The Full Wiki

Lower respiratory tract: Wikis


Note: Many of our articles have direct quotes from sources you can cite, within the Wikipedia article! This article doesn't yet, but we're working on it! See more info or our list of citable articles.


From Wikipedia, the free encyclopedia

Lower respiratory tract
Illu conducting passages.jpg
Conducting passages.

The lower respiratory tract refers to the portions of the respiratory system from the trachea to the lungs.

Lower respiratory tract infections can be the cause of several serious illnesses, namely pneumonia.


Main Parts of the Lower Respiratory Tract

The "lower respiratory tract" consists of the lower part of the respiratory system. This consists of the larynx(voice box) (although, some argue that the larynx is part of the upper respiratory tract), trachea(wind pipe), bronchial tubes, bronchioles, and lungs.[1] The upper respiratory tract consists of the nasal cavity (nose), pharynx, and ends at the larynx. The upper and lower respiratory tracts make up our whole respiratory system and work in a synchronizing pattern to make it possible to breathe.

Function of The Lower Respiratory Tract

The larynx is not just our voice box, it also serves as protection for our trachea. The larynx has a flap called the epiglottis which prevents food and water from entering our lungs when we breathe.(1) If the epiglottis does not close when swallowing food or water, there is an involuntary reaction to cough. The larynx also has cilia. The tracheal tube, consists of cartilage, and is the largest tube in the respiratory system. At the bottom of the tube, it branches off into two individual tubes, called the bronchial tubes. The bronchial tubes then branch off into smaller sections inside the lungs called bronchioles. These bronchia’s hold the air sacs in the lungs called the alveoli.[2] The lungs are the biggest organ in the lower respiratory tract. The diaphragm is the main muscle involved for the lungs to breathe and is the largest muscle. There are smaller muscles in between our rib cage that help the lungs expand and contract.

How the system Works and Functions

When we take a breath air travels down to our tracheal tube, to our bronchial tube, then enters our lungs. This tract is protected by the rib cage, spinal cord, and sternum bone. When an organism inhales it takes in oxygen, and then our lungs take in the oxygen, and circulates it through our blood system. This process nourishes the rest of our organs and blood.(2) It happens every time we breathe, and when an organism exhales the oxygen gas is converted into carbon dioxide. “This cycle of transpiring oxygen occurs in our circulatory system. The oxygen travels in our lungs, then enters the pulmonary veins on the left side of the heart. The carbon dioxide enters the right side of our heart through the superior and inferior vena cava. The carbon dioxide rich blood is pumped through our pulmonary artery, to the lungs, where the oxygen is absorbed and the carbon dioxide is released.” (1)

Vital System

The lower respiratory tract is a vital system. This tract is responsible for receiving oxygen, and distributing it through-out our whole body. All of our organs are dependent on this system, such as the brain. This is a key organ that is dependent on oxygen. If the lower respiratory tract shuts down, the body cant receive this vital oxygen, and organs that are deprived of oxygen shut down like the brain, which leads to severe brain damage, and death.

The Cell Structure of the Lower Respiratory Tract and the Inside of the Lungs

Our lungs are made up of thirteen different kinds of cells, eleven are called epithelial and the other two are mesenchymal cells. (6)[3] The epithelial cells make the lining of our tracheal, and bronchial tubes, while the mesenchymal cells line the lungs. At the end of the trachea, the two bronchial tubes split of into a left and right branch. In these two branches, there are bronchi and bronchial. The left and right bronchi that connect the two lungs. These tubes help retrieve air to the lungs and help us breathe. Inside the bronchi, there are tiny tree like branches called Bronchioles. The bronchioles fill most of the lungs, and at the end of each bronchial there are the alveoli.(8) The alveoli are tiny little air sacs in the lungs where gas exchange takes place. there are “about 150 million per lung”. (1) When the diaphragm contracts, a negative pressure is generated in the thorax and air rushes in to fill the cavity. when that happens These sacs fill with air making the lung expand. The alveoli are rich with capillaries, called alveolor capillaries. Here the red blood cells absorb oxygen from the air and then carry it back to nourish the cells. The red blood cells also carry carbon dioxide away from the cells and releases it into the alveoli through the alveolor capillaries. When the diaphragm relaxes, a positive pressure is generated in the thorax and air rushes out of the alveoli expelling the carbon dioxide.

