Physiology of the Respiratory System PDF

Physiology of the Respiratory System 1  ❖ Definition of the Respiratory system The respiratory system is responsible for gaseous exchange between the circulatory system and the atmosphere. The respiratory system consists of the nose, pharynx (throat), larynx (voice box), trachea, bro...

Physiology of the Respiratory System 1  ❖ Definition of the Respiratory system The respiratory system is responsible for gaseous exchange between the circulatory system and the atmosphere. The respiratory system consists of the nose, pharynx (throat), larynx (voice box), trachea, bronchi, and lungs. Its parts can be classified according to either structure. or function. A. Structurally, the respiratory system consists of two parts: (1) The upper respiratory system. -includes the nose, nasal cavity, pharynx, and associated structures. (2) the lower respiratory system -includes the larynx, trachea, bronchi, and lungs. B. Functionally, the respiratory system also consists of two parts. (1) The conducting zone consists of a series of interconnecting cavities and tubes both outside and within the lungs. These include the nose, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles; their function is to filter, warm, and moisten the air and conduct it lungs. (2) The respiratory zone consists of tubes and tissues within the lungs where gas exchange occurs. These include the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli and are the main sites of gas exchange between air and blood.  The Function of the Respiratory System The respiratory system has many functions. 1. Allows talk and to smell. 2. Delivers air to body temperature according to the body needs. 3. Humid air according to the body's needs. 2  4. Delivers oxygen to the cells. 5. Removes waste gases, including carbon dioxide, from the body. 6. Protects airways from harmful substances and irritants.  The Breath Process Breathing starts when the person inhales air into the nose or mouth. It travels down the throat and into the trachea, divided into air passages called bronchial tubes. As the bronchial tubes pass through the lungs, they divide into smaller air passages called bronchioles. The bronchioles end in tiny balloon-like air sacs called alveoli. The human body has about 600 million alveoli. The alveoli are surrounded by a mesh of tiny blood vessels called capillaries. Here, oxygen from inhaled air passes into the blood.  Internal respiration Internal respiration describes the exchange of oxygen and carbon dioxide between blood and tissue cells.  Lung lobes: Sections of the lungs – three lobes in the right lung and two in the left lung.  Pleura: Thin sacs that surround each lung lobe and separate your lungs from the chest wall.  Cilia: Tiny hairs that move in a wave-like motion to filter dust and other irritants out of your airways.  Epiglottis: Tissue flap at the entrance to the trachea that closes when you swallow to keep food and liquids out of your airway.  Larynx (voice box): Hollow organ that allows you to talk and make sounds when air moves in and out. 3   Mechanics of pulmonary ventilation The lungs can be expanded and contracted in two ways: (1) by downward and upward movement of the diaphragm to lengthen or shorten the chest cavity (2) by elevation and depression of the ribs to increase and decrease the anteroposterior diameter of the chest cavity. Breathing is accomplished almost entirely by the first method, that is, by the movement of the diaphragm. During inspiration, contraction of the diaphragm pulls the lower surfaces of the lungs downward. Then, during expiration, the diaphragm relaxes, and the elastic recoil, chest wall, and abdominal structures compress the lungs and expel the air. The second method for expanding the lungs is to raise the rib cage. Raising the rib cage expands the lungs because the ribs slant downward in the natural resting position, as shown on the left side. Contraction and expansion of the thoracic cage during expiration and inspiration ❖ Pleural pressure and its changes during respiration. 4 Pleural pressure is the fluid pressure in the thin space between the lung pleura and the chest wall pleura. This pressure is normally a slight suction, which means a slightly negative pressure. At the beginning of inspiration, the normal pleural pressure is about 5 centimeters of water, which is the amount of suction required to hold the lungs open to their resting level. During normal inspiration, expansion of the chest cage pulls outward on the lungs with greater force and creates more negative pressure, to an average of about −7.5 centimeters of water.  Alveolar pressure (the air pressure inside the lung alveoli) When the glottis is open, and no air is flowing into or out of the lungs, the pressures in all parts of the respiratory tree, all the way to the alveoli, are equal to atmospheric pressure, which is zero reference pressure in the airways, that is, 0 centimeters of water pressure. To cause inward flow of air into the alveoli during inspiration, the pressure in the alveoli must fall to a value slightly below atmospheric pressure (below 0). During normal inspiration, alveolar pressure decreases to about −1 centimeters of water. This slight negative pressure is enough to pull 0.5 liters of air into the lungs in the 2 seconds required for normal quiet inspiration. During expiration, alveolar pressure rises to about +1 centimeter of water, which forces the 0.5 liters of inspired air out of the lungs during the 2 to 3 seconds of expiration.  