Gestation & Timeline
Name the 3 phases of gestation in order, including their weeks.
1. Fertilization: 1-3 weeks
2. Embryonic: 4-7 weeks
3. Fetal: 8 weeks to term
During week 4-7, name at least 3 structures that begin to develop
Upper/lower jaw, umbilical cord, tongue, tracheal rings, and diaphragm
Surfactant is a mixture of these two types of substances
Phospholipids and proteins
During week 4, what does the heart chamber form and what becomes recognizable?
Bulbus cordis, ventricular bulge, and atrial bulge are formed. Truncus Arteriosus becomes recognizable.
How many umbilical arteries and veins are present, and which direction does each carry fetal blood?
2 umbilical arteries - fetus to placenta
1 umbilical vein - placenta to fetus
Greatest chance of malformation because the majority of organogenesis occurs during it
What week does major lung lobes differentiate?
Week 12
Which cells secrete surfactant, and what is its main function?
Reduce surface tension at the alveolar level
What happens during week 6?
The septum secundum and a flat from the septum primum form the foramen ovale
Which fetal vessel contains the highest oxygen saturation, and approximately what are its saturation and PaO2?
Umbilical vein:
- Sat: 80%
- PaO2: 28 - 30 mmHg
A pregnancy is considered term at this gestational age.
40 +/- 2 weeks
This stage of lung development occurs from 7-16 weeks and involves bronchial buds branching to form the conducting airways.
Pseudoglandular stage
Identify the surfactant:
1. Major surfactant; concentration rises at 18 weeks and peaks at 38 weeks
2. Found in amniotic fluid; rises at 18 weeks and peaks at 30 weeks
1. Lecithin (phosphatidylcholine)
2. Sphingomyelin
Which aortic arches disappear?
Aortic arches 1, 2, and 5
Trace the highest-oxygen fetal blood beginning at the placenta through the point where it reaches the IVC
Placenta -> umbilical vein -> ductus venosus -> IVC
What baby has the best chance of surviving premature birth?
Black females: GOOD
White males: BAD
A fetus is 20 weeks gestation. Which stage of lung development is occurring, and what TWO major changes characterize it?
The canalicular stage
- acinus develops
- connective tissue decreases
- vasculature increases
Compare surfactant produces before 34 weeks with surfactant after 34 weeks. Include the pathway and stability.
Before 34 weeks:
- Methylation pathway
- immature
- unstable
- very short half-life
- hypoxia or acidosis can cause production to cease
After 34 weeks:
- Cholination pathway
- very mature
- stable
- produced until death
Match the aortic arches to its adult structure:
- arch 3
- arch 4
- arch 6
3 - carotid arteries
4 - aortic arch on the LEFT and brachiocephalic on the RIGHT
6 - pulmonary circulation
Blood begins with an O2 saturation of approximately 80% in the umbilical vein What happens to the saturation after mixing in the IVC and then after additional mixing in the RA?
Umbilical vein: 80% -> IVC: 67% -> RA: 62%
Put these in order from earliest to latest:
- primitive respiratory movement
- major lung lobes differentiated
- pulmonary capillary bed growth
- primitive alveoli form
- upper/lower jaw, tracheal rings and diaphragm begin developing
NAME THE WEEK EACH ONE HAPPENS
1. Week 4-7: jaw, tracheal rings, diaphragm, etc.
2. Week 12: major lung lobes differentiated
3. Week 18: primitive respiratory movement
4. Week 22-24: primitive alveoli form
5. Week 26-28: pulmonary capillary bed growth
Identify each developmental period:
1. 17-24 weeks; gas-exchange potion of the lung develops
2. Birth - 8 years; alveoli increase in number and size
3. 7-16 weeks; conducting airways form
1. Canalicular
2. Postnatal
3. Pseudoglandular
An infant has an L/S ration of 0.8. Interpret the result. Explain what and L/S ration of 1.5 and 2.3 would indicate.
- 0.8: severe lung immaturity; RDS likely
- 1.5: RDS may or may not develop
- 2.3: mature lungs; rarely associated with respiratory distress
What happens in week 8 to the heart?
cardiac structures are complete; blood flows through fetal circulation pathway
Trace the pathway that allows the fetus‘ better-oxygenated IVC blood to reach the brain, beginning with the placenta.
placenta -> umbilical vein -> ductus venosus -> IVC -> RA -> foramen ovale -> LA -> LV -> ascending aorta -> brain
the brain receives the blood with the highest PaO2 aside from the umbilical vein.