PHYSIOLOGY OF RESPIRATION.pptx

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1. RESPIRATORY SYSTEM (CONTD) THE PHYSIOLOGY OF RESPIRATION BY M. SHAWA

2. Lesson objectives Describe pulmonary ventilation Explain the mechanism of pulmonary ventilation Relate the Boyle’s law to events of inspiration and expiration Mention physical factors influencing pulmonary ventilation Identify the various pulmonary volumes and capacity

3. Respiratory physiology Respiration is the process of exchange of gases in the body. It involves the following processes: External respiration Transport of gases by blood Internal respiration Overall regulation of respiration.

4. Pulmonary ventilation The process of gas exchange (respiration) has three basic steps: Pulmonary ventilation or breathing – is the inhalation (inflow) and exhalation (outflow) of air and involves the exchange of air between the air and the alveoli of the lungs

5. Pulmonary ventilation (contd..) External (pulmonary) respiration- is the exchange of gases between the alveoli of the lungs and the blood in pulmonary capillaries across the respiratory membrane. In this process the pulmonary capillary blood gains oxygen and losses carbon dioxide.

6. Pulmonary ventilation (contd..) Internal (tissue) respiration – is the exchange of gases between blood in the systemic capillaries and tissue cells. In this step blood loses oxygen and gains carbon dioxide. Pulmonary ventilation depends on volume changes in the thoracic cavity.

7. mechanism of pulmonary ventilation Primary principle of ventilation: Air moves into lungs when air pressure inside lungs is less than the air in the atmosphere. Air moves out of the lungs when air pressure inside lungs is greater than air pressure in the atmosphere.

8. mechanism of pulmonary ventilation Before each inhalation, air pressure in the lungs is equal to the atmospheric air pressure. Under standard conditions atmospheric air exerts a pressure of 760mm Hg.

9. mechanism of pulmonary ventilation (Contd..) Alveolar air at the end of one expiration, and before the beginning of another inspiration also exerts 760mm Hg.

10. mechanism of pulmonary ventilation – (contd..) When atmospheric pressure is greater than pressure within the lungs, air flows down the pressure gradient from the atmosphere into the lungs. This is when inspiration occurs.

11. mechanism of pulmonary ventilation – (contd..) When pressure in the lungs becomes greater than atmospheric pressure, air moves down the pressure gradient from the lungs into the atmosphere. During this time expiration occurs.

12. mechanism of pulmonary ventilation – (contd..) Pulmonary ventilation mechanism establishes the two gas pressure gradient that produce respiration. (These are - one in which alveolar pressure is lower than atmospheric pressure to produce inspiration and on in which it is higher than atmospheric pressure to produce expiration)

13. mechanism of pulmonary ventilation – (contd..) These pressure gradients are established by: changes in the size of the thoracic cavity which are produced by contraction and relaxation of respiratory muscles.

14. GAS LAWS Gas laws are statements about the nature of gases. They are based on the concept of the ‘ ideal gas’ – i.e. a gas whose molecules are so far apart that its molecules rarely collide with one another.

15. GAS LAWS (contd..) Gas laws are also based on the assumption that gas molecules continually collide with the container and thus producing a force against it called gas pressure.

16. GAS LAWS (contd..) Some of the gas laws are: Boyle’s law Charles’ law Dalton’s law (law of partial pressure) Henry’s law

17. BOYLE’S LAW This law states that at constant temperature a gas’s volume is inversely proportional to its pressure. When the volume of a container increases, the pressure of the gas inside it decreases and when the volume decreases the gas pressure increases.

18. Boyles law and ventilation In ventilation, when thoracic volume increases, air pressure in the airways decreases ( allowing air to move inward) and when thoracic volume decreases air pressure in the airways increases (allowing air to move outward).

19. INSPIRATION Contraction of the diaphragm alone or contraction of both the diaphragm and the external inter-costal muscles produces quiet respiration. When the diaphragm contracts, it descends and makes the thoracic cavity longer.

20. INSPIRATION (contd..) Contraction of the external inter-costal muscles pulls the anterior end of each rib up and out. This also elevates the sternum and enlarges the thorax from front to back and from side to side.

