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1 Chapter 3 HUMAN ORGAN SYSTEMS AND BIO-DESIGNS - 2 3.1 Lungs as Purification System: Figure: Representing the oxygen-carbon dioxide exchange in the alveoli and capillary Lungs as Purifier The lung purifies air by removing harmful substances and adding oxygen to the bloodstream. The process of purifying air in the lungs can be described as follows: • Filtration: The nose and mouth serve as a first line of defense against harmful substances in the air, such as dust, dirt, and bacteria. The tiny hairs in the nose, called cilia, and the mucus
2 produced by the respiratory system trap these substances and prevent them from entering the lungs. • Moisturization: The air is also humidified as it passes over the moist lining of the respiratory tract, which helps to keep the airways moist and prevent them from drying out. • Gas Exchange: Once the air reaches the alveoli, the gas exchange process occurs, where oxygen diffuses across the thin alveolar and capillary walls into the bloodstream, and carbon dioxide diffuses in the opposite direction, from the bloodstream into the alveoli to be exhaled. This process ensures that the bloodstream is supplied with fresh, oxygen-rich air, while waste carbon dioxide is removed from the body. Overall, the lung serves as a vital purification system, filtering out harmful substances, adding oxygen to the bloodstream, and removing waste carbon dioxide. It plays a critical role in maintaining the body's homeostasis and supporting life. 3.1.1 Architecture of Lungs as Purification System Figure: Representing structure of lung The architecture of the lung is designed to maximize surface area for efficient gas exchange. The lung is divided into several parts, including the trachea, bronchi, bronchioles, and alveoli. • Trachea: The trachea is the main airway that leads from the larynx (voice box) to the lungs. It is lined with cilia and mucus-secreting glands that help to filter out harmful substances and trap them in the mucus. • Bronchi: The trachea branches into two main bronchi, one for each lung. The bronchi are larger airways that continue to branch into smaller airways called bronchioles.
3 • Bronchioles: The bronchioles are smaller airways that eventually lead to the alveoli. They are surrounded by tiny air sacs called alveoli, which are the sites of gas exchange. • Alveoli: The alveoli are tiny air sacs that are lined with a network of capillaries. This close proximity of the alveoli and capillaries allows for efficient diffusion of oxygen and carbon dioxide between the air in the alveoli and the bloodstream. Overall, the architecture of the lung is designed to provide a large surface area for gas exchange, while filtering out harmful substances and humidifying the air. The close proximity of the alveoli and capillaries, along with the moist lining of the respiratory tract, ensures that the air is properly purified and the bloodstream is supplied with fresh, oxygen-rich air. 3.1.2 Gas Exchange Mechanism of Lung The gas exchange mechanism in the lung involves the transfer of oxygen from the air in the alveoli to the bloodstream, and the transfer of carbon dioxide from the bloodstream to the air in the alveoli. This process is known as diffusion and occurs due to differences in partial pressures of oxygen and carbon dioxide. • Oxygen Diffusion: The partial pressure of oxygen in the air in the alveoli is higher than the partial pressure of oxygen in the bloodstream. This difference creates a gradient that causes oxygen to diffuse from the alveoli into the bloodstream, where it binds to hemoglobin in red blood cells to form oxyhemoglobin. • Carbon Dioxide Diffusion: The partial pressure of carbon dioxide in the bloodstream is higher than the partial pressure of carbon dioxide in the air in the alveoli. This difference creates a gradient that causes carbon dioxide to diffuse from the bloodstream into the alveoli, where it is exhaled. 3.1.3 Spirometry Spirometry is a diagnostic test that measures the function of the lungs by measuring the amount and flow rate of air that can be exhaled. The test is commonly used to diagnose lung conditions such as asthma, chronic obstructive pulmonary disease (COPD), and interstitial lung disease. Principle: The principle behind spirometry is to measure the volume of air that can be exhaled from the lungs in a given time period. By measuring the volume of air exhaled, spirometry can provide information about the functioning of the lungs and the ability of the lungs to move air in and out. Working: Spirometry is performed using a spirometer, a device that consists of a mouthpiece, a flow sensor, and a volume sensor. The patient is asked to exhale as much air as possible into the spirometer, and the spirometer measures the volume and flow rate of the exhaled air. The volume of air exhaled is displayed on a graph called a flow-volume loop, which provides information about the lung function.
4 Figure: Image of a spirometer Interpretation of Results The results of spirometry can be used to determine if the lungs are functioning normally and to diagnose lung conditions. For example, a decrease in the volume of air exhaled or a decrease in the flow rate of the exhaled air can indicate a restriction in the airways, which can be a sign of a lung condition such as asthma or COPD. 3.1.4 Abnormal Lung Physiology - COPD Figure: Representing the causes of COPD