1Topic 2.2 Aviation Medicine CHAPTER 02 resp and circ flash notes

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  1. ANATOMY OF THE RESPIRATORY SYSTEM
  2. Vapour pressure is always 47mmHg
  3. ANATOMY OF THE RESPIRATORY SYSTEM
    • THE UPPER RESPIRATORY TRACT
    • nose, mouth, sinuses, pharynx and larynx which filters, warms and humidifies the air (to100% relative humidity).
  4. membranes and hairs in the nasal passage-filters
  5. ANATOMY OF THE RESPIRATORY SYSTEM
    THE UPPER RESPIRATORY TRACT
  6. Air
    • - humidified by the addition of water vapour
    • -warmed to body temperature (37?C) prior to entering the lungs
    • -at 37?C, water vapour pressure is always 47mmHg
  7. ANATOMY OF THE RESPIRATORY SYSTEM
    THE UPPER RESPIRATORY TRACT
  8. Sinuses
    • - aid in temperature and humidity regulation,
    • - add resonance to the voice and
    • -reduce the weight of the skull.
    • - add small amounts of nitrous oxide, a smooth muscle relaxant, to the air during inspiration aiding in the expansion of the lungs.
  9. ANATOMY OF THE RESPIRATORY SYSTEM
    THE UPPER RESPIRATORY TRACT
  10. nitrous oxide
    • -a smooth muscle relaxant,
    • -small amounts produced in the sinus
    • -added to the air during inspiration
    • -aiding in the expansion of the lungs.
  11. ANATOMY OF THE RESPIRATORY SYSTEM
  12. THE THORAX
  13. ANATOMY OF THE RESPIRATORY SYSTEM
    BRONCHI AND BRONCHIOLES
  14. ANATOMY OF THE RESPIRATORY SYSTEM
    • ALVEOLI
    • - (diameter 0.1 ? 0.4mm) with walls one cell layer thick.
    • -Each alveolus has a capillary bed of blood vessels.
    • -The inner walls of the alveoli are bathed in fluid (surfactant) which decreases surface tension to prevent collapse and facilitates gas diffusion.
    • -An average healthy adult has between 250 ? 350 million alveoli giving a surface area of approximately 100 square metres (about the size of a tennis court).
  15. MECHANICS OF RESPIRATION
  16. Consider a balloon enclosed in a flexible flask capable of being expanded (Figure 2?6). When at rest, the pressure inside the balloon equals the ambient pressure in the flask. When the flask is expanded, the balloon's volume is increased thereby decreasing the pressure inside (Boyle?s Law). As a consequence, air flows into the balloon until the pressures are equal. When the flask walls are released, they return to their original shape and the excess air is forced out of the balloon.
  17. Consider now the chest during a breathing cycle. To breathe in, muscular effort of the intercostal muscles raises the ribs and expands the chest cavity, at the same time, the muscular diaphragm is pulled down. During quiet breathing, the diaphragm is the most important muscle in expanding the chest cavity, while intercostals and other muscles are activated during intense exercise and deep breathing.
  18. As lung volume increases, the internal pressure decreases and air will flow into the lungs. To breathe out, the muscles of the diaphragm and rib cage simply return to their resting state. Therefore, for normal respiration, inspiration is ACTIVE and expiration is PASSIVE. This normal cycle can be adversely affected by breathing on some oxygen systems at high altitude.
  19. LUNG VOLUMES--6 litres.
    • Tidal Volume
    • -500ml
    • -volume of air inspired and expired with each normal breath.
    • -varies considerably with activity level and the size of the individual,
    • LUNG VOLUMES
    • Inspiratory Reserve Volume:
    • -3300
    • - extra volume of air that can be inspired over and above the normal tidal volume by a forceful conscious inspiration
    • LUNG VOLUMES
    • Expiratory Reserve Volume:
    • -1000ml
    • - volume of air that can still be exhaled by forceful exhalation after the end of a normal tidal exhalation
    • LUNG VOLUMES
    • Residual Volume:
    • -1200ml
    • -is the volume of air in the lungs that cannot be exhaled
    • -the lungs were completely emptied, they would then collapse.
