Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 16 Respiratory Physiology 16-1

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Respiration  Encompasses 3 related functions: ventilation, gas exchange, & 0 2 utilization (cellular respiration)  Ventilation moves air in & out of lungs for gas exchange with blood (external respiration)  Gas exchange between blood & tissues, & O 2 use by tissues is internal respiration  Gas exchange is passive via diffusion 16-3

Respiratory Structures 16-4

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Structure of Respiratory System  Air passes from mouth to trachea to right & left bronchi to bronchioles to terminal bronchioles to respiratory bronchioles to alveoli 16-5

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Gas exchange occurs only in respiratory bronchioles & alveoli (= respiratory zone)  All other structures constitute the conducting zone  Alveoli are clustered at ends of respiratory bronchioles, like units of honeycomb. Air in 1 cluster can pass to others through pores Structure of Respiratory System continued Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Structure of Respiratory System continued  Gas exchange occurs across the 300 million alveoli (60-80 m 2 total surface area)  Each alveolus is 1 cell layer thick.  Total air barrier is 2 cells across (2  m).  2 types of cells:  Alveolar type I:  Structural cells.  Alveolar type II:  Secrete surfactant. Insert

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Conducting Zone  Warms & humidifies inspired air  Mucus lining filters & cleans inspired air  Mucus moved by cilia to be expectorated Insert fig Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Thoracic Cavity  Is created by the diaphragm, a dome-shaped sheet of skeletal muscle  Contains heart, large blood vessels, trachea, esophagus, thymus, & lungs  Below diaphragm is abdominopelvic cavity  Contains liver, pancreas, GI tract, spleen, & genitourinary tract  Intrapleural space is thin fluid layer between visceral pleura covering lungs & parietal pleura lining thoracic cavity walls 16-10

Physical Aspects of Ventilation 16-11

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Physical Aspects of Ventilation  Ventilation results from pressure differences induced by changes in lung volumes  Air moves from higher to lower pressure  Compliance, elasticity, & surface tension of lungs influence ease of ventilation 16-12

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Intrapulmonary & Intrapleural Pressures  Visceral and parietal pleurae are flush against each other. The intrapleural space (pleural cavity) contains only a film of fluid secreted by the membranes.  Pleural cavity = potential space 16-13

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Lungs normally remain in contact with the chest wall. Lungs expand and contract along with the thoracic cavity.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Intrapulmonary and Intrapleural Pressures  Intrapulmonary pressure :  Intra-alveolar pressure (pressure in the alveoli).  Intrapleural pressure:  Pressure in the intrapleural space is negative due to lack of air in the intrapleural space.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Intrapulmonary and Intrapleural Pressures  During inspiration:  Atmospheric pressure is > than intrapulmonary pressure (- 3 mm Hg).  During expiration:  Intrapulmonary pressure (+ 3 mm Hg) is > atmospheric pressure.  Due to lack of air in the intrapleural space.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Intrapulmonary & Intrapleural Pressures  Positive transpulmonary pressure (intrapulmonary - intrapleural pressure) keeps lungs inflated 16-14

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Boyle’s Law (P = 1/V)  Implies that changes in intrapulmonary pressure occur as a result of changes in lung volume  Pressure of gas is inversely proportional to volume  Increase in lung volume decreases intrapulmonary (alveolar) pressure below atmospheric p.  Air goes in.  Decrease in lung volume, raises intrapulmonary pressure above atmosphere p.  Air goes out

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Compliance  Is how easily lung expands with pressure  Or change in lung volume per change in transpulmonary pressure (  V/  P)  Is reduced by factors that cause resistance to distension 16-16

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Elasticity  Is tendency to return to initial size after distension  Due to high content of elastin proteins  Elastic tension increases during inspiration & is reduced by recoil during expiration 16-17

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Surface Tension (ST)  And elasticity are forces that promote alveolar collapse & resist distension  Lungs secrete & absorb fluid, normally leaving a thin film of fluid on alveolar surface  Fluid absorption occurs by osmosis driven by Na + active transport  Fluid secretion is driven by active transport of Cl - out of alveolar epithelial cells This film causes ST because H 2 0 molecules are attracted to other H 2 0 molecules  Force of ST is directed inward, raising pressure in alveoli  Cystic fibrosis due to defect in a Cl - carrier so fluid gets thick and can’t clear it

