Respiratory system includes the lungs and the network of air passageways that connects them to the nose and mouth . The respiratory system is one of the body’s major organ systems.
The respiratory system handles the exchange of gases between the air and the blood . It functions to take from the air the oxygen needed to fuel cellular respiration. Cellular respiration is the process by which the cells of the body obtain energy from glucose , a simple sugar. Cellular respiration produces a waste gas called carbon dioxide . The respiratory system also serves to remove carbon dioxide from the body.
Organs.
The lungs are the main organs of the respiratory system. The lungs are a pair of spongy organs that take up much of the thorax ( chest ). The left and right lungs differ slightly in size and shape to accommodate the heart , which extends into the left side of the chest. The right lung is larger and is composed of three lobes. The left lung is smaller and has only two lobes. The cardiac notch, a depression on the left lung, provides a space for the heart.
Other organs of the respiratory system make up the network of passages to the lungs. They include the nasal cavity, pharynx , larynx (voice box), trachea (windpipe), and bronchi. Within the lungs, the bronchi branch many times, getting smaller each time. They eventually end in microscopic sacs called alveoli .
Inspiration
is the process by which air is inhaled (breathed into the body). The most important muscle involved in inspiration is the diaphragm , a muscular sheet that separates the chest cavity from the abdomen (midsection). When the diaphragm contracts (pulls tight), the chest cavity expands, and air is drawn into the body.
In the nose, air passes through the nasal cavity, where it is warmed, moistened, and filtered. Air then passes into the pharynx, which functions as a muscular funnel. The pharynx passes air to the larynx and also passes food to a tube called the esophagus . The larynx is commonly called the voice box because the sounds of speech originate there. The larynx helps ensure that only air passes into the trachea, the tube leading to the lungs. The epiglottis, a flap of rubbery cartilage, helps to direct food away from the trachea during swallowing to prevent choking. The trachea carries air through the neck and into the chest. There, the trachea divides into a left and right bronchus (the singular of bronchi), which carry air into the lungs.
The airways in the lungs branch into smaller and smaller bronchi. All the airways eventually end in alveoli. Alveoli have thin walls and are surrounded by tiny blood vessels called capillaries . Gases can pass through the thin walls of the alveoli and capillaries from a higher concentration to a lower concentration. Oxygen thus passes from the air into the blood, which is depleted of oxygen.
Expiration.
Carbon dioxide can also pass through the walls of the capillaries and alveoli. It is released from the blood, where it has accumulated, and moves into the lungs, which have a much lower concentration of the gas. Expiration is the process by which air is exhaled (pushed out of the body) after gas exchange has occurred. In normal breathing, expiration is a passive process that only requires the diaphragm to relax. In heavy breathing, abdominal muscles help to forcefully exhale air from the lungs.
