The movement of air between the atmosphere and the lungs is known as ventilation or breathing. Inspiration and expiration are the two phases of breathing. Inspiration is the movement of atmospheric air into the lungs and expiration is the movement of alveolar air that diffuse out of the lung.
Lungs do not contain muscle fibres but expands and contracts by the movement of the ribs and diaphragm. The diaphragm is a sheet of tissue which separates the thorax from the abdomen. In a relaxed state, the diaphragm is domed shaped. Ribs are moved by the intercostal muscles.
Inspiration is initiated by the contraction of the diaphragm muscles and external intercostal muscles, which pulls the ribs and sternum upwards and outwards and increases the volume of the thoracic chamber in the dorso ventral axis, forcing the lungs to expand the pulmonary volume. The increase in pulmonary volume and decrease in the intrapulmonary pressure forces the fresh air from outside to enter the air passages into the lungs to equalize the pressure. This process is called inspiration.
Relaxation of the diaphragm allows the diaphragm and sternum to return to its dome shape and the internal intercostal muscles contract, pulling the ribs downward reducing the thoracic volume and pulmonary volume. This results in an increase in the intra-pulmonary pressure slightly above the atmospheric pressure causing the expulsion of air from the lungs. This process is called expiration.
The respiratory system has many different parts that work together to help you breathe. Each group of parts has many separate components.
Your airways deliver air to your lungs. Your airways are a complicated system that includes your:
- Mouth and nose: Openings that pull air from outside your body into your respiratory system.
- Sinuses: Hollow areas between the bones in your head that help regulate the temperature and humidity of the air you inhale.
- Pharynx (throat): Tube that delivers air from your mouth and nose to the trachea (windpipe).
- Trachea: Passage connecting your throat and lungs.
- Bronchial tubes: Tubes at the bottom of your windpipe that connect into each lung.
- Lungs: Two organs that remove oxygen from the air and pass it into your blood.
From your lungs, your bloodstream delivers oxygen to all your organs and other tissues.
Muscles and bones help move the air you inhale into and out of your lungs. Some of the bones and muscles in the respiratory system include your:
- Diaphragm: Muscle that helps your lungs pull in air and push it out.
- Ribs: Bones that surround and protect your lungs and heart.
When you breathe out, your blood carries carbon dioxide and other waste out of the body. Other components that work with the lungs and blood vessels include:
- Alveoli: Tiny air sacs in the lungs where the exchange of oxygen and carbon dioxide takes place.
- Bronchioles: Small branches of the bronchial tubes that lead to the alveoli.
- Capillaries: Blood vessels in the alveoli walls that move oxygen and carbon dioxide.
- Lung lobes: Sections of the lungs — three lobes in the right lung and two in the left lung.
- Pleura: Thin sacs that surround each lung lobe and separate your lungs from the chest wall.
Some of the other components of your respiratory system include:
- Cilia: Tiny hairs that move in a wave-like motion to filter dust and other irritants out of your airways.
- Epiglottis: Tissue flap at the entrance to the trachea that closes when you swallow to keep food and liquids out of your airway.
- Larynx (voice box): Hollow organ that allows you to talk and make sounds when air moves in and out.
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