Respiratory Zone of the Lungs Overview Illustration

Respiratory Zone of the Lungs: An Overview (2024)

by | Updated: Jun 4, 2024

The respiratory zone of the lungs serves as the critical juncture where actual gas exchange occurs between the air we breathe and our blood.

Comprised of structures like the respiratory bronchioles, alveolar ducts, and alveoli, this intricate system ensures that oxygen enters our bloodstream and carbon dioxide is expelled.

This article will provide a comprehensive overview of the respiratory zone, detailing its components, function, and importance to overall pulmonary health.

What is the Respiratory Zone of the Lungs?

The respiratory zone of the lungs is where gas exchange occurs. It comprises the smallest and most distal respiratory bronchioles, alveolar ducts, and alveoli. These structures are intimately associated with the pulmonary capillaries, facilitating the exchange of oxygen and carbon dioxide between the air and blood. It’s distinct from the conducting zone, which transports air to the respiratory zone.

Respiratory Zone of the Lungs Labeled llustration

Parts of the Respiratory Zone

The respiratory zone of the lungs is the site where actual gas exchange occurs. It is made up of the following components:

  • Respiratory Bronchioles: These are the smallest type of bronchioles, which contain a few alveoli budding from their walls. They mark the beginning of the respiratory zone.
  • Alveolar Ducts: These are elongated pathways attached to the respiratory bronchioles. They are lined with alveoli and lead to alveolar sacs.
  • Alveolar Sacs: These are cluster-like structures at the end of the alveolar ducts. Each sac consists of a collection of individual alveoli.
  • Alveoli: These are tiny, balloon-like structures where the actual gas exchange happens. Their walls, known as alveolar walls or septa, are extremely thin and surrounded by a dense network of capillaries. Oxygen from the air inside the alveoli diffuses into the blood in the surrounding capillaries, and carbon dioxide from the blood diffuses into the alveoli to be exhaled.

Together, these structures provide a vast surface area for gas exchange to occur efficiently.

It’s estimated that the combined surface area of the alveoli in an average human adult is about the size of a tennis court.

This extensive area ensures the body receives adequate oxygen and can efficiently remove carbon dioxide with each breath.

What is Gas Exchange?

Gas exchange is a vital physiological process where oxygen and carbon dioxide are swapped between the air we breathe and our bloodstream.

As we inhale, air containing oxygen fills the tiny alveoli in the lungs. The walls of these alveoli are extremely thin and closely associated with a dense network of capillaries.

This proximity allows oxygen from the air to diffuse across the alveolar membrane and into the blood in the capillaries.

Simultaneously, carbon dioxide, a waste product produced by the body’s metabolic processes, diffuses from the blood into the alveoli. This carbon dioxide is then expelled from the body when we exhale.

This continuous cycle ensures that our body’s cells receive the oxygen they need for energy production and that waste carbon dioxide is efficiently removed, maintaining a stable internal environment.

What is the Conducting Zone?

The conducting zone of the respiratory system is a series of interconnected pathways through which air is drawn into or expelled from the lungs. Unlike the respiratory zone, where gas exchange occurs, the primary function of the conducting zone is to transport air, filter and humidify it, and adjust its temperature to match the body’s internal conditions.

Parts of the Conducting Zone

Starting from the nose or mouth, the conducting zone comprises the following structures in sequence:

  • Nasal Cavity/Mouth: This is the primary external opening through which air enters the respiratory system. The nasal cavity, specifically, warms, humidifies, and filters the incoming air with the help of hairs and mucus.
  • Pharynx (throat): It serves as a common pathway for both air and food. The pharynx connects the nasal cavity and mouth to the larynx.
  • Larynx (voice box): This structure not only routes air to the lungs but also houses the vocal cords, which vibrate to produce sound.
  • Trachea (windpipe): This is a tubular structure that connects the larynx to the bronchi. Its walls are strengthened by C-shaped cartilage rings, preventing it from collapsing.
  • Bronchi: The trachea divides into two primary bronchi (left and right) that enter each lung. Each primary bronchus then branches out into smaller secondary and tertiary bronchi.
  • Bronchioles: These are even smaller, thinner-walled tubes that arise from the tertiary bronchi. They further branch and subdivide multiple times within the lungs.
  • Terminal Bronchioles: These are the smallest bronchioles and represent the last part of the conducting zone before the respiratory zone begins.

Throughout the conducting zone, the mucosa or lining secretes mucus that traps dust, pathogens, and other particles while tiny hair-like structures called cilia move rhythmically, pushing this mucus and trapped particles upwards to be either coughed out or swallowed.

This ensures that the air reaching the delicate structures of the respiratory zone is as clean, warm, and moist as possible, optimizing conditions for efficient gas exchange.

Diseases That Affect the Respiratory Zone

The respiratory zone, given its primary role in gas exchange, can be particularly vulnerable to diseases and disorders.

When compromised, the patient’s oxygen intake and carbon dioxide expulsion can be significantly hindered, leading to various systemic complications.

