Physio chapter 13 lungs


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Physio chapter 13 lungs

  1. 1. The Respiratory System <ul><li>Chapter 13 </li></ul>
  2. 2. . <ul><li>External respiration is the sequence of events involved in the exchange of O 2 and CO 2 between the external environment and cells of the body. </li></ul><ul><ul><li>This includes breathing– the movement of air in & out of the lungs </li></ul></ul><ul><ul><li>O 2 and CO 2 are then exchanged between the air in the alveoli and blood of the pulmonary capillaries. </li></ul></ul><ul><ul><li>O 2 and CO 2 are transported by the blood from the lungs to the tissues. </li></ul></ul><ul><ul><li>These gases are exchanged between the blood & the tissues by diffusion. </li></ul></ul><ul><li>Internal respiration refers to the metabolic processes occurring in the mitochondria. </li></ul><ul><ul><li>O 2 is used by tissue cells. </li></ul></ul><ul><ul><li>CO 2 is produced. </li></ul></ul><ul><li>The respiratory quotient is the CO 2 produced divided by the O 2 consumed. </li></ul>
  3. 3. Atmosphere Tissue cell Alveoli of lungs Pulmonary circulation Systemic circulation CO 2 O 2 Food + O 2 CO 2 + H 2 O + ATP O 2 CO 2 CO 2 O 2 1 External respiration Breathing --Gas exchange between the atmosphere & (alveoli) in the lungs Exchange of O 2 & CO 2 between air in the alveoli and the blood Transport of O 2 & CO 2 between the lungs and the tissues Exchange of O 2 & CO 2 between the blood and the tissues Internal respiration 2 3 4 The term respiration has a broad meaning
  4. 4. The respiratory system also carries out nonrespiratory functions. <ul><li>It provides a route for water & heat elimination. </li></ul><ul><li>It enhances venous return—respiratory pump. </li></ul><ul><li>It contributes to the maintenance of normal acid-base balance—elimates CO 2 . </li></ul><ul><li>It enables various kinds of vocalizations. </li></ul><ul><li>It defends against inhaled foreign matter. </li></ul><ul><li>It modifies, activates, and inactivates materials passing through the circulatory system. </li></ul><ul><ul><li>Activates angiotensin II </li></ul></ul><ul><ul><li>Inactivates prostoglandins </li></ul></ul>
  5. 5. Nasal passages Mouth Pharynx Larynx Trachea Right bronchus Bronchiole Terminal bronchiole Terminal bronchiole Respiratory bronchiole Alveolar sac Respiratory airways conduct air between the atmosphere & alveoli. reinforced with rings of cartilage. Below the trachea, the respiratory tract forms progressively smaller and more numerous airways (bronchi to bronchioles to alveoli).
  6. 6. <ul><li>Cartilage is absent in the bronchioles. </li></ul><ul><li>The bronchioles are smooth muscle tubes, capable of changing the airflow through them by dilating & constricting. </li></ul>Bronchioles can control airflow Terminal bronchiole Respiratory bronchiole Branch of pulmonary artery Alveolus Pores of Kohn Smooth muscle Branch of pulmonary vein Pulmonary capillaries Alveolar sac
  7. 7. The alveoli are thin-walled, inflatable sacs <ul><li>The alveoli are encircled by pulmonary capillaries, offering tremendous surface area for gas exchange by diffusion. </li></ul><ul><li>Aveoli are formed by a single layer of flattened Type I alveolar cells. </li></ul><ul><li>Type II alveolar cells secretes pulmonary surfactant. </li></ul><ul><ul><li>This substance facilitates lung expansion. </li></ul></ul>Alveolar fluid lining with pulmonary surfactant Type II alveolar cell Type I alveolar cell Interstitial fluid Alveolus Alveolar macrophage Erythrocyte Pulmonary capillary