21. INSPIRATION (CONTD..) During forceful respiration additional muscles aid in elevation of sternum and rib cage. These additional muscles are sternocleidomastoid , scalenes , pectoralis minor, and serratus anterior muscles

22. INSPIRATION (CONTD..) As the size of the thorax increases, the intra-pleural (intra-thoracic) and alveolar pressures decreases (Boyle’s law) and inspiration occurs. As the thorax enlarges, it pulls the lungs along with it because of the cohesion between two moist pleura covering the lungs and the thorax.

23. INSPIRATION (CONTD..) The lungs expands and pressure in the tubes and the alveoli decrease. Air then moves into the lungs until a pressure equilibrium is established between atmosphere and the alveoli, then the flow of air stops.

24. INSPIRATION (CONTD..) The ability of the lungs and thorax to stretch is known as ‘ Compliance’ and is essential for normal breathing. If compliance is reduced due to disease or injury inspiration becomes difficult.

25. Process of breathing Boyle’s law: p 1 V 1 =p 2 V 2 Marieb, Human Anatomy & Physiology, 7 th edition

26. Expiration Quiet expiration in a healthy person is a passive process and depends more on the elasticity of the lungs than on muscle contraction. It begins when the pressure gradients that resulted in inspiration are reversed.

27. Expiration (contd..) As the inspiratory muscles relax, the size of the thorax decreases. The rib cage descends and the lungs recoil. Both the thoracic and intrapulmonary volume decrease.

28. Expiration (contd..) The decreased volume compresses the alveoli and increases its pressure above the atmospheric pressure. The pressure gradient forces gases to flow out of the lungs.

29. Expiration (contd..) Forced expiration is an active process produced by contraction of abdominal wall muscles, primarily the oblique and transversus muscles. These contractions increase the intra-abdominal pressure forcing the abdominal organs superiorly against the diaphragm and also depress the rib cage.

30. Expiration (contd..) The tendency of the lungs to return to their pre-inspiration volume is called ‘elastic recoil’. If a disease condition reduces the elasticity of pulmonary tissue, expiration becomes forced even at rest.

31. Physical factors influencing pulmonary ventilation Lungs stretch during inspiration and recoil passively during expiration. Energy is also used to overcome various factors that hinder air passage and pulmonary ventilation

32. Physical factors influencing (Contd..) The factors include: Airway resistance – gas flow decreases as resistance increases. Resistance in respiratory tree is determined mainly by the diameter of tubes.

33. Physical factors influencing (Contd..) Alveolar surface tension – Surfactant ( a liquid film coating the alveoli) decreases the surface tension of alveoli and prevents alveolar collapse.

34. Physical factors influencing (Contd..) Lung compliance – healthy lungs are stretchy and distensible. Lung compliance is determined by distensibility of lung tissue and alveolar surface tension Lung disease like tuberculosis can replace lung tissue with scar tissue and decrease compliance.

35. PULMONARY AIR VOLUME AND CAPACITY At rest, a healthy adult takes an average of 12 breaths a minute, moving 500ml of air into and out of the lungs with each inhalation and exhalation. The volume of one breath is called the Tidal volume (V T ).

36. PULMONARY AIR VOLUME AND CAPACITY (contd..) The minute ventilation (MV) – the total volume of air inhaled and exhaled each minute – is respiratory rate multiplied by tidal volume: MV= 12 breaths/min x 500ml/breath

37. PULMONARY AIR VOLUME AND CAPACITY (contd..) A lower than normal minute ventilation is a sign of pulmonary malfunction. The apparatus used to measure the volume of air exchanged during breathing and respiratory rate is a Spirometer or respirometer and the record is called spirogram .

38. Pulmonary volumes and capacities Marieb, Human Anatomy & Physiology, 7 th edition

39. Tidal volume Tidal volume varies from one person to another and in the same person at different times. In a typical adult, about 70% of tidal volume (350ml) actually reaches the respiratory zone and participate in external respiration.

