Human Respiratory System.

The word respiration describes two processes.
Internal or cellular respiration is the process by which glucose or other small molecules are oxidised to produce energy: this requires oxygen and generates carbon dioxide.
External respiration (breathing) involves simply the stage of taking oxygen from the air and returning carbon dioxide to it.

Following are the parts of Respiratory System:

  1. NOSE
  4. LUNGS


1. The nose is the first and last organ that air passes through. The nose serves some very most important functions. As part of the conducting zone, it cleans the air of dust and other impurities, warms the air if it is too cool, and moistens the air if it is dry. Though not related to respiration, your nose also helps you to speak, and is the organ that gives you the power to smell.

2. After passing through the external nares (nostrils), it passes through the nasal cavities. Your nasal septum separates the two nasal cavities. Immediately after passing through the nostrils into the nasal cavities, the air begins to be purified, humidified and warmed. The skin of the vestibule, the part of the nasal cavities behind the nostrils, has sebaceous and sweat glands and hair follicles, which catch the dirt or other impurities that may be in the air. The hair growing out of the follicles are called vibrissae.

3. The olfactory mucosa is what detects scents that you inhale. The serous glands excrete enough lysozyme, an enzyme that destroys bacteria, to keep the air you breathe mostly pure. That is about a quart a day. It will kill the bacteria that is caught by the vibrissae.

4. In the pharynx, the cilia moves bacteria up away from the lungs so that you can swallow it into your stomach, where the bacteria can do little harm. Because of the shape of your organs, air swirls and twists as it moves down. This make sit virtually impossible for impurities to not make contact with the mucous lining your organs. This will catch most particles larger than 4┬Ám.


1. The trachea, or windpipe connects the larynx to the bronchi. This organ differs from others in the neck in that it is flexible, stretching to be between four and five inches long, and about one inch in diameter. The trachea is lined with mucous called the mucociliary escalator, which represents the mucous and cilia and carry the foreign substances up to be swallowed.

2. The trachea is made up of between 16 and 20 cartilage rings in the shape of a "C". Because the trachea is so flexible and twistable, without these cartilage rings, it would collapse under the partial vacuum formed when inhaling. The open part of the "C" shape is covered with the Trachealis muscle, which can stretch itself to prevent tracheal tearing when swallowing large things. When you cough, the muscle also contracts to force air out at a faster speed to dislodge food or other foreign objects stuck.


1. The trachea branches off into two main bronchi, your left and right primary bronchi, which lead to the left and right lung respectively. Your right lung is slightly wider, shorter, and taller that the left, which makes it more vulnerable to foreign invasion. At this point in breathing, the air has been moistened, purified and warmed.

2. Each bronchi enters its lung and begins on a series of branches, called the bronchial or respiratory tree. The first of these branches is the lobar (secondary) branch. On the left, there are two lobar branches, while on the right, there are three. Each lobar branches into one lobe. The next branch is called the segmental (tertiary) branch. Each branch continues to branch into smaller and smaller bronchioles. The final branch is called the terminal bronchioles. These bronchioles are smaller than 0.5 mm in diameter.

3. The first few levels of bronchi are supported by rings of cartilage. Branches after that are supported by irregularly shaped discs of cartilage, while the latest levels of the tree have no support whatsoever.


1. The lungs are a vital organ in our body, located in our chests. These pairs of cone-shaped breathing organs bring oxygen into our body and releases carbon dioxide. It is very important to make sure that they are functioning accurately because our life depends on it.

2. Each lung is made up of lobes. The left lung has 2 lobes and the right lung has 3. A hin membrane called pleura surrounds the lungs. Lungs are protected by rib-cage. Beneath the lungs is a dome-shaped muscle called diaphragm, that works with lungs allowing us to inhale (breath the air in) and to ex-hale (breath the air out).

3. From outside lungs look pink and they are sponge like in structure. At the bottom of wind-pipe (trachea) are the 2 tubes (main stem bronchi) that head into the respective lobes. Each main stem bronchi is then gets branched into smaller and smaller tubes (bronchi). So they from a tree like structure. The tiniest branch is called bronchioles. It has a thickness of a human hair. There are bout 30,000 bronchioles in each lung.

4. At the end of each bronchiole is a lump of tiny little air sac called Alveoli. Each alveolus (singular of Alveoli) has a mesh of tiny blood vessels called capillaries. These capillaries are so tiny that blood cell have to line up to march through them.

5. When we breath in air though mouth or nose the air gets pushed down windpipe (trachea) and then travels into the series of branches (bronchi and bronchioles) in the lungs and finally reaches alveoli. All the cells in the body need oxygen all the time. Alveoli allow oxygen from air to pass into blood. The oxygen gets attached to red blood cells and then travels unto heart via blood vessels. The heart then sends the pure blood ( with oxygen) out to all other cells in the body.


The main role of the Respiratory System is the inhalation of fresh oxygen (O2) needed by the body's cells and the exhalation of waste carbon dioxide (CO2). It also helps maintain body temperature and eliminate excess water from the body. The Respiratory system is dependent on the proper functioning of the circulatory system as the O2 and waste CO2 are carried in the blood stream.

The flow of air from the nose to the lungs

1. The nose is a PASSAGEWAY FOR AIR and is also a sensory organ. It warms and moistens air, and hair like processes (cilia) filter the air before it reaches the lungs.

2. The pharynx or "throat" is a funnel shaped tube acting as a passage way for air and food. The lowest portion of the pharynx joins the esophagus (food tube).

3. The larynx or "voice box" is lined with mucous membrane, two folds of membrane divide the larynx in two, between these is the GLOTTIS which is the narrowest part of the air passage. The glottis is protected by a lid of fibro cartilage (the EPIGLOTTIS), this closes over the glottis when you swallow.

4. The trachea or "windpipe" is a tube composed of cartilage and lined with mucus membrane lying in front of the esophagus. The trachea diverges into the right and left bronchi.

5. The bronchi are "C" shaped rings of cartilage lined with ciliated mucus membrane that 'sweeps' out dust particles. The bronchi branch into SECONDARY BRONCHI as they enter the lungs, these further divide into BRONCHIOLES. As the secondary bronchi and bronchioles divide the walls become thinner and more elastic, branching into minute ALVEOLI which transfer gases in the lungs.

6. The lungs are the main organ of respiration. In the lungs millions of ALVEOLI and blood Capillaries exchange Oxygen and carbon dioxide. Each lung is housed in a separate PLEURAL CAVITY (which in turn are located in the larger THORACIC CAVITY). PLEURA are SACS of membrane that line the pleural cavity to lessen friction caused by breathing.

7. The diaphragm is the main muscle of respiration located at the base of the thoracic cavity. The muscle contracts and flattens so that the thorax and lungs have room for incoming air causing you to INHALE, it then relaxes causing you to EXHALE.