Structure, Function, and Alterations of the Pulmonary System (Research Paper Sample)

Structure, Function, and Alterations of the Pulmonary System
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Pulmonary System: Structure and Function
By tracing an air molecule traveling through the pulmonary system after being inhaled from the environment, it is established that the upper and the lower conducting airways are involved. The former comprises of the nasopharynx, laryngopharynx and the oropharynx, while the latter comprises of the trachea, the bronchi and the terminal bronchioles, with the larynx connecting the lower and the upper airways. The upper conducting airways are located in the pharynx, and their function includes ensuring healthy vocalization (Rahilly, Muller, Carpenter and Swenson, 1983). The lower conducting airways are located within the lower respiratory tract, and their function is to convey inhaled air to the gas exchange structures of the respiratory system.
The structures involved in the gas exchange process include the alveoli, the respiratory bronchioles and the alveolar ducts. The significance of the surfactant in the pulmonary system is to reduce surface tension, thus enhancing the expansion of the alveoli, besides serving as a crucial biological detergent. The structures surrounding the pulmonary system include the chest wall, the mediastinum, and the lungs, the last being composed of five lobes, segments and lobules (Huether and McCance, 2013). The factors indispensable to successful diffusion, ventilation, and perfusion are high lung compliance, minimum airway resistance, minimum alveolar surface tension, and positive lung distensibility (Marzlin, 2008).
The mechanical receptors in the respiratory system include the irritant, stretch and J or juxtacapillary receptors, all located in the lungs. The J receptors play the role of increasing ventilation by responding to factors such as heart failure and pneumonia, which decrease oxygenation. While the irritant receptors cause an increase in breathing frequency in case histamine aerosols are inhaled, the stretch receptors enhance the interaction between the J and the irritant receptors during the reflex breathing response. The importance of these receptors, according to Gaga, Vignola and Chanez (2001) is to stimulate the sensory nerves in such a way that triggers several reflex reactions that include bronchoconstriction, cough and mucus release, among others. The mechanical chemoreceptors in the respiratory system include the central and the peripheral chemoreceptors. The former are located on the ventrolateral medullary cranial nerve surface, while the latter are located on the arteries of the neck. Their primary function is to control the respiratory activity, and their importance is to maintain arterial blood oxygen, pH and carbon dioxide within the suitable functional ranges.
The property of lung compliance refers to the degree of ease with which the thorax and the lungs expand, as determined by respiratory elasticity and volume. On the other hand, elastic recoil is the inverse of lung compliance, and thus, it refers to the degree of ease with which the lungs rebound after an episode of stretching through inhalation. Concerning the mechanics of breathing, it is clear that the breathing action is as a result of variations of pressure within the thorax as compared with the pressures outside. During inhalation, the contraction of the intercostal muscles found between the diaphragm and the ribs takes place, thus expanding the chest cavity. The flattening and downward movement of the diaphragm as well as the upward and outward movement of the rib cage by the intercostal muscles decreases the internal air pressure. The higher pressure air from the outside rushes into the lungs in an attempt to achieve pressure equalization, with the entire process reversing during exhalation, as Huether and McCance (2013) illustrate schematically.
Oxygen partial pressure refers to the pressure that oxygen exerts in a gas mixture, and it is measured in PaO2, which is simply a measure of oxygen in arterial blood. Leader (2014) mentions that 75 - 100 mmHg is the range of normal PaO2, meaning that a value less than this is an indication of not getting insufficient oxygen. It is worth noting that the oxygen partial pressure is significant in explaining the interrelationship between ventilation and perfusion.
In this sense, an increase in the ventilation-perfusion ratio implies that ventilation is higher that perfusion and vice versa, keeping in mind that this ratio influences alveolar gases and end-capillary gases (Marzlin, 2008). Furthermore, oxygen partial pressure is an important parameter in explaining the importance of the oxyhemoglobin dissociation curve. This curve, which relates the partial pressure of oxygen and oxygen saturation plotted in the x and y axes respectively, is useful in defining the variations in hemoglobin’s affinity for oxygen with varying rates of oxygen molecule binding (Varjavand, 2000).
