Respiratory System

INTRODUCTION

Through experimental analysis of the physiological aspects of the human respiratory system, one can truly gain a better understanding of its inner-workings. A deeper look into the anatomy and the physiological mechanisms of the human lungs requires using the knowledge gained from research, lab and coursework of the respiratory system. The respiratory system begins with respiratory airways that lead into the lungs. These airways include nasal passages, pharynx, trachea, larynx, right and left bronchi, bronchioles and clusters of alveoli. The lungs themselves occupy most of the thoracic cavity and each lung is divided into several lobes. The diaphragm and pleural sac are important components to the respiratory system as well. The pleural sac is a thin layer of tissue covering the lungs and the wall of the chest cavity to protect and cushion the lungs. The diaphragm is a sheet of skeletal muscle that lies inferior to the lungs. When this sheet of muscle contracts, air is pulled into the lungs and when the muscle relaxes air is pushed out of the lungs. Alternate contractions and relaxations of the diaphragm and other inspiratory muscles indirectly produce inflation and deflation. Breathing is mechanically accomplished by alternately shifting the direction of the pressure gradient for airflow between the atmosphere and alveoli through the cyclic expansion and recoil of the lungs. Changes in intra-alveolar pressure produce flow of air into and out of the lungs. If this pressure is less than atmospheric pressure, air enters the lungs. If the opposite occurs, air exits from the lungs (Sherwood 2004; Sherwood 2007). The air and blood undergo a gas exchange which occurs in these alveolar air sacs. This occurs through the capillary network around each alveolus, a gas exchange occurs where carbon dioxide is released into the alveolar sacs and into the air (LabTutor 2008). This process is referred to as diffusion – moving from a high concentration to a low concentration. Basically, the body takes in oxygen and expels carbon dioxide. The necessity for breathing and exchanging gases can further be expressed through something everyone, including most animals, do – yawn. Yawning occurs in order to “cool” the brain. Cerebral blood flow increases due to the facial muscle movement, which draws heat to the brain – however, the cool air entering the lungs decreases the temperature of the blood in the brain through convection (Marano 2007).

Through the process of breathing, a technique known as spirometry can be performed in order to record respiratory variables. Spirometry is a technique of measuring breathing through measuring lung function, specifically the measurement of the volume and/or speed of air that can be inhaled and exhaled (Sherwood 2004, Sherwood 2007). Spirometry can be used to assess conditions such as asthma, pulmonary fibrosis and Chronic Obstructive Pulmonary Disease (COPD). Asthma is a condition in which the airway occasionally constricts, becomes inflamed, and is lined with excessive amounts of mucus, often in response to one or more triggers (Taylor 2008). Pulmonary fibrosis is a chronic progressive interstitial lung disease of unknown etiology (Sherwood 2004; Sherwood 2007). COPD is a disease characterized by the pathological limitation of airflow in the airway that is not fully reversible – caused by a number of factors such as smoking, airborne irritants, as well as congenital conditions (Stallord 2007). COPD is the 12th leading cause of death in the world, and the 5th leading cause of death in Western countries (LabTutor 2008).

There are many different lung capacities and volumes that should be taken into consideration when using spirometry. Forced vital capacity (FVC) is the total amount of air that can forcibly be blown out after full inspiration, measured in liters. Vital capacity (VC) is the maximum amount of air that can be expelled in a single breath following FVC. Forced expiratory volume in one second (FEV1) is the amount of air that you can forcibly blow out in one second, measured in liters. Along with FVC it is considered one of the primary indicators of lung function. Percent FVC expired in one second is the ratio of FEV1 to FVC. When using spirometry to test asthma, the measurement of forced expiratory volume in one second (FEV1) and of forced vital capacity (FVC) are the most beneficial tools (Taylor 2008). Peak expiratory flow (PEF) is the speed of the air moving out of your lungs at the beginning of the expiration, measured in liters per second. Peak inhalation flow (PIF) would then be the speed of the air moving into the lungs. Tidal volume (VT) is the specific volume of air that is drawn into and then expired out of the lungs during a respiratory cycle. Inspiratory reserve volume (IRV) is the extra volume of air that can be expelled after a