PSY210H1 Chapter Notes - Chapter 2: Embryonic Stem Cell, Prenatal Development, Zygote
ProfessorAnna Grivas Matejka
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Chapter 2 Prenatal Development and the Newborn Period
⚫ Prenatal Development
⚫ Epigenesist： the emergence of new structures and functions in the course of development.
⚫ gametes (germ cells): reproductive cells—egg and sperm—that contain only half the genetic material
of all the other cells in the body.
⚫ meiosis: cell division that produces gametes.
⚫ conception： the union of an egg from the mother and a sperm from the father
⚫ zygote： a fertilized egg cell
2. Developmental Process
⚫ Embryo: the name given to the developing organism from the 3rd to 8th week of prenatal
⚫ Fetus: the name given to the developing organism from the 9th week to birth
⚫ Mitosis: cell division that results in two identical daughter cells
⚫ embryonic stem cells： embryonic cells, which can develop into any type of body cell
⚫ apoptosis: genetically programmed cell death.
⚫ The four major processes of the underlie the transformation of a zygote into an embryo and the
fetus:1). Cell division—mitosis. 2). Cell migration—the movement of newly formed cells away from
their point of origin. 3). Cell differentiation—all of embryonic stem cells are equivalent and
interchangeable. 4). Death— programmed “cell suicide”.
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3. Early Development
⚫ identical twins: twins that result from the splitting in half of the zygote, resulting in each of the two
resulting zygotes having exactly the same set of genes.
⚫ fraternal twins: twins that result when two eggs happen to be released into the fallopian tube at the
same time and are fertilized by two different sperm; fraternal twins have only half their genes in
⚫ The differentiation of the embedded ball of cells: The inner cell mass becomes the embryo,
and the rest of the cells become an elaborate support system-- amniotic sac and placenta-- that
enables the embryo to develop
⚫ The inner cell mass is to be from a single layer thick to 3 layers thick: 1). The top layer
becomes the nervous system, the nails, teeth, inner ear, lens of the eyes, and the outer surface of the
skin. 2). The middle layer eventually becomes muscles, bones, the circulatory system, the inner
layers of the skin, and other internal organs. 3). The bottom layer develops into the digestive system,
lungs, urinary tract, and glands.
⚫ After the differentiation of the three layers: An U-shaped groove forms down the center of the
top layer. The folds at the top of the groove move together and fuse, creating the neural tube-- One
end of the neural tube will swell and develop into the brain, and the rest will become the spinal cord.
⚫ neural tube: a groove formed in the top layer of differentiated cells in the embryo that eventually
becomes the brain and spinal cord.
⚫ amniotic sac: a transparent, fluid-filled membrane that surrounds and protects the fetus.
⚫ placenta: a support organ for the fetus; it keeps the circulatory systems of the fetus and mother
separate, but as a semipermeable membrane permits the exchange of some materials between them
(oxygen and nutrients from mother to fetus and carbon dioxide and waste products from fetus to
⚫ umbilical cord: a tube containing the blood vessels connecting the fetus and placenta
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