Lecture 2: Development and Teratogenesis Flashcards
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
What did the tragedy of thalidomide use lead to?
the development of testing pharmaceuticals for adverse effects of fetal development
What are the deformities associated with thalidomide use?
Amelia- complete absence of limbs
Meromelia- partial absence of a limb
Phocomelia- absence of long bones; hands and feet attached to trunk by small bones
deafness, blindness, cleft palate, congenital heart disease, malformations of inner and outer ear, intellectual disability and autism, urogenital and gastrointestinal defects
What is diethylstilbestrol?
DES is a potent estrogen that was used in order to prevent spontaneous abortion and premature labor
What were the effects on women prescribed DES while pregnant?
some studies found an increase in risk for breast cancer; in these patients mammograms and self exams should be encouraged
What were the effects of DES on daughters?
vaginal clear cell adenocarcinoma, two fold increase in vaginal and cervical intraepithelial neoplasm, structural defects in cervix, uterus or fallopian tubes, infertility and poor pregnancy outcomes due to malformation of uterus
What is vaginal clear cell adenocarcinoma?
a rare form of vaginal cancer; seen in DES exposure; incidence peaks at age 20 in DES daughters; the incidence peaks at age 60 for those not exposed to DES
What were the effects of DES on sons?
increased risk for epididymal cysts, microphallus, undescended testicle, testicular hypoplasia, decreased sperm count… but there is no decrease in fertility or increase in cancer risk
What is the amount of Vitamin A that has showed an increase risk in deformity in the fetus?
more than 10,000 units
What deformities could babies born to mothers taking 20,000 units or more of Vitamin A have?
they are 4x more likely to have a cleft lip, cleft palate, hydrocephalus, cardiac deformities
What vitamin A isomer has not been associated with teratogenicity?
beta-carotene
What is isotretinoin?
a vitamin A isomer used in the treatment of cystic acne (Accutane)
What is the percent of neonates that have evidence of abnormalities with use of isotretinoin?
20-30%
What program began to reduce prenatal exposure to isotretinoin?
iPLEDGE program - all female patients of childbearing age must start two forms of birth control 1 month prior to starting, during, and 1 month after isotretinoin use
What must female patients do in order to be prescribed isotretinoin?
they must have two negative urine or blood pregnancy tests and they must have additional test monthly during therapy and one month after end of therapy
What defects can taking ACE inhibitors during the 2nd and 3rd trimester cause?
growth retardation, renal dysfunction, fetal demise, and oligohydraminos
What are the 1st trimester risks associated with ACE inhibitors?
risks are unclear but possible cardiovascular and central nervous system abnormalities
What are some common medication names for ACE inhibitors?
lisinopril, captopril, ramipril, enalapril,