  8. 9. <ul><li>Surfactant </li></ul><ul><li>Surfactant is a complex substance containing phospholipids and a number of apoproteins. This essential fluid is produced by the Type II alveolar cells, and lines the alveoli and smallest bronchioles. Surfactant reduces surface tension throughout the lung, thereby contributing to its general compliance. It is also important because it stabilizes the alveoli. LaplaceÕs Law tells us that the pressure within a spherical structure with surface tension, such as the alveolus, is inversely proportional to the radius of the sphere (P=4T/r for a sphere with two liquid-gas interfaces, like a soap bubble, and P=2T/r for a sphere with one liquid-gas interface, like an alveolus: P=pressure, T=surface tension, and r=radius). That is, at a constant surface tension, small alveoli will generate bigger pressures within them than will large alveoli. Smaller alveoli would therefore be expected to empty into larger alveoli as lung volume decreases. This does not occur, however, because surfactant differentially reduces surface tension, more at lower volumes and less at higher volumes, leading to alveolar stability and reducing the likelihood of alveolar collapse. </li></ul><ul><li>Surfactant is formed relatively late in fetal life; thus premature infants born without adequate amounts experience respiratory distress and may die </li></ul>
  9. 10. The lungs occupy much of the thoracic cavity. <ul><li>Each has several lobes. </li></ul><ul><ul><li>Lung tissue is highly branched airways, alveoli, pulmonary blood vessels, and large amounts of elastic connective tissue. </li></ul></ul><ul><li>A pleural sac separates the lungs from the thoracic wall </li></ul>Right lung Left lung Thoracic wall Diaphragm Parietal pleura Visceral pleura Parietal cavity filled with intrapleural fluid <ul><li>The pleural cavity is the inside of the pleural sac and is filled with fluid </li></ul><ul><li>The diaphragm separates the thoracic cavity from the abdominal cavity. </li></ul><ul><li>The diaphragm is used for breathing. </li></ul>
  10. 11. Vacuum 760 mm Mercury (Hg) Pressure exerted by atmospheric air above Earth’s surface Pressure is measured in mm of mercury.
  11. 12. There are several pressures inside & outside the lungs. <ul><li>Atmospheric pressure (760 mm of Hg at sea level) is produced by the weight of the air on the Earth. </li></ul><ul><li>Atm Pressure ~ = Intra-alveolar (intrapulmonary) pressure </li></ul><ul><li>Intrapleural pressure is in the intrapleural cavity. </li></ul><ul><li>It has a slight vacuum compared to normal atm pressure & averages 756 mm Hg at rest. </li></ul><ul><li>The lungs stretch to fill the large thorax due, in part, to: </li></ul><ul><ul><li>intrapleural fluid’s cohesiveness. </li></ul></ul><ul><ul><li>transmural pressure pushes the lungs outward. </li></ul></ul>Atmospheric pressure 760 mm Hg Intra-alveolar pressure 760 mm Hg Intrapleural pressure Airways Thoracic wall Plural wall Lungs 756 mm Hg
  12. 13. 760 760 760 Collapsed lung 760 760 756 760 Puncture wound in chest wall 760 760 760 Traumatic pneumothorax 760 756 756 760 760 760 Spontaneous pneumothorax 760 756 760 756 Hole in lung
  13. 14. Changes in the intra-alveolar pressure produces the flow of air into and out of the lungs. <ul><li>If pressure in the lungs is less than atmospheric pressure, air enters the lungs. </li></ul><ul><li>If the opposite occurs, air exits from the lungs. </li></ul><ul><li>Boyle’s law states an inverse relationship between the pressure exerted by a quantity of gas and its volume. </li></ul><ul><li>Assuming temperature remains constant. </li></ul>Volume = 1/2 Pressure = 2 Volume = 1 Pressure = 1 Volume = 2 Pressure = 1/2 Piston Closed container with a given number of gas molecules
  14. 15. Equilibrated; no net movement of air 760 756 Before inspiration 759 754 During inspiration 760 761 756 During expiration 760 760 Inspiration & expiration are dependent on changing the size of the the thorax: Increasing throcic volume Decreasing throcic volume
  15. 16. Intra-Aveolar and Intrapleural Pressures Inspiration Expiration Atm pressure Intra-alveolar pressure Intraplural pressure Transmural pressure gradient across the lung wall
