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05.29.09: The Fetus at Birth


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School's M1 Embryology sequence

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05.29.09: The Fetus at Birth

  1. 1. Author: R. Schumacher, 2009 License: Unless otherwise noted, this material is made available under the terms of the Creative Commons Attribution – Non-Commercial – Share Alike 3.0 License : We have reviewed this material in accordance with U.S. Copyright Law and have tried to maximize your ability to use, share, and adapt it. The citation key on the following slide provides information about how you may share and adapt this material. Copyright holders of content included in this material should contact with any questions, corrections, or clarification regarding the use of content. For more information about how to cite these materials visit Any medical information in this material is intended to inform and educate and is not a tool for self-diagnosis or a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional. Please speak to your physician if you have questions about your medical condition. Viewer discretion is advised: Some medical content is graphic and may not be suitable for all viewers.
  2. 2. Citation Key for more information see: Use + Share + Adapt Make Your Own Assessment Creative Commons – Attribution License Creative Commons – Attribution Share Alike License Creative Commons – Attribution Noncommercial License Creative Commons – Attribution Noncommercial Share Alike License GNU – Free Documentation License Creative Commons – Zero Waiver Public Domain – Ineligible: Works that are ineligible for copyright protection in the U.S. (USC 17 § 102(b)) *laws in your jurisdiction may differ Public Domain – Expired: Works that are no longer protected due to an expired copyright term. Public Domain – Government: Works that are produced by the U.S. Government. (USC 17 § 105) Public Domain – Self Dedicated: Works that a copyright holder has dedicated to the public domain. Fair Use: Use of works that is determined to be Fair consistent with the U.S. Copyright Act. (USC 17 § 107) *laws in your jurisdiction may differ Our determination DOES NOT mean that all uses of this 3rd-party content are Fair Uses and we DO NOT guarantee that your use of the content is Fair. To use this content you should do your own independent analysis  to determine whether or not your use will be Fair. { Content the copyright holder, author, or law permits you to use, share and adapt. } { Content Open.Michigan believes can be used, shared, and adapted because it is ineligible for copyright. } { Content Open.Michigan has used under a Fair Use determination. }
  3. 3. The First Breath: M1 2009 R. Schumacher M1 Embryology Spring 2009 Source Undetermined
  4. 4. Beaker A
  5. 5. Pierre Simon Laplace <ul><li>French mathematician, physicist, and astronomer </li></ul><ul><li>Taught Napoleon - Ecole Militaire de Paris </li></ul><ul><li>Traite de Mecanique Celeste </li></ul><ul><ul><li>1806-7 in Tome IV discusses capillary action and relates surface tension and radius of curvature </li></ul></ul>Source Undetermined
  6. 6. Laplace Relationship <ul><li>∆ P =2γ/r </li></ul><ul><li>Trans-surface pressure = 2(surface tension) / radius of curvature </li></ul>Source Undetermined
  7. 7. Pulmonary Surfactant <ul><li>A liquid film that comes in contact with air covers alveoli, hence surface tension forces are at work in the lung. </li></ul><ul><li>If surface tension can be lowered then the work of breathing should be easier. </li></ul><ul><li>Since the forces are due to molecular forces of attraction, one way to lower surface tension would be to physically separate the molecules. This is what pulmonary surfactant does. </li></ul>
  8. 8. Source Undetermined
  9. 9. <ul><li>If this surface film is compressed the phospholipids will be packed more tightly and more water excluded from the surface. This is ideal: the smaller the radius of curvature the more important surface tension forces become (LaPlace), the smaller the radius of curvature the tighter the surfactant molecular pack and the greater the reduction in surface tension forces. </li></ul>Source Undetermined Source Undetermined
  10. 10. LAWS OF LUNG DEVELOPEMENT <ul><li>Law I- Airways </li></ul><ul><ul><li>The airways are present by the 16th week of intrauterine life </li></ul></ul><ul><li>Law II - Alveoli </li></ul><ul><ul><li>Alveoli develop principally after birth </li></ul></ul><ul><ul><ul><li>At birth the alveoli are primitive </li></ul></ul></ul><ul><ul><ul><li>At birth there are 20,000,000 alveoli, at age eight years- 300,000,000 </li></ul></ul></ul><ul><li>Law III- Vascular </li></ul><ul><ul><li>preacinar arteries follow the development of the airways </li></ul></ul><ul><ul><li>intraacinar arteries appear as alveoli grow </li></ul></ul>
  11. 11. Source Undetermined Source Undetermined
