HDF 351 Lecture Notes - Lecture 3: Trisomy, Neural Tube, Twin
18 Sep 2018
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Prenatal Development and Childbirth:
Prenatal Development:
From conception to birth at about 38 weeks gestational age.
Occurs along a predetermined schedule and involves incredible differentiation and rapid
growth.
Three Periods of Prenatal Development:
Germinal (period of the zygote): weeks 1-2
• From conception to implantation in the uterus
Embryonic: weeks 2-8
• From implantation until the major organs and structures are differentiated
Fetal: weeks 8-birth (~40 weeks)
• Brain development, refinement, and growth of major organs.
Conception:
An ovum ripens in one of the woman’s ovaries over a period of about 28 days.
When it is ready for fertilization, ovulation occurs – the ovum is released into the fallopian tube
and travels to the uterus.
Without fertilization within 24 hours, the ovum disintegrates.
More than one ovum may be released and fertilized by different sperm, resulting in dizygotic
twins (di = two, zygotic = fertilized egg) if two ova were released.
If a fertilized egg splits into two, monozygotic twins (mono = one, zygotic = fertilized egg) are
formed.
Zygote: The Fertilized Egg
The zygote floats down from the fallopian tube and towards the uterus.
Smaller than a pinhead
3 weeks:
• Blastocyst – implants in uterus.
Document Summary
From conception to birth at about 38 weeks gestational age. Occurs along a predetermined schedule and involves incredible differentiation and rapid growth. Germinal (period of the zygote): weeks 1-2: from conception to implantation in the uterus. Embryonic: weeks 2-8: from implantation until the major organs and structures are differentiated. Fetal: weeks 8-birth (~40 weeks: brain development, refinement, and growth of major organs. A(cid:374) o(cid:448)u(cid:373) ripe(cid:374)s i(cid:374) o(cid:374)e of the (cid:449)o(cid:373)a(cid:374)"s o(cid:448)aries o(cid:448)er a period of a(cid:271)out 28 days. When it is ready for fertilization, ovulation occurs the ovum is released into the fallopian tube and travels to the uterus. Without fertilization within 24 hours, the ovum disintegrates. More than one ovum may be released and fertilized by different sperm, resulting in dizygotic twins (di = two, zygotic = fertilized egg) if two ova were released. If a fertilized egg splits into two, monozygotic twins (mono = one, zygotic = fertilized egg) are formed.
