2. Neonatal Pulmonary Development and Transition

Question 1

What are Reid’s 3 Laws of development of the human lung?

Answer 1

1. bronchial tree developed by 16th week gestation
2. alveoli increase in # until age 8 and in size until growth of chest wall is complete
3. airway arteries/veins follow development of conducting bronchial tree, alveolar blood vessels follow development of alveoli

Question 2

Q1 when does the embryonal stage happen?

Q2 what is the significance of the embryonal stage?

Answer 2

Q1A embryonal stage happens day 26-day 52

Q2A significance: development of trachea and major bronchi

Question 3

Q1 when does the pseudoglandular stage happen?

Q2 what is the significance of the pseudoglandular stage?

Answer 3

Q1A pseudoglandular stage happens day 52-16th week gestation
Q2A significance: development of rest of conducting airways ending in terminal bronchioles

Question 4

Q1 when does the canalicular stage happen?

Q2 what is the significance of the canalicular stage?

Answer 4

Q1A canalicular stage happens 17th-26th week gestation

Q2A significance: development of vascular bed and framework of respiratory acinar (alveoli sacs)

Question 5

Q1 when does the saccular stage happen?

Q2 what is the significance of the saccular stage?

Answer 5

Q1A saccular stage 27th-36th week gestation

Q2A significance: increased complexity of saccules (alveolar saccules)

Question 6

Q1 when does the alveolar stage happen?

Q2 what is the significance of the alveolar stage?

Answer 6

Q1A 36th week gestation to term

Q2A significance: development of alveoli

Question 7

Q1 how many branches of the bronchioles are present in the embryonal phase?
Q2 what other two structures form during this stage and by what week?
Q3 what is a Congenital Diaphragmatic Hernia?
Q4 what is a Tracheal Esophageal Fistula?

Answer 7

Q1A 10 branches on the right and 9 branches on the left (tube separates into trachea and esophagus)
Q2A right and left pulmonary arteries and veins, diaphragm developed by 7th week
Q3A diaphragm fails to develop fully by week 7 and abdominal contents herniates into chest cavity
Q4A a defect where abnormal connection between the trachea and esophagus exists

Question 8

what other structures develop during the pseudoglandular stage? (hint: 6 answers)

Answer 8

• cilia
• goblet cells
• submucosal glands
• smooth muscle cells
• lymphatics
• airway cartilage

Question 9

Q1 what other structures are developed during the canalicular phase? (hint: 3 answers)
Q2 what type of cells form and differentiate at this point?
Q3 can you describe the alveoli and surfactant at this stage?
Q4 can the fetus survive at this stage? If so how far along during gestation can the baby survive?

Answer 9

Q1A acinar units containing respiratory bronchioles, alveolar ducts and alveolar sacs
- capillaries develop and increase in number
- smooth muscle formed
Q2A type 1 and 2 pneumocytes differentiate, immature surfactant appears
Q3A primitive alveoli with minimal surfactant
Q4A survival of fetus is possible during the late canalicular stage at 22-24 weeks gestation

Question 10

Q1 what potential is markedly increased during the saccular phase?
Q2 what types of cells further differentiate? How does this affect surfactant?

Answer 10

Q1A marked increase in potential of gas exchange and surface area
Q2A type 1 and 2 pneumocytes further differentiate and results in increased storage/production of surfactant

Question 11

Q1 what happens to the alveoli during the alveolar stage? (hint: what increases?)
Q2 how many alveoli are present by term?

Answer 11

Q1A alveoli increase in number and surfactant production

Q2A 50-150 million alveoli by term

Question 12

Q1 how many alveoli are babies born with?
Q2 how many alveoli are present by 8 years old?
Q3 what happens to lung volume during postnatal lung development?