  16. 17. Inspiration begins with the contraction of the respiratory muscles: <ul><li>The diaphragm (phrenic nerve) & the external intercostal muscles account for 75 % of the enlargement of the thoracic cavity during quiet respiration </li></ul><ul><li>The lungs expand to fill the expanded space. </li></ul><ul><li>This increase in volume lowers the intra-alveolar pressure drawing in air under atmospheric pressure. </li></ul>Accessory muscles of Inspiration: Muscles of active expiration Major muscles of inspiration Sternocleido-mastoid Scalenes External intercostal muscles Diaphragm Internal intercostal muscles Abdominal muscles
  17. 18. External intercostal muscles (relaxed) Contractions of external intercostal muscles causes elevation of ribs, which increases side-to-side dimension of thoracic cavity Lowering of diaphragm on contraction increases vertical dimension of thoracic cavity Elevation of ribs causes sternum to move upward and outward, which increases front-to back dimension of thoracic cavity Before inspiration Inspiration Elevated rib cage Contraction of external intercostal muscles Sternum Diaphragm (relaxed) Contraction of diaphragm
  18. 19. The onset of expiration begins with the relaxation of the inspiratory muscles. <ul><li>Relaxation of the diaphragm and the muscles of the chest wall, plus the elastic recoil of the alveoli, decrease the size of the chest cavity. </li></ul><ul><li>The intrapleural pressure increases and the lungs are compressed. </li></ul><ul><li>The intra-alveolar pressure increases. </li></ul><ul><li>When it increases to a level above atmospheric pressure, air is driven out - an expiration. </li></ul><ul><li>Forced expiration can occur by the contraction of expiratory muscles. </li></ul><ul><li>These skeletal muscles are ones in the abdominal wall and the internal intercostal muscles. </li></ul><ul><li>Their contraction further increases the pressure gradient between the alveoli & the atmosphere. </li></ul>
  19. 20. Relaxation of external intercostal muscles Return of diaphragm, ribs, and sternum to resting position on relaxation of inspiratory muscles restores thoracic cavity to preinspiratory size Contractions of abdominal muscles cause diaphragm to be pushed upward, further reducing vertical dimension of thoracic cavity Contraction of internal intercostal muscles flattens ribs & sternum, further reducing side- to-side and front to-back dimensions of thoracic cavity Passive expiration Active expiration Contraction of internal intercostal muscles Relaxation of diaphragm Contraction of diaphragm Position of relaxed abdominal muscles
  20. 21. Airway resistance in the respiratory tract influences the rate of airflow. <ul><li>F =  P / R where </li></ul><ul><li> P is the difference between the atmospheric and intra-alveolar pressures. </li></ul><ul><ul><li>The greater the difference the greater the flow </li></ul></ul><ul><li>However, if the resistance (R) increases, the airflow is decreased (inversely proportional). </li></ul><ul><li>The autonomic nervous system control of bronchiolar dialation is the major determinant of resistance </li></ul><ul><ul><li>Sympathetic stimulation and epinephrine from the adrenal medula cause bronchodilation. </li></ul></ul>
  21. 22. Airway resistance is increased abnormally with chronic obstructive pulmonary disease. 760 756 756 756 756 760.5 761 760 786 786 786 791 786 788 786 <ul><li>Expiration is more difficult than inspiration. </li></ul><ul><ul><li>Chronic bronchitis involves long-term inflammation </li></ul></ul><ul><ul><li>Asthma involves muscle spams and/or inflammation </li></ul></ul><ul><ul><li>Emphysema is the collapse of the alveoli. </li></ul></ul>760 770 770 770 770 772 775 760 772 775 772 774 772 769 786 772 772
