1. Components and mechanisms of the respiratory system
The respiratory system is the system that allow humans and animals to breathe. The main function of the system is to provide oxygen to the body through the blood. Breathing involves two main actions: inhaling and exhaling air. Inhalation brings oxygen into the body via the blood and exhalation chases out carbon dioxide.
The respiratory system is composed of different tissues and organs, including the airways, lungs, bloods vessels and muscles connected to each other to assure a proper breathing process (National Heart, Lung and Blood Institute, 2012). The airways include e.g. the nose, mouth, larynx (voice box), trachea (windpipe) and bronchial tubes. The lungs are the main components of the respiratory system and the diaphragm the main muscle that helps pump the air in and out the body.
The respiratory mechanism starts by inhaling air through the nose or the mouth. The air is humidified and travels through the larynx and trachea to reach the lungs and then the blood and the rest of the body. The trachea is a tube that enters the chest cavity where it divides into two smaller pipes, the bronchi. Each bronchus is subdivided into smaller tubes forming the bronchial tubes. The latter tubes are also subdivided into even smaller tubes, which are attached in the lungs to miniscule bags surrounded by capillaries called alveoli. The inhaled oxygen-rich air is taking to the blood arteries via the alveoli, whereas the carbon dioxide-rich air is discharged into the alveoli via the blood veins and follows the same path as the oxygen-rich air to exit. When for some reasons (e.g. sickness, disorder) the breathing process does operate properly, the body will not receive the required amount of oxygen for its metabolism and will also be poisoned by the carbon dioxide that accumulate in the system.
Some of the airway organs are lined with cilia that filter the entering air by entrapping some particles and germs inhaled with air. The phenomenon provokes sneezing and/ or coughing in order to eject the compounds out of the system.
The inhalation and exhalation mechanisms are supported by the diaphragm and other muscles such as the abdominal, intercostal and neck muscles. The diaphragm is a sheet of the internal skeletal muscle situated at the base of the chest cavity. It separates the thoracic and abdominal cavities and with other muscles helps the lungs to expand and contract, allowing thereby the inhalation and exhalation processes. Air is pulled into the lungs when the diaphragm contracts, whereas a relaxation of the diaphragm muscles induces the release of carbon dioxide from the lungs.
2. Diseases related to the respiratory system
2. 1. Pneumonia
Pneumonia is an infection of the lungs resulting in an inflammation of the alveoli and a solidification of the lungs. When inflamed, some of the alveoli are invaded by white blood cells and secretions, preventing thereby a proper transfer of the air into/from the bloodstream. The infection usually affects one lung, but in serious cases, both lungs can be affected.
Causative agents: Usually pneumonia is caused by microorganisms, including mainly bacteria, but also fungi, viruses and protozoa (The World Health Organization, 2013). In a few cases, the disease is the result of an inhalation of chemicals or vomit. Different species of bacteria can be responsible for the disease. These include e.g. Streptococcus pneumonia, Legionella pneumophila, Staphylococcus aureus, Haemophilus influenza, Mycoplasma pneumonia, and klebsiella pneumonia. Viral causes of pneumonia include e.g. the causative agents of influenza and chickenpox.
Symptoms: Various symptoms are associated with pneumonia and can be mild or severe, depending on the causative agent and individuals. Infants and the elderly are usually at high risk and more affected. The symptoms generally develop within few hours and include e.g. high fever, convulsions (especially in infants), headaches, malaise, chest pain (pronounced when inhaling), shortness of breath, confusion, cough accompanied or not with a bloody and/or purulent discharge, loss of appetite and vomiting (especially in infants). In severe cases, pneumonia can lead to life threatening conditions such as septicaemia and respiratory failure.
Diagnosis: Pneumonia is first diagnosed by physical examination, followed by e.g. a chest X-ray to confirm the diagnosis and screen the extension of the infection, a microbial screening of the sputum to identify the specific microorganism responsible for the infection and a blood test to each a precise diagnosis.
Treatment: Mild forms of pneumonia can be treated at home, but severe cases require a hospital admittance. Microbial types of pneumonia are treated with antibiotics including antibacterial medications such as fluoroquinolones (moxifloxacin, gemifloxacin), beta-lactams (amoxicillin, penicillin) and macrolides as well as antifungal and anti-viral drugs. Antibiotics are provided to kill the microorganisms present in the system and stop the infection. Pain killers and antipyretic drugs may be given to address the pain and fever. In severe cases, oxygen may be provided through a face mask and sessions of chest physiotherapy regularly operated to help remove the excess of mucus accumulated in the lungs.
2. 2. Tuberculosis
Tuberculosis is a bacterial infection characterized by a formation of nodula lesions called tubercles in the body tissues. When the disease is contracted by inhalation through the nose, the tubercles are primary formed in the lungs and spreads to the closest lymph nodes; but when it is contracted through the mouth by consumption of e.g. unpasteurised milk, the tubercles are initially formed in the abdominal lymph nodes. One main characteristic of tuberculosis is the spitting of blood.
Causative agent: The causative agent of tuberculosis is a bacterium known as Mycobacterium tuberculosis. The bacterium spreads through the air and is transmitted to others when infected people cough or sneeze (Talip et al., 2013). Many people get infected by the bacterium, but a limited fraction develops the disease depending on the strength of the individual immune system. Various infections are stopped after the formation of the initial tubercles. However, dormant bacteria can remain in the lungs and become active months or years later when the immune system of the individual weakens.
Symptoms: The symptoms of tuberculosis are variable according to the stages of the disease and at the early stage, many people do not have any symptoms. Initial stage symptoms include e.g. cough, malaise, enlarged lymph nodes mainly in the neck. Further symptoms appearing within 2-6 weeks include e.g. persistent cough accompanied with purulent and bloody sputum, chest pain, shortness of breath, fever, loss of appetite and weight lost, tiredness and excessive sweating at night. In severe cases, the disease can spread to other parts of the body provoking e.g. septicaemia and meningitis.
Diagnosis: Tuberculosis is first diagnosed by physical examination, followed by e.g. a chest X-ray, a microbial screening of the sputum to identify the specific microorganism responsible for the infection and a bronchoscopy to sample a piece of a lung for examination.
Treatment: The main treatment of tuberculosis is based on administration of antibiotics and last for at least six months. Usually a combination of different antibiotics is used to treat the infection. Common anti-tuberculosis medications include, Capreomycin, Cycloserine, Ethambutol, Isoniazid, Rifampicin, and Streptomycin. For prevention, it is recommended to administrate the vaccine BCG against tuberculosis to people at risk, such as new-borns, infants and health care workers.
2. 2. Asthma
Asthma is a condition causing sporadic inflammation, swelling and narrowing of an individual airways that provoke coughing, wheezing and shortness of breath due to insufficient air intake by the lungs. During an asthmatic episode, the major airway tubes produce an excess of mucus that can obstruct the smaller airways (van den Berge et al., 2011). Asthma is a condition, which can sometimes be passed through family generations and seems to occur more in children than adults, and more in male children and female adults.
Causative agents: Asthma can be related to a genetic factor or to the exposure to various stimuli such as allergens (e.g. dust, pollens, and pet fur), drugs (e.g. aspirin), exhaustion, emotion, infections, and air pollution.
Symptoms: Manifestations of the condition can be mild, develop gradually or severe. These include symptoms such as wheezing. painless tightening in the chest, shortness of breath, difficulty breathing, dry and persistent cough, panic, sweating, blue lips, tongue, fingers, and toes due to the absence of oxygen, exertion, confusion, and coma. In some cases, asthma may be accompanied by hypersensitivity manifestations such as hay-fever and dermatitis.
Diagnosis: Diagnosis of asthma includes physical examination followed by more advance tests such as spirometry (to screen the efficiency of the lungs), induction of an asthmatic episode, induction of an irritation of the airways, measure of the exhalation speed using a peak flow meter and measure of oxygen level in the blood.
Treatment: This includes mainly the use of bronchodilators (aerosol, nebulizer) such as Bambuterol, Formoterol and Aminophylline to enlarge the airways and allow a better air flow, and the use of corticosteroids such as Beclometasone, Budesonide and Fluticasone to decrease the production of mucus and inflammation in the airways, and to prevent the narrowing process. A prevention measure is to avoid known triggering agents and have a healthy lifestyle in order to decrease the frequency of the attacks.
References
National Heart Lung and Blood Institute (2012, July 07). The respiratory system. Retrieve from http://www.nhlbi.nih.gov/health/health-topics/topics/hlw/system.html
Talip, B.A., Sleator, R.D., Lowery, C.J., Dooley, J.S., Snelling, W.J. (2013). An update on global tuberculosis (TB). Infectious Diseases: Research and Treatment, 6, 30-50.
The World Health Organization (2013). Pneumonia, Fact sheet N°331. Retrieved from http://www.who.int/mediacentre/factsheets/fs331/en/
van den Berge, M,. ten Hacken, N.H., Cohen, J., Douma, W.R., Postma, D.S. ( 2011). Small airway disease in asthma and COPD: clinical implications. Chest Journal, 139(2), 412-423.
