Ebook Guyton and hall textbook of medical physiology (13/E): Part 2
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Ebook Guyton and hall textbook of medical physiology (13/E): Part 2
CHAPTER 38 MPulmonary VentilationUNIT VHie main functions of respiration are to provide oxygen to the tissues and remove carbon dioxide, The four majo Ebook Guyton and hall textbook of medical physiology (13/E): Part 2or components of respiration are (1) pulmonary ventilation, which means the inflow and outflow of air between the atmosphere and the lung alveoli; (2) diffusion of oxygen (OJand carbon dioxide (COJ between the alveoli and the blood; (3) transport of oxygen and carbon dioxide in the blood and body fl Ebook Guyton and hall textbook of medical physiology (13/E): Part 2uids to and from the body's tissue cells: and (4) regulation of ventilation and other facets of respiration. This chapter is a discussion of pulmonaryEbook Guyton and hall textbook of medical physiology (13/E): Part 2
ventilation. and the subsequent five chapters cover other respiratory functions plus the physiology of special respiratory abnormalities.MECHANICS OFCHAPTER 38 MPulmonary VentilationUNIT VHie main functions of respiration are to provide oxygen to the tissues and remove carbon dioxide, The four majo Ebook Guyton and hall textbook of medical physiology (13/E): Part 2d movement of the diaphragm to lengthen or shorten the chest cavity, and (2) by elevation and depression of the ribs to increase and decrease the anteroposterior diameter of the chest cavity. Figure 38-1 shows these two methods.Normal quiet breathing is accomplished almost entirely by the first meth Ebook Guyton and hall textbook of medical physiology (13/E): Part 2od, that is, by movement of the diaphragm. During inspiration, contraction of the diaphragm pulls the lower surfaces of the lungs downward. Then, duriEbook Guyton and hall textbook of medical physiology (13/E): Part 2
ng expiration, the diaphragm simply relaxes, and the elastic recoil of the lungs, chest wall, and abdominal structures compresses the lungs and expelsCHAPTER 38 MPulmonary VentilationUNIT VHie main functions of respiration are to provide oxygen to the tissues and remove carbon dioxide, The four majo Ebook Guyton and hall textbook of medical physiology (13/E): Part 2ved mainly by contraction of the abdominal muscles, which pushes the abdominal contents upward against the bottom of the diaphragm, thereby compressing the lungs.The second method for expanding the lungs is to raise the rib cage. Raising the rib cage expands the lungs because, in the natural resting Ebook Guyton and hall textbook of medical physiology (13/E): Part 2 position, the ribs slant downward, as shown on the left side of Figure 38-1, thus allowing the sternum to fall backward toward thevertebral column. WEbook Guyton and hall textbook of medical physiology (13/E): Part 2
hen the rib cage is elevated, however, the ribs project almost directly forward, so the sternum also moves forward, away from the spine, making the anCHAPTER 38 MPulmonary VentilationUNIT VHie main functions of respiration are to provide oxygen to the tissues and remove carbon dioxide, The four majo Ebook Guyton and hall textbook of medical physiology (13/E): Part 2te the chest cage are classified as muscles of inspiration, and the muscles that depress the chest cage are classified as muscles of expiration.The most important muscles that raise the rib cage are the external intercostals, but others that help arc the (1) sternocleidomastoid muscles, which lift u Ebook Guyton and hall textbook of medical physiology (13/E): Part 2pward on the sternum; (2) anterior serrati, which lift many of the ribs; and (3) scalcni, which lift the first two ribs.The muscles that pull the ribEbook Guyton and hall textbook of medical physiology (13/E): Part 2
cage downward during expiration are mainly (1) the abdominal recti, which have the powerful effect of pulling downward on the lower ribs at the same tCHAPTER 38 MPulmonary VentilationUNIT VHie main functions of respiration are to provide oxygen to the tissues and remove carbon dioxide, The four majo Ebook Guyton and hall textbook of medical physiology (13/E): Part 238-1 also shows the mechanism by which the external and internal intcrcostals act to cause inspiration and expiration. To the left, the ribs during expiration are angled downward, and the external intercostals are elon gated forward and downward. As they contract, they pull the upper ribs forward in Ebook Guyton and hall textbook of medical physiology (13/E): Part 2 relation to the lower ribs, which causes leverage on the ribs to raise them upward, thereby causing inspiration. The internal intercostals function eEbook Guyton and hall textbook of medical physiology (13/E): Part 2
