A -year-old healthy nulligravid woman presents for a preconception evaluation. She asks detailed questions regarding early pregnancy development. To accurately explain the normal progression of fetal and placental development, arrange the following physiological milestones in the correct chronological order from earliest to latest based on estimated gestational age.
- 1Implantation of the blastocyst into the secretory endometrium
- 2Initiation of embryonic cardiac contractions
- 3Transition of primary progesterone synthesis from the corpus luteum to the placenta
- 4Complete fusion of the amnion and chorion membranes
- 5Initial secretion of surfactant by fetal type II pneumocytes
Answer
The correct chronological sequence of fetal and placental developmental milestones is: 1) Implantation of the blastocyst, 2) Initiation of embryonic cardiac contractions, 3) Transition of progesterone synthesis to the placenta, 4) Complete fusion of the amnion and chorion, and 5) Initial secretion of surfactant.
Gestational age is standardly calculated from the first day of the last menstrual period, meaning fertilization typically occurs at 2 weeks of gestation. Blastocyst implantation into the endometrium happens 6-7 days post-fertilization (approximately 3-4 weeks gestation). The cardiovascular system is the first to function, with cardiac contractions starting around 5.5-6 weeks. The luteal-placental shift, where the placenta becomes the primary source of progesterone, occurs between 7 and 10 weeks. The expanding amnion completely fuses with the chorion by 14-16 weeks. Finally, fetal type II pneumocytes begin the initial secretion of surfactant into the alveoli between 20 and 24 weeks.
Step-by-Step Solution
Key Concept
Normal gestational milestones follow a predictable timeline: implantation (~3-4 weeks), cardiac activity (~5.5-6 weeks), luteal-placental shift (~7-10 weeks), amnion-chorion fusion (~14-16 weeks), and initial surfactant production (~20-24 weeks).
Estimated Time:2m 0s