Pulmonary volumes and capacities Pulmonary ventilation can be studied by recording the volume movement of air into and out of the lungs. A method called spirometry indicates changes in lung volume under different conditions of breathing. For ease in describing the events of pulmonary ventilation, the air in the lungs has been subdivided in this diagram into four volumes and four capacities, which are the average for a young adult man. 5  A. Pulmonary volumes equal the maximum volume to which the lungs can be expanded. The significance of each of these volumes is the following: 1. The tidal volume is the volume of air inspired or expired with each normal breath; it amounts to about 500 milliliters in the average adult male. 2. The inspiratory reserve volume is the extra volume of air that can be inspired over and above the average tidal volume when the person inspires with full force; it is usually equal to about 3000 milliliters. 3. The expiratory reserve volume is the maximum extra volume of air that can be expired by forceful expiration after the end of a normal tidal expiration; this volume typically amounts to about 1100 milliliters. 4. The residual volume is the volume of air remaining in the lungs after the most forceful expiration; this volume averages about 1200 milliliters. B. Pulmonary capacities 1. The inspiratory capacity equals the tidal volume plus the inspiratory reserve volume. This capacity is the amount of air (about 3500 milliliters) a person can breathe in, beginning at the normal expiratory level and distending the lungs to the maximum amount. 2. The functional residual capacity equals the expiratory reserve volume plus the residual volume. This capacity is the amount of air in the lungs at the end of normal expiration (about 2300 milliliters). 3. The vital capacity equals the inspiratory reserve volume plus the tidal volume plus the expiratory reserve volume. This capacity is the maximum amount of air a person can expel from the lungs after first filling the lungs to their maximum extent and then expiring to the full size (about 4600 milliliters). 6 4. The total lung capacity is the maximum volume to which the lungs can be expanded with the greatest possible effort (about 5800 milliliters); it is equal to the vital capacity plus the residual volume. ❖ Factors affecting respiratory systems. 1. The surface tension of the alveolar fluid 2. Airway resistance 3. Compliance of the lungs 4. Temperature 5. Pain 6. Allergies: such as dust, mold, and pollen, can cause respiratory allergies in some people. 7  7. Asthma: A chronic (long-term) disorder, asthma causes inflammation in the airways that can make breathing difficult. 8. Infection: Infections can lead to pneumonia (inflammation of the lungs) or bronchitis (inflammation of the bronchial tubes). Common respiratory infections include the flu (influenza) or a cold. 9. Disease: Respiratory disorders include lung cancer and chronic obstructive pulmonary disease (COPD). 10.Aging: Lung capacity decreases as you get older. 11.Damage: Damage to the respiratory system can cause breathing problems. ❖ Diffusion of gases through the respiratory membrane The respiratory unit (also called “respiratory lobule”) comprises a respiratory bronchiole, alveolar ducts, and alveoli. There are about 300 million alveoli in the two lungs, and each alveolus has an average diameter of about 0.2 millimeters. 8 -The alveolar walls are extremely thin, and between the alveoli is an almost solid network of interconnecting capillaries. The flow of blood in the alveolar wall has been described as a “sheet of flowing blood. Thus, it is evident that the alveolar gases are in very close proximity to the blood of the pulmonary capillaries. Further, gas exchange between the alveolar air and the pulmonary blood occurs through the membranes of all the terminal portions of the lungs, not merely in the alveoli. All these membranes are collectively known as the respiratory membrane, also called the pulmonary membrane. The ultrastructure of the respiratory membrane is drawn in a cross-section on the left and a red blood cell on the right. The diffusion of O2 from the alveolus into the red blood cell and diffusion of CO2 in the opposite direction. 9 The following different layers of the respiratory membrane: 1. A layer of fluid containing surfactant that lines the alveolus and reduces the surface tension of the alveolar liquid. 2.The alveolar epithelium, which is composed of thin epithelial cells. 3.An epithelial basement membrane. 4.A narrow interstitial space between the alveolar epithelium and the capillary membrane. 5.A capillary basement membrane that in many places fuses with the alveolar epithelial basement membrane. 6. The capillary endothelial membrane. ❖ How can I keep the respiratory system healthy? Avoid pollutants that can damage airways, Avoid smoking. Eat a healthy diet with lots of fruits and vegetables and drink water to stay hydrated. Exercise regularly to keep the lungs healthy. Prevent infections by washing hands often and getting a flu vaccine each year. 10