  20. Respiration is a dynamic process with a constant mixing and exchange of gases between the alveoli and the blood in the alveolar capillaries. The body continuously takes in oxygen and produces carbon dioxide that is eliminated through the lungs. Figure 2?8 shows average equilibrium pressures attained at sea level.
  21. FIGURE 2?8. COMPOSITION OF INSPIRED & EXPIRED AIR (MSL)
  22. GAS EXCHANGE AND TRANSPORTATION
  23. Venous blood
    • -low oxygen pressure of 40mmHg and
    • -a high carbon dioxide pressure of 46mmHg.
    • -PaO2-103 mmHg.
    • -PaCO2-40 mmHg.
    • - This pressure differential causes oxygen to diffuse across the alveolar membrane into the blood plasma, and then across into the red blood cells and onto the haemoglobin, which can transport it to the tissues.
    • - By a similar pressure gradient carbon dioxide will diffuse into the alveoli where it is expelled from the lungs on expiration. After flowing past the alveoli, the partial pressure of oxygen in the blood is raised to 95mmHg and carbon dioxide reduced to 40mmHg.
  24. GAS EXCHANGE AND TRANSPORTATION
    • - transit time for one red blood cell to move past the alveoli is approximately 0.75 seconds
    • - 10?12 seconds for the oxygenated blood to reach the brain.
    • -heart pumps at a rate of about 5 litres per minute,
    • - 60 seconds for the entire blood volume to complete a circuit around the body.
  25. GAS EXCHANGE AND TRANSPORTATION
    • -most of the oxygen is attached to haemoglobin in the red blood cells (forming oxy?heamoglobin: O2 + Hb ?HbO2)
    • - carbon dioxide dissolved in solution in the form of carbonic acid (H2CO3).
  26. GAS EXCHANGE AND TRANSPORTATION
    LUNG GAS EXCHANGE
  27. FIGURE 2?9. LUNG GAS EXCHANGE
  28. GAS EXCHANGE AND TRANSPORTATION
    TISSUE GAS EXCHANGE
  29. FIGURE 2?10. TISSUE GAS EXCHANGE
  30. CONTROL OF RESPIRATION
    - most important factors governing the control of respiration are:
  31. a) CO2 dissolved in the blood which determines blood pH, and
    b) Partial pressure of oxygen in the arterial blood (arterial oxygen tension, PAO2).
  32. CONTROL OF RESPIRATION
    • Primary control mechanisms
    • - central nervous system providing both automatic and voluntary control.
    • - Chemoreceptors in the brain stem
    • - stretch receptors in the lungs are the normal control mechanisms for respiration,
  33. CONTROL OF RESPIRATION
    • Secondary control
    • - peripheral chemoreceptors in the aorta and carotid arteries.
  34. FIGURE 2?11. CONTROL OF RESPIRATION
  35. CONTROL OF RESPIRATION
    • THE CENTRAL NERVOUS SYSTEM Respiratory centre
    • - brain stem (Pons and Medulla) and the cerebral cortex.
    • -sensitive to the carbon dioxide levels in the blood
    • - sensitive to the carbon dioxide levels in cerebrospinal fluid or CSF
  36. CONTROL OF RESPIRATION
    Ph Blood
  37. Normally 7.3 ? 7.4 (slightly alkaline)
    Is directly related to the carbon dioxide level
  38. CONTROL OF RESPIRATION
    • -The conversion of CO2 to an acid and back again is facilitated by an enzyme called carbonic anhydrase
    • CO2 + H2O ? H2CO3 ? H+ + HCO3?
  39. CONTROL OF RESPIRATION
    • Carbonic anhydrase
    • - enzyme than facilitates conversion of CO2 to an acid and back again
  40. CONTROL OF RESPIRATION
    • Holding your breath
    • -tissues will continue to produce carbon dioxide so the blood becomes more acidic (more H+).