  22. 23. The lungs have elastic behavior. <ul><li>The lungs have elastic recoil, rebounding if they are stretched. </li></ul><ul><li>Compliance is the effort required to stretch or distend the lungs. </li></ul><ul><ul><li>A thin balloon is more compliant than a thick balloon </li></ul></ul><ul><li>A highly-compliant lung stretches further for a given increase in pressure than a lung with less compliance. </li></ul><ul><li>Pulmonary elastic behavior depends on the pulmonary elastic behavior and alveolar surface tension. </li></ul><ul><li>Numerous factors decrease lung compliance. </li></ul>
  23. 24. The work of breathing normally requires 3% of total energy expenditure. <ul><li>Factors such as a decrease of pulmonary compliance and an increase in airway resistance can increase this percentage. </li></ul><ul><li>During each quiet breathing cycle, about 500 ml of air is inspired and expired. The lungs do not completely empty about each expiration. </li></ul>
  24. 25. Surface tension H 2 O An alveolus <ul><li>This tension is determined by the thin liquid film that lines the outside of each alveolus. </li></ul><ul><li>This film allows the alveolus to resist expansion. </li></ul><ul><li>This film also squeezes the alveolus, producing recoil. </li></ul><ul><li>A coating of pulmonary surfactant prevents the alveoli from collapsing from this surface tension. </li></ul><ul><li>Insufficient pulmonary surfactant can produce newborn respiratory distress syndrome. </li></ul>
  25. 26. Aveoli are interconnected. Thus aveoli must expand & contract as a unit. Interconnected alveoli Alveolus starts to collapse Collapsing alveolus pulled open
  26. 27. Airways Alveoli Pulmonary surfactant molecule Airways Alveoli Surfactant equalizes the inward pressure differences in between large & small aveoli created by surface tension
  27. 28. Variations in lung volume Total lung capacity at maximum inflation Variation in lung with normal, quiet breathing Minimal lung volume (residual volume) at maximum deflation Normal expiration (average 2,200 ml) normal inspiration (average 2,200 ml) Avg. 500 ml
  28. 29. Figure 13.19b Page 477 TV = Tidal volume (500ml) IRV = Inspiratory reserve volume (3,000 ml) IC = Inspiratory capacity (3,500 ml) ERV = Expiratory reserve volume (1,000 ml) RV = Residual volume (1,200 ml) FRC = Functional residual capacity (2,200 ml) VC = Vital capacity (4,500 ml) TLC = Total lung capacity (5,700 ml) Time Time (sec)
  29. 30. Lung volumes and capacities can be measured by a spirometer. Spirogram Floating drum Air Water Expired air Inspired air
  30. 31. Figure 13.22a Page 479 Obstructive lung disease
  31. 32. Figure 13.22b Page 479 Restrictive lung disease Normal total lung capacity
  32. 33. “ Old” alveolar air that has exchanged O 2 and CO 2 with the blood Fresh atmospheric air that has not exchanged O 2 and CO 2 with the blood 150 During expiration 350 150 500 ml “old” alveolar air expired Fresh air from inspiration 150 dead space volume (150 ml) After inspiration, before expiration Alveolar air 150 350 150 During inspiration Alveolar ventilation is less because of the anatomic dead space.
  33. 34. Pulmonary ventilation is the tidal volume x respiratory rate. <ul><li>Due to dead space: </li></ul><ul><li>alveolar ventilation = (tidal volume - dead space volume) x respiratory rate </li></ul><ul><li>Breathing patterns (e.g., deep and slow) can affect alveolar ventilation. </li></ul><ul><li>An alveolar dead space also exists, but it is usually small. </li></ul>
  34. 35. <ul><li>There are local controls on the smooth muscle of the airways. </li></ul><ul><li>An accumulation of CO 2 in the alveoli decreases airway resistance. </li></ul><ul><li>An increase of O 2 in the alveoli causes pulmonary vasodilation. </li></ul><ul><li>It causes vasoconstricion of pulmonary arterioles </li></ul>
