The term lower respiratory tract refers to the portions of the respiratory system

Respiratory system

The respiratory system is the anatomical system of an organism that introduces respiratory gases to the interior and performs gas exchange. In humans and other mammals, the anatomical features of the respiratory system include airways, lungs, and the respiratory muscles...

 from the trachea

Vertebrate trachea

In tetrapod anatomy the trachea, or windpipe, is a tube that connects the pharynx or larynx to the lungs, allowing the passage of air. It is lined with pseudostratified ciliated columnar epithelium cells with goblet cells that produce mucus...

 to the lung

Lung

The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...

s.

Lower respiratory tract infection

Lower respiratory tract infection

Lower respiratory tract infection while often used as a synonym for pneumonia, can also be applied to other types of infection including lung abscess and acute bronchitis...

s can be the cause of several serious illnesses, including pneumonia

Pneumonia

Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...

.

Main parts of the lower respiratory tract

The lower respiratory tract consists of:

• the trachea
  Vertebrate trachea
  In tetrapod anatomy the trachea, or windpipe, is a tube that connects the pharynx or larynx to the lungs, allowing the passage of air. It is lined with pseudostratified ciliated columnar epithelium cells with goblet cells that produce mucus...
  
   (wind pipe)
• the two bronchial tubes (one to each lung)
• the bronchioles, and the lungs.

haemoptysis is expectoration of blood from lower respiratory tract.
Some sources include the larynx

Larynx

The larynx , commonly called the voice box, is an organ in the neck of amphibians, reptiles and mammals involved in breathing, sound production, and protecting the trachea against food aspiration. It manipulates pitch and volume...

 as part of the lower respiratory tract, whereas others include it in the upper respiratory tract

Upper respiratory tract

The upper respiratory tract or upper airway primarily refers to the parts of the respiratory system lying outside of the thorax or above the sternal angle. Another definition commomly used in medicine is the airway above the glottis or vocal cords...

 (which also comprises the nasal cavity

Nasal cavity

The nasal cavity is a large air filled space above and behind the nose in the middle of the face.- Function :The nasal cavity conditions the air to be received by the other areas of the respiratory tract...

 (nose) and the pharynx

Pharynx

The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...

).

Between them, the upper and lower respiratory tracts make up the whole respiratory system.

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

Epiglottis

The epiglottis is a flap that is made of elastic cartilage tissue covered with a mucous membrane, attached to the entrance of the larynx. It projects obliquely upwards behind the tongue and the hyoid bone, pointing dorsally. The term, like tonsils, is often incorrectly used to refer to the uvula...

 which prevents food and water from entering our lungs when we breathe. If the epiglottis does not close when swallowing food or water, there is an involuntary reaction to cough. The larynx also has cilia. The trachea 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, or bronchi

Bronchus

A bronchus is a passage of airway in the respiratory tract that conducts air into the lungs. The bronchus branches into smaller tubes, which in turn become bronchioles....

. The bronchial tubes then branch off into smaller sections inside the lungs, called bronchioles. These bronchioles hold the air sacs in the lungs called the alveoli. The lungs are the biggest organ in the lower respiratory tract. The diaphragm

Thoracic diaphragm

In the anatomy of mammals, the thoracic diaphragm, or simply the diaphragm , is a sheet of internal skeletal muscle that extends across the bottom of the rib cage. The diaphragm separates the thoracic cavity from the abdominal cavity and performs an important function in respiration...

 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.

When a human being inhales, air travels down the trachea, through the bronchial tubes, and into the lungs. The entire tract is protected by the rib cage, spinal cord, and sternum bone. In the lungs, oxygen from the inhaled air is transferred into the blood and circulated throughout the body. Carbon dioxide (CO2) is transferred from returning blood back into gaseous form in the lungs and exhaled through the lower respiratory tract and then the upper, to complete the process of breathing

Breathing

Breathing is the process that moves air in and out of the lungs. Aerobic organisms require oxygen to release energy via respiration, in the form of the metabolism of energy-rich molecules such as glucose. Breathing is only one process that delivers oxygen to where it is needed in the body and...