    • - respiratory centre detects the increase in acidity and you will automatically breath faster and deeper.
  41. CONTROL OF RESPIRATION
    • Exercise
    • - arterial carbon dioxide does not rise.
    • - not known what stimulates the respiratory centre to cause you to breathe faster and deeper during exercise.
  42. CONTROL OF RESPIRATION
    • Hyperventilation
    • -reduced dissolved carbon dioxide
    • -rate and depth of breathing increases
    • - CO2 is eliminated more rapidly from the lungs.
  43. CONTROL OF RESPIRATION
    • THE CEREBRAL CORTEX
    • - conscious control may over?ride the chemoreceptor and respiratory centre in control of respiration, to a point.
    • -In circumstances of fear or stress, the cortical control may cause hyperventilation regardless of the other control mechanisms.
  44. It is possible to voluntarily hold your breath or over?breathe if desired.
    • It is possible to hyperventilate willingly to the extent that you pass out,
    • however it is impossible to resist the automatic urge to take a breath after a period of breath holding.
  45. CONTROL OF RESPIRATION
    • STRETCH RECEPTORS
    • - in the lungs send information about lung expansion to the respiratory centre.
    • -As the lungs expand on inhalation, the stretch receptors send nerve impulses to the respiratory centre inhibiting further inspiration.
    • The stretch receptors are not used during normal respiration but become increasingly active with laboured breathing. This is referred to as the Herring?Breuer Reflex.
  46. CONTROL OF RESPIRATION
    Herring?Breuer Reflex
  47. CONTROL OF RESPIRATION
    • CHEMORECEPTORS
    • -carotid arteries and aorta sense the oxygen level in arterial blood.
    • -stimulated by a reduced oxygen level,
    • -signalling the respiratory centre when alveolar PO2 drops below about 55 mmHg, equivalent to an altitude of about 10,000 feet.
    • -result in automatic hyperventilation, called the ?hypoxic ventilatory response?.
  48. CONTROL OF RESPIRATION
    ?hypoxic ventilatory response
  49. CONTROL OF RESPIRATION
    PO2 55 mmHg, equivalent to an altitude ?feet.
  50. 10,000 feet
  51. CIRCULATION
    • Primary Function:
    • - maintain homeostasis (a consistent internal environment for optimum cellular and body functions).
    • - accomplished by the blood transporting the necessary gases (eg., O2 and CO2), hormones and a vast number of various chemical substances throughout the body.
  52. CIRCULATION
    • Secondary Functions:
    • - nutrition,
    • - waste excretion,
    • - protection from disease,
    • - body heat balance.
  53. CIRCULATION
    • THE BLOOD
    • - 5?7 percent of body weight,
    • - 5 litres in an average sized person.
  54. CIRCULATION
    • Extracellular
    • -Plasma
    • -55%
    • - largely water, electrolytes and large molecules
  55. CIRCULATION
    • Intracellular
    • -(45%)
  56. CIRCULATION
    • Red Blood Cells:
    • -5 million RBC/ml blood
    • -transport O2
    • -haemoglobin (Hb) which reacts with O2 to form Oxy?haemoglobin
    • -100ml of blood can carry about 20ml of O2).
    • -Arterial blood, which is saturated with O2, has a bright red colour while de?oxygenated blood appears as darker red to purple in colour.
  57. CIRCULATION
    -100ml of blood can carry about ?O2
  58. 20ml of O2).
  59. CIRCULATION
    -The haemoglobin molecule
  60. - has four binding sites on central chemical molecules called haeme, w
    • -each haeme containing one atom of ferrous iron (Fe2+).
    • -One oxygen molecule can attach to each atom of ferrous iron in a reversible reaction as described below,
    • - thus delivering oxygen to the tissues.
  61. Hb4 + 4O2 ? Hb4(O2)4
  62. CIRCULATION
    White Blood Cells:
  63. - contains between 5,000?10,000 white blood cells per ml of blood.
    • - Their primary function is protection from disease and infection.
