Pulmonary respiration occurs every time you breathe. Air is taken in through the airways, travels to the lungs and oxygen is exchanged through blood vessels into your body. Carbon dioxide is expelled out of your lungs, and the process begins again with the next breath you take. The organs and tissues that enable you to breathe are called the respiratory system.

Airways

Air enters your body through your mouth or nose. Your nose contains small hairs called cilia that trap dirt and foreign substances from entering your lungs. Your trachea, or windpipe, splits into two bronchial tubes that lead to each lung.

Inhalation

Each lung has five divisions, called lobes. In these lobes are bronchial tubes that branch out and form bronchioles. The bronchioles split even further and form alveoli, which are small, round air sacs. Within the alveoli are blood vessels that absorb the oxygen from the air you breathe and carry it to your heart to be distributed throughout your body.

Exhalation

Blood from your heart enters the lungs through blood vessels, and the capillaries in the alveoli release carbon dioxide collected from your body to be exhaled through the airways.

Muscles in the Respiratory System

The diaphragm is a large muscle located under the lungs that moves up and down and helps you to breathe. Intercostal muscles in your chest and abdominal muscles also aid in the act of breathing. The muscles in your neck and collarbone area help you to breathe and can take over some of the work if your intercostal or abdominal muscles are injured or diseased.

Role of the Brain

Your brain controls the rate of respiration. A small area at the base of your brain is responsible for the act of breathing. While you are able to change your rate of breathing, your brain controls it automatically most of the time.

Source:

National Heart Lung and Blood Institute: The Respiratory System

National Heart Lung and Blood Institute: What Controls Your Breathing?