  35. 36. Gas exchange occurs by partial pressure gradients. <ul><li>The exchange of O 2 and CO 2 as the pulmonary and tissue capillaries is by simple diffusion. </li></ul><ul><li>Air is a mixture of gases. </li></ul><ul><li>The partial pressure of each gas depends on its percentage in the total atmospheric pressure. </li></ul><ul><ul><li>For example, nitrogen is 79% of the air. </li></ul></ul><ul><ul><li>Its partial pressure is 0.79 x 760 = 600.4 </li></ul></ul><ul><li>A partial pressure gradient is established when there are two partial pressures for a gas in different regions of the body. </li></ul><ul><li>For example the partial pressure of O 2 is greater in the alveoli (e.g., 100) diffuses down its partial pressure gradient towards into the blood of the pulmonary capillaries where the pressure is 40 </li></ul>
  36. 37. Composition and partial pressure in atmospheric air Total atmospheric pressure = 760 mm Hg 79% N 2 Partial pressure N 2 = 600 mm Hg 21% O 2 Partial pressure O 2 = 160 mm Hg Partial pressure of N 2 in atmospheric air: P N2 = 760 mm Hg X 0.79 = 600 mm Hg Partial pressure of O 2 in atmospheric air: P O2 = 760 mm Hg X 0.21 = 160 mm Hg
  37. 38. Across pulmonary capillaries: O 2 partial pressure gradient from alveoli to blood = 60 mm Hg (100 –> 40) O 2 partial pressure gradient from blood to alveoli = 6 mm Hg (46 –> 40) Across pulmonary capillaries: O 2 partial pressure gradient from blood to alveoli = 6 mm Hg (46 –> 40) O 2 partial pressure gradient from tissue cell to blood = 6 mm Hg (46 –> 40) Inspiration Expiration Pulmonary circulation Systemic circulation Alveoli Diffusion gradients for O 2 & CO 2 between the lungs & tissues Tissue cell Atmospheric air
  38. 39. Area in which blood flow (perfusion) is greater than airflow (ventilation) Helps balance Helps balance Small airflow CO 2 in area Relaxation of local-airway smooth muscle Dilation of local airways Airway resistance Airflow O 2 in area Contraction of local pulmonary smooth muscle Constriction of blood vessels Vascular resistance Blood flow Large bloodflow
  39. 40. Area in which blood flow (ventilation) is greater than blood (perfusion) Helps balance Helps balance Large airflow Small blood flow CO 2 in area Contraction of local airway smooth muscle Constriction of local-airway Airway resistance Airflow O 2 in area Relaxation of local pulmonary smooth muscle Dilation of local blood vessels Vascular resistance Blood flow
  40. 41. The partial pressures for O 2 & CO 2 in the pulmonary capillaries equilibrate with the partial pressures for these gases in the alveoli by simple diffusion,. <ul><li>The greater the partial pressure gradients between the alveoli and the blood, the greater the rate of transfer for the gases. </li></ul><ul><li>The blood passing through the lungs gains O 2 and eliminates some of its CO 2 . </li></ul><ul><li>This blood passes through the left side of the heart and enters the systemic circulation. It arrives at the tissues with the same gas content (e.g., 100 for O 2 and 40 for CO 2 ) established at lung equilibration. </li></ul>
  41. 42. Other factors contributing to the pressure gradient affect the rate of gas transfer. <ul><li>As surface area increases the diffusion rate increases. </li></ul><ul><ul><li>The alveoli collectively offer a tremendous surface area. </li></ul></ul><ul><ul><li>Increased pulmonary blood pressure, from an increased cardiac output, increases the area. </li></ul></ul><ul><li>The walls of the alveoli and pulmonary capillaries are thin for rapid gas transfer. </li></ul><ul><ul><li>Pulmonary edema, pulmonary fibrosis, and pneumonia thicken the barriers for gas exchange. </li></ul></ul><ul><li>Gas exchange is also directly proportional to the diffusion coefficient for a gas. </li></ul><ul><ul><li>This coefficient is twenty times as great for CO 2 compared to O 2 , as CO 2 is more soluble. </li></ul></ul>
