Respiratory System PDF

Respiratory System BIOLS312F Dr Emily Wong 1 Respiratory System 2 Respiratory System The main function of the respiratory system is to supply the body tissues with oxygen and dispose of carbon dioxide generated by cellular metabolism. Respiration is collectively made up of 4 processes: 1. Pulmonary...

Respiratory System BIOLS312F Dr Emily Wong 1 Respiratory System 2 Respiratory System The main function of the respiratory system is to supply the body tissues with oxygen and dispose of carbon dioxide generated by cellular metabolism. Respiration is collectively made up of 4 processes: 1. Pulmonary ventilation (breathing) 2. External respiration (movement of O2 from lungs into blood; CO2 from blood to lungs) 3. Transport of respiratory gases in the blood 4. Internal respiration (movement of O2 from blood into tissue cells; CO2 from cells into blood) 3 Functions of the Respiratory System 4 5 The Airways and Blood Vessels The Airways The structures that comprise the system are: Nose, nasal cavity, pharynx, larynx, trachea, bronchi, lungs, alveoli These can be divided into the respiratory zone (where the gas exchange happens) and the conducting zone (top of the trachea to the respiratory bronchioles). 6 The Airways The trachea is also known as the “windpipe.” It has 3 layers and the mucosa has the goblet cells and cilia. Smoking kills the cilia. So coughing is the only way to keep mucus from accumulating in the lungs. (hence the chronic cough seen in many long-term smokers) 7 Site of Gas Exchange: The Alveoli The alveoli are tiny, hollow sacs whose open ends are continuous with the lumen of the airways. Most of the air-facing surfaces of the wall are lined by a continuous layer, one cell thick, of flat epithelial cells termed type I alveolar cells. Type II alveolar that produce a detergent-like substance called surfactant. The total alveolar surface area is very large and this permits the rapid exchange of large quantities of oxygen and carbon dioxide by diffusion. In some of the alveolar walls, pores permit the flow of air between alveoli. 8 Site of Gas Exchange: The Alveoli 9 Relation of the Lungs to the Thoracic Wall 10 Pleurae The pleurae form a thin double-layered serosa. The parietal pleura covers the thoracic wall and superior face of the diaphragm. The visceral pleura covers the external surface of the lung. The pleura produce fluid that remains in the pleural cavity. This lubricates the lung to prevent friction while breathing. Pleurisy is an infection or inflammation of the pleura and often results from pneumonia. This results in a roughening of the pleura, which creates friction and a stabbing pain with each breath. As the disease progresses there is a build-up of fluid, which hinders breathing. 11 Steps of Respiration 12 Ventilation and Air Flow Ventilation is defined as the exchange of air between the atmosphere and alveoli. F = ΔP/R Remember that flow (F) is proportional to the pressure difference (Δ P) between two points and inversely proportional to the resistance (R). 13 Ventilation Remember that a volume change leads to a pressure change and that pressure changes lead to the flow of gases to equalize the pressure. Boyle’s law says that at a constant temperature the pressure of a gas varies inversely with its volume. P1V1=P2V2 Remember that gases always fill their container. So in a large container the molecules in a given amount of gas will be far apart (low pressure). In a smaller container that same amount of gas will have molecules close together (high pressure). 14 Pressure Measurements The respiratory pressures are always relative to atmospheric pressure! We measure this in mm Hg or atmospheres (atm). At sea level this is 760 mm Hg or 1 atm. If you were to go to higher altitudes (i.e., up in the Andes Mountains), then the pressures would be different. 15 Intrapulmonary Pressure Palv is the pressure in the alveoli. It rises and falls with breathing and determines the direction of air flow. When Palv < Patm, air flows into the lung. This is known as “negative pressure breathing”. When Palv > Patm, air flows out. 16 Intrapleural Pressure Pip is the pressure in the pleural cavity. It also fluctuates with breathing, but it is always 4 mm Hg less than Palv. IF Pip = Palv THE LUNGS WILL IMMEDIATELY COLLAPSE! 