| A | B |
|---|
| amnion | a thick fibrous lining, made up of several layers, that helps protect the fetus and forms the inner part of the sac in which the fetus grows |
| amnionic fluid | the specialized fluid that fills the amniotic cavity and serves to protect the fetus |
| blastocyst | the structure that forms about 5 days after fertilization when the dividing cell mass develops a hollow, fluid-filled core |
| chorion | a second layer of thick fibrous tissue that surrounds the amnion |
| chorionic villi | finger-like projections that extend out from the chorion giving it a rough appearance |
| cleavage | the process of mitotic division performed by the zygote |
| decidua | the endometrium that has changed to support a pregnancy |
| dizygotic | fraternal twins that develop from separate egg and sperm fertilization |
| ductus arteriosus | prenatal blood vessel between the pulmonary artery and the aorta that closes functionally within the first 3 or 4 days of life |
| ductus venosus | prenatal blood vessel between the umbilical vein and the inferior vena cava; does not achieve complete closure until the end of the second month of life |
| ectopic pregnancy | a pregnancy that occurs outside of the uterus |
| embryo | the developing conceptus, from weeks 2 through 8 |
| fetus | term for the organism after it has reached the eighth week of life and acquires human likeness |
| foramen ovale | opening between the left and right atria of the fetal heart that closes with the first breath |
| gametogenesis | the formation and development of gametes or germ cells by the process of meiosis |
| monozygotic | identical twins that are derived from one zygote; one egg and one sperm divide into two zygotes shortly after fertilization |
| morula | the solid cell cluster that forms about 3 days after fertilization, when the total cell count has reached 32 |
| teratogen | an agent or influence that causes a defect or disruption in the prenatal growth process |
| Wharton's jelly | a clear gelatinous substance that gives support to the cord andhelps prevent compressions of the cord, which could impair blood flow to the fetus |
| zygote | results when and ovum and a spermatozoon unite (has the full complement of 46 chromosomes) |
