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Conception & Fetal Development Terminology


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Amniotic fluid
the liquid surrounding the fetus in utero. It absorbs shocks, permits fetal movement & prevents heat loss.
the inner solid mass of cells within the morula.
the fetal membrane closest to the intrauterine wall that gives rise to the placenta and continues as the outer membrane surrounding the amnion.
The threadlike structures within the nucleus of a cell that carry the genes.
Rapid mitotic division of the zygote; cells produced are called blastomeres.
Union of sperm & ovum; fertilization.
Decidua basalis
the part of the deidua that unites with the chorion to form the placenta. It is shed in lochial discharge after childbirth.
Dizygotic or two fertilized zygotes, fraternal twins. There are always 2 amnions, 2 chorions, and 2 placentas that may be fused together. These are no more alike than siblings.
outer layer of cells in the developing embryo that gives rise to the skin, nails, and hair.
the early stage of development of the young of any organism. In humans the embryonic period is from 2-8 weeks gestation
Impregnation of ovum by a spermatozoon; conception.
the child in utero from about the 7th - 9th week of gestation until birth
Foramen ovale
special opening between the atria of the fetal heart. Normally closes shortly after birth; if remains open, it requires surgery.
ovum or sperm – contains a haploid number of chromosomes.
A gene contains the coded information that determines an individuals unique characteristics, they are small pieces of DNA and when linked together form chromosomes.
A complete copy of genetic material in an organism.
Karyotyping –
the set of chromosomes arranged in a standard order.
The process of cell division that occurs in the maturation of sperm and ova that decreases their number of chromosomes by one half
the intermediate layer of germ cells in the embryo that gives rise to connective tissue, bone marrow, muscles, blood, lymphoid tissue & epithelial tissue.
Process of cell division whereby both daughter cells have the same number and pattern of chromosomes as the original cell.
Identical twins, develop from one fertilized ovum which then divides. They are same sex and have the same genotype.
Developmental stage of the fertilized ovum in which there is a solid mass of cells.
Normal process of discharging a mature ovum from an ovary approx 14 days prior to onset of menses.
Specialized disk-shaped organ that connects the fetus to the uterine wall for gass and nutrient exchange. Also called afterbirth.
Pulmonary surfactants
Specialized alveolar cells secrete pulmonary surfactants to line the interior of the alveoli. After 32 wk. sufficent amount is present for a good chance of survival. Lecithin (L) is the most critical surfactant required for postnatal lung expansion and can be detected after the 21st week. Detection of these surfactants in amniotic fluid is used to determine the degree of fetal lung maturity. Sphingomyelin (S) remains in amniotic fluid in constant amounts. The L/S ratio should be 2:1 for fetal lungs to be considred mature. This occurs around week 35.
Nongenetic factors that can produce malformations of the fetus.
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.
When life is possible outside of the uterus, after 24th week or a fetal weight of 500 g or more. The limitations on survival outside the uterus are based on CNS function & oxygenation capability of the lungs.
Wharton’s jelly
Yellow-white gelatinous material surrounding the vessels of the umbilical cord.
Yolk sac
This forms the same time as the amniotic cavity, but on the other side of the embryonic disk. It is surrounded by a membrane and helps in transferring maternal nutrients and )2, which have diffused through the chorion to the embryo. Blood vessels, blood cells, and plasma are formed here during 2nd & 3rd week. Then a heartbeat and fetal circulation begin and the yok sac starts to degenerate, and is separated from the embryo by the 5th or 6th week.
Zona pellucida
Transparent inner layer surrounding an ovum.
A fertilized ovum (egg)

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