The Respiratory System: How We Breathe and Exchange Gases
The Human Respiratory System: An Overview
The respiratory system is responsible for gas exchange. It captures oxygen from the air and transports it via blood to the body’s cells. It also collects carbon dioxide from the blood to expel it. The airways, which conduct air containing oxygen, include the nostrils, pharynx, larynx, trachea, bronchi, and bronchioles. The lungs facilitate gas exchange between blood and air.
Air Transport and Preparation
Before air reaches the lungs, it must be clean, moist, and warm. This is achieved through mucus, a viscous substance that traps dust particles and moistens the air. The air is also heated as it travels through the respiratory system.
Key Components of the Respiratory System
Nostrils
The nostrils are the entry point for air. The nasal cavity walls contain abundant capillaries that warm the circulating air. Mucus purifies and humidifies the air.
Pharynx
The pharynx belongs to both the digestive and respiratory systems. Food continues into the esophagus, while air passes into the larynx. The tonsils, located on the pharynx’s side walls, produce white blood cells.
Larynx
The larynx’s entry is regulated by the epiglottis, a fibrous structure that closes when food is present in the pharynx. The larynx’s wall is composed of cartilage, which keeps it open.
Trachea
The trachea is a conduit with cartilage rings open at its posterior. Inside, mucus traps foreign particles, and cells with filaments called cilia vibrate. When cilia and mucus are insufficient, the body uses coughs and sneezes to expel particles from the airways.
Bronchi and Bronchioles
The trachea splits into two bronchi, which also have cartilage rings. Each bronchus enters a lung and branches into bronchioles, which lack cartilage rings. The set of each bronchiole with its bronchial tree is called the last branches of the bronchioles terminate in lung alveoli.
Gas Exchange in the Lungs
The lungs are elastic organs formed by the bronchi, bronchioles, alveoli, and an extensive network of capillaries. The right lung has three lobes, while the left lung has only two. The lungs are surrounded by the pleura, a laminated composite of two membranes with a liquid between them that allows them to remain united.
After traveling through the respiratory system, air reaches the alveoli. The air in the alveoli has a higher concentration of oxygen and a lower concentration of carbon dioxide than the blood. Atmospheric oxygen enters the blood to be transported to all cells, and carbon dioxide from the blood passes into the alveoli, mixes with the air, and is expelled during exhalation.
Pulmonary Ventilation
For effective gas exchange, the air in the alveoli must be constantly renewed through pulmonary ventilation, which occurs in two stages:
Inspiration (Inhalation)
During inspiration, air enters the lungs. Since the lungs have no muscles, this movement results from the contraction of the ribcage muscles and the diaphragm. The diaphragm flattens and lowers, while the ribs elevate outward, increasing the ribcage volume and allowing air to enter the lungs.
Exhalation
During exhalation, air exits the lungs. The diaphragm relaxes, and the ribcage volume decreases, forcing air out.