Term
Time range of male meiosis.
Evolution of male gamete. |
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Definition
Begins at puberty and goes throughout adult life.
Spermatogonia - primary spermatocytes - (Meiosis I) - secondary spermatocytes - (Meiosis II) - 4 spermatids |
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Term
| Time range of female meiosis. |
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Definition
- Meiosis I begins at 5th month of fetal life and arrests at synapsis/crossing over of Meiosis I at least until puberty and some through perimenopause.
- Meiosis I complete around the time of ovulation due to luteinizing hormone surge
- Arrests again in metaphase of Meiosis II
- Fertilization triggers completion of Meiosis II
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Term
| What leads to aneuploidy? |
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Definition
| Nondisjunction in meiosis I or II. |
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Term
| Explain the nondisjunction errors in femal meiosis I in advancing maternal age. |
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Definition
| Prolonged female meiosis I is vulnerable to problems with synapsis, where premature resolution of cross overs (chiasmata) leads to maternal and paternal homologues aligning separately on the metaphase plate. Also, premature degradation of the cohesions holding sister chromatids together can contribute to errors in distribution. |
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Term
What nondisjunction type is most common in men and equal to the nondisjunction rate in women.
What percent of autosomal aneuploidies are due to egg? Sperm? |
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Definition
Sex chromosome aneuploidies occur at the same rate in sperm and egg because of the limited region of homology that supports synapsis of X and Y.
80% of autosomal aneuploidies occur in egg. 20% in sperm. |
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Term
| What is a difference in mitosis and meiosis (especially female meiosis) that contributes to aneuploidies? |
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Definition
| The spindle "tensional" checkpoint functions poorly in meiosis. Anaphase begins even if chromosomes are not properly aligned with tension exerted by each spindle pole. |
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Term
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Definition
| sac of digestive enzymes that will bore through the zona pellucida |
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Term
| Mitochondrial sheath (of sperm cell) |
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Definition
| provides energy to drive flagellum |
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Term
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Definition
| microtubule motor-based structure that drives swimming movement of sperm |
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Term
zona pellucida
3 important functions |
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Definition
matrix layer around the oocyte
- Sperm recognition/ binding site; contact triggers acrosome reaction
- block to polyspermy: upon fusion, the cortical reaction (release of cross-linking enzymes from cortical granules) causes rapid cross-linking and impermeability of the ZP to further sperm entry
- barrier to premature/ectopic implantation: hatching of blastocyst from the ZP is needed for blastocyst to be able to implant
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Term
| Fertilization process (of the sperm) |
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Definition
- Acrosome reaction - penetrates ZP
- Fusion of sperm and egg cell membranes
- entire sperm enters egg (mitochondria and tail degenerate, while paternal centrosome is preserved)
- sperm nucleus decondenses to male pronucleus
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Term
Fertilization process (of the egg)
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Definition
- Fusion of egg and sperm cell membranes triggers cortical reaction (exocytosis of enzymes that cross-link ZP to prevent polyspermy); A second minor polyspermy block is caused by a rapid temporary depolarization of egg membrane.
- Fusion triggers meiosis II of egg
- egg nucleus is now the female pronucleus
- fusion of pronuclei completes formation of zygote
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Term
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Definition
| products of zygotic cell mitosis |
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Term
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Definition
| Formed after about 3 days, a grape-like cluster of cells which undergoes compaction, formation of a smooth ball of cells, via formation of cell-cell adhesions called adheren junctions, especially in the outermost layer (involves protein called E-cadherin) |
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Term
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Definition
| Formed by fluid secretion into morula to form a blastocyst cavity. Outer cells of blastocyst are trophoblast cells - will become fetal chorion (placenta) |
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Term
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Definition
| ball of cells within the blastocyst at the "embryonic pole". Will subdivide into epiblast (form the embryo proper and amniotic sac) and hypoblast (will become the yolk sac). Blastocyst will hatch from ZP at 5-6 days. |
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Term
| Where is implantation most common and ok? |
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Definition
| Implantation is in the uterine endometrium, most commonly at the posterior position; other positions within the main body or fundus (rounded top) are ok |
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Term
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Definition
| implantation that occurs too close to the cervix in which the placenta grows over the cervix. Prepared for as hemmorhage and death of mother and baby can result. |
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Term
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Definition
- Binding of trophoblast to uterine endometrium triggers proliferation of the trophoblast with maintenance of a cytotrophoblast and formation of an invasive syncytiotrophoblast
- Syncytiