Lungs are the major organ of the respiratory system. Lungs supply the body tissue of multi-cellular organisms with the oxygen needed to convert glucose to energy and provide a way for these organisms to eliminate the carbon dioxide produced during cellular respiration. Lungs are found in the thoracic cavity . The boundaries of this cavity are created by the diaphragm , ribs, and neck muscles. All boarders and organs contained in this cavity (heart, lungs) are covered by a plueral membrane that provides lubrication and allows the organs to slide past one another. The respiratory system can be split up into two zones, the conducting zone and the respiratory zone. The conducting zone is comprised of the trachea , bronchi , bronchioles , and terminal bronchioles . The structures of the conducting zone are the parts of the respiratory system not directly involved in gas exchange. They are the airways that deliver warm, clean oxygen to the respiratory zone. The respiratory zone consists of the alveoli ducts and the alveolar sacs . Aided by a surrounding net of pulmonary capillaries , these structures are where gas exchange between the lungs and blood stream occur. Oxygen from the atmosphere is delivered to the lungs through the process of inspiration . The phrenic nerve delivers signals that cause the diaphragm and intercoastal muscles to contract. This creates the negative pleural pressure needed for air from the atmosphere to move down the pressure gradient and into the lungs. When the diaphragm and intercostal muscles relax, the thoracic cavity has positive plueral pressure and the air once again moves down the pressure gradient and back to the atmosphere. This is the process of expiration . The barriers that separate the alveolar sacs from the pulmonary capillaries are so thin that oxygen from the alveolar sacs is able to passively diffuse across the alveolar epithelium into the pulmonary capillaries and conversely carbon dioxide from the bloodstream is able to passively diffuse across the capillary epithelium into the alveolar sacs. Alveoli walls are made of elastic fibers , collagenous fibers , and 2 types of epithelial cells: Type I and Type II. Type I cells make up 95% of the alveoli epithelium and create the barrier, while Type II cells provide stability by secreting surfactant into the air spaces of the alveoli. Type II cells are also important for ion transport. Ozone is a colorless gas made of three oxygen atoms. It is an oxidant with two unpaired electrons and reacts readily with other molecules. Naturally occurring ozone in the stratosphere constitutes the ozone layer. Ozone in the stratosphere protects living things from exposure to dangerous amounts of ultraviolet light and maintains the temperature of Earth's atmosphere by converting UV rays into a source of heat. When ozone comes in direct contact with living organisms the effects are harmful. Exposure to ozone in the troposphere destroys living tissue, acts as a greenhouse gas , stunts the growth of vegetation, and causes reduced lung function. Ozone in the troposphere is a secondary pollutant formed when volatile organic compounds and nitric oxides emitted by motor vehicles, power plants, and paints react with sunlight to form smog. Chlorofluorocarbons released by refrigerator coolants, air conditioners, and propellants thin and destroy ozone molecules. This is a problem because chlorofluorocarbons target good ozone in stratosphere. The thinning of the ozone layer allows more ultraviolet light to reach living organisms on Earth's surface. Ultraviolet light mutates DNA, weakens immune systems, and increases the prevalence of skin cancer. Urate and ascorbate are antioxidants in the epithelial lining fluid that detoxify ozone before it reaches epithelial cells. By acting as reducing agents, urate and ascorbate prevent oxidation of important lipids and proteins as well as the negative health effects that accompany structural changes of molecules. In 1997 the Environmental Protection Agency (EPA) developed the Air Quality Index (AQI) in order to quantify safe versus unsafe levels of ozone exposure. Although children, the elderly, and anyone performing strenuous physical activity in the presence of ozone have a heightened sensitivity to the gas, the EPA has determined that exposure to ozone levels that exceed 0.075 parts per million ( ppm ) for 8 hours is dangerous to the health of all people. In order to inform the public about air quality in a quick and easy way, the EPA has assigned colors to ozone concentrations based on their effect on human health. Meteorologists are able to forecast ozone levels by looking at the intensity of sunlight, temperature, and wind speed. Greater ozone concentrations are found during the 6 month period from April to October, with the highest level of ozone occurring in August.
|
|---|