Upper vs Lower Respiratory Tract

What Is the Difference Between the Upper and Lower Respiratory Tract?

The main difference is location and job: the upper respiratory tract sits in the head and neck and prepares the air, while the lower respiratory tract sits mostly in the chest and carries that air to the alveoli, where gas exchange happens. Both are parts of one continuous tube, so the split is a way of organizing the anatomy rather than a wall inside the airway.

The upper respiratory tract is built around bone and cartilage: the nose, the nasal cavity with its curled conchae, the air-filled paranasal sinuses, the pharynx and the larynx. These parts filter, warm and humidify air, hold the receptors for smell, make the voice and protect the airway when you swallow.

The lower respiratory tract is a branching tree that starts with the trachea, divides into the bronchi and bronchioles, and ends in millions of alveoli packed inside the lungs. Its first part only conducts air; its final part is the only place in the body where air meets blood.

Explained simply: the upper tract is the front porch and hallway, where air wipes its feet and warms up. The lower tract is the branching set of corridors and tiny rooms inside the house, where the real work of swapping oxygen for carbon dioxide gets done.

What Are the Parts of the Upper and Lower Respiratory Tract?

The upper respiratory tract has five main parts (nose, nasal cavity, paranasal sinuses, pharynx and larynx), and the lower respiratory tract has four levels of airway (trachea, bronchi, bronchioles and alveoli) inside or leading to the lungs. The mouth, or oral cavity, is a backup airway that joins the upper tract at the pharynx.

Upper respiratory tract

• Nose and nostrils: the entrance, lined with hairs that catch large particles.
• Nasal cavity: the space behind the nose, divided by the nasal septum and shaped by three nasal conchae on each side.
• Paranasal sinuses: four pairs of air spaces in the skull bones that drain into the nasal cavity.
• Pharynx: the throat, in three parts: nasopharynx, oropharynx and laryngopharynx.
• Larynx: the voice box, guarded by the epiglottis and holding the vocal folds.

Lower respiratory tract

• Trachea: the windpipe, held open by C-shaped rings of hyaline cartilage.
• Bronchi: the right and left main bronchi and their lobar and segmental branches.
• Bronchioles: small airways with no cartilage, ending in terminal and respiratory bronchioles.
• Alveolar ducts, sacs and alveoli: the gas exchange surface of the lungs.

Some textbooks count the larynx as the first part of the lower tract, and a few place the boundary at the vocal folds. Most anatomy and clinical sources, including this site, use the lower edge of the cricoid cartilage, the ring at the base of the larynx, as the dividing line.

Where Is the Upper and Lower Respiratory Tract?

The upper respiratory tract lies in the head and neck, and the lower respiratory tract runs from the lower neck down into the chest. The boundary between them sits at about the level of the sixth cervical vertebra, where the cricoid cartilage of the larynx meets the first ring of the trachea.

From there, the trachea runs down in front of the esophagus into the thoracic cavity. It splits at the carina, at about the level of the sternal angle, into the two main bronchi. Each bronchus enters a lung at its hilum, and from that point the whole lower tract is enclosed in the lungs and their pleura.

The upper tract, by contrast, is spread across several regions of the skull and neck: the nasal cavity sits above the hard palate, the sinuses sit inside the frontal, maxillary, ethmoid and sphenoid bones, and the pharynx hangs behind the nose, mouth and larynx. The pathway of air page follows a breath through every part in order.

Upper vs Lower Respiratory Tract Function

The upper respiratory tract conditions and guards the air, while the lower respiratory tract distributes it and exchanges gases. Most of the cleaning, warming and humidifying is done before air ever reaches the trachea, so the delicate alveoli receive air that is close to body temperature and fully saturated with water vapor.

What the upper tract does

• Filters large particles with nasal hairs and traps smaller ones in mucus.
• Warms and humidifies air over the large, blood-rich surface of the conchae.
• Detects smells through the olfactory area in the roof of the nasal cavity; see sense of smell.
• Produces the voice in the larynx and shapes it in the pharynx, mouth and sinuses.
• Keeps food out of the airway by closing the larynx during swallowing.

What the lower tract does

• Conducts air through the branching bronchial tree to every part of both lungs.
• Clears trapped dust and germs upward with the mucociliary escalator and the cough reflex.
• Adjusts airflow by tightening or relaxing smooth muscle in the bronchioles.
• Exchanges oxygen and carbon dioxide with the blood across the walls of the alveoli; see gas exchange.

Functionally, the airway can also be split another way: the conducting zone, from the nose to the terminal bronchioles, and the respiratory zone, from the respiratory bronchioles to the alveoli. Our conducting zone vs respiratory zone page explains that second division.

Upper vs Lower Respiratory Tract Anatomy: Lining and Support

The two tracts differ in their lining and in what holds them open: the upper tract is supported mainly by bone and large cartilages, while the lower tract relies on cartilage rings and plates that give way to smooth muscle and finally to walls only one cell thick.

Most of the airway from the nasal cavity to the bronchi is lined with respiratory epithelium, a pseudostratified ciliated columnar layer with mucus-making goblet cells. Places that rub against food or vibrate, such as the oropharynx, laryngopharynx and the vocal folds, are covered instead with tougher stratified squamous epithelium. A small patch in the roof of the nasal cavity carries the olfactory epithelium for smell.

In the lower tract the lining becomes simpler as the airways narrow. Ciliated columnar cells in the bronchi give way to ciliated cuboidal cells in the small bronchioles, where club cells replace most goblet cells. In the alveoli, the wall is made of very thin type I pneumocytes, with type II cells making surfactant. Cartilage follows a similar pattern: C-shaped rings in the trachea, irregular plates in the bronchi and none at all in the bronchioles. The respiratory system histology page shows each lining in detail.

How Do the Upper and Lower Respiratory Tract Work Together?

The upper and lower tracts work together as one continuous airway: every breath passes through the upper tract on its way to the lower tract and back out again, and both share the same defenses and the same lining of mucus and cilia. The two halves divide the labor so that the alveoli receive clean, warm, moist air.

• One air stream: the diaphragm lowers the pressure in the lungs and air is pulled in through the whole tract; neither part pumps air on its own.
• Shared cleaning: cilia in the nose sweep mucus back toward the throat, and cilia in the trachea and bronchi sweep it up toward the throat, where it is swallowed.
• Shared protection: sneezing clears the nose, and coughing clears the larynx, trachea and bronchi.
• Temperature and moisture: on the way out, the cooler nasal lining takes back some of the heat and water from the exhaled air.

Because the tracts are joined, a problem in one can spread to the other. Mucus from an inflamed nose or sinuses can drip down the back of the throat, and an infection that starts in the throat can travel down into the bronchi.

Upper vs Lower Respiratory Tract Infection Symptoms

Upper respiratory tract infections mainly cause nose and throat symptoms, while lower respiratory tract infections mainly cause chest symptoms such as a deep cough and breathlessness. This section is for general education only and is not a way to diagnose an illness.

Upper respiratory tract infections, which include the common cold, sinusitis, pharyngitis, tonsillitis and laryngitis, typically bring a runny or blocked nose, sneezing, a sore throat, a hoarse voice and sometimes a mild fever. They are the most common infections people get and are usually caused by viruses.

Lower respiratory tract infections, such as acute bronchitis, bronchiolitis in young children and pneumonia, tend to cause a cough that may bring up mucus, chest tightness, wheezing and shortness of breath. Because the lower tract is where oxygen enters the blood, these infections are generally more serious. The full list of conditions by part is on our respiratory diseases page, and anyone with trouble breathing should see a doctor.