The respiratory system comprises various structures and respiratory centers that facilitate effective respiration. Three of these structures are the nose, pharynx and larynx. The nose constitutes a visible external nose and an internal nasal cavity. The nose performs several crucial functions that condition the air before it enters the pharynx. Air from outside constitutes various impurities such as dust. It is the role of the external nose to eliminate these impurities. In addition, it warms and moistens the air. The nasal cavity acts as a conducting zone for the air received by the external nose. As air passes through the nasal cavity, it undergoes further purification, moistening and warming. Sebaceous glands, sweat glands and hair follicles clean the remnants of impurities in the air. Other processes within the nose include purifying the air from any bacteria.
The pharynx, commonly known as the throat, comprises three main regions, which perform a variety of functions. These regions are the nasopharynx, oropharynx and laryngopharynx. The nasopharynx is the first region of the throat where air enters from the internal nasal cavity. It comprises the pendulous uvula, which helps to regulate acts of breathing and swallowing. This ensures that food does not enter the respiratory system. From the nasopharynx, air enters the oropharynx. The last region of the throat is the laryngopharynx, which receives air from the nasopharynx and passes it to the larynx. The laryngopharynx comprises an aesophagus, which directs food and air to appropriate systems.
The larynx, commonly known as the voice box, comprises cartilages, membranes and ligaments. The epiglottis, a section of the larynx, regulates swallowing and prevents food from entering the respiratory system. The thyroid cartilage acts as a protective system for the larynx. The paired arytenoid cartilages create a mechanism that regulates breathing during muscular pressure. The larynx constitutes other cartilages such as the cricoid and corniculate cartilage.
The contraction of the diaphragm and intercostal muscles relies on signals from certain areas of the brain. Collective efforts by various respiratory centers are essential for a complete respiratory process. These centers function as a group rather than as distinct units of the system for controlling respiration. The contraction of the inspiratory muscles occurs due to the effects of the nerve impulses generated by the medullary inspiratory center (McMillan and Cecie 178). This center controls the relaxation of the inspiratory muscles and the stimulation of the expiratory muscles during normal expiration and rapid breathing respectively. The pheumotaxic area regulates the contraction of the inspiratory muscles by influencing the inspiratory center so that the lungs do not overinflate. The apneustic area sends signals to the inspiratory center to facilitate prolonged contractions of the inspiratory muscles.
The respiratory centers discussed above function under the influence of three groups of sensory neurons. Changes in the inspiration rate depend on the functioning of the central chemoreceptors, which send relevant signals to the respiratory centers. These receptors function by monitoring the chemical composition of the cerebrospinal fluid and stimulating appropriate actions. Central chemoreceptors respond to changes in the pH value of the cerebrospinal fluid. The peripheral chemoreceptors instigate appropriate responses by the respiratory centers depending on the chemical composition of the blood (McMillan and Cecie 195). These chemoreceptors respond to changes in either the pH or the pCO2 value of the blood. When there is the need to minimize or discontinue the stimulation of the inspiratory muscles, stretch receptors send signals to the respiratory centers. Stretch receptors respond to instances whereby lungs expand to their physical limit.
Works Cited
McMillan, Beverly , and Cecie Starr. Human Biology. Burlington, MA: Cengage Learning, 2011. Print.