CHAPTER 2 Pulmonary Ventilation © IT Stock/Polka Dot/ inkstock Chapter Objectives By studying this chapter, you should be able to do Name two things that cause pleural pressure the following: to decrease. 8. Describe the mechanics of ventilation with 1. Identify the basic structures of the conducting respect to the changes in pulmonary pressures. and respiratory zones of the ventilation system. 9. Identify the muscles involved in inspiration and 2. Explain the role of minute ventilation and its expiration at rest. relationship to the function of the heart in the 10. Describe the partial pressures of oxygen and production of energy at the tissues. carbon dioxide in the alveoli, lung capillaries, 3. Identify the diff erent ways in which carbon tissue capillaries, and tissues. dioxide is transported from the tissues to the 11. Describe how carbon dioxide is transported in lungs. the blood. 4. Explain the respiratory advantage of breathing 12. Explain the significance of the oxygen– depth versus rate during a treadmill exercise. hemoglobin dissociation curve. 5. Describe the composition of ambient air and 13. Discuss the eff ects of decreasing pH, increasing alveolar air and the pressure changes in the pleu- temperature, and increasing 2,3-diphosphoglyc- ral and pulmonary spaces. erate on the HbO dissociation curve. 6. Diagram the three ways in which carbon dioxide 2 14. Distinguish between and explain external res- is transported in the venous blood to the lungs. piration and internal respiration. 7. Defi ne pleural pressure. What happens to alve- olar volume when pleural pressure decreases? Chapter Outline Pulmonary Structure and Function Pulmonary Volumes and Capacities Anatomy of Ventilation Lung Volumes and Capacities Lungs Pulmonary Ventilation Mechanics of Ventilation Minute Ventilation Inspiration Alveolar Ventilation Expiration Pressure Changes Copyright ©2014 Jones & Bartlett Learning, LLC, an Ascend Learning Company Content not final. Not for sale or distribution. 17097_CH02_Pass4.indd 17 07/01/13 3:10 PM 18 Chapter 2 Pulmonary Ventilation Gas Exchange in the Lungs and the Body Oxyhemoglobin (HbO 2 ) Dissociation Curve Gas Exchange Myoglobin and Storage of Oxygen Ambient Air Carbon Dioxide Transport in the Blood In the Trachea In Solution Alveolar Air As Carbamino Compounds In Tissues As Bicarbonate Oxygen and Carbon Dioxide Transport Diff using Capacity and Transit Time Oxygen Transport in the Blood Ventilation–Perfusion Ratio In Physical Solution Oxygen Delivery and Utilization Combined with Hemoglobin Pulmonary Structure and Function Th e respiratory system is responsible for the movement of air in and out of the Pulmonary ventilation lungs through a process called pulmonary ventilation . Th is system, also known A term that refers to as the ventilation system, meets the body’s needs for gas exchange at the lungs and breathing (ventilation of the at the tissues. Th e primary function of pulmonary ventilation is to make oxygen lungs). available to the blood, which is transported by the cardiovascular system throughout Cardiorespiratory system the body to all the cells. Th e exchange of oxygen (O2 ) and carbon dioxide (CO2 ) at the Th e purpose of the cellular level is necessary to produce energy for muscle contraction while regulating cardiorespiratory (heart and lung) system is to deliver the internal environment of the tissues. oxygen to the mitochondria of cells that has previously been extracted from the Anatomy of Ventilation atmosphere via the lungs. Th e respiratory and circulatory systems work together to bring in oxygen and trans- Primary bronchi One of port it to the tissues throughout the body. Together, both systems are known as the the two main air passages cardiorespiratory system . Th is system is primarily responsible for aerobic capacity, that branch from the which is a signifi cant factor in health and athletics. With an increase in the capac- trachea and convey air to ity of the cardiorespiratory system to make more oxygen available at the tissues, the lungs as part of the respiratory system. more energy can be produced for muscle contraction. Th is allows the muscles to do more work. Secondary bronchi Secondary bronchi arise from the primary bronchi. Lungs Each one serves as the airway to a specifi c lobe of the lung. Oxygen is moved in and out of the lungs through the conduction zone of the lung tree. Th is is necessary to bring the atmospheric air temperature to body temperature. Bronchioles Branches off the bronchi that become Th e air is also fi ltered and humidifi ed as it passes through the nose, mouth, and the increasingly smaller airways trachea, which divides into right and left primary bronchi that divide further into that send the air to the the secondary bronchi within each lung ( Figure 2- 1 ). Th e branching tubes become alveoli. narrower and more numerous as they divide into segmental bronchi, terminal bron- Alveoli Tiny saclike chioles, respiratory bronchioles , and, fi nally, alveolar ducts, which are lined with dilations where gas tiny air sacs called alveoli . exchange (oxygen and The conducting zone extends from the trachea to the terminal bronchioles. carbon dioxide) takes place It is composed of 16 generations of tubes branching into smaller tubes supported in the lungs. by a composition of 15–20 C-shaped cartilage rings and smooth muscle to help ensure that the inspired air gets to the respiratory zone. The parasympathetic Copyright ©2014 Jones & Bartlett Learning, LLC, an Ascend Learning Company Content not final. Not for sale or distribution. 