Lecture 2: Development and Teratogenesis Flashcards
(103 cards)
How does movement of sperm occur in fertilization?
occurs primarily through the muscular contractions of the uterus
Where does fertilization usually occur?
in the widest part of the fallopian tube, the ampullary region
What is the first phase of human development?
pre-embryonic
What is the time period for the pre-embryonic stage?
occurs after fertilization and ends with implantation= week 1
When does a zygote start to undergo cellular division and in what developmental stage is this?
at day 3 and this is in the pre-embryonic stage
What are the developmental steps in pre-embryonic stage?
zygote forms as sperm enters the ovum -> forms a morula -> morula accumulates fluid and forms into a blastocyte -> inner cell mass develops into an embryo -> trophoblast (trophoectoderm) develops into placenta -> at day 6 or 7 blastocyte will attach to the uterine wall and begins to digest uterine wall for nourishment -> end with implantation
What is the time period for the embryonic stage?
occurs from day 8 through week 8
What are the developmental steps in the embryonic stage?
uterine wall grows over blastocyte -> tissues continue to become placenta -> amniotic cavity forms -> 3 germ layers begin to differentiate (ectoderm, mesoderm, and endoderm form in blastocyte)
When do the three germ layers give rise to the organs in the embryonic stage?
around day 16
What comprises the endoderm?
digestive tract lining, respiratory tract lining, urethra and bladder, gallbladder, liver and pancreas, thyroid and parathyroid, thymus, kidneys
What comprises the mesoderm?
dermis, muscles, cartilage, bone, blood, other connective tissue, reproductive organs, teeth enamel
What comprises the ectoderm?
epidermis, hair, nails, sweat glands, brain and spinal cord, cranial, spinal nerves, ocular structures, inner ear, nasal and oral and anal epithelium
When do the endoderm, ectoderm, and mesoderm form?
during gastrulation the cells of the blastocyte push inward forming the endoderm, the cells that remain on the outside are the ectoderm, and the mesoderm is formed when additional cells move inward in-between the endoderm and ectoderm
What is the time period for the fetal stage of development?
begins at week 8 of pregnancy and ends at birth
When does rapid weight accelerations occur?
in the fetal stage in the last 2 months of pregnancy
Is teratogenesis dose dependent?
YES! and the mechanism is specific for each teratogen
What is the percentage of fertilizations that end in spontaneous abortion?
31%
What is the critical period for teratogenesis?
between 3-16 weeks due to impairment of organogenesis
What is the effect when there is teratogenic exposure to the fetus during preimplantation?
spontaneous abortion
What is the effect when there is teratogenic exposure to the fetus during the embryonic stage (2-8 weeks)?
spontaneous abortion or structural malformations
What is the effect when there is teratogenic exposure to the fetus during the fetal stage of development (8-40 weeks)?
central nervous system, growth restriction, neurobehavioral, reproductive effects, fetal demise
When do most birth defects occur?
prior to 8 weeks, which is before the first prenatal appointment usually
How can medications in mothers blood cross the placenta to the fetus’s blood?
some of the fetuses blood vessels are contained in tiny hairlike projections (villi) of the placenta that extend into the wall of the uterus; there is only a thin membrane that separates the mothers blood in the intervillous space from the fetus’s blood in the villi; drugs can then pass through the umbilical cord to the fetus
In the 1950’s what was thalidomide used for?
as an effective medication to treat nausea in pregnant women