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Conception & Fetal Development
Audio Glossary
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- Acrosomal reaction
- Breakdown of the hyaluronic acid in the corona radiata by enzymes from the heads of sperm; allows one spermatozoon to penetrate the ovum zona pellucida.
- Amnion
- The inner of the two membranes that form the sac containing the fetus and the amniotic fluid.
- Amniotic fluid
- The liquid surrounding the fetus in utero. It absorbs shocks, permits fetal movement, and prevents heat loss.
- Bag of waters (BOW)
- The membrane containing the amniotic fluid and the fetus.
- Blastocyst
- The inner solid mass of cells within the morula.
- Capacitation
- Removal of the plasma membrane overlying the spermatozoa's acrosomal area with the loss of seminal plasma proteins and the glycoprotein coat. If the glycoprotein coat is not removed, the sperm will not be able to penetrate the ovum.
- Chorion
- The fetal membrane closest to the intrauterine wall that gives rise to the placenta and continues as the outer membrane surrounding the amnion.
- Chromosomes
- The threadlike structures within the nucleus of a cell that carry the genes.
- Cleavage
- Rapid mitotic division of the zygote; cells produced are called blastomeres.
- Cotyledon
- One of the rounded portions into which the placenta's uterine surface is divided, consisting of a mass of villi, fetal vessels, and an intervillous space.
- Decidua basalis
- The part of the decidua that unites with the chorion to form the placenta. It is shed in lochial discharge after childbirth.
- Decidua capsularis
- The part of the decidua surrounding the chorionic sac.
- Decidua vera (parietalis)
- Nonplacental decidua lining the uterus.
- Diploid number of chromosomes
- Containing a set of maternal and a set of paternal chromosomes; in humans, the diploid number of chromosomes is 46.
- Ductus arteriosus
- A communication channel between the main pulmonary artery and the aorta of the fetus. It is obliterated after birth by rising PO2 and changes in intravascular pressure in the presence of normal pulmonary functioning. It normally becomes a ligament after birth but sometimes remains patent (patent ductus arteriosus, a treatable condition).
- Ductus venosus
- A fetal blood vessel that carries oxygenated blood between the umbilical vein and the inferior vena cava, bypassing the liver; it becomes a ligament after birth.
- Ectoderm
- Outer layer of cells in the developing embryo that gives rise to the skin, nails, and hair.
- Embryo
- The early stage of development of the young of any organism. In humans the embryonic period is from about 2 to 8 weeks' gestation and is characterized by cellular differentiation and predominantly hyperplastic growth.
- Embryonic membranes
- The amnion and chorion.
- Endoderm
- The inner layer of cells in the developing embryo that give rise to internal organs such as the intestines.
- Fertilization
- Impregnation of an ovum by a spermatozoon; conception.
- Fetus
- The child in utero from about the seventh to ninth week of gestation until birth.
- Foramen ovale
- Special opening between the atria of the fetal heart. Normally, the opening closes shortly after birth; if it remains open, it can be repaired surgically.
- Gamete
- Female or male germ cell; contains a haploid number of chromosomes.
- Gametogenesis
- The process by which germ cells are produced.
- Haploid number of chromosomes
- Half the diploid number of chromosomes. In humans there are 23 chromosomes, the haploid number, in each germ cell.
- Lanugo
- Fine, downy hair found on all body parts of the fetus, with the exception of the palms of the hands and the soles of the feet, after 20 weeks' gestation.
- Meiosis
- The process of cell division that occurs in the maturation of sperm and ova that decreases their number of chromosomes by one-half.
- Mesoderm
- The intermediate layer of germ cells in the embryo that gives rise to connective tissue, bone marrow, muscles, blood, lymphoid tissue, and epithelial tissue.
- Mitosis
- Process of cell division whereby both daughter cells have the same number and pattern of chromosomes as the original cell.
- Morula
- Developmental stage of the fertilized ovum in which there is a solid mass of cells.
- Placenta
- Specialized disk-shaped organ that connects the fetus to the uterine wall for gas and nutrient exchange. Also called afterbirth.
- Postconception age periods
- Period of time in embryonic/fetal development calculated from the time of fertilization of the ovum.
- Teratogen
- Nongenetic factor that can produce malformations of the fetus.
- Trophoblast
- The outer layer of the blastoderm that will eventually establish the nutrient relationship with the uterine endometrium.
- Umbilical cord
- The structure connecting the placenta to the umbilicus of the fetus and through which nutrients from the woman are exchanged for wastes from the fetus.
- Vernix caseosa
- A protective, cheeselike, whitish substance made up of sebum and desquamated epithelial cells that is present on the fetal skin.
- Wharton's jelly
- Yellow-white gelatinous material surrounding the vessels of the umbilical cord.
- Zygote
- A fertilized egg.
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