Here are some diseases that affect the respiratory zone:

  • Pneumonia: An infection that inflames the alveoli. When affected, the alveoli can fill with pus or other liquid, making breathing difficult and reducing the efficiency of gas exchange.
  • Pulmonary Edema: A condition in which fluid accumulates in the alveoli, often due to heart failure. This accumulation of fluid can impede effective gas exchange.
  • Pulmonary Fibrosis: A disease characterized by the thickening and scarring (fibrosis) of lung tissue, including the alveolar walls. This scarring can reduce the efficiency of oxygen transfer from the alveoli to the bloodstream.
  • Chronic Obstructive Pulmonary Disease (COPD): Although COPD primarily affects the airways (and thus the conducting zone), it can also impact the alveoli, leading to reduced effectiveness in gas exchange.
  • Emphysema: A type of COPD where the alveoli become damaged, stretched, or enlarged. This results in a decreased surface area for gas exchange and reduced lung elasticity.
  • Tuberculosis (TB): A bacterial infection that primarily affects the lungs. TB can cause the formation of granulomas, or nodules, which can impede normal lung function and gas exchange.
  • Lung Cancer: The growth of malignant cells in the lung tissue can obstruct or damage the alveoli and other structures of the respiratory zone.
  • Acute Respiratory Distress Syndrome (ARDS) A severe lung condition that causes inflammation and fluid buildup in the alveoli. It can severely hamper gas exchange and can be life-threatening.
  • Respiratory Syncytial Virus (RSV): While it primarily affects small airways in young children, in severe cases, it can reach the alveoli, interfering with gas exchange.
  • Pneumoconiosis: A category of conditions caused by inhaling various types of dust, leading to lung damage. For example, asbestosis from asbestos exposure and silicosis from silica dust.

Note: Any disease or condition that affects the respiratory zone can have significant implications for an individual’s overall health and well-being, given the essential nature of gas exchange for life.

FAQs About the Respiratory Zone of the Lungs

What are the Major Zones of the Respiratory System?

The respiratory system is primarily divided into two major zones: the conducting zone and the respiratory zone.

The conducting zone includes structures like the nasal cavity, pharynx, larynx, trachea, bronchi, and bronchioles. The respiratory zone comprises the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli.

What is the Main Function of the Respiratory Zone?

The primary function of the respiratory zone is to facilitate gas exchange.

This is where oxygen from the inhaled air diffuses into the bloodstream, and carbon dioxide from the blood is released into the lungs to be exhaled.

The structures in this zone, particularly the alveoli, provide a vast surface area that enables the efficient transfer of gases between the air and the circulatory system.

Where Does the Respiratory Zone Start and End?

The respiratory zone begins with the respiratory bronchioles, which branch off from the terminal bronchioles of the conducting zone.

It extends to include the alveolar ducts, alveolar sacs, and ends with the alveoli, which are the tiny air sacs where actual gas exchange takes place.

What is the Main Function of the Conducting Zone?

The main function of the conducting zone is to transport, warm, moisten, and filter the air as it travels from the external environment to the respiratory zone.

It ensures that the air reaching the alveoli is in optimal condition for gas exchange while also preventing foreign particles and pathogens from reaching the delicate structures of the respiratory zone.

What Respiratory Region is the First to Develop?

The laryngotracheal tube is the first respiratory region to develop during embryonic growth, which gives rise to the trachea, bronchi, and other components of the conducting zone.

As development progresses, the branching of the bronchi and formation of the alveoli in the lungs occur, establishing the basis for the complete respiratory system.

Is the Respiratory Zone Found Within the Trachea?

No, the respiratory zone is not found within the trachea. The trachea is a part of the conducting zone, which is responsible for transporting, warming, humidifying, and filtering air.

The respiratory zone, where gas exchange occurs, begins with the respiratory bronchioles and includes the alveolar ducts, alveolar sacs, and alveoli.

Is the Respiratory Zone the Site of External Ventilation?

No, external ventilation typically refers to the movement of air in and out of the lungs, which involves structures in both the conducting and respiratory zones.

The respiratory zone is where gas exchange occurs between the air and the bloodstream.

External ventilation ensures that fresh air reaches the respiratory zone for this gas exchange to occur.

Final Thoughts

The respiratory zone plays an essential role in the exchange of gases between the atmosphere and our bloodstream.

Its specialized structures are meticulously engineered to optimize the diffusion process.

Understanding the respiratory zone’s anatomy and function is indispensable for healthcare professionals, researchers, and anyone interested in the intricacies of human physiology.

John Landry, BS, RRT

Written by:

John Landry, BS, RRT

John Landry is a registered respiratory therapist from Memphis, TN, and has a bachelor's degree in kinesiology. He enjoys using evidence-based research to help others breathe easier and live a healthier life.


  • Faarc, Kacmarek Robert PhD Rrt, et al. Egan’s Fundamentals of Respiratory Care. 12th ed., Mosby, 2020.
  • Cardiopulmonary Anatomy & Physiology: Essentials of Respiratory Care. Cengage Learning, 2019.
  • Powers KA, Dhamoon AS. Physiology, Pulmonary Ventilation and Perfusion. [Updated 2023 Jan 23]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023.
  • Ananda Rao A, Johncy S. Tennis Courts in the Human Body: A Review of the Misleading Metaphor in Medical Literature. Cureus. 2022.

Recommended Reading