  42. 43. Gas exchange across systemic capillaries also occurs down partial pressure gradients. <ul><li>The O 2 in the systemic capillaries has a high partial pressure (100) compared to tissue cells (40). </li></ul><ul><ul><li>O 2 diffuses into the tissue cells (100  40). </li></ul></ul><ul><li>The partial pressure for CO 2 in the systemic capillaries is low (40) compared to the tissue cells (46). </li></ul><ul><ul><li>CO 2 diffuses into the blood (46  40). </li></ul></ul><ul><li>Having equilibrated with the tissue cells, the blood leaving the systemic capillaries is low in O 2 & high in CO 2 . </li></ul><ul><li>This blood is then pumped by the right side of the heart to the lungs. </li></ul><ul><li>At in the lungs, the blood acquires O 2 & releases CO 2 . </li></ul>
  43. 44. Most O 2 in the blood is transported by binding with hemoglobin. <ul><li>Hemoglobin combines with O 2 to form oxyhemoglobin. </li></ul><ul><li>This is a reversible process, favored to form oxyhemoglobin in the lungs. </li></ul><ul><li>Hemoglobin tends to combine with O 2 as O 2 diffuses from the alveoli into the pulmonary capillaries. </li></ul><ul><li>A small percentage of O 2 is dissolved in the plasma. </li></ul><ul><li>The dissociation of oxyhemoglobin into hemoglobin and free molecules of O 2 occurs at the tissue cells. </li></ul><ul><li>The reaction is favored in this direction as O 2 leaves the systemic capillaries and enters tissue cells. </li></ul>
  44. 45. Alveoli Pulmonary capillary blood = O 2 molecule = Partially saturated hemoglobin molecules = Fully saturated hemoglobin molecules Hemoglobin increases the concentation gradient of O 2 in pulmonary capillaries.
  45. 46. The partial pressure of O 2 is the main factor determining the % hemoglobin saturation. <ul><li>The plateau part of the curve is where the partial pressure of O 2 is high (lungs). </li></ul><ul><li>The steep part of the curve exists at the systemic capillaries, where hemoglobin unloads O 2 to the tissue cells. </li></ul>Average resting P O2 at systemic capillaries Normal P O2 at pulmonary capillaries Hemoglobin saturation curve
  46. 47. Hemoglobin promotes the net transfer of O 2 at both the alveolar and tissue levels. <ul><li>There is a net diffusion of O 2 from the alveoli to the blood. </li></ul><ul><ul><li>This occurs continuously until hemoglobin is as saturated as possible (97.5% at 100 mm of Hg). </li></ul></ul><ul><li>At the tissue cells hemoglobin rapidly delivers O 2 into the blood plasma and on to the tissue cells. </li></ul><ul><ul><li>Increases in CO 2 & acidity increase unloading </li></ul></ul><ul><ul><ul><li>This shift of the curve to the right (more dissociation) is called the Bohr effect. </li></ul></ul></ul><ul><ul><li>Increased temperature as well as BPG also produces this shift. </li></ul></ul><ul><li>Hemoglobin has more affinity for carbon monoxide compared to O 2 . </li></ul>
  47. 48. Figure 13.30 Page 491 Arterial P CO2 & acidity, normal body temperature (as at pulmonary level) P CO2 Acid (H + ) Temperature or 2,3-Bisphosphoglycerate (from normal tissue levels)
  48. 49. Most CO2 (about 60%) is transported as the bicarbonate ion. <ul><li>30% of the CO 2 is bound to hemoglobin in the blood. This is another means of transport. </li></ul><ul><ul><li>Haldane effect increases the ability of hemoglobin to bind with CO 2 . </li></ul></ul><ul><li>About 10% of the transported CO2 is dissolved in the plasma. </li></ul><ul><li>60% of CO 2 is transported as carbonic acid which is formed by carbonic anhydrase from CO 2 & H 2 0 </li></ul><ul><ul><li>Carbonic acid dissociates into H + & bicarbonate ions </li></ul></ul><ul><ul><li>This process is reversible and CO 2 is reformed in the in the lungs. </li></ul></ul><ul><ul><li>The chloride shift  Erythrocytes passively transport bicarbonate ions out of the cell & Cl - in. </li></ul></ul>
  49. 50. CO 2 transport Tissue cell Alveolus Plasma From systemic circulation to pulmonary circulation