    • - key role in the inflammatory response and tissue healing.
  64. CIRCULATION
    Platelets:
  65. - to coagulate blood and maintain the integrity of the circulatory system.
    • -ability to join together forming a barrier to prevent further bleeding,
    • - and form clots together with large amounts of a substance called fibrin.
  66. CIRCULATION
    • Plasma:
    • -water and various proteins, electrolytes and waste chemicals.
    • -The water is used to dissolve the other substances and allow the blood cells to flow easily through the smallest blood vessels.
  67. ANATOMY OF THE CIRCULATORY SYSTEM
    • Pulmonary Circuit:
    • - right side of the heart, the pulmonary arteries, the lungs and the pulmonary veins.
    • -Deoxygenated blood enters the right atrium of the heart from the vena cava.
    • -BP in the vena cava and right atrium is normally close to atmospheric pressure.
    • -BP in this circuit is much lower than the systemic circui
    • -Pulmonary artery systolic pressure averaging around 25 mmHg
    • -Pulmonary artery diastolic pressure averaging around 8 mmHg.
  68. Systemic Circulation:
    • - systemic circulation comprises about 84% of the total blood volume
    • -systolic pressure of about 120 mmHg
    • -diastolic pressure of about 80 mmHg,
  69. FIGURE 2?12. SCHEMATIC CIRCULATION
  70. THE VASCULAR TREE
    • a) arteries,
    • b) arterioles,
    • c) capillaries,
    • d) venules, and
    • e) veins.
  71. IGURE 2?13. CAPILLARY BED
  72. PHYSIOLOGY OF THE HEART
  73. -Both sides of the heart contract (beat) simultaneously, the atria about 0.25 seconds before the ventricles
    - Timing of the contractions is automatic and controlled electrically by two nodes of nerve tissue located on the inside surface of the right heart (the sino?atrial and atrio?ventricular nodes).
  74. Cardiac Output: Two factor
    • - heart rate,
    • -how much blood the heart pumps with each contraction (stroke volume) govern the output from the heart.
    • -The reflex control of the autonomic nervous system maintains the heart rate and stroke volume appropriate to the body's requirements.

    • Blood Pressure:
    • 120/80mmHg measured at heart level, where 120 represents the systolic pressure and 80 represents the diastolic pressure.
  75. a) large arteries: 100mmHg (called mean arterial pressure),
    • b) medium arteries: 85mmHg,
    • c) capillaries: 10?30mmHg,
    • d) small veins: 9mmHg, and
    • e) large veins: 0?8mmHg.
  76. CONTROL OF BLOOD FLOW
    • For blood flow to occur, pressure gradients are required. There are five main factors governing this flow:
    • a) work of the heart (cardiac output), b) peripheral resistance,
    • c) elasticity of artery walls,
    • d) pressure receptors, and
    • e) blood volume and viscosity.
  77. FIGURE 2?15. CONTROL OF BLOOD FLOW
  78. Peripheral Resistance: As the arteries become smaller, peripheral resistance to flow increases and the pressure decreases. Additionally, peripheral vasoconstriction adds to the rapid reduction of pressure in the peripheral circulation.
  79. Elasticity: The post?ventricular contraction of artery walls is a primary factor in the maintenance of blood flow.
  80. Pressure Receptors: Pressure receptors (baroreceptors) are located in two main arteries (aorta and carotid). These receptors provide information to the brain to either increase or decrease cardiac output or to change the resistance of blood vessels dependent on the blood pressure, to maintain blood pressure homeostasis. They are designed to maintain blood pressure as hydrostatic pressure in the circulation varies with posture under the influence of Earth?s normal gravity.
  81. Blood Volume and Viscosity: The thicker or more viscous the blood, the more difficult it is to pump through the blood vessels. A major factor in blood viscosity is the number of red blood cells present relative to the amount of plasma. This is a factor in dehydration.

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1Topic 2.2 Aviation Medicine CHAPTER 02 resp and circ flash notes
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