Ch10 Flashcards
Fetal Development length
Measured in NUMBER OF WEEKS after fertilization
Pregnancy is 40 WEEKS from the time of fertilization (equates to 9 months / approximately 266 calendar days)
Fetal development stages
Preembryonic Stage (fertilization – 2nd week) Embryonic Stage (end of 2nd week – the 8th week) Fetal Stage (end of the 8th week – until birth)
Preembryonic Stage of Development
Begins with fertilization (also called conception). This occurs with the union of the sperm and ovum & takes place in the ampulla of the fallopian tube. Lasts through the 2nd week Fertilization; cleavage; morula Blastocyst and trophoblast Implantation Human Development
Cleavage
(Cell division) occurs as the zygote is transported toward the uterine cavity via muscular movements
Morula
after 4 cleavages, a 16-cell ball of cells is present (morula)
It reaches the uterine cavity 72 hours after fertilization
cell division continues within the morula, resulting in specialized cells that later form fetal structures
Blastocyst
develops from dividing morula and is a hollow ball of cells (inner cell mass and trophoblast) implants into the uterus
Inner cell mass
will form the embryo and amnion
Trophoblast
outer layer of cells of blastocyst, that will eventually develop into the chorion and helps form the placenta
Embryonic Layers(Primary Germ Layers)
Ectoderm, mesoderm, endoderm
Ectoderm
Central nervous system Peripheral nervous system Special senses Glands Hair & nails
Mesoderm
Skeletal (bones & teeth) Skeletal muscles Urinary organs Circulatory organs Reproductive organs
Endoderm
Respiratory system
Liver
Pancreas
Digestive system
Embryonic Stage
End of 2nd week through the 8th week.
Basic structures of major body organs and main external features are formed
chorion, amnion, amniotic sac
Chorion
Made up of trophoblast cells & a mesodermal lining. Fingerlike projections called CHORIONIC VILLI are on its surface
Amnion
Originates from the ectoderm & is the thin innermost membranous sac enclosing the developing embryo, and containing the amniotic fluid
Amniotic Sac
Made up of the chorion & amnion. Often referred to as the bag of waters
Role of amniotic fluid
Helps maintain a constant body temperature for the fetus
Permits symmetric growth and development
Cushions the fetus from trauma
Allows the umbilical cord to be relatively free of compression
Promotes fetal movement to enhance musculoskeletal development
Hydramnios
Too much amniotic fluid. Associated with maternal diabetes, neural tube defects, chromosomal deviations, malformations of the CNS and or GI tract
Oligohydramnios
Too little amniotic fluid. Associated with uteroplacental insufficiency & fetal renal abnormalities.
Umbilical cord
Formed from the amnion
Lifeline from the mother to the growing embryo
One large vein and two small arteries
Wharton’s jelly surrounding the vein and arteries to prevent compression
At term, the average umbilical cord is 22 inches long and about 1 inch in width
Placenta
Serves as the interface (pass thorough) between the mother and fetus
Induces the mother to bring more food to the placenta
Protects the fetus from immune attack by the mother
Removes waste products from the fetus
Produces hormones that mature the fetal organs
Hormones made by placenta
hCG, hPL, Estrogen Progesterone Relaxin
Fetal Stage
End of the 8th week until birth
Period of dramatic growth & refinement of all organ systems
Fetal circulation
Blood from the placenta to and through the fetus and then back to placenta