40. Tidal volume (contd..) The other 30% (150ml) remains in the conducting zone of the nose, pharynx, larynx, trachea, bronchi bronchioles. Collectively the conducting airways with air that does not undergo respiratory exchange are known as anatomic (respiratory) dead space.

41. Tidal volume (contd..) Alveolar ventilation refers to the volume of inspired air that actually reaches or ‘ventilates’ the alveoli. Only this volume of air takes part in the exchange of gases between air and blood.

42. Other lung volumes Several other lung volumes are defined relative to forceful breathing. These volumes are larger in males, taller individuals and younger adults They are smaller in females, shorter individuals, and the elderly.

43. Inspiratory reserve volume When you take a very deep breath you can inhale more than 500ml. This additional air is called the inspiratory reserve volume (IRV). It is about 3100ml in an average adult male and 1900ml in an adult female.

44. inspiratory reserve volume Even more air can be inhaled if inhalation follows forced exhalation.

45. Expiratory reserve volume After expiration of tidal air (500ml), an individual can still force more air out of the lungs. The largest volume of air that one can forcibly expire after expiring tidal air is called expiratory reserve volume (ERV)

46. Expiratory reserve volume (contd..) An average adult normally has an ERV of between 1000 and 1200ml.

47. Residual volume Even after forceful exhalation, a considerable amount of air still remains trapped in the alveoli. This amount of air that cannot be forcibly expired is known as residual volume (RV).

48. Residual volume (contd..) Residual volume amounts to about 1200ml in males and 1100ml is females. Between breaths, an exchange of oxygen and carbon dioxide occurs between trapped residual air in the alveoli and the blood.

49. Pulmonary capacities A pulmonary capacities are a combination sum of two or more pulmonary volumes. Pulmonary capacities include: Vital capacity Inspiratory capacity Functional residual capacity Total lung capacity.

50. Vital capacity (VC) It represents the largest volume of air an individual can move in and out of the lungs. It is determined by measuring the largest possible expiration after the largest possible inspiration.

51. Vital capacity (contd..) VC is the sum of inspiratory reserve volume, tidal volume and expiratory reserve volume (VC = IRV + TV + ERV). It is about 4800ml in males and 3100ml in females.

52. Vital capacity (contd..) The VC of an individual depends on the size of the thoracic cavity, posture, and other factors. The VC is larger when standing erect than when stooped over or lying down. VC is decreased if lungs contain more blood than normal e.g. In CCF.

53. Inspiratory capacity (IC) This is the maximum amount of air an individual can inspire after a normal expiration. It is the sum of tidal volume and inspiratory reserve volume (IC = TV + IRV)

54. Inspiratory capacity (IC) It is (500ml + 3100ml = 3600ml) in males and (500ml + 1900ml = 2400ml in females)

55. Functional residual capacity (FRC) This is the amount of air left in the lungs at the end of a normal expiration. It is the sum of residual volume and expiratory reserve volume (FRC = RV + ERV). FRC is 2200 to 2400ml.

56. Total lung capacity (TLC) This is the total volume of air a lung can hold. TLC is the sum of vital capacity and residual volume (TLC = VC + RV)

57. Pulmonary gas exchange The exchange of O 2 and CO 2 between alveolar air and pulmonary blood occurs via passive diffusion. It is governed by behaviour of gases as described by two gas laws namely; Dalton’s law and Henry’s law

58. Dalton’s Law and pulmonary gas exchange Daltons law states that each gas in a mixture of gases exerts its own pressure as if no other gases were present. This pressure of a specific gas in a mixture is called partial pressure ( P x ); the subscript is the chemical formula of the gas.

59. Atmospheric and partial pressure The total pressure of the mixture is calculated by adding all the partial pressures. Atmospheric air is a mixture of nitrogen N 2 , O 2 , H 2 O, and CO 2 plus other gases present in small quantities.

60. Atmospheric and partial pressure (contd..) Atmospheric pressure is the sum of all these gases: Atmospheric pressure (760mmHg) = P N + P O2 + P H2O +P CO2 + P other gases To determine the partial pressure exerted by each gas in a mixture, multiply the percentage of the gas by the total pressure of the mixture.

