Overview
The purpose of the respiratory system is cellular respiration. Cellular respiration is a group of metabolic reactions which occur in the mitochondria of the cell. During cellular respiration, glucose and oxygen are converted to carbon dioxide, oxygen, and ATP. ATP, which is a “coenzyme”, is three bonded phosphate groups which when broken release energy into the cell for metabolic activities. Thus, cellular respiration provides a key source of energy for all metabolic activities occurring within animals. Cellular respiration’s unique formula though requires for there to be a constant exchange of carbon dioxide and oxygen occurring between an animal and the atmosphere, as oxygen must be constantly entering the body as carbon dioxide and other wastes are leaving it. This exchange is also known as external respiration. All mammals (including the Tree Pangolin) use the mammalian respiratory system in order to maintain and control this gas exchange. In the mammalian respiratory system, the lungs are the main organ involved in gas exchange. With each inhalation and exhalation, oxygen enters capillaries within the lungs and carbon dioxide is released from the bloodstream and then body. Along with the lungs, numerous other organs also form the mammalian respiratory system. These organs aid in moving gases in and out of the lungs. These organs include the mouth, nose, nasal cavity, larynx, trachea, bronchi and alveoli.
Parts of the Respiratory System
1) Lungs: The Lungs are the location of all gases exchange occurring within a mammal. They are a spongy mass of tissue located in the thoracic cavity [1]. Due to the contractions of the diaphragm, the lungs inflate during inhalation and deflate during exhalation. Their movement pulls and releases air from the body.
2) Diaphragm: The diaphragm (also known as the thoracic diaphragm) is a muscle located between the thoracic cavity and abdominal cavity of all mammals [2]. When relaxed, the diaphragm appears to be in the shape of a dome. During inhalation though, the diaphragm contracts, expanding the thoracic cavity and lungs. These movements initiate the process of gas exchange occurring within a mammal. 3) Nasal Cavity: Once inhaled through the nose (which is located on the upper tip of the Tree Pangolin's snout), the air flows into the nasal cavity. Inside the nasal cavity, tiny cilia and a mucous membrane filter the air, cleaning, warming and humidifying it before it reaches the lungs [3]. 4) Larynx: Located between the pharynx and trachea, the larynx is commonly known as the voice box as it produces all mammalian sounds. The larynx is formed by both muscle and cartilage and holds the vocal chords [4]. When air passes through the larynx during ventilation, the vocal cords produce vibrations which are commonly used as a form of speech [5]. 5) Trachea: The trachea is a long respiratory tube which extends from the larynx to the bronchi. Inside the trachea are small cartilage disks to prevent the trachea from collapsing upon itself. Also, lining the inside of the trachea is a moist tissue called mucosa, which further prevents any particles from entering the lungs [6]. 6) Bronchi: The bronchi, the right bronchus and left bronchus are airway tracts located within the lungs. They are subdivisions of the trachea and in fact are very similar as, like the trachea, they too are supported by cartilage rings. Within their respective lungs, the bronchus divide into smaller air tracts called bronchioles which carry oxygenated air to the alveoli. 7) Alveoli: The alveoli are tiny air sacs that are attached to the bronchioles. During inhalations, the alveoli inflate and become filled with oxygen. This oxygen diffuses through the alveolus permeable skin and into the bloodstream. During an exhalation, the alveoli deflate and force carbon dioxide out of the lungs [7]. |
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Inhalation and Exhalation
During inhalation, the diaphragm contracts and the thorax cavity and lungs expand. Air is inhaled through the nose and mouth. In the nasal cavity, the air is filtered by cilia and mucous glands. The air then passes through the larynx. If the vocal chords are stretched whilst air passes through, then vibrations (sounds) are created [8]. The air flows through the trachea where it is once again filtered and into the bronchi. Once in the bronchi, the air branches off into the bronchioles (smaller air tracts). This air flows into millions of alveoli, inflating them. In the alveoli, a gas exchange occurs. Oxygen within the inhaled air diffuses into the surrounding capillaries. Simultaneously, carbon dioxide and other wastes diffuse from the capillaries into the alveoli to be exhaled [9].
