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Definition
| Cells surrounding the oocyte that sperm must penetrate before fertilization |
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| Outer Layer of oocyte: penetration of this layer by a sperm results in a zona reaction, making it impermeable to other sperm |
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| Area at head of sperm carrying important enzymes that react with the oocyte upon fertilization to make the zona pellucida impermeable to other sperm |
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| A period of conditioning after ejaculation in the uterus or uterine tubes, lasting about 7 hours, in which the sperms acrosome is altered. Sperm cannot fertilize until this has occured |
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Definition
| When the acrosome of a sperm binds to the zona pellucida of the oocyte, binding occurs that releases enzymes that cause complex changes which makes fertilization possible |
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| Six Phases of Fertilization |
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Definition
Passage of Sperm through Corona Radiata
Penetration of Zona Pellucida
Fusion of Plasma Membranes of oocyte and sperm
Completion of 2nd meiotic division & formation of female pronucleus (from decondensation of 1n chromosomes)
Formation of male pronucleus (by dissolution of sperm tail inside now-mature oocyte)
As pronuclei fuse into singe 2n aggregation, ootid becomes zygote |
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| 5 results of fertilization |
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Definition
Stimulation of oocyte to complete 2nd meiotic division
Restores diploidy of chromosomes (to 46)
Variation of species by chromosomal mingling
Determines gender of embryo
Begins metabolic activation of ootid and cell division of zygote |
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Term
| Dispermy (or generally, Polyspermy) |
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Definition
| When a egg is fertilized by more than one sperm |
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Definition
| Having a third set of chromosomes, usually due to polyspermy. Fatal. |
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| The product of fertilization, after pronuclear membranes have intermixed. From 1 cell to about 8 cells. |
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| What each cell is called in the zygote stage. During each division of this stage, the blastomeres simply get smaller (the zygote does not get larger as a whole). It is still wrapped in the zona pellucida. |
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Definition
| After the zygote has reached about 9 cells, the blastomeres change shape (compaction) and tighten against the wall of the zona pellucida. These cells become the outer cell layer of the morula. |
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Term
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Definition
| About 3 days in, 12 to 32 blastomere stage, when blastomeres form a dense sphere due to compaction. Inner cell mass not visually separated from outer cell mass, but outer cell mass (touching zona pellucida) will become trophoblast, inner cell mass will become embryoblast. Still in fellopian tubes |
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Term
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Definition
Forms around day 4, after the morula has entered the uterus. Forms as fluid flows in from uterus to inside of morula, changing it into a blastocyst. Separates thin outer-cell layer from inner cell mass
AKA Blastocele |
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Term
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Definition
| Starts about day 4. Thin outer cell wall (trophoblast) and distinct inner cell mass (embryoblast). During this stage the zona pellucida disintegrates (about day 5). Enters and implants onto uterine lining during this stage (about day 6) |
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Term
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Definition
| Inner cell mass of blastocyst - becomes embryo. By day 8 or so, splits into the amnion (layer of cells adjacent to cytotrophoblast at the embryonic pole) and the Epiblast, with a fluid-filled Amniotic cavity in between. |
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Definition
| Thin outer wall of blastocyst - becomes placenta |
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Definition
| The embryo and all it's parts (yolk sack, placenta, etc). Can be called a conceptus only after implantation into the uterine lining |
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Definition
| When aneuploidy in some chromosome is not copied correctly in an early zygotic cleavage stage, and some cell lines are aneuploid and some are normal (diploid). With triploidy 21 (Down's Syndrome), for example, mosaic means that only some cells are affected - so the condition is not as bad |
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Term
| When does the blastocyst attach to the endometrial epithelium? |
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Definition
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Definition
| Immediately after the blastocyst implants onto the endometrial epithelium, the trophoblast quickly proliferates and separates into this and the syncytiotrophoblast. The cytotrophoblast is the trophoblast analogue - a thin layer of cells around the embryoblast and the blastocele. |
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Term
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Definition
