How Breathing Works: Organs and Processes

Components of the Respiratory Tract

These are the nasal cavities, pharynx, larynx, trachea, bronchi, and bronchioles. Inside the larynx, there are two ring-shaped folds (vocal cords). They create sound when the passage of air makes them vibrate.

Lungs: Site of Gas Exchange

This is where the gas exchange between blood and air takes place.

Respiratory Tract Function

When air reaches the lungs, it needs to be clean, humid, and warm. This preparation process takes place in the respiratory tract.

Nasal Cavity: Air Entry Point

This is the place where air enters the body. In the first section, the internal wall has several capillaries which warm up the air because they carry blood. Mucus purifies and humidifies the air.

Pharynx: Shared Passageway

This area is common to the respiratory and digestive tracts. Food continues its journey into the esophagus, while air passes into the larynx.

Larynx: Voice Box and Air Passage

Entry into the larynx is regulated by a fibrous structure known as the epiglottis. The walls of the larynx are formed by cartilage that continually keeps it open. From the larynx, air goes into the trachea.

Trachea: The Windpipe

This tube, about 12cm long, has open cartilage rings at the back. There is mucus present in the interior of the trachea that traps foreign particles in the air. In addition, there are certain cells with vibrating filaments known as cilia.

Bronchi and Bronchioles: Branching Airways

The trachea divides into two bronchi, each one entering a different lung and branching into progressively smaller ducts named bronchioles. Bronchioles do not have cartilage rings. They end in tiny sacs called pulmonary alveoli.

Gas Exchange in the Lungs

The group formed by bronchi, bronchioles, alveoli, and an extensive network of capillaries constitutes the lungs: highly elastic bodies whose appearance resembles that of a sponge. We have two lungs: the right lung, which has three parts called lobes, and the left lung, which only has two lobes. Lungs are enveloped by the pleura, a sheet composed of two membranes. After traveling through the respiratory tract, air filled with oxygen reaches the pulmonary alveoli where gas exchange occurs.

Pulmonary Alveoli: Tiny Air Sacs

Pulmonary alveoli only have a layer of flat cells (endothelium) and are covered by a network of capillaries that facilitate gas exchange between air and blood.

Diffusion: Gas Movement Principle

Diffusion is the process where oxygen travels from the area where its concentration is greater to the area where it is lower. Oxygen concentration is higher in our alveoli than in our blood. Carbon dioxide concentration is lower in our alveoli than in our blood. The oxygen found in air goes into the blood after passing through the alveolar wall and the wall of the capillary to be transported to the body's cells. Carbon dioxide found in the blood passes to the alveoli. The air in the alveoli mixes with carbon dioxide, and it is released as we exhale.

Pulmonary Ventilation Mechanics

The intercostal muscles and the diaphragm (a muscle that separates the thorax from the abdomen) are responsible for pulmonary ventilation.

Inspiration (Inhalation)

This is the respiratory movement in which air enters the lungs. The diaphragm flattens and lowers. The ribs rise, increasing the capacity of the rib cage. The lungs become enlarged, increasing their volume, and air enters them.

Expiration (Exhalation)

This is the respiratory movement that releases air from the lungs. The diaphragm relaxes, curves, and rises as the ribs sink, reducing the rib cage capacity. This forces the lungs to reduce their volume and release the air inside them.

Ventilation Rate

While resting, pulmonary ventilation is performed about 16 times every minute. If we are exercising, pulmonary ventilation can be 8 to 10 times more frequent.