17 Transpulmonary Pressure Transpulmonary pressure = Palv – Pip Transpulmonary pressure is the transmural pressure that governs the static properties of the lungs. Transmural means “across a wall” and is represented by the pressure in the inside of the structure (Pi) minus the pressure outside the structure (PO). Inflation of a balloon-like structure like the lungs requires an increase in the transmural pressure such that Pi increases relative to PO. 18 Ventilation and Lung Mechanics 19 20 Inspiration 21 Expiration 22 Lung Compliance Compliance can be considered the inverse of stiffness. The greater the lung compliance, the easier it is to expand the lungs at any given change in transpulmonary pressure. There are two major determinants of lung compliance: 1. The stretchability of the lung tissues 2. The surface tension at the air-water interfaces within the alveoli 23 Lung Compliance 24 Lung Compliance and Surfactant The type II alveolar cells secrete the detergent-like substance known as surfactant. Surfactant markedly reduces the cohesive forces between water molecules on the alveolar surface. Therefore, surfactant lowers the surface tension, which increases lung compliance and makes it easier to expand the lungs. 25 Airway Resistance Airway resistance is normally very small, but changes in airway resistance follow changes in airway radii. Airway radii may change in response to physical, neural, and chemical factors. 26 Asthma Asthma is a disease characterized by intermittent episodes in which airway smooth muscle contracts strongly, markedly increasing airway resistance. The basic defect in asthma is chronic inflammation of the airways, the causes of which vary from person to person and include, among others; allergy, viral infections, and sensitivity to environmental factors. The underlying inflammation makes the airway smooth muscle hyperresponsive and causes it to contract strongly in response to such things as exercise (especially in cold, dry air), cigarette smoke, environmental pollutants, viruses, allergens, normally released bronchoconstrictor chemicals, and a variety of other potential triggers. 27 Asthma The first aim of therapy for asthma is to reduce the chronic inflammation and airway hyperresponsiveness with antiinflammatory drugs, particularly leukotriene inhibitors and inhaled glucocorticoids. The second aim is to overcome acute excessive airway smooth muscle contraction with bronchodilator drugs, which relax the airways. For example, one class of bronchodilator drugs mimics the normal action of epinephrine on beta-adrenergic (beta-2) receptors. Another class of inhaled drugs block muscarinic cholinergic receptors, which have been implicated in bronchoconstriction. 28 Chronic Obstructive Pulmonary Disease (COPD) The term chronic obstructive pulmonary disease refers to emphysema, chronic bronchitis, or a combination of the two. These diseases cause severe difficulties not only in ventilation, but in oxygenation of the blood. Emphysema is caused by destruction and collapse of the smaller airways. Chronic bronchitis is characterized by excessive mucus production in the bronchi and chronic inflammatory changes in the small airways. The cause of obstruction is an accumulation of mucus in the airways and thickening of the inflamed airways. 29 Lung Volumes and Capacities 30 Alveolar Ventilation 31 32 Exchange of Gases in Alveoli and Tissues 33 34 The Airways and Blood Vessels Partial Pressures of Gases 35 Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in presentation mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Slide Show mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. 36 Normal Gas Pressures 37 Gas Exchange Between Alveoli and Blood 38 Matching of Ventilation and Blood Flow in Alveoli 39 Transport of Oxygen in Blood Oxygen is transported in the blood bound to hemoglobin. 40 What Is the Effect of PO2 on Hemoglobin Saturation? 41 Hypoxia Hypoxia is an inadequate oxygen delivery to tissues. The pathophysiology of emphysema is a major cause of hypoxia. 1. Anemic hypoxia: poor O2 delivery because of too few RBCs or abnormal hemoglobin 2. Ischemic hypoxia: blood circulation is impaired 3. Histotoxic hypoxia: the body’s cells are unable to use O2 (cyanide causes this) 4. Hypoxemic hypoxia: reduced arterial O2 (can be caused by lack of oxygenated air, pulmonary problems, lack of ventilation-perfusion coupling) 42 Carbon Monoxide Poisoning This is a type of hypoxemic hypoxia. It is the leading cause of death from fire. CO is an odorless, colorless gas that competes with O2 for the binding sites on the hemoglobin. It has a 200times greater affinity for hemoglobin than O2 does. The symptoms are confusion, respiratory distress, the skin becomes cherry red. NO CYANOSIS is detectable. To treat it, hyperbaric treatment or 100% oxygen is used. 43