Pediatric and Neonatal Respiratory Care Embryologic Development

2. Pediatric and NeonatalRespiratory CareEmbryologic Development Mary P. Martinasek, BS, RRT

3. Overview • Introduction • Development of the Pulmonary System • Development of the Cardiovascular System • Fetal Circulation • Development of Other Intrauterine Structures

4. Introduction • General Fetal Development • Ovum • Embryo • Fetus • Cellular Development

9. Germ Layers of the Embryo • Endoderm • Respiratory Tract • Mesoderm • Ectoderm

11. General Development

12. Development of the Pulmonary System Embryonic Period Pseudoglandular Period Canalicular Period Saccular and Alveolar Period

13. Embryonic Period • From Conception to 4-6 weeks gestation • Development of proximal airways • 0-24 days one central tube • 24 days - primitive lung bud appears

16. Embryonic Period (continued) • 26-28 days form right and left lung buds • Primitive airways progress in dividing • Lobar bronchi - day 31 • diaphragm starts and is completely developed by 8th week

17. Pseudoglandular Period • 7-16 week gestation • development of conducting airways • 7th week - epiglottis formation starts • 7th week - choana disintegrates and palates development begins

18. Pseudoglandular Period (cont.) • 8th week - vocal cord development begins • Lung resembles gland • Dichotomy results • 11th week - cartilage in airways appears • 12th week - major lobes identifiable

20. Pseudoglandular Period (cont.) • 13th week - goblet cells form • 13th-24th week bronchial glands develop • 10 week - ciliated cells start to appear

21. Canalicular Period • 17-24 weeks gestation • Development of acinus • Tremendous amount of vasularization • Outpouchings appear on wall of bronchioles

22. Canalicular Period (continued) • Two types of cells start to differentiate • Capillaries present but too far away from alveolar cavity

23. Saccular (Alveolar) Period • 24th week - birth • Development of gas exchange units • 25th-26th week alveolar-capillary membrane able to sustain extrauterine life

25. Saccular Period (continued) • 28-29th week terminal sacs line with mature Type II cells - surfactant appears • 34-36th week mature alveolar structure evident • approximately 55 million alveoli (10 m2)

28. Surfactant • Composition • Phospholipids and Protein Phosphoatidylcholine (Lecithin) – Major surfactant appears at 18 weeks and peaks at 38 weeks Sphingomyelin – Surfactant found in the amniotic fluid (decreases after 30 weeks) • Production • Secreted by Type II Alveolar Cells

32. Fetal Lung Fluid • Composition • Different than amniotic fluid • Decreased levels of bicarbonate and protein • Increased levels of Sodium and Chloride

33. Fetal Lung Fluid cont. • Function: Maintain patency Term = 20-30 ml/kg in lungs Production decreases days prior to clinical detection of labor

34. Hazards of Retention • TTN – Transient tachypnea of the newborn • May present as RDS • Grunting, flaring and retracting (GFR)

35. Determination of Lung Maturity • Shake (Foam) Test • LS ratio (Lecithin to sphingomyelin ratio) • Lungs mature when 2:1 (35 weeks) • PG detection (Phosphatidylglycerol) • Lipid • Absent until about 35 weeks gestation

36. Lung Maturity Cont. • FLM or FP Assay – Fluorescence Polarization • Surfactant to Albumin • Quick and Reliable • Lung Profile • L:S and PG detection

38. Acidemia Hypoxia Shock Overinflation Underinflation Pulmonary Edema Mechanical Ventilation Hypercapnia Maternal Diabetes (A,B,C) Smaller of Twins Conditions that DelaysSurfactant Production

39. Maternal diabetes (D, F, and R) Maternal heroin addiction Premature rupture of membranes Maternal hypertension Maternal infection Placental insufficiency Betamethasone or thyroid hormone Abruptio placentae Conditions that AccelerateSurfactant Production

40. Development of theCardiovascular System

41. Development of Cardiovascular System • 3rd week - two tubes surrounded by myocardial tissue • Tubes fuse form single chamber

42. Development of Cardiovascular System(continued) • 4th week - heart begins to beat • Heart begins to twist and fold • Eventually will form four chambers

43. Development of Cardiovascular System(continued) • Sinus venosus - horns at bottom of embryonic heart - will become vena cava’s and portion of right atrium • Truncus arteriosus - will form pulmonary artery and aorta

44. Development of Cardiovascular System(continued) • Bends in middle - S shape • Rapid growth • Development of chambers • Blood flow begins - one way flow

45. Development of Cardiovascular System(continued) • 5th week - heart takes on shape of adult heart • Developing veins and arteries couple the heart to circulatory system • Separate blood paths created

46. Development of Cardiovascular System(continued) • Four chambers formed with openings between the atria and the ventricles • Truncus arteriosus allows blood to exit right ventricle

48. Fetal Circulation • Pressure in the fetal vasculature • Systemic – Low resistance • Placental – Low resistance • Pulmonary – High resistance

49. Characteristics of Fetal Circulation • Normal shunts in the fetus • Foramen ovale – bypasses lung • Ductus arteriosus – bypasses lung • Ductus venosus – bypasses liver