61. Atmospheric and partial pressure (contd..) The partial pressure of the inhaled air is as follows: P N2 = 0.786 x 760mmHg = 597.4mmHg P O2 = 0. 209 x 760mmHg = 158.8mmHg P H2O = 0.004 x 760mmHg = 3.0mmHg P CO2 = 0.0004 x 760mmHg = 0.3mmHg P other gases = 0.0006 x 760mmHg = 0.5mmHg Total = 760mmHg

62. Pulmonary gas exchange (contd..) These partial pressures determine the movement of O 2 and CO 2 between the atmosphere and the lungs, between the lungs and the blood, and between the blood and body cells.

63. Pulmonary gas exchange (contd..) Each gas diffuses across a permeable respiratory membrane from the area of greater partial pressure to an area of less partial pressure. The greater the difference in partial pressure, the faster the rate of diffusion.

64. Pulmonary gas exchange (contd..) As compared to inhaled air, the alveolar air has less O 2 and more CO 2. The gas exchange in the alveoli increases the CO 2 content and decreases the O 2 content of alveolar air.

65. Pulmonary gas exchange (contd..) O 2 enters the blood from the alveolar air because the P O2 of alveolar air is greater than the P O2 of incoming blood. The gases diffuse down the pressure gradient.

66. Pulmonary gas exchange (contd..) The two way exchange of gases between alveolar air and pulmonary blood converts deoxygenated blood to oxygenated blood.

67. Pulmonary gas exchange (contd..) The amount of O 2 diffusing into blood each minute depends on: The O 2 pressure gradient between alveolar air and incoming pulmonary blood (alveolar P O2 – blood P O2 ). The total functional surface area of the respiratory membrane.

68. Pulmonary gas exchange (contd..) The respiratory minute volume (respiratory rate per minute times the volume of air inspired per respiration. Alveolar ventilation.

69. Pulmonary gas exchange (contd..) Anything that decreases these factors causes a decreases in the oxygen diffusion into the blood.

70. The henry’s law This law states that the concentration of a gas in a solution depends on the partial pressure of the gas and solubility of the gas as long as the temperature remains constant.

71. The henry’s law (contd..) The ability of the gas to stay in solution is greater when its partial pressure is higher and when the it has a high solubility in water. The higher the partial pressure of a gas over a liquid and the higher the solubility, the more the gas will stay in solution

72. The henry’s law (contd..) When a mixture of gases is in contact with a liquid, each gas will dissolve in the liquid in proportion to its partial pressure gradient. H 2 O H 2 O

73. Gas solubility CO 2 is highly soluble in water than O 2 O 2 is poorly soluble N 2 almost insoluble H 2 O H 2 O H 2 O Carbondioxide Oxygen Nitrogen

74. Gas solubility The solubility of CO 2 is 24 times greater than that of O 2 . Therefore much more CO 2 is dissolved in blood plasma. O 2 is poorly soluble in water and therefore only 1.5% is transported in dissolved form.

75. Transportation of gases (contd..) Fluids can only hold small amounts of gas in solution. This causes most O 2 and CO 2 to rapidly bind with other molecules such as plasma, protein, or water.

76. Transportation of gases (contd..) The binding of gas molecules with another molecule reduces its plasma concentration and more gas can diffuse into plasma.

77. Transportation of gases Blood transports O 2 and CO 2 either as solute of combine with other chemicals. Soon after entering the blood stream O 2 and CO 2 dissolve in plasma.

78. transport of oxygen 1.5 % dissolved 98.5 % bound to haemoglobin Iron in Hb binds to oxygen 4 O 2 molecules per Hb molecule Marieb, Human Anatomy & Physiology, 7 th edition

79. transport of oxygen The portion of haemoglobin contains four atoms of iron, each capable of binding to a molecule of O 2. Each haemoglobin molecule carries 4 O 2 molecules. Each 100ml of oxygenated blood contains the equivalent of 20ml of gaseous O 2.

80. transport of oxygen O 2 does not dissolve easily in water. Only about 1.5% of inhaled O 2 is dissolved in plasma. 98.5% of blood O 2 is bound to haemoglobin in RBCs.

81. transport of oxygen O 2