Answer 12

Q1A babies are born with 50 million alveoli
Q2A increases to 300 million alveoli by age 8
Q3A lung volume will increase 23 fold (surface area for gas exchange)

Question 13

Q1 what factors adversely affect lung development during premature birth? (hint: 2 answers)
Q2 how does this affect ventilation?
Q3 what is pulmonary hypoplasia?
Q4 what causes this? (hint: 3 answers)

Answer 13

Q1A immature and underdeveloped lungs, immature surfactant leading to respiratory distress
Q2A alveoli become stiff therefore, hard to open and ventilate (high pressures can destroy further growth process)
Q3A incomplete development of the lungs leading to reduced # and size of alveoli
Q4A caused by anything preventing the chest wall/lungs from developing such as:
- chest wall compression (ex./ diaphragmatic hernia)
- oligohydramnios (lack of amniotic fluid therefore not helping to distend alveoli and aid in growth)
- diminished respirations in utero (with no respirations baby cannot train respiratory muscles)

Question 14

Q1 what is the shape of type 1 alveolar cells?
Q2 what is the purpose of type 1 alveolar cells? (hint: 3 answers)
Q3 what is the shape of type 2 alveolar cells?
Q4 what is the purpose of type 2 alveolar cells? (hint: 1 answer)
Q5 what are the 2 key reasons why surfactant is important?

Answer 14

Q1A squamous pneumocytes
Q2A thin/gas permeable for diffusion, barrier against leakage, 97% of lung surface area
Q3A cuboidal pneumocytes
Q4A principle structure in surfactant management (production, secretion, storage, reuse)
Q5A surfactant lines the surface of alveoli to decrease surface tension preventing alveolar collapse and improves compliance for easier breathing/ventilation

Question 15

Q1 what 3 factors help to stimulate surfactant production?
Q2 when does surfactant production start and when is it adequate during gestation?
Q3 what 2 key points help to accelerate endogenous production?

Answer 15

Q1A beta-adrenergic agonists, prostaglandins, epidermal growth factor
Q2A production begins at 24-28 weeks and adequate by the end of the 34th week gestation
Q3A maternal steroid administration and fetal stress can accelerate production

Question 16

Q1 what glucocorticoids are most commonly given for maternal steroid administration? (include dosage)
Q2 what is the purpose of maternal steroid administration?
Q3 what are the 2 indications for this type of therapy?
Q4 when should this therapy be given for best outcome and when are benefits greatest?

Answer 16

Q1A Betamethasone 2 doses 12 mg given IM 24 hours apart (most common) OR Dexamethasone 4 doses 6 mg given IM 12 hours apart
Q2A purpose is to accelerate development of type 1 and 2 pneumocytes and increases surfactant production
Q3A all women at high risk of preterm delivery between 24-34 weeks and over 34 weeks gestation when there is evidence of pulmonary immaturity
Q4A best if given 48 hours before delivery and benefits are greatest if delivery within 7 days

Question 17

Q1 how much fluid is secreted from fetal lungs per day?
Q2 what is secreted from type 2 cells creating lung fluid?
Q3 where is the fluid moved? where does it go?
Q4 what do fetal lung volumes approximate?
Q5 what is the lung fluid regulated by? How does this structure do this?
Q6 why is this regulation important? (hint: 2 answers)

Answer 17

Q1A fetal lungs secrete 250-300 ml per day
Q2 active secretion of Cl- from type 2 cells into alveolar space is accompanied by Na+ and water creating lung fluid
Q3A fluid moves up the trachea and is either swallowed or goes into amniotic fluid (this is why amniotic fluid can tell us lung maturity)
Q4A fetal lung volumes approximate FRC post birth
Q5A regulated by larynx, acts as a one-way valve and creates pressure gradient of 1 cmH2O in the lungs to keep the lungs distended
Q6A essential for lung growth and decrease in fetal lung fluid (oligohydramnios) can result in pulmonary hypoplasia as there is no fluid to help lungs grow

Question 18

Q1 what causes the lungs to switch from net secretion to net reabsorption? (hint: 2 answers)
Q2 what happens to interstitial lung liquid?

Answer 18

Q1A with onset of labour, circulating epinephrine switches the lungs from net secretion to absorption of some fluid but not all so baby can breathe air in/out. Also, vaginal squeeze of thorax contributes to small portion of lung fluid reabsorption
Q2A interstitial lung liquid moves into pulmonary circulation (giving baby self transfusion of fluid) or drains via the lung lymphatics

Question 19

Q1 what is the primary job of the placenta?
Q2 is this organ a low or high resistance/pressure system?
Q3 how does transport occur? does the blood mix?
Q4 what is fetus -> mother circulation responsible for?
Q5 what is mother -> fetus circulation responsible for?