xactly in the opposite manner, functioning as expiratory muscles because they angle between the ribs in the opposite direction and cause opposite leveCHAPTER 38 MPulmonary VentilationUNIT VHie main functions of respiration are to provide oxygen to the tissues and remove carbon dioxide, The four majo Ebook Guyton and hall textbook of medical physiology (13/E): Part 2ir through the trachea whenever there is no force to keep it inflated. Also, there arc no attachments between the lung and the walls of the chest cage, except where it is suspended at its hilum from the mediastinum, the middle section of the chest cavity. Instead, the lung "floats’’ in the thoracic Ebook Guyton and hall textbook of medical physiology (13/E): Part 2cavity, surrounded by a thin layer of pleural fluid that lubricates movement of the497Unit VII RespirationFigure 38-1. Contraction and expansion of thEbook Guyton and hall textbook of medical physiology (13/E): Part 2
e thoracic cage during expiration and msprration, demonsvating diaphragmatic conưaction. function of the intercostal muscles, and elevation and depresCHAPTER 38 MPulmonary VentilationUNIT VHie main functions of respiration are to provide oxygen to the tissues and remove carbon dioxide, The four majo Ebook Guyton and hall textbook of medical physiology (13/E): Part 2 suction between the visceral surface of the lung pleura and the parietal pleural surface of the thoracic cavity. Therefore, the lungs are held to the thoracic wall as if glued there, except that they are well lubricated and can slide freely as the chest expands and contracts.Pleural Pressure and It Ebook Guyton and hall textbook of medical physiology (13/E): Part 2s Changes during Respiration. Pleural pressure is the pressure of the fluid in the thin space between the lung pleura and the chest wall pleura. As noEbook Guyton and hall textbook of medical physiology (13/E): Part 2
ted earlier, this pressure is normally a slight suction, which means a slightly negative pressure. The normal pleural pressure at the beginning of insCHAPTER 38 MPulmonary VentilationUNIT VHie main functions of respiration are to provide oxygen to the tissues and remove carbon dioxide, The four majo Ebook Guyton and hall textbook of medical physiology (13/E): Part 2ation, expansion of the chest cage pulls outward on the lungs with greater force and creates more negative pressure, to an average of about -7.5 centimeters of water.These relationships between pleural pressure and changing lung volume are demonstrated in Figure 38'2, showing in the lower panel the Ebook Guyton and hall textbook of medical physiology (13/E): Part 2increasing negativity of the pleural pressure from -5 to -7.5 during inspiration and in the upper panel an increase in lung volume of 0.5 liter. Then,Ebook Guyton and hall textbook of medical physiology (13/E): Part 2
during expiration, the events are essentially reversed.Alveolar Pressure—The Air Pressure Inside the Lung Alveoli. When the glottis is open and no aiCHAPTER 38 MPulmonary VentilationUNIT VHie main functions of respiration are to provide oxygen to the tissues and remove carbon dioxide, The four majo Ebook Guyton and hall textbook of medical physiology (13/E): Part 2re, which is considered to be zero reference pressure in the airways—that is, 0 centimeters of water pressure. To cause inward flow of air into theFigure 38-2. Chortges in lung volume. oK-edar pressure, pleural pressure, end transpulmonary pressure during normal breathingalveoli during inspiration, Ebook Guyton and hall textbook of medical physiology (13/E): Part 2the pressure in the alveoli must fall to a value slightly below atmospheric pressure (below 0). The second curve (labeled ‘alveolar pressure”) of FiguEbook Guyton and hall textbook of medical physiology (13/E): Part 2
re 38-2 demonstrates that during normal inspiration. alveolar pressure decreases to about -1 centimeters of water. This slight negative pressure is enCHAPTER 38 MPulmonary VentilationUNIT VHie main functions of respiration are to provide oxygen to the tissues and remove carbon dioxide, The four majo Ebook Guyton and hall textbook of medical physiology (13/E): Part 2t + 1 centimeter of water, which forces the 0.5 liter of498ChaptFigure 28-3. ( nnifilimxc' (ÌMt)tdrn in rt hmlthy poison Ihf. riidCỊMtri shows changes in kxx| volume durax) chorxjcs in trampUbnnnnry pn-.uirr (alvroLw pressure minus pleural pressure)0-2468Pleural pressure (cm HjO)Figure 38-4. cEbook Guyton and hall textbook of medical physiology (13/E): Part 2
II/)) and pleural IXCSSIXC is changed in order to change the transpulnxnary pressure.UNIT Vinspired air out of the lungs during die 2 to 3 seconds of CHAPTER 38 MPulmonary VentilationUNIT VHie main functions of respiration are to provide oxygen to the tissues and remove carbon dioxide, The four majoCHAPTER 38 MPulmonary VentilationUNIT VHie main functions of respiration are to provide oxygen to the tissues and remove carbon dioxide, The four majoGọi ngay
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