  50. 51. <ul><li>The DRG has inspiratory neurons that signal to the inspiratory muscles. </li></ul><ul><li>The VRG activate inspiratory & expiratory muscles for exercise . </li></ul><ul><li>Pre-Botzinger complex apperas to contro rhythm </li></ul><ul><li>The apneustic center in the pons prevents increases depth of breathing –keeps inspiratory muscles active. </li></ul><ul><li>The pneumotaxic center has final say and limits depth of inhalation. </li></ul>Respiratory centers in the brain stem establish a rhythmic breathing pattern. <ul><li>The Hering-Breuer reflex  stretch receptors in the lungs are activated when the lungs inflate with air from an inspiration. </li></ul>
  51. 52. Effects of hyperventilation and hypoventilation on arterial P O2 & P CO2 Hypoventilation Hyperventilation Normal alveolar and arterial P O2 Normal alveolar and arterial P C O2 P CO2 P O2
  52. 53. Output from the DRG goes through the phrenic nerve to the diaphagm Input from other areas– some excitatory, some inhibitory Inspiratory neurons in DRG (rhythmically firing) Phrenic nerve Diaphragm Spinal cord Medulla
  53. 54. The magnitude of ventilation is adjusted in response to three chemical factors. <ul><li>Peripheral and central chemoreceptors detect chemical changes in the blood & signal the medulla to change respiratory rate </li></ul><ul><li>Respiratory rate increases by: </li></ul><ul><li>Primary  CO 2 -generated hydrogen ions in the brain are normally the primary regulators of ventilation. </li></ul><ul><li>Secondary  A decrease in the partial pressure of arterial O 2 or an increase in the partial pressure of arterial CO 2 or in hydrogen ions in the blood also can increase the breathing rate. </li></ul><ul><li>These responses keep the partial pressure of O 2 and CO 2 remarkably constant. </li></ul><ul><li>A very low partial pressure of O 2 in the blood depresses the respiratory center. </li></ul>Carotid sinus Carotid bodies Aortic bodies Heart
  54. 55. Arterial P CO2 Relieves Brain ECF P CO2 Brain ECF H + Central Chemo-receptors Medullary respiratory center Ventilation Arterial P CO2 Peripheral Chemo-receptors Weakly Brain ECF  when arterial P CO2 >70-80 mm Hg
  55. 56. Low levels of O2 can trigger increased external respiration Arterial P O2 <60 mm Hg Emergency life-saving mechanism Medullary respiratory center Ventilation Arterial P O2 Central chemoreceptors Peripheral chemoreceptors No effect on Relieves
  56. 57. Figure 13.38 Page 5O2 Acidosis Arterial non-CO 2 -H + Peripheral Chemo-receptors Medullary respiratory center Central Chemo-receptors Cannot penetrate blood-brain barrier No effect on Ventilation Arterial P CO2 Arterial -CO 2 -H + Relieves
  57. 58. Other factors on the control of respiratory rate include: <ul><li>Measuring O 2 concentrations is not useful since most O 2 is bound to hemoglobin </li></ul><ul><li>By default the C0 2 concentrations are more reliable </li></ul><ul><ul><li>Adjustments of H+ concentrations are a rapid mechanism for controlling blood pH. </li></ul></ul><ul><ul><li>Removal of CO 2 from the lungs increases blood pH </li></ul></ul><ul><li>Exercise significantly increases ventilation, but the mechanisms are not clear. </li></ul><ul><ul><li>Factors such as increased body temperature and epinephrine release may contribute. </li></ul></ul><ul><li>Ventilation can be influenced by factors unrelated to gas exchange such as protective reflexes and pain. </li></ul>
  58. 59. Respiratory failures <ul><li>During apnea there is a transient interruption of ventilation. </li></ul><ul><ul><li>Most common during REM sleep </li></ul></ul><ul><ul><li>In respiratory arrest it does not continue. </li></ul></ul><ul><ul><ul><li>Results in sudden infant death syndrome </li></ul></ul></ul><ul><ul><ul><li>Neuronal controls are often not well developed </li></ul></ul></ul><ul><li>During dyspnea there is “shortness of breath.” </li></ul><ul><ul><li>It often accompanies other conditions such as pulmonary edema with congestive heart failure. </li></ul></ul><ul><ul><li>Is not directly linked to a physical shortness of breath </li></ul></ul>