As far as the mechanisms of carbon dioxide transport from the body tissues to the lungs is concerned, about ten percent of gaseous carbon dioxide in a simple dissolved form. The dissolved gaseous carbon dioxide resulting from cells under metabolic activity diffuses into the erythrocytes cytosol present in blood capillaries. The carbonic anhydrase available in large quantities in the erythrocytes catalyzes the diffused carbon dioxide reaction with a water molecule, resulting in the formation of carbonic acid (H2CO3). Once this acid is generated, it spontaneously dissociates into free bicarbonate (HCO3-) and hydrogen (H+) ions, whereby the latter is absorbed by the erythrocyte hemoglobin molecule. This hydrogen ion absorption may encourage boosted peripheral oxygen unloading owing to the Bohr Effect (Zubieta and Paulev, 2002).
On the other hand, the bicarbonate ion resulting from the reaction is transported into the blood plasma across the erythrocyte membrane, where it is exchanged with an ion of chlorine. This bicarbonate, exchanged using an electro-neutral antiporter of the bicarbonate chloride travels to the lungs via the venous plasma where the reverse of the outlined reactions occurs. This leads to the generation and exhalation of gaseous carbon dioxide, which is exhaled, with the reactions reversal being enhanced by high oxygen partial pressures and the Haldane Effect (Zubieta and Paulev, 2002). Lungs’ diffusion capacity, overall surface area of alveolar, alveolar oxygen partial pressure, diffusion distance and alveolar wall thickness are the factors influencing the diffusion of carbon dioxide across the alveolar membrane. Regarding the causes of pulmonary vasoconstriction, Huether and McCance (2013) state that acidemia and low oxygen partial pressure in the alveolar are the major cause.
Pulmonary Function Alterations
The clinical indicators of the pulmonary disease include dyspnea, abnormal sputum, cough, abnormal breathing patterns and hemoptysis. Other indicators highlighted by Huether and McCance (2013) are hyperventilation, cyanosis, hypoventilation, pain and clubbing. Hyperventilation is the respiratory condition in which a person experiences sudden fast breathing as a result of the quantity and rate of alveolar carbon dioxide ventilation exceeds the carbon dioxide produced by the body. On the other hand, hypoventilation is the condition in which a person breathes at an unusually slow rate, culminating in an augmented quantity of carbon dioxide in the person’s blood.
The alterations in arterial blood gas values that indicate pulmonary disease include hypoxemia, hypercapnia and acute respiratory failure. While hypoxemia refers to a condition of oxygen deficiency in arterial blood, hypoxia refers to a condition in which generalized or localized oxygen supply deprivation occurs in the body or body regions. A condition in which there is restricted blood supply to body tissues, leading to a deficiency in glucose and oxygen needed for normal cellular metabolism is referred to as ischemia. On its side, acute respiratory failure is the condition characterized by the buildup of fluid in the lungs’ air sacs, making the lungs incapable of releasing air oxygen into the blood. Consequently, the body organs fail to access sufficient oxygen-rich blood to function, a condition that may be worsened by the failure of removal of carbon dioxide from the blood. Macon and Yu (2012) say that smoking of tobacco products, excessive alcohol consumption, spine, chest and brain injury, chronic respiratory complications and family history of pulmonary ailments are risk factors of acute respiratory failure.
There are basically two types of pneumothorax, and these include the traumatic and the non-traumatic pneumothorax. Krause and Roth (2012) say that the former is caused by the occurrence of shock to the lung walls or the chest, thus causing injury to these structures and allowing air into the pleural space. According to these authors, the latter occurs in some spontaneous way after subjection to acute infections, lung cancer, asthma and cystic fibrosis among other chronic respiratory complications. The manifestations of the traumatic pneumothorax are breath shortness and soft bulges under the skin, while those of the non-traumatic pneumothorax are mild breathlessness and pain in the chest. Other conditions of the pulmonary system are pleural effusion and empyema, the former of which refers to a condition characterized by excessive buildup of fluid around the lung, while the latter refers to pus collection in the pleural cavity.
During a respiratory cycle, the lungs interact with the chest wall and this in turn influence the lung volume, leading to a noticeable effect on the inspiration pressure-volume relation curve. It is important to note that, besides maintaining the residual volume, the chest wall plays a supporting role to the lungs. Atelectasis is a condition occurring eithe...