During exhalation this same process is reversed. The diaphragm relaxes and the lungs once again are decreased in size. This movement causes the alveoli to deflate and release carbon dioxide into the bronchioles [10]. From the bronchioles, the carbon dioxide travels upward through the bronchi, then trachea, larynx and nasal cavity when it is finally released from the nose and mouth into the atmosphere.
During exhalation this same process is reversed. The diaphragm relaxes and the lungs once again are decreased in size. This movement causes the alveoli to deflate and release carbon dioxide into the bronchioles [10]. From the bronchioles, the carbon dioxide travels upward through the bronchi, then trachea, larynx and nasal cavity when it is finally released from the nose and mouth into the atmosphere.
Circulation of Oxygen
Once having been diffused into the capillaries, oxygen travels to the heart via the pulmonary vein. In the heart, oxygen passes through the left atrium and ventricle and is released into the aorta. The aorta disperses the oxygen to the bodies cells for cellular respiration. The oxygen diffuses into the cells, through their permeable membranes. This diffusion is caused by a difference in pressure. Because there is a high oxygen partial pressure within the bloodstream and a low oxygen partial pressure within the cell, oxygen diffuses into the cell (in diffusion molecules move from high to low) [11]. In order for cellular respiration to occur though, oxygen must then enter the mitochondria. The oxygen does so by diffusing through the permeable mitochondrial membrane and the inner membrane of the mitochondrial matrix (where cellular respiration occurs) [12]. This diffusion occurring within the cell is an example of simple diffusion as oxygen is moving from an area of high concentration to an area of low concentration [13].
Once cellular respiration has occurred, the process is reversed in order so that its waste, carbon dioxide, can be released from the body. The carbon dioxide diffuses out of the mitochondrial membrane via simple diffusion. The carbon dioxide then diffuses out of the cell and into the bloodstream due to partial pressure. This is because carbon dioxides has a high partial pressure within the cell and a low partial pressure within the bloodstream (the opposite of oxygen)m [14]. From the bloodstream, the carbon dioxide enters the heart via the vena cava and is pumped through the right atrium and ventricle. The carbon dioxide flows into the pulmonary artery in which it travels to the lungs. The carbon dioxide diffuses into the alveoli of the lungs (by simple diffusion) and is exhaled by the body.
Once cellular respiration has occurred, the process is reversed in order so that its waste, carbon dioxide, can be released from the body. The carbon dioxide diffuses out of the mitochondrial membrane via simple diffusion. The carbon dioxide then diffuses out of the cell and into the bloodstream due to partial pressure. This is because carbon dioxides has a high partial pressure within the cell and a low partial pressure within the bloodstream (the opposite of oxygen)m [14]. From the bloodstream, the carbon dioxide enters the heart via the vena cava and is pumped through the right atrium and ventricle. The carbon dioxide flows into the pulmonary artery in which it travels to the lungs. The carbon dioxide diffuses into the alveoli of the lungs (by simple diffusion) and is exhaled by the body.
Respiratory Diseases
Numerous diseases have been known to affect the respiratory system. Many of these diseases though infect only one respiratory organ, but their inimical consequences can have an effect on the entire respiratory system and body. Laryngitis, is an infection of the larynx and leads to the inflammation of the vocal cords [15]. Asthma and bronchitis both affect the bronchi of the lungs. Asthma compresses the bronchi making it harder for air to reach the alveoli while bronchitis is an inflammation of the bronchi which causes mucous glands in the bronchi to over excrete mucous [16] [17]. Empyema and Pleurisy are diseases known to attack the thoracic cavity. Empyema is a bacterial infection of the thoracic cavity while pleurisy is an infection of the pleural membranes which line both the lungs and thoracic cavity which causes breathing to become unpleasant and painful [18] [19]. Similarly, pneumonia, tuberculosis and emphysema all affect the lungs. Pneumonia and tuberculosis are bacterial infections of the lungs whilst emphysema is an infection of the alveoli which leads to a shortness of breath and chronic cough [20] [21] [22].