PSC140Y-VL6

📗 -> 10/05/25: PSC140Y-VL6

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Lecture Slide Link

🎤 Vocab

❗ Unit and Larger Context

Synopsis - presents the germinal, embryonic, and fetal periods of prenatal development

✒️ -> Scratch Notes

Zygote

Fertilized egg that ocntains chromosomes from both sperm and eggs. Germinal stage, 6-12 day, around 2 weeks

• zygote begins to divide over and over again

• After 3 days, the organisms travels through the fallopian tube toward the uterus, transforming into a hollow ball of cells known as a blastocyst

  • Once in the uterus, it implants in the uterine wall (between 6-12 days after conception)

• once implanted, the germinal period is over

• The blastocyst develops into the new organism, with membranes including the placenta, umbilical cord, and amniotic sac

Embryonic stage

Begins at implantation and lasts until the eighth week fo development. The embryo develops basic support systems and organs

• 4th week:
  • the embryo curves (shrimplike)
  • The top of the neural tube will form the brain, heart begins to circulate blood, facial structue emerges, eyes and ears, limb buds and digestive system begin to develop
• 5th week, Rapid brain dev as it grows and differentiates
• 6th week, embryo develops a straighter form, and the head becomes the dominant feature (accomodating the brain)
• 7th week, cartilage begins to form making the embryo more substatial, as well as the muscles and brain wave development. Systems continue to develop and gonads appear
• 8th (final) week, all of the essential structures of the human being are in place
  • circulatory, respiratory, gastrointestinal, … are in place
  • brain linked to nerves and muscles

Fetal Period

At the beginning of the fetal period (around 8-9 weeks):

• embryos weigh about one gram and are about an inch long
• fetus (latin meaning “offspring” or “young one”)

Fetal stage will last from around 9 weeks after conception till birth at around 38 weeks

• Fetus gets bigger (from 5g to normal birth weight)
• Most of the development time is developing the brain
  • For every minute of the fetal period, 250,000 neurons are laid down

Two main tasks:

1. Continue dev of organ systems. Must be functional by birth
2. Continue overall body growth (add fat, and eventually body grows in line with oversize embryo head)

Traditionally

Stages divided into trimesters

First trimester (weeks 1-13)

Baby moves through germinal, and embryonic periods, and into the first four weeks of the fetal period
By 13 weeks: limbs are fully formed down to fingers and fingernails, and external genitals are distinc for boys and girls

Second trimester (weeks 14-26)

Morning sickness fades, and there is a surge in fetal brain growth
Fetal movements large enough to be felt by mother

Third trimester (weeks 27-birth)

Fetus reaches the age of viability, by which point they could survive outside the mother
At this point, fetus weighs around 3 pounds
Fetus can move, but gravity pulls the head down, and eventually get wedged into position pressing against the mother’s cervix

At 38 weeks, the fetus is full-term.

• Wedged in place
• Averages around 7 pounds and 20in length,
• Bones of the skull grow more rigid, but the skull is not fully solid, allowing the skull to compress into a bullet shape to make delivery less difficult

Birth is triggered about 266 days after conception

• The fetus’s brain secretes a hormone that triggers the fetus’s lungs to prepares for breathing air and the mother’s uterus to prepare for labor
  Labor lasts around 8-12 hours

🧪 -> Refresh the Info

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Did a specific aspect of the reading raise questions for you or relate to other ideas and findings you’ve encountered, or are there other related issues you wish had been covered?)

🔗 -> Links

Resources

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Connections

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