Answer 19

Q1A facilitates gas and nutrient exchange between maternal and fetal circulation
Q2A low resistance organ with low pressure
Q3A transport occurs through simple and facilitated diffusion, where blood does NOT mix
Q4A carbon dioxide clearance and elimination of wastes (urea, hormones)
Q5A oxygenation and nutrients

Question 20

Q1 how many arteries and veins are located in the umbilical cord?
Q2 what is the role of umbilical arteries?
Q3 what is the role of the umbilical vein?
Q4 what is Wharton’s Jelly?

Answer 20

Q1A 2 arteries and 1 vein
Q2A umbilical arteries carry deoxygenated blood from baby off internal iliac arteries to mother (placenta)
Q3A umbilical vein carries oxygenated blood from mother (placenta) to baby
Q4A Wharton’s jelly is a gelatinous substance that protects vessels and prevents kinking

Question 21

Q1 what is the first organ to be formed during fetal development?
Q2 when during gestation is this structure complete?
Q3 when are cardiac contractions detectable?

Answer 21

Q1A the heart
Q2A complete by week 8, fully functional, all chambers complete, including valves and vessels
Q3A cardiac contractions are detectable by day 22

Question 22

Q1 what are the 3 fetal shunts?

Q2 when must all 3 shunts close?

Answer 22

Q1A ductus arteriosus, foramen ovale and ductus venosus

Q2A all 3 shunts must close shortly after birth

Question 23

Q1 what happens at the ductus venosus?

Q2 why do we not want blood to travel through the liver? (hint: 2 answers)

Answer 23

Q1A oxygenated blood from umbilical vein bypasses the liver through the ductus venosus
Q2A liver will use up a lot of the O2 when we want the blood to go to the brain AND liver does NOT function a lot in utero therefore, mom does most filtering

Question 24

Q1 what is the foramen ovale and where is it located?
Q2 which way does blood flow move? which lung has higher pressures?
Q3 what happens at the foramen ovale?

Answer 24

Q1A one-way flap in the atrial septal wall
Q2A blood flow from R to L atrium, pressure in R lung > pressure in L lung
Q3A blood bypasses the lungs because of the high right sided pressures

Question 25

Q1 what is the ductus arteriosus?
Q2 which way does blood flow move?
Q3 what is bypassed and why does this occur?

Answer 25

Q1A connection between the PA and the aorta shunting blood away from the lungs
Q2A blood flow moves from R to L
Q3A blood bypasses the lungs because of the high PVR (small amount goes to the lungs)

Question 26

Q1 where does gas exchange occur?
Q2 do fetal lungs participate in gas exchange? why or why not?
Q3 which 2 structures are low pressure circuits?
Q4 why is PVR high?
Q5 how much blood roughly goes through the lungs?
Q6 which organs receive the “best blood” in utero?

Answer 26

Q1A in the placenta
Q2A fetal lungs do NOT participate in gas exchange due to being filled with fluid
Q3A placenta and SVR are low pressure circuits
Q4A physical compression due to low lung volumes and hypoxic pulmonary vasoconstriction
Q5A 13-25% of blood goes to the lungs
Q6A brain and the heart receive the best blood

Question 27

Q1 what does the large gradient between maternal and fetal PaO2 help with?
Q2 what are the 3 advantages of fetal Hb?

Answer 27

Q1A promotes transfer of O2 and higher Hb concentration in fetus to allow baby to oxygenate
Q2A greater affinity for O2 as fetal circulation is relatively hypoxic, higher SaO2 for same PaO2 than adult Hb and left shift of oxyhemoglobin dissociation curve

Question 28

Q1 what is the relative O2 concentration in the umbilical vein?
Q2 what is the normal O2 saturation in utero?

