Structures of the Respiratory System
Objective 2
Describe functions for each of the structures of the respiratory system: nose and paranasal sinuses, pharynx, larynx, trachea, bronchi, lungs, pleural membranes, diaphragm and intercostal muscles, phrenic nerves and pulmonary plexus. Be able to identify each of these on a diagram or photograph.
Let’s turn our attention to the structures of the respiratory system. Anatomically, these structures can be divided into the upper and lower respiratory tracts. The nose, paranasal sinuses, and pharynx make up the upper respiratory system. The larynx, or voice box separates the upper from lower respiratory system. The trachea, bronchi, and lungs make up the lower respiratory system.
We’ll begin with the structures of the upper respiratory tract.
Air enters through the external nares (nostrils). Nose hairs act as a filter for dirt and other particles in the inhaled air.
In the internal nose are scroll-like bones that make up the nasal conchae also called turbinates. The conchae provide a turbulent area that air passes through before reaching the rest of the respiratory passages. The conchae are lined with a mucous membrane which helps trap foreign particles and warms and humidifies the air. The olfactory epithelium, which is near the superior nasal concha, increases the surface area and mixes the air to help with olfaction.
Sinuses are cavities within cranial and facial bones that are lined with a mucous membrane. In the image, we can see the ethmoid, maxillary, and frontal sinuses. These hollow spaces lighten the weight of the head so we have an easier time carrying our head around. They also serve as chambers that resonate sound as we speak or sing. This is why you may sound funny when your sinuses are stuffed up with a cold. Due to our upright posture, our sinuses don’t drain as easily. They may trap microorganisms and fluid and we can find ourselves with a nasty sinus infection!
Pharynx
The pharynx or throat is a hollow tube that starts at the posterior part of the internal nares and descends to the opening of the larynx. The pharynx serves as a passageway for air and food, is a resonating chamber for sound, and houses the tonsils.
The pharynx can be divided into three anatomical regions.
- Nasopharynx: Lies behind the internal nares and has a purely respiratory function.
- Eustachian tubes (auditory tubes)
- Houses the pharyngeal tonsils (adenoids)
- Oropharynx: Lies behind the mouth with both reparatory and digestive functions.
- Houses the palatine tonsils (removed in a tonsillectomy) and the lingual tonsils
- Laryngopharynx: Lies inferior to the oropharynx and opens into the larynx and esophagus and has respiratory and digestive functions.
Larynx
The larynx, or voice box, connects the laryngopharynx with the trachea. It sits in the midline of the neck anterior to the esophagus and superior to the trachea. The hyoid bone, an unattached, free-floating U-shaped bone, sits superior to the larynx. The ope