageway:  the superior meatus, middle meatus, and inferior meatus.  Breathing through the nasal cavity helps to filter, warm and humidify air before it reaches the lower respiratory tract.  Additional warming is contributed by the paranasal sinuses, air-filled spaces within the skull bones that connect to the nasal cavity.  In the sagitally sectioned head model, only the frontal sinus and sphenoidal sinus are visible (there are also ethmoid sinuses and maxillary sinuses). 

Posterior to the nasal and oral cavities is the pharynx, a passageway that is common territory for air, food, and water. The pharynx is subdivided according to whether it is closest to the nasal cavity (nasopharynx) the oral cavity (oropharynx), or the larynx (laryngopharynx).  Certain structures in the larynx (epiglottis, thyroid cartilage, cricoid cartilage, vestibular fold, vocal fold, glottis) can be identified in this model, but are described below.

Upper Respiratory Tract:  Larynx Models

The larynx is a structure found at the top of the trachea.  The larynx is made up of a set of specialized cartilages, and contains the vocal folds, which are used to produce sounds.  Besides vocalization, the other important function of the larynx is to close off the pathway to the respiratory tract during swallowing.  During swallowing, two things occur to close off the respiratory tract.  First, muscles elevate the larynx, causing the epiglottis to tip back and cover the larynx.  Second, muscular contractions close off the glottis, the passageway through the larynx.

There are two models of the larynx.  One model is a skeletal model, showing the hyoid bone and the cartilages that give the larynx its structure.  The large, superior cartilage is the thyroid cartilage, which has a central laryngeal prominence commonly known as the adam's apple.  The epiglottis is the tongue-shaped cartilage protruding above the thyroid cartilage.  Just below the thyroid cartilage lies the cricoid cartilage, which forms a complete circle.  The cricoid cartilage is narrow anteriorly (the cricoid arch) and wide posteriorly (the cricoid lamina).  Sitting atop the posterior side of the cricoid cartilage are the two arytenoid cartilages.  The vocal ligaments (the connective tissue part of the vocal folds) stretch between the arytenoid cartilages and the thyroid cartilage.    

The second model shows a midsagittal section of the larynx, and includes the soft tissues on the inner surface.  Note the pattern of the sectioned cartilages in light blue. Superiorly, there is the epiglottis which is long and angled. Below that lies the large thyroid cartilage anteriorly. Then below that, the sectioned cricoid cartilage is small anteriorly, and large posteriorly. The arytenoid cartilages are not in view because they lie on either side of the midline.

The lateral wall of the larynx has a cavity called the vestibule. Above the vestibule lies the vestibular fold; below the vestibule lies the vocal fold. Movements of the arytenoid cartilages move the vocal folds close together, where their vibration produces sound. Finally, the passageway through the vocal folds is called the glottis.

Lower Respiratory Tract: Acland's Video Atlas videos showing lungs and pleura

We will look at two videos that illustrate how the lungs are situated in the body.  The lungs are contained within the thoracic cavity, which is separated from the abdominal cavity by the large sheet-like muscle, the diaphragm.  The thoracic cavity is divided into two pleural cavities (each containing one lung) by the central mediastinum, the mass of tissue containing the heart, large blood vessels, trachea, and esophagus.  The top of the lungs is called the apex, the bottom surface that is adjacent to the diaphragm is called the base.  The region on the medial surface where the primary bronchus and the blood vessels enter the lung is called the hilum.

The lungs are contained within a pair of connected membranes called the pleura. One pleural membrane, the visceral pleura, is attached to the surface of the lungs. The other pleural membrane, the parietal pleura, is attached to the surrounding structures.  The two pleural membranes are stuck together by a small amount of fluid.  This is important for ventilation (moving air into and out of the lungs), because changing the volume of the pleural cavities effectively changes the volume of the lungs.  The beginning of video 5.1.2 illustrates the "pleural seal" and shows how an injury that punctures the parietal pleura would allow air to enter the pleural cavity and cause the lung to collapse.