Answer 28

Q1A about 70%

Q2A about 60-70% in utero

Question 29

Q1 what happens when the umbilical cord is clamped?
Q2 when a baby takes the first few breaths several changes happen, can you list these 5 changes?
Q3 why is the umbilical cord cut between 2 clamps? (hint: 2 answers)

Answer 29

Q1A removes low pressure system (placenta) and increases SVR
Q2A - lungs inflate stretching pulmonary parenchyma physically expanding pulmonary vessels
- gas exchange occurs as amniotic fluid is being cleared
- increase PaO2, pH, decrease CO2
- decrease in vasoconstricting agents
- dilation of pulmonary vessels therefore, PVR is decreased
Q3A to avoid open circulation and bleeding

Question 30

Q1 during fetal transition, are the pressures increased or decreased in the left and right side of the heart?
Q2 what does this help to do? (hint: 2 answers)
Q3 what happens to the pressure in the aorta?
Q4 what does this help to do? (hint: 2 answers)

Answer 30

Q1A decrease pressure in right heart and increase pressure in left heart
Q2A flap of foramen ovale closes and increase in blood flow to the lungs
Q3A pressure in aorta increases and becomes higher than PA pressures
Q4A less shunting through ductus arteriosus and PaO2 increases

Question 31

Q1 when does functional closure of the ductus arteriosus occur?
Q2 what does this closure help to do? (hint: 3 answers)
Q3 what does the ductus arteriosus become once it closes? how long does this take?
Q4 what happens if the DA does not close?

Answer 31

Q1A closure begins to start at birth
Q2A causes increased PaO2, decreased flow and decreased prostaglandins
Q3A becomes ligamentum arteriousum in about 3 months
Q4A becomes a patent ductus arteriosus (PDA)

Question 32

Q1 where is preductal arteriosus blood flow measured?
Q2 where is post ductal arteriosus blood flow measured?
Q3 if pre ductal > post ductal, what does this indicate?
Q4 what does this mean? (hint: 2 answers)

Answer 32

Q1A measured at the right hand
Q2A measured in the lower limbs or left hand
Q3A this indicates a shunt is present causing oxygenated and deoxygenated blood to mix
Q4A a patent ductus arteriosus is present (open) and PA pressures are > than systemic pressures

Question 33

Q1 what is the affinity of fetal Hb?
Q2 what is this affinity less affected by?
Q3 what is the P50 for term babies? what about in adults?
Q4 why does fetal Hb have a higher affinity for O2 than maternal Hb?

Answer 33

Q1A higher affinity of hemoglobin than adult (left shift)
Q2A presumably less affected by 2,3 DPG
Q3A P50 for term babies = 20 mmHg, adults = 27 mmHg
Q4A allows the fetal Hb to attract oxygen from the mother

Question 34

Q1 what is the fetal Hb at term?
Q2 by 1-2 months what does the Hb drop to?
Q3 by 6 months what does the Hb drop to?
Q4 after 6 months, what happens to fetal Hb?
Q5 if a baby needs a blood transfusion will adult or fetal blood be used? why?

Answer 34

Q1A term = 85%
Q2A 1-2 months = drops to 50%
Q3A 6 months = drops to 5%
Q4A after 6 months fetal Hb drops to normal adult levels (<2%)
Q5A adult blood is used to facilitate transition to adult Hb levels

Question 35

Q1 why is Erythromycin eye ointment used after birth?
Q2 why is a vitamin K injection IM given after birth?
Q3 what happens to the umbilical cord after birth?
Q4 why is newborn screening tests done after birth?
Q5 what is the congenital heart disease oxygen saturation test value to determine if a baby has this disease or not?
Q6 what are we looking for from the baby in a hearing test?

Answer 35

Q1A an antibiotic to prevent eye infections
Q2A needed for clotting to prevent bleeding and babies have very little vitamin K @ birth
Q3A cord will eventually fall off
Q4A blood test from babies heal to send off and test for over 100 different diseases/disorders including metabolic, endocrine, sickle cell, CF, severe combined immune deficiency
Q5A should be > 90% and if not = congenital heart disease may be present
Q6A looking or some type of movement or response to sound/noise