The respiratory tract consists of several structures in the head and chest that directs air into the lungs for gas exchange at the alveolar membrane. Oxygen from the atmosphere crosses the thin membrane in the lungs and is carried to every tissue and cell in the body by red blood cells. Carbon dioxide, a cellular waste, is exchanged from the blood into the lungs across the same membrane, and then released into the atmosphere. This process of air movement is breathing, and it is accomplished by the various parts of the respiratory system.
Respiratory Muscles
The main breathing muscles are the diaphragm and intercostals. The diaphragm is a dome-shaped muscle underneath the lungs between the chest and abdominal cavities. Contraction of the diaphragm expands the abdomen and helps regulate the pressure that allows air to flow into the lungs. The muscle also pushes up against the lungs to aid in emptying them of air. Diaphragmatic breathing, also known as abdominal breathing, is a technique used for relaxation and singing, taking advantage of active and conscious control of a usually passive process.
The intercostals are the muscles lining the ribcage. The internal intercostals (inside the ribs) pull the ribs downward and inward, aiding in exhalation. The external intercostals (outside the ribs) pull the ribs upward and outward, aiding in inhalation.
The Upper Respiratory Tract
The upper respiratory tract includes the sinuses and nasal passages, as well as the oral cavity (also known as the mouth). These cavities are connected via a continuous mucus membrane to the physiological tubes leading to the lungs.
The pharynx is better known as the throat and is divided into three parts:
- Oropharynx - opening behind the oral cavity, and the only anatomical structure to handle both food and air besides the mouth itself.
- Nasopharynx - where the nasal passages extend upward through the nose and nostrils.
- Laryngopharynx - extending downward from the oropharynx to the larynx and windpipe.
The larynx, also known as the voicebox, is made of cartilage and tissue folds more commonly called vocal cords. Air passing over the folds form sounds and speech. The epiglottis is a flap that covers the larynx during swallowing because the esophagus and windpipe both extend from the oropharynx.
The Lower Respiratory Tract
- The windpipe (trachea) - The trachea is held open by cartilage. The incomplete rings of cartilage allow the windpipe to partially collapse when food is swallowed by the esophagus, which lies next to the trachea.
- Lung - The major organ of the respiratory tract is the lung. Normally, each person has two lungs, one on each side of the chest cavity. Each lung is made of lobes, three on the right and two on the left. The lack of a third lobe on the left leaves room for the heart, which is connected directly to the lungs via the pulmonary blood supply. The lungs are connected to the trachea by the bronchial tree.
- Bronchial tree - The bronchi branch off of the windpipe. Each lung side receives air via its own bronchus; the left bronchus branches off the trachea into the left lung, the right bronchus branches off the trachea into the right lung. The bronchial tree describes the increasingly smaller branches (bronchioles) of bronchials that feed deeper into the lung lobes. The bronchioles terminate in the alveolar sacs, which contain the smallest units of the lungs, the alveoli.
Reference:
Scanlon and Sanders. Essentials of Anatomy and Physiology, 4th edition. Saunders.
Alicia Mae Prater - Alicia received her doctorate in Experimental Pathology in 2007. She has been a freelance writer and scientific editor since 2008.
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