The larynx, or voice box, contains the vocal cords, which are the source of sound production. The pharynx, or throat, has a dual role in respiration and digestion. The pharynx receives air from the nasal cavity and food and drink from the oral cavity. The trachea, or windpipe, is a rigid tube that transports air from the larynx to the bronchi. The bronchi in turn transport air into the lungs. The alveoli are thin-walled sacs where the exchange of gasses between the lungs and the blood occurs.

The larynx, or voice box, contains the vocal cords, which are the source of sound production. The pharynx, or throat, has a dual role in respiration and digestion. The pharynx receives air from the nasal cavity and food and drink from the oral cavity. The trachea, or windpipe, is a rigid tube that transports air from the larynx to the bronchi. The bronchi in turn transport air into the lungs. The alveoli are thin-walled sacs where the exchange of gasses between the lungs and the blood occurs.

The diaphragm separates the thoracic cavity from the abdominal cavity. When it contracts, it flattens downward and permits the lungs to expand, promoting inhalation. When it relaxes, it rises and compresses the lungs, promoting exhalation. The internal oblique muscle fibers are directed upward from the iliac crest (hip bone) to the lower ribs. The masseter muscle is involved in chewing. The deltoid is a large triangular muscle that covers the shoulder joint. The vastus lateralis extends the leg and is located in the anterior thigh.

The diaphragm separates the thoracic cavity from the abdominal cavity. When it contracts, it flattens downward and permits the lungs to expand, promoting inhalation. When it relaxes, it rises and compresses the lungs, promoting exhalation. The internal oblique muscle fibers are directed upward from the iliac crest (hip bone) to the lower ribs. The masseter muscle is involved in chewing. The deltoid is a large triangular muscle that covers the shoulder joint. The vastus lateralis extends the leg and is located in the anterior thigh.

Hiccups are reflex spasms of the diaphragm, causing an involuntary inhalation followed by a sudden closure of the glottis that produces an audible sound, the "hic." Snoring is the sound produced while breathing through the mouth during sleep. Sneezing is caused by irritants in the nasal cavity. The glottis stays open while the tongue and soft palate block the flow of air from getting out. Then they suddenly release to let air burst through the nose. Coughing is triggered by irritants in the respiratory tract. High pressure forms in the lower respiratory tract when the glottis closes and muscles contract. The glottis then suddenly opens to release an explosive blast of air. Anxiety may trigger an increase in respiration, hyperventilation, which results in lowered carbon dioxide levels.

Hiccups are reflex spasms of the diaphragm, causing an involuntary inhalation followed by a sudden closure of the glottis that produces an audible sound, the "hic." Snoring is the sound produced while breathing through the mouth during sleep. Sneezing is caused by irritants in the nasal cavity. The glottis stays open while the tongue and soft palate block the flow of air from getting out. Then they suddenly release to let air burst through the nose. Coughing is triggered by irritants in the respiratory tract. High pressure forms in the lower respiratory tract when the glottis closes and muscles contract. The glottis then suddenly opens to release an explosive blast of air. Anxiety may trigger an increase in respiration, hyperventilation, which results in lowered carbon dioxide levels.

The larynx contains the vocal cords and conducts air from the pharynx to the trachea.

The pharynx is the region of the back of the mouth/nose and upper throat. The trachea conducts air between the larynx and the bronchi. The bronchi conduct air from the trachea to the lungs. The epiglottis is a flap of cartilage in the pharynx that covers the opening to the larynx during swallowing and directs food and liquids down the esophagus.

The larynx contains the vocal cords and conducts air from the pharynx to the trachea.

The pharynx is the region of the back of the mouth/nose and upper throat. The trachea conducts air between the larynx and the bronchi. The bronchi conduct air from the trachea to the lungs. The epiglottis is a flap of cartilage in the pharynx that covers the opening to the larynx during swallowing and directs food and liquids down the esophagus.

The respiratory system is composed of the mouth, trachea, bronchi, bronchioles, and alveoli in the lungs. The primary function of the system is to bring air to the alveoli, where it can interact with blood in nearby capillaries. Oxygen diffuses into the blood from the alveoli, while carbon dioxide is transferred out of the blood, in a process known as gas exchange.

While the respiratory system is responsible for re-oxygenating blood, it is the circulatory system that actually delivers the oxygen to the tissues of the body. The immune system battles foreign pathogens, and the excretory system maintains fluid balance.

Alveoli, like most bodily structures, are part of an aqueous environment, making them subject to the surface tension of water. Surfactant lowers surface tension, allowing the alveoli to expand with much less pressure than they would against full surface tension. As a result, inspiration of air requires less effort, making it more energetically efficient.