17097_CH02_Pass4.indd 18 07/01/13 3:10 PM Anatomy of Ventilation 19 division of the autonomic nervous system causes Nasal Artery Alveolus cavity the smooth muscle to constrict, and the sympa- Bronchiole thetic division causes the smooth muscle to relax (or dilate). Aside from warming and humidifying the air, Mouth Vein (oral cavity) the conducting zone is lined with ciliated mucous membranes that filter incoming air to keep the pas- Pharynx sageways clean. During rest, with each inspiration, Larynx Capillary about 500 mL of air enters the conducting zone (called Trachea network tidal volume; VT) to reach the alveoli (the respiratory zone), where each alveolus is surrounded by capil- laries to permit gas exchange of oxygen and carbon dioxide (Figure 2-2). Because no exchange of gases takes place in the conducting zone, it is called the anatomical dead space. The dead space volume can be estimated as 1 mL Terminal of air for each 1 lb of ideal body weight. Thus, a VT of bronchiole 500 mL per breath minus the dead space of 150 mL of Right Le B AlveoliCapillaries air for a 150-lb person would approximate the volume A bronchus bronchus of air transported to the alveoli (350 mL). This means Figure 2-1 The respiratory system. T ÷ = × = 30% of the V (150 500 0.3 100 30%) does not (A) The upper and lower airway divisions. participate in the gas exchange and constitutes wasted (B) Alveoli. air (Table 2-1). Bronchiole Artery Smooth muscle 1 Deoxygenated blood is Vein carried from the heart (to the lungs) by the Capillary pulmonary arteries and arterioles. 2 Gas exchange takes place at the capillaries CO2 covering the alveoli. CO2 CO2 Alveolar wall CO CO 2 Capillary wall 2 O2 O2 3 Alveoli Oxygenated blood is O 2 O2 carried from the lungs Carbon dioxide and oxygen (to the heart) by the CO2 are exchanged across two pulmonary veins layers of epithelial cells. and venules. O2 One layer makes up the wall of the capillary, and one O2 layer makes up the wall of the alveolus. Figure 2-2 Exchange of gases in the lungs. Copyright ©2014 Jones & Bartlett Learning, LLC, an Ascend Learning Company Content not final. Not for sale or distribution. 17097_CH02_Pass4.indd 19 07/01/13 3:10 PM 20 Chapter 2 Pulmonary Ventilation Conducting zone Th e nose, Table 2- 1 Anatomical Dead Space in the Lungs Varies with Body Size pharynx, larynx, trachea, An estimate of anatomical dead space in milliliters is body weight expressed in pounds. bronchi, bronchioles, and terminal bronchioles If a subject weighs 180 lb, the dead space is close to 180 mL, or 0.18 L. Th us, for the function to fi lter, warm, and average 500 mL or 0.5 L of air inspired per breath (VT) at rest, 64% [(0.5 L – 0.18 L) ÷ moisten air, and conduct it (0.5 L × 100)] ventilates the alveoli, and 36% remains in the dead space. to the alveoli. Tidal volume Th e amount of air that is inspired Th e respiratory zone extends from the terminal bronchioles to the alveolar ducts, or expired in a normal alveolar sacs, and alveoli, where gas exchange between the lungs and blood takes breathing cycle. place. First, the terminal bronchioles divide to form the respiratory bronchioles, Respiratory zone Th e which become even smaller bronchioles with some capacity for gas exchange as they respiratory zone is the site of ultimately give rise to alveolar ducts that end as clusters of thin-walled, infl atable oxygen and carbon dioxide alveolar sacs composed of alveoli. Macrophages in the alveoli protect the alveoli from exchange with the blood. foreign particles. Each alveolus is surrounded by a dense network of pulmonary Anatomical dead space All capillaries that facilitate diff usion of oxygen and carbon dioxide. airways such as the mouth, Respiratory gas exchange by simple diff usion occurs between the alveoli and nose, pharynx, larynx, pulmonary capillaries. Th ere are about 300 million to 500 million alveoli in the two trachea, bronchi, and 2 bronchioles that do not lungs with an internal surface area for diff usion that is the equivalent of 60–80 m participate directly in (i.e., the size of a tennis court). Inspired oxygen diff uses from the alveoli to the pul- the diff usion of oxygen monary capillaries to gain entrance into the blood where it is bound to hemoglobin from the alveoli into the (Hb), forming oxyhemoglobin (HbO2 ).