BSCI440 Exam 3 Chapter 17 18 Notes Respiratory Chapter 17 Mechanics of Breathing Four primary functions of the respiratory system 1 Exchange of gases between the atmosphere and the blood body brings in O2 for distribution to the tissues and eliminates CO2 waste produced by metabolism 2 Homeostatic regulation of body pH lungs alter pH by selectively retaining or excreting CO2 3 Protection from inhaled pathogens and irritating substances respiratory epithelium has defense mechanisms to trap and destroy harmful substances 4 Vocalization air moving across vocal cords creates vibrations for speech Respiratory system exchanges air between the environment and interior air spaces of lungs bulk flow of air Flow takes place from regions of higher pressure to lower pressure A muscular pump creates pressure gradients Resistance to air flow is influenced by the diameter of tubes The Respiratory System cellular respiration refers to the intracellular reaction of O2 with organic molecules to produce CO2 H2O and ATP external respiration movement of gases between environment and the body s cells a The exchange of air between atmosphere and the lungs ventilation inhalation moves air into lungs and exhalation moves air out of lungs b The exchange of O2 and CO2 between lungs and blood c The transport of O2 and CO2 by blood d The exchange of gases between blood and the cells external respiration requires coordination between the respiratory and cardiovascular system the respiratory system consists of structures involved in ventilation and gas exchange conducting system of airways alveoli alveolus a series of interconnected sacs and their associated pulmonary capillaries form the exchange surface where O2 moves from inhaled air to blood and CO2 moves from blood to air that is exhaled bones and muscles of the thorax and abdomen diaphragm intercostal muscles pleural sacs o Each lung is surrounded by a double walled pleural sac whose membrane lines the inside of the thorax and cover the outer surface of the lungs o Each pleural membrane contains several layers of elastic connective tissue and capillaries membranes connected by pleural fluid o The pleural fluid reduces friction and holds the lungs tight against thoracic wall think of two planes of glass stuck together by water Trachea right and left primary bronchi secondary and tertiary bronchi bronchioles 12 23 alveoli Diameter of the airways becomes smaller from trachea to bronchioles but numbers increase total cross sectional area increases with each division of the airways The airways warm the air to body temperature add water vapor until the air reaches 100 humidity and filter out foreign material Alveoli Alveoli are clustered at ends of terminal bronchioles and function in gas exchange between themselves and the blood Each alveolus is composed of a single layer of epithelium Type II alveolar cells synthesize and secrete surfactant which mixes with the fluid lining of the alveoli to decrease surface tension during lung expansion The walls do not contain muscle because muscle fibers would block rapid gas exchange lungs do not contract connective tissue between alveolar epithelial cells contains elastin and collagen fibers that create elastic recoil when lung tissue is stretched Pulmonary Circulation High Flow Low Pressure receives low oxygen blood from right ventricle pulmonary trunk pulmonary arteries one for each lung lungs receive the entire CO of the right ventricle 5 L min but blood pressure is low due to shorter length of pulmonary blood vessels and the distensibility and large cross sectional area of pulmonary arterioles Gas Laws Atmospheric pressure 0 mmHg Dalton s law total pressure exerted by a mixture of gases is the sum of the pressures exerted by the individual gases Partial pressure Pgas the pressure of a single gas in a mixture determined by its relative abundance in the mixture and is independent of the molecular size or mass of the gas bulk flow of air moves from areas of high pressure to low pressure Boyle s Law P1V1 P2V2 If the volume of gas is reduced pressure increases if volume increases the pressure decreases When chest volume increases alveolar pressure falls and air flows into the system Ventilation Air moved during breathing can be divided into four lung volumes 1 Tidal volume VT volume of air that moves during a single inspiration or expiration 500 mL 3000 mL 2 Inspiratory reserve volume the additional volume you inspire above the tidal volume 3 Expiratory reserve volume the amount of air forcefully exhaled after the end of a normal expiration 1100 mL 4 Residual volume the volume of air after maximal exhalation 1200 mL The vital capacity is the sum of the inspiratory reserve volume expiratory reserve volume and tidal volume represents the maximum amount of air that can be voluntarily moved in or out of the respiratory system with one breath Decreases with age as muscle weakens and lungs become less elastic Vital capacity residual volume total lung capacity Tidal volume inspiratory reserve volume inspiratory capacity Expiratory reserve volume residual volume functional residual capacity Primary muscles involved in quiet breathing diaphragm external intercostals and scalenes Air flows into and out of lungs due to pressure gradients F P R Flow decreases as the resistance of the system to flow increases Total pulmonary ventilation ventilation rate tidal volume volume of air moved into and out of the lungs each minute Some air does not reach the alveoli because some remains in the conducting airways anatomical dead space 350 mL of fresh air and 150 mL of old air mix in lungs Neuromuscular diseases that weaken skeletal muscles or damages their motor neurons can adversely affect ventilation Decreased ventilation less fresh air enters lungs and loss of ability to cough increases risk of pneumonia i e myasthenia gravis and polio Hyperventilation causes PO2 to increase and PCO2 to decrease vice versa with hypoventilation In lungs increase in PO2 causes vasoconstriction doesn t make sense to send blood to areas with low O2 levels Inspiration for air to move into lungs alveoli pressure inside lungs must become lower than the atmospheric pressure Boyle s Law an increase in volume will create a decrease in pressure External intercostals and scalenes contract and pull ribs upward and out diaphragm pulls downward widened thoracic cavity Volume increases pressure decreases air flows in lungs During the pause between breaths alveolar