  12. 12. Jean L. Poiseuille Poiseuille, Jean Léonard Marie (1799-1869) was a French physiologist who made a key contribution to our knowledge of the circulation of blood in the arteries. Poiseuille's Law of The Flow of Liquids Through a Tube: Where: l = the length of the tube in cm r = the radius of the tube in cm p = the difference in pressure of the two ends of the tube in dynes per cm2 c = the coefficient of Viscosity in poises (dyne-seconds per cm2) v = volume in cm3 per second Then: v = r 4 p/8cl Source Undetermined
  13. 13. <ul><li>Arteriogram: </li></ul><ul><ul><li>Newborn lacks intra-acinar arteries </li></ul></ul><ul><ul><li>Lacks background “haze” seen in the adult lung </li></ul></ul><ul><ul><li>So resistance is high </li></ul></ul>Source Undetermined
  14. 14. Pulmonary vascular resistance “high” in the newborn because: <ul><li>1.There is a relative lack of alveoli and intraacinar cross sectional area for blood flow (Pouseuille). </li></ul><ul><li>2. In smaller arterioles, pulmonary vascular smooth muscle exists the medial thickness of the arteriole is higher than the adult. (not from laws of development) </li></ul>
  15. 15. Pulmonary vascular resistance low in the newborn because: <ul><li>1. Larger arteries are less muscular in the newborn than in the adult. </li></ul><ul><li>2. Vascular smooth muscle does not exist/extend to the same vascular “level” as it does in the adult. </li></ul>
  16. 16. “ THE FIRST BREATH” <ul><li>What has to happen? </li></ul><ul><ul><li>Think big easy general ideas </li></ul></ul><ul><li>2. How does it happen? </li></ul><ul><li>Think: “In the body, how can I move water from one place to another” </li></ul>
  17. 17. THE FIRST BREATH:  Goal #1: Fluid out, Air in. Source Undetermined
  18. 18. Fetal Pulmonary Fluid: Chloride Secreting Epithelium <ul><li>Prior to birth the lung is a fluid filled organ with transepithelial chloride secretion as the major driving force for active production of lung fluid. There is net flow of fluid out of the lungs. </li></ul><ul><li>Multiple (but not all) studies suggest decrease in Cl pump activity is responsible for decrease in lung water prior to labor. </li></ul>
  19. 19. Fetal Pulmonary Fluid: Na “Reabsorption” <ul><li>At birth lung epithelia change from Cl secreting to Na reabsorption mode. </li></ul><ul><li>ENaC expression is developmentally regulated with peak expression in the alveolar epithelium achieved at term gestation </li></ul><ul><li>α ENaC “pumps” increase activity. Why/ Not clear. Exposure to air?, Stretch?, Steroids?, β adrenergic influences </li></ul><ul><li>(Nasal Na epithelial activity in premies……) </li></ul>
  20. 20. Fetal Pulmonary Fluid: Na “Reabsorption” <ul><li>At birth lung epithelia change from Cl secreting to Na reabsorption mode. </li></ul><ul><li>ENaC expression is developmentally regulated with peak expression in the alveolar epithelium achieved at term gestation </li></ul><ul><li>α ENaC “pumps” increase activity. Why/ Not clear. Exposure to air?, Stretch?, Steroids?, β adrenergic influences </li></ul><ul><li>(Nasal Na epithelial activity in premies……) </li></ul>
  21. 21. What About the Squeeze? <ul><li>1917 radiographic studies suggest compression of thorax in labor. </li></ul><ul><li>1935-56 German texts state lung water is jetted from the mouth with squeezing. </li></ul><ul><li>Recent xray (rabbits) and MRI studies still suggest squeezing plays a role </li></ul>
  22. 22. Source Undetermined
  23. 23. <ul><li>At the time of birth some (but not the majority) of lung water may be squeezed from the fetal lung as the infant passes through the birth canal. This removes some fluid and “loads” the diaphragm (decrease radius of curvature and aligns sarcomeres) for “the first breath.” </li></ul>Source Undetermined
  24. 24. <ul><li>Starling forces at work to clear lung fluid </li></ul>Source Undetermined
  25. 25. Source Undetermined
  26. 26. <ul><li>Functional Residual Capacity is established </li></ul>Source Undetermined
  27. 27. Source Undetermined
  28. 28. Source Undetermined
  29. 29. Source Undetermined
  30. 30. Goal #2. Blood In <ul><li>Fetal circulation: </li></ul><ul><ul><li>“ right-to-left shunting” at the level of the atria and the ductus arteriosus. </li></ul></ul>Source Undetermined
  31. 31. Pulmonary Vascular Resistance Falls at Birth: Why? <ul><li>Mechanical </li></ul><ul><li>Biochemical </li></ul><ul><ul><li>Simple examples pH, pO2 </li></ul></ul><ul><ul><li>More…….. </li></ul></ul>
  32. 32. Source Undetermined
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  36. 36. Source Undetermined (Both Images)
  37. 37. Additional Source Information for more information see: Slide 3: Source Undetermined Slide 5: Source Undetermined Slide 6: Source Undetermined Slide 8: Source Undetermined Slide 9: Source Undetermined Slide 11: Source Undetermined; Source Undetermined Slide 12: Source Undetermined Slide 13: Source Undetermined Slide 17: Source Undetermined Slide 22: Source Undetermined Slide 23: Source Undetermined Slide 24: Source Undetermined Slide 25: Source Undetermined Slide 26: Source Undetermined Slide 27: Source Undetermined Slide 28: Source Undetermined Slide 29: Source Undetermined Slide 30: Source Undetermined Slide 32: Source Undetermined Slide 33: Source Undetermined Slide 34: Source Undetermined Slide 35: Source Undetermined Slide 36: Source Undetermined (Both Images)