The cells of the human body require a constant stream of oxygen to stay alive. The respiratory system provides oxygen to the body?s cells while removing carbon dioxide, a waste product that can be lethal if it accumulates. There are 3 major parts of the respiratory system: the airway, the lungs, and the muscles of respiration. The airway, which includes the nose, mouth, pharynx, larynx, trachea, bronchi, and bronchioles, carries air between the lungs and the body?s exterior. The lungs act as the functional units of the respiratory system by passing oxygen into the body and carbon dioxide out of the body. Finally, the muscles of respiration, including the diaphragm and intercostal muscles, work together to act as a pump, pushing air into and out of the lungs during breathing.
Nose and Nasal Cavity
The nose and nasal cavity form the main external opening for the respiratory system; they are the first section of the body?s airway-the respiratory tract through which air moves. The nose is a structure of the face made of cartilage, bone, muscle, and skin that supports and protects the anterior portion of the nasal cavity. The nasal cavity is a hollow space within the nose and skull that is lined with hairs and mucus membrane.
Mouth
The mouth, or the oral cavity, is the secondary external opening for the respiratory tract. The pathway of air entering the body from the mouth is shorter than the pathway for air entering from the nose, the mouth does not warm and moisturize the air entering the lungs. It lacks the hairs and sticky mucus, so it cannot filter the air as the nasal cavity does.
Pharynx
The pharynx, also known as the throat, is a muscular funnel that extends from the posterior end of the nasal cavity to the superior end of the esophagus and larynx. As the inhaled air descends it is diverted into the opening of the larynx by the epiglottis. The epiglottis is a flap of elastic cartilage that acts as a switch between the trachea and the esophagus. It also ensures that air passes into the trachea by covering the opening to the esophagus.