Term
week 1
stage and main events |
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Definition
pre-implantation (pre-embryonic) period
formation of morula; development of morula into a blastocyst; implantation |
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Term
week 2-8
stage and main events |
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Definition
embryonic period (period of greatest sensitivity to teratogens (environmental factors that cause birth defects))
formation of germ layers that give rise to major body systems (gastrulation); formation of central nervous system (neurulation); formation of the general body form (embryonic folding); formation of major body systems |
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Term
week 8 - 38
stage and main events |
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Definition
fetal period
structural and functional growth of major body systems |
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Term
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Definition
| beginning of human development when a sperm invades an ovum, which usually occurs in the uterine tube |
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Definition
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Definition
rapid mitotic cell division without increasing in size; continues until there are 16 daughter cells (blastomeres) contained within the zona pellucida
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Term
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Definition
| Any of the cells resulting from the cleavage of a fertilized ovum during early embryonic development |
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Term
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Definition
| The strong membrane that forms around an ovum as it develops in the ovary. The membrane remains in place during the egg's travels through the Fallopian tube. To fertilize the egg, a sperm must penetrate the thinning zona pellucida. If fertilization takes place, the membrane disappears as it becomes a blastocyst to permit implantation in the uterus. |
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Term
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Definition
compact sphere of cells resulting from cleavage of zygote
~4days |
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Definition
| the morula becomes a blastocyst as it enters the uterine cavity because a fluid-filled space (blastocoele or blastocyst cavity) forms within the sphere of cells |
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Definition
(aka blastocyst cavity)
fluid-filled center region of a blastocyst |
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Definition
inner cell mass concentrated at the embryonic pole of the blastocyst and will form the embryo proper
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Definition
| the outer cell mass, which surrounds the embryoblast and blastocyst cavity, will contribute to the placenta |
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Term
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Definition
| when implantation occurs outside the uterine cavity, usually due to the slow transit of the ovum along the uterine tube. |
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Definition
| Implantation continues for about a week as the blastocyst sinks into the endometrium. The trophoblast differentiates into two layers and the embryoblast differentiates into two layers that together form a flat bilaminar disc. |
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Term
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Definition
| outer layer of trophoblast that invades the endometrium, and eventually forms lacunae that make contact with maternal blood vessels (sinusoids), establishing utero-placental circulation |
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Definition
| inner single layer of trophoblast that provides new cells for the syncytiotrophoblast. |
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Definition
| layer of embryoblast that differentiates into cells adjacent to the blastocyst cavity. |
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Definition
| layer of embryoblast that differentiates into cells adjacent to the cytotrophoblast. |
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Definition
| Develops within the epiblast. Epiblast cells adjacent to the cytotrophoblast at the embryonic pole specialize to secrete amniotic fluid, and are called amnioblasts. |
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Term
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Definition
| The hypoblast sends out a layer of cells that form the exocoelomic (Heuser’s) membrane along the inner surface of the blastocyst cavity. The cavity lined by the membrane is now called the exocoelomic cavity or primary yolk sac (the source of nutrition for the embryo before the placenta is functional). |
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Definition
| a layer of loose connective tissue produced by the exocoelomic membrane, which fills the space between the cytotrophoblast, and the primary yolk sac and amniotic cavity. |
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Term
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Definition
Lacunae form within the extraembryonic mesoderm, which coalesce to form the extraembryonic coelom.
This space (now called the chorionic cavity) grows to completely surround the bilaminar germ disc (developing embryo), primitive yolk sac, and amniotic cavity. |
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Term
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Definition
| Growth of the chorionic cavity “pinches off” the primary yolk sac and a smaller secondary or definitive yolk sac is created. |
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Definition
The connecting stalk is the extension of extraembryonic mesoderm that connects the embryo to the cytotrophoblast, and forms the umbilical cord.
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Term
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Definition
| Gastrulation is the process that results in the formation of three embryonic germ layers. |
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Term
primitive streak
+ 3 main body axes of the embryo |
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Definition
Gastrulation begins with the formation of the primitive streak, a thickened line at the caudal (posterior) end of the epiblast that establishes three main body axes of the embryo – craniocaudal, dorsoventral, left-right |
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Definition
| The primitive node is a raised area that surrounds the primitive pit at the cranial (anterior) end of the streak. |
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