.

Vital System

The lower respiratory tract is a vital system. This tract is responsible for receiving oxygen (O2) 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

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) 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 off into a left and right branch. In these two branches, there are bronchi and bronchioles. These tubes help take air into 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 bronchiole 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 in the form of oxyhaemaglobin, to nourish the cells. The red blood cells also carry carbon dioxide (CO2) away from the cells in the form of carboxyhaemaglobin 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 (CO2).

Lobes of the Lungs

The lungs are connected by the pleural cavity

Pleural cavity

In human anatomy, the pleural cavity is the potential space between the two pleura of the lungs. The pleura is a serous membrane which folds back onto itself to form a two-layered, membrane structure. The thin space between the two pleural layers is known as the pleural cavity; it normally...

. This cavity is attached to the chest. The pleura is a small membrane, singled celled, that surrounds the lungs. This 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 trachea (windpipe) 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 lungs. The reason why we cough is because the cilia push up the mucus, so not too much enters our lungs. If these hairs are not functioning properly, an organism is at risk of a lower respiratory tract infection

Lower respiratory tract infection

Lower respiratory tract infection while often used as a synonym for pneumonia, can also be applied to other types of infection including lung abscess and acute bronchitis...

.(7)

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 are not as strong in fighting off these infections. Most of these infections used 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 have environmental factors such as smoking. When you inhale a tobacco product, the smoke paralyzes the cilia, causing mucus to enter the lungs. If you smoke frequently, over time these cilia hairs die, and can no longer filter mucus. Tar from the smoke inhaled enters your lungs, turning the pink-coloured lungs black. The accumulation of this tar could eventually lead to lung cancer, emphysema or chronic obstructive pulmonary disease (C.O.P.D.).(5)

Emphysema

This is a common lower respiratory disease that can be caused by exposure to harmful chemicals, or prolonged use of tobacco. This disease is chronic and progressive, 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, hyperventilation, and raised chest. The decreased amount of alveoli causes loss of oxygen (O2) to the lungs, and more accumulation of carbon monoxide (CO). There are two types of emphysema

Emphysema

Emphysema is a long-term, progressive disease of the lungs that primarily causes shortness of breath. In people with emphysema, the tissues necessary to support the physical shape and function of the lungs are destroyed. It is included in a group of diseases called chronic obstructive pulmonary...

: 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/have smoked and have a history of chronic bronchitis.(5)

Pneumonia

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

Pneumonia

Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...

 is the most common, and frequent lower respiratory tract infection. This can be either viral, bacterial, or fungal. This infection is very common, because pneumonia can be airborne, 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 respiratory 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

Bronchitis

Bronchitis

Acute bronchitis is an inflammation of the large bronchi in the lungs that is usually caused by viruses or bacteria and may last several days or weeks. Characteristic symptoms include cough, sputum production, and shortness of breath and wheezing related to the obstruction of the inflamed airways...

 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 and can go away without treatment, 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

Tuberculosis

Tuberculosis

Tuberculosis, MTB, or TB is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis usually attacks the lungs but can also affect other parts of the body...

 is one of many other infections that occurs in the lower respiratory tract. You can contract this infection from airborne droplets, and if inhaled you are at risk of this disease. This is a bacterial infection which 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. These tubes
carry the oxygen (O2) to the bronchioles inside the lungs. If these tubes swell up, this is the result of asthma

Asthma

Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...

which could lead to an asthma attack. This results in wheezing, tightness of the chest and severe difficulty in breathing. There are different types of asthma that affects the functions of the bronchial tubes. Allergies can also set off an allergic reaction causing swelling to the bronchial tubes, and as a result the air passage will swell up, or close up completely. (7)

External links

• http://training.seer.cancer.gov/module_anatomy/unit9_4_resp_passages.html