Lobes of the Lungs

The lungs are connected by the pleural cavity. This cavity is attached to the chest. The pleura is a small membrane, singled celled, that surrounds the lungs. Thie membrane helps the lungs expand and contract, while breathing. This membrane can be inflated by a viral or bacterial infection to the lungs. The lungs are divided into different lobes. The right lung is larger in size then the left, so the right lung has three lobes, and the left two. The three lobes are called the costal surface, diaphragmatic, and mediastinal. The part of the lung that is closest to the rib cage is the costal area. The lobes have three different types: anterior, posterior and inferior borders. These borders have different locations in the lungs. The left lung is smaller, than the right because it is pushed out farther by the heart. The Roots of the left and right lung “Root of the right lung bronchi lie posterior pulmonary arteries are superior pulmonary veins are inferior and anterior”

“Root of the left lung

bronchus lies posterior pulmonary artery is superior pulmonary vein is inferior and anterior”(6)

Infections of the Lower Respiratory Tract

Our tracheal tract has a membrane lining that produces a layer of mucus that helps filter waste that an organism breathes in through the air. There is also a small lining of tiny hairs in our lungs called cilia. These tiny hairs act as a filter in our lungs, and control the amount of mucus that enters our lung. The reason why we cough is because the cilia push up the mucus, so not too much enters ours lungs. If these hairs aren’t functioning properly, an organism is at risk of a lower respiratory tract infection.(7) The Infections Our respiratory system is very prone to developing infections in the lungs. Infants and older adults are more likely to develop infections in their lungs, because their lungs aren’t as strong in fighting off theses infections. Most of these infections use to be fatal, but now with new research and medicine, they are now treatable. With bacterial infections, antibiotics are prescribed, while viral infections are harder to treat, but still curable. Some of these infections are environmental factors such as smoking. When you inhale a tobacco product, the smoke paralyzes the cilia hairs, causing mucus to enter to the lungs. If you smoke frequently, over time these cilia hairs die, and no longer can filter mucus. Tar from the smoke inhaled, enters your lungs, turning the pink colored lungs black. The accumulation of this tar could eventually lead to lung cancer, mesothelioma, or emphysema.(5)


This is a common lower respiratory infection that can be caused by the exposure to harmful chemicals, or long use of tobacco inhalation. This infection is chronic, and like Alzheimer’s disease, the damage to your lungs is irreversible, and eventually fatal. This disease destroys the alveoli, and lung tissue. Damage to these air sacs, and tissue makes breathing very difficult, causing shortness in breath, hyperventilating, and raised chest. The decreased amount of alveoli causes loss of oxygen to the lungs, and more accumulation of carbon monoxide. There are two types of emphysema: primary and secondary. Primary emphysema can be found in younger adults. This type of emphysema deteriorates the air sacs, and lung mass. Secondary emphysema can be found in older adults who smoke and have a history of chronic bronchitis.(5)


The common cold/flu is the most common cause for the upper respiratory tract infection, which can cause more serious illness that can develop in the lower respiratory tract. Pneumonia is the most common, and frequent lower respiratory tract infection. This can be either viral, bacterial, or fungi. This infection is very common, because pneumonia can be air born, and when you inhale this infection in the air, the particles enter the lungs and move into the air sacs. This infection quickly develops in the lower part of the lung, and fills the lung with fluid, and excess mucus. This causes difficulty in breathing, and coughing as the lower repertory tract tries to get rid of the fluid in the lungs. You can be more prone to developing this infection if you have asthma, flu, heart disease, or cancer(7)


Bronchitis is another common infection that takes place in the lower respiratory tract. It is an inflammation of the bronchial tubes. There are two forms of this infection: acute bronchitis, which is treatable and goes away, or chronic bronchitis, which comes and goes, but will always affect ones lungs. Bronchitis increases the amount of mucus that is natural in your respiratory tract. Chronic bronchitis is common in smokers, because the tar from smoking accumulates over time, causing the lungs to work harder to repair themselves. (7)


Tuberculosis is one of many other infections that occurs in the lower respiratory tract. You can contract this infections from air born droplets, and if inhaled you are at risk of this disease. This is a bacterial infection, deteriorates the lung tissue resulting in coughing up blood. (7) This infection is deadly if not treated.

Bronchial Tubes associated with Asthma

Our bronchial tubes are the main passages to our right and left lungs. Theses tubes carry in the oxygen to the braches inside the lungs. If these tubes swell up, this is the result of asthma which could lead to an asthma attack. This results in wheezing, tightness of chest and severe difficulty in breathing. There are different types of asthma that effects the functions of the bronchial tubes. Allergies can also offset an allergic reaction causing swelling to the bronchial tubes, and in result the air passage will swell up, or close up completely. (7)


  1. ^ "“Respiratory System Lower Repertory.”". Retrieved 5 Oct. 2008. 
  2. ^ "Human Respiratory System". Retrieved 5 Oct. 2008. 
  3. ^ "Cellular structure, function and organization in the lower respiratory tract". Retrieved 5 Oct. 2008. 

External links

External images
Lower respiratory tract


Got something to say? Make a comment.
Your name
Your email address