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1、Pediatric and Neonatal Respiratory Care Embryologic Development,Mary P. Martinasek, BS, RRT,Overview,Introduction Development of the Pulmonary System Development of the Cardiovascular System Fetal Circulation Development of Other Intrauterine Structures,Introduction,General Fetal Development Ovum Em
2、bryo Fetus Cellular Development,Germ Layers of the Embryo,Endoderm Respiratory Tract Mesoderm Ectoderm,General Development,Development of the Pulmonary System,Embryonic Period Pseudoglandular Period Canalicular Period Saccular and Alveolar Period,Embryonic Period,From Conception to 4-6 weeks gestati
3、on Development of proximal airways 0-24 days one central tube 24 days - primitive lung bud appears,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,Pseudoglandu
4、lar Period,7-16 week gestation development of conducting airways 7th week - epiglottis formation starts 7th week - choana disintegrates and palates development begins,Pseudoglandular Period (cont.),8th week - vocal cord development begins Lung resembles gland Dichotomy results 11th week - cartilage
5、in airways appears 12th week - major lobes identifiable,Pseudoglandular Period (cont.),13th week - goblet cells form 13th-24th week bronchial glands develop 10 week - ciliated cells start to appear,Canalicular Period,17-24 weeks gestation Development of acinus Tremendous amount of vasularization Out
6、pouchings appear on wall of bronchioles,Canalicular Period (continued),Two types of cells start to differentiate Capillaries present but too far away from alveolar cavity,Saccular (Alveolar) Period,24th week - birth Development of gas exchange units 25th-26th week alveolar-capillary membrane able to
7、 sustain extrauterine life,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),Surfactant,Composition Phospholipids and ProteinPhosphoatidylcholine (Lecithin
8、) Major surfactant appears at 18 weeks and peaks at 38 weeksSphingomyelin Surfactant found in the amniotic fluid (decreases after 30 weeks)Production Secreted by Type II Alveolar Cells,Fetal Lung Fluid,Composition Different than amniotic fluid Decreased levels of bicarbonate and protein Increased le
9、vels of Sodium and Chloride,Fetal Lung Fluid cont.,Function: Maintain patencyTerm = 20-30 ml/kg in lungsProduction decreases days prior to clinical detection of labor,Hazards of Retention,TTN Transient tachypnea of the newborn May present as RDS Grunting, flaring and retracting (GFR),Determination o
10、f 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,Lung Maturity Cont.,FLM or FP Assay Fluorescence Polarization Surfactant to Albumin Quick and Reliable Lung Pr
11、ofile L:S and PG detection,Conditions that Delays Surfactant Production,Acidemia Hypoxia Shock Overinflation Underinflation Pulmonary Edema,Mechanical Ventilation Hypercapnia Maternal Diabetes (A,B,C) Smaller of Twins,Conditions that Accelerate Surfactant Production,Maternal diabetes (D, F, and R) M
12、aternal heroin addiction Premature rupture of membranes Maternal hypertension,Maternal infection Placental insufficiency Betamethasone or thyroid hormone Abruptio placentae,Development of the Cardiovascular System,Development of Cardiovascular System,3rd week - two tubes surrounded by myocardial tis
13、sue Tubes fuse form single chamber,Development of Cardiovascular System (continued),4th week - heart begins to beat Heart begins to twist and fold Eventually will form four chambers,Development of Cardiovascular System (continued),Sinus venosus - horns at bottom of embryonic heart - will become vena
14、 cavas and portion of right atrium Truncus arteriosus - will form pulmonary artery and aorta,Development of Cardiovascular System (continued),Bends in middle - S shape Rapid growth Development of chambers Blood flow begins - one way flow,Development of Cardiovascular System (continued),5th week - he
15、art takes on shape of adult heart Developing veins and arteries couple the heart to circulatory system Separate blood paths created,Development of Cardiovascular System (continued),Four chambers formed with openings between the atria and the ventricles Truncus arteriosus allows blood to exit right v
16、entricle,Fetal Circulation,Pressure in the fetal vasculature Systemic Low resistance Placental Low resistance Pulmonary High resistance,Characteristics of Fetal Circulation,Normal shunts in the fetus Foramen ovale bypasses lung Ductus arteriosus bypasses lung Ductus venosus bypasses liver,Fetal Circulation,Flow chart of the most oxygenated fetal blood Bypasses liver - ductus venosus Bypasses lungs - foramen ovale,Fetal Circulation (continued),Flowchart of least oxygenated fetal blood Small amount feed lungs (high resistance) Most bypasses lungs - ductus arteriosus,
