Respiratory System
The respiratory system includes the nose, mouth, throat, windpipe, branching airways and lungs. Its main function is to deliver oxygen from the air to the bloodstream and to remove carbon dioxide from the blood and return it to the lungs to be breathed out. It also warms and filters the air we breathe, and assists in speech production by providing air for the voice box and the vocal cords. The average adult breathes in and out between 18 and 20 times per minute, and every day about 150 cubic meters (490 cubic feet) of air, the equivalent of a balloon about 7 meters (23 feet) in diameter, passes through the respiratory tract. Breathing processes Breathing, or respiration, has two phases: inhalation, or inspiration, in which air is sucked into the lungs, and exhalation, or expiration, where the air is forced back out of the lungs. The main muscle for breathing is the diaphragm, a large dome-shaped muscle separating the chest and abdominal cavities. When the diaphragm contracts, it flattens, enlarging the chest cavity, causing air to rush into the lungs. Relaxation of the diaphragm allows the chest cavity to return to its normal size, forcing air out of the lungs. Breathing is an automatic process, controlled by a part of the nervous system called the brainstem. This control is so strong that it is impossible to stop breathing for any significant length of time. Mouth and nasal passages During respiration, air enters the body through the mouth and the nasal passages. The nose filters the air that we breathe: its lining - the mucous membrane - has thousands of tiny hairs that move waves of mucus back towards the throat. Dust, chemical particles and bacteria are trapped in the mucus, carried back towards the throat and swallowed out of harm's way. The mucous membrane warms and moisturizes the air breathed in. The nose is also the site of organs of the sense of smell. Throat Once air has entered the body through the nose and mouth, it passes through the throat or pharynx, a muscular tube connecting the back of the nose and the mouth with the voice box. The throat also forms part of the digestive system. Within the walls of the throat are the tonsils and adenoids, collections of tissue that help to trap and destroy many infectious organisms that enter the airways. Windpipe and branching airways Once air has passed through the voice box, it enters the windpipe, or trachea, which branches into two main air passages, each leading to a lung. Within each lung, these air passages divide, branch and subdivide into thousands of tiny air passages. At the end of the tiniest air passages are balloon-like sacs called alveoli. Alveoli and gas exchange Rather like the capillaries (tiny blood vessels) that surround them, alveoli have walls only one cell thick, allowing the rapid transmission of oxygen from air to the bloodstream and equally rapid diffusion of carbon dioxide from blood into the lungs to be breathed out. Efficient gas exchange is enhanced by the huge surface area of the alveoli, and the fact that at the site of gas exchange, the distance between air and blood is only one-thousandth of a millimeter. There are more than 700 million alveoli in the lungs, and their internal surface area is about the size of a tennis court. After crossing the walls of the alveoli into surrounding tiny blood vessels, oxygen binds with hemoglobin in red blood cells. Carbon dioxide is released from blood plasma into the alveoli and breathed out. |
|||
|
|
| Home | About Disease-Condition | Resources | Contact | Copyright © 2005 - Disease Condition |
Diseases & Conditions || Symptoms Checker || Herbal Remedies || Asthma || Deep Skin Disorders || Drugs
Featured Listings: Walking Canes - the walking cane does wonders for your everyday life and greatly improves mobility.