| A division of the trophoblast that begins seeping into the endometrial epithelium, where the cell walls combine to form a large polynucleated protoplasmic mass. By day 7 (1 day after implantation) it has encompassed maternal arterial and veinous capillaries and is supplying blood to the developing blastomeres. By the time the extra-embryonic coelomic space is forming it has totally surrounded the cytotrophoblast and the entire conceptus is on the other side of the endometrial lining of the uterus. |
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Definition
| The normal point of implantation, also the area of the embryoblast |
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| In the uterus, the thin, external layer of cells that is where the blastocyst attaches |
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Definition
| The thick smooth muscle layer just past the endometrium in the uterus |
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Definition
| The primary endoderm of the embryoblast, this cell layer appears about day 7 on the embryoblast facing the blastocele. Will form the ventral side of the embryo. |
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Definition
| In fertilization, when uterine endometrial cells die a preprogrammed death as the syncytiotrophoblast cells of the conceptus approach to replace them |
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Definition
| Connective tissue cells around the implantation site that accumulate glycogen and lipids, then die, and in so doing provide nutrients for the syncytiotrophoblast when it absorbs that area |
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Definition
| When the syncytiotrophoblast expanded sufficiently, it develops small vacuoles which merge into lacunae (hollow cavities) by day 11. Blood begins to flow through these cavities from the acquired arterial and veinous capillaries - and the conceptus has a supply of 02 and a method of waste disposal! |
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Term
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Definition
| A layer of cells that differentiates from the embryoblast, it forms the embryonic-pole facing lining of the amniotic cavity |
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Definition
| Formed from the embryoblast, the epiblast is a layer of large cells beneath the amniotic cavity, above the blastocystic cavity (now called the exoceolomic cavity). Will form the dorsal side of the embryo. |
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Definition
| After the first week (when amniotic cavity begins to form), the new name for the blastocystic cavity (to reduce ambiguity) |
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Definition
| Grows out from the sides of the hypoblast and grows around the inside of the cytotrophoblast, and soon separates from it, leaving an interstitial space known as the extraembryonic mesoderm. When the separation is complete (by day 12) this membrane becomes known as the endoderm! |
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Definition
| Cells that form between the cytotrophoblast and the exoceolomic membrane, separating the two |
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Definition
| Consisting of the epiblast (thick, upper layer below the amniotic cavity) and the hypoblast (thin, lower layer above the exoceolomic cavity). Forms the embryo. |
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Term
| Primary umbilical vessicle (yolk sac) |
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Definition
| New name for exoceolomic cavity (itself once just the blastocystic cavity), once it's separated from the cytotrophoblast by the extraembryonic mesoderm. |
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Term
| Extraembryonic Coelem (or chorionic cavity) |
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Definition
| Small cavities that form within the extraembryonic mesoderm that merge together to form a large fluid-filled space between the cytotrophoblast and the exocoelomic lining (or by now the extra-embryonic endodermal lining of the umbilical vesicle / yolk sac). This fluid filled space is almost continuous, except for one area where the mesoderm still connects the amniotic cavity to the cytotrophoblast. This becomes the umbilical cord. |
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Term
| Extraembryonic somatic mesoderm |
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Definition
| The extraembryonic coelom splits the extraembryonic mesoderm into two layers - this one surrounds the trophoblast (as before) |
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Term
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Definition
| The extraembryonic somatic mesoderm (the one lining the trophoblast) and the two layers of the trophoblast (the cytotrophoblast and the syncytiotrophoblast) form the Chorion, which forms the wall for the chorionic sac |
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Term
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Definition
| Surrounded by the chorion, this is everything - the embryo, the amniotic sac, and the umbilical vesicle (yolk sac), all of which are now suspended by the connecting stalk |
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Term
| Primary umbilical vesicle |
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Definition
| Drops off the original umbilical vesicle and remains connected by a small amount of mesoderm (the secondary umbilical vesicle remains where the original was, but is somewhat smaller) |
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Term
| Secondary umbilical vesicle (or secondary yolk sac) |
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Definition
| Remnants from the pinching off of the primary umbilical vesicle (or primary yolk sac) by the chorionic cavity |
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