PCB3743 final exam Chapter 16 Respiratory Physiology Respiratory System Introduction o Includes Ventilation breathing mechanical process that moves air into and out of the lungs Gas exchange between blood and lungs and between blood and tissues Oxygen utilization by tissues to make ATP cellular respiration o Ventilation and gas exchange in lungs external respiration o Oxygen utilization and gas exchange in tissues internal respiration o Has exchange in lungs Occurs via diffusion O2 concentration is higher in lungs than in blood so O2 diffuses into blood CO2 concentration in blood is higher than in lungs so CO2 diffuses out of blood o Anatomically divided into Conduction zone gets air to respiratory zone Respiratory zone site of gas exchange Structure of respiratory system o Alveoli Provide large surface area 760 square feet to increase diffusion rate Air sacs in lungs where gas exchange occurs 300 million of them Each alveolus is one cell layer thick Form clusters at ends of respiratory bronchioles Alveolar cells Type 1 95 97 total surface area where gas exchange occurs Type 2 secrete pulmonary surfactant and reabsorb sodium and water o Pathway of air prevent fluid buildup Air travels down nasal cavity pharynx larynx through glottis and vocal cords trachea right and left primary bronchi secondary bronchi tertiary bronchi more branching terminal bronchioles respiratory zone respiratory bronchioles terminal alveolar sacs o Functions of conducting zone Transports air to lungs Warms humidifies filters and cleans air Mucus traps small particles and cilia move it away from lungs Voice production in larynx as air passes over vocal folds Thoracic cavity o Contains heart trachea esophagus and thymus within central mediastinum o Lungs fill rest of the cavity Parietal pleura lines thoracic wall Visceral pleura covers lungs Parietal and visceral pleura are normally pushed together with a potential space between called the intrapleural space o Diaphragm is a dome shaped skeletal muscle of respiration that separates the thoracic and abdominal cavities Physical aspects of ventilation Intro o Air moves from higher to lower pressure o Pressure differences between 2 ends of the conducting zone occur due to changing lung volumes o Compliance elasticity and surface tension are important physical properties of lungs Intrapulmonary and intrapleural pressures o Type of pressure Atmospheric pressure pressure of air outside body Intrapulmonary or intraalveolar pressure pressure in the lungs o Pressure differences when breathing Inspiration inhalation intrapulmonary pressure is lower than atmospheric pressure Pressure below that of the atmosphere is called subatmospheric or negative pressure Generally about 3mm Hg Expiration exhalation intrapulmonary pressure is greater than atmospheric pressure o Generally about 3mm Hg o Intrapleural pressure expiration Lower than intrapulmonary and atmospheric pressure in both inspiration and Difference between intrapulmonary and intrapleural pressure is called transpulmonary pressure Keeps lungs against thoracic wall and allows lungs to expand during inspiration o Boyle s Law States that pressure of a gas is inversely proportional to its volume An increase in lung volume during inspiration decreases intrapulmonary pressure A decrease in lung volume during expiration increases intrapulmonary pressure to subatmospheric levels air goes in above atmospheric levels air goes out Physical properties of the lungs o Lung compliance Lungs can expand when stretched Defined as change in lung volume per change in transpulmonary pressure deltaV deltaP Ease with which lungs expand under pressure Reduced by factors that produce a resistance to distention such as the infiltration of connective tissue proteins in pulmonary fibrosis Lungs return initial size after being stretched recoil Lungs have lots of elastin fibers Because lungs are stuck to the thoracic wall they are always under elastic tension Tension increases during inspiration and is reduced by elastic recoil during o Elasticity expiration o Surface tension Resists distension Exerted by fluid secreted on alveoli Fluid is absorbed by active transport of Na and secreted by active transport of Cl Raises pressure of alveolar air as it acts to collapse the alveolus People with cystic fibrosis have genetic defect that causes imbalance of fluid absorption and secretion Law of laplace Pressure is directly proportional to surface tension and inversely proportional to radius of alveolus Small alveoli would be at greater risk of collapse without surfactant o Surfactant and respiratory distress syndrome Surfactant surface active agent Secreted by type 2 alveolar cells Consists of hydrophobic protein and phospholipids Reduces surface tension between H2O molecules by reducing number of H bonds More concentrated as alveoli get smaller during expiration Prevents collapse Allows a residual volume of air to remain in lungs Respiratory distress syndrome RDS Production of surfactant begins late in fetal life so premature babies may be born with high risk for alveolar collapse called RDS treated with surfactant Similar problem may occur in adults caused by septic shock reduced lung compliance and reduced surfactant acute RDS not treatable with surfactant Mechanics of breathing Intro o Breathing is also called pulmonary ventilation Inspiration breathing in Expiration breathing out Inspiration and expiration o Muscles involved in breathing Diaphragm most important o Accomplished by changing thoracic cavity lung volume o Thorax must be rigid enough to protect yet flexible enough to act as bellows for breathing o Mechanisms of breathing Contracts in inspiration lowers making thoracic cavity larger Relaxes in expiration raises making thoracic cavity smaller Internal intercostal muscles lowers rib cage during forced expiration External intercostal muscles raises rib cage during inspiration Parasternal intercostal muscles works with external intercostals Quiet expiration occurs with relaxation of inspiratory muscles passive process Abdominal muscles are also used for forced expiration Scalenes pectoralis minor and sternocleidomastoid are used for forced inspiration Inspiration volume of thoracic cavity and lungs increases vertically when diaphragm contracts flattens and laterally when parasternal and external intercostals raise ribs Thoracic and lung volume increase intrapulmonary pressure decreases air in Expiration volume of thoracic cavity and lungs
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