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Law of Laplace states that pressure in alveolus is directly proportional to ST; & inversely to radius of alveoli  Thus, pressure in smaller alveoli would be greater than in larger alveoli, if ST were same in both, but ST decreases as r decreases. Why? Insert fig Surface Tension continued Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Surfactant  Consists of phospholipids secreted by type II alveolar cells  Lowers ST by getting between H 2 0 molecules, reducing their ability to attract each other via hydrogen bonding 16-20

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Surfactant continued  Prevents ST from collapsing alveoli  Surfactant secretion begins in late fetal life  Premies are often born with immature surfactant system (= Respiratory Distress Syndrome or RDS)  Have trouble inflating lungs  In adults, septic shock may cause acute respiratory distress syndrome (ARDS) which decreases compliance & surfactant secretion. Blood leaves with decrease in O

Mechanics of Breathing 16-22

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mechanics of Breathing  Pulmonary ventilation consists of inspiration (= inhalation) & expiration (= exhalation)  Accomplished by alternately increasing & decreasing volumes of thorax & lungs Fig expiration inspiration 16-23

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Quiet Breathing  Inspiration occurs mainly because diaphragm contracts, increasing thoracic volume vertically  Parasternal & external intercostal contraction contributes a little by raising ribs, increasing thoracic volume laterally  Pressure in lung less than atmospheric p.  Expiration is due to passive recoil. Decrease in lung volume raises the pressure above atmosphere and pushes air out

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Deep Breathing  Inspiration involves contraction of extra muscles to elevate ribs: scalenes, pectoralis minor, & sternocleidomastoid muscles  Expiration involves contraction of internal intercostals & abdominal muscles 16-25

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Insert fig Mechanics of Pulmonary Ventilation Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pulmonary Function Tests  Assessed clinically by spirometry, a method that measures volumes of air moved during inspiration & expiration  Anatomical dead space is air in conducting zone where no gas exchange occurs 16-27

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pulmonary Function Tests continued  Tidal volume is amount of air expired/breath in quiet breathing  Vital capacity is amount of air that can be forcefully exhaled after a maximum inhalation  = sum of inspiratory reserve, tidal volume, & expiratory reserve Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Anatomical Dead Space  Not all of the inspired air reached the alveoli.  As fresh air is inhaled it is mixed with anatomical dead space.  Conducting zone and alveoli where 0 2 concentration is lower than normal and C0 2 concentration is higher than normal.  Alveolar ventilation: f x (TV- DS)  F = frequency (breaths/min.).  TV = tidal volume.  DS = dead space.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display

Pulmonary Disorders 16-30

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Restrictive Disorders  Are characterized by reduced vital capacity but with normal forced vital capacity  E.g. pulmonary fibrosis 16-31

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Obstructive Disorders  Have normal vital capacity but expiration is retarded  E.g. asthma  Diagnosed by tests, such as forced expiratory volume, that measure rate of expiration Insert fig Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pulmonary Disorders  Are frequently accompanied by dyspnea, a feeling of shortness of breath  Asthma results from episodes of obstruction of air flow thru bronchioles  Caused by inflammation, mucus secretion, & broncho constriction  Inflammation contributes to increased airway responsiveness to agents that promote bronchial constriction  Provoked by allergic reactions that release IgE, by exercise, by breathing cold, dry air, or by aspirin 16-33

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Emphysema is a chronic, progressive condition that destroys alveolar tissue, resulting in fewer, larger alveoli  Reduces surface area for gas exchange & ability of bronchioles to remain open during expiration  Collapse of bronchiole during expiration causes air trapping, decreasing gas exchange  Commonly occurs in long-term smokers  Cigarette smoking stimulates macrophages & leukocytes to secrete protein-digesting enzymes that destroy tissue Pulmonary Disorders continued 16-34

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. normal lung emphysema Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Sometimes lung damage leads to pulmonary fibrosis instead of emphysema  Characterized by accumulation of fibrous connective tissue  Occurs from inhalation of particles <6  m in size, such as in black lung disease (anthracosis) from coal dust Pulmonary Disorders continued 16-36