23.1 Introduction to the Upper Respiratory System

Anatomy and Physiology of the Upper Respiratory System

The upper respiratory system stretches from the nose down to the larynx. Every structure along this path filters, warms, and humidifies inhaled air before it reaches the lungs. For nurses, understanding these structures matters because upper respiratory problems are among the most common complaints you'll encounter in clinical settings. Recognizing how each part functions helps you assess symptoms accurately and anticipate treatment needs.

Nose, Nasal Cavity, and Sinuses

The nose is the primary entry point for air. The two nostrils (also called nares) allow air in and out, while the external structure helps direct airflow inward.

The nasal cavity sits behind the nose and is divided into left and right halves by the nasal septum. It's lined with mucous membranes and tiny hair-like projections called cilia, which work together as a filtration system:

• Mucus traps inhaled particles, dust, and pathogens before they can travel deeper into the airways.
• Cilia beat in coordinated waves, sweeping trapped debris toward the pharynx where it's swallowed and neutralized by stomach acid.
• A rich network of blood vessels just beneath the mucosal surface warms cool inhaled air to near body temperature and adds moisture, protecting the delicate lower airways from dry or cold air.
• Olfactory receptors in the roof of the nasal cavity detect odors. These are separate from the respiratory function but share the same space.

The paranasal sinuses are air-filled cavities within the bones surrounding the nasal cavity. There are four pairs: frontal (above the eyes), maxillary (in the cheekbones), ethmoid (between the eyes), and sphenoid (behind the nasal cavity). They're lined with mucous membranes that are continuous with the nasal cavity lining, which is why nasal infections can easily spread to the sinuses. The sinuses lighten the weight of the skull, contribute to voice resonance, and produce additional mucus that drains into the nasal cavity.

Rhinitis and Sinusitis

Rhinitis is inflammation of the nasal mucosa. It can be allergic (triggered by pollen, dust mites, pet dander) or non-allergic (triggered by irritants, infections, or temperature changes). Common symptoms include:

• Nasal congestion and discharge (clear and watery in allergic; thicker in infectious)
• Sneezing
• Itching of the nose, eyes, or throat

Treatment depends on the cause:

• Antihistamines for allergic rhinitis (e.g., cetirizine, loratadine)
• Decongestants to reduce mucosal swelling (e.g., pseudoephedrine, oxymetazoline nasal spray)
• Nasal corticosteroids for persistent inflammation (e.g., fluticasone)

Sinusitis is inflammation of the paranasal sinuses, often developing after a viral upper respiratory infection when swollen mucosa blocks normal sinus drainage. Key symptoms include:

• Facial pain or pressure (location depends on which sinuses are affected)
• Thick, discolored nasal discharge
• Headache and nasal congestion
• Sometimes fever and fatigue

Treatment options:

• Antibiotics only if bacterial sinusitis is suspected (symptoms lasting 10+ days or worsening after initial improvement)
• Decongestants and nasal corticosteroids to promote drainage
• Saline irrigation (e.g., neti pot or squeeze bottle) to flush mucus and reduce congestion

Pharynx and Larynx

The pharynx (throat) is a muscular tube about 12–13 cm long that serves as a shared passageway for both air and food. It connects the nasal and oral cavities to the larynx and esophagus. It has three distinct regions:

• Nasopharynx: the uppermost section, behind the nasal cavity. Air passes through here during breathing. The adenoids (pharyngeal tonsils) are located here.
• Oropharynx: the middle section, behind the oral cavity. Both air and food pass through this region. The palatine tonsils sit here.
• Laryngopharynx: the lowest section, where the pathway splits. Air is directed anteriorly toward the larynx, and food is directed posteriorly toward the esophagus.

The pharynx also plays a role in speech by modifying sound waves produced in the larynx.

The larynx (voice box) is a cartilaginous structure that connects the pharynx to the trachea. It has three main functions: maintaining an open airway, producing sound, and protecting the lower airways during swallowing.

• The vocal cords (vocal folds) are two bands of tissue that vibrate as air passes between them, producing sound. Pitch varies with the tension and length of the cords: tighter and thinner cords produce higher-pitched sounds.
• The epiglottis is a leaf-shaped flap of elastic cartilage that folds down over the laryngeal opening during swallowing. This prevents aspiration, which is the entry of food or liquid into the airway. If the epiglottis doesn't close properly (due to impaired swallowing reflexes, sedation, or neurological conditions), aspiration risk increases significantly. This is a critical assessment point for nurses, especially in patients who are post-stroke, intubated, or heavily sedated.