22.3 Human Embryonic and Fetal Development Flashcards
allantois
The allantois is an extraembryonic membrane involved in waste removal and gas exchange in early development. It later helps form the umbilical cord in humans.
amnion
The amnion is an extraembryonic membrane that surrounds the embryo, forming the amniotic sac. It is filled with amniotic fluid, which protects and cushions the developing baby.
blastocyst
A blastocyst is a hollow ball of cells that forms from the morula. It has an inner cell mass that develops into the embryo and an outer layer (trophoblast) that helps form the placenta. It implants in the uterus to begin pregnancy.
chorion
The chorion is an extraembryonic membrane that surrounds the embryo and contributes to the formation of the placenta. It develops finger-like projections called chorionic villi that help with nutrient and gas exchange between the mother and the developing baby.
embryo
An embryo is the early stage of development after fertilization and before becoming a fetus. It begins as a zygote and undergoes rapid cell division, forming key structures like the germ layers and organs. This stage typically lasts until about the 8th week of pregnancy.
fetus
A fetus is the stage of human development that begins after the 8th week of pregnancy, following the embryonic stage. During this time, the major organs and body systems continue to develop and mature, and the fetus begins to take on a more recognizable human form. This stage lasts until birth.
HCG
hCG (human chorionic gonadotropin) is a hormone produced by the placenta after implantation of the fertilized egg. It helps maintain the corpus luteum, which continues producing progesterone to support the early stages of pregnancy. hCG is also the hormone detected in pregnancy tests.
teratogen
A teratogen is any substance, organism, or environmental factor that can cause birth defects or abnormal development in a fetus. Examples include certain drugs, infections, radiation, and chemicals. Exposure to teratogens during critical periods of fetal development can lead to physical or developmental abnormalities.
trophoblast cells
Trophoblast cells are the outer layer of cells of a blastocyst. They play a crucial role in the implantation of the embryo into the uterine wall and help form part of the placenta. These cells also secrete human chorionic gonadotropin (hCG), which supports pregnancy in its early stages.
umbilical cord
The umbilical cord is a flexible, tube-like structure that connects the developing fetus to the placenta. It contains two arteries and one vein, which carry oxygen and nutrients from the placenta to the fetus and remove waste products. The cord is essential for fetal growth and development throughout pregnancy.
yolk sac
The yolk sac is an early extraembryonic membrane that provides nutrients to the developing embryo before the placenta is fully functional. It also plays a role in the formation of the blood cells and the germ cells (which later become eggs or sperm). In humans, the yolk sac is small and its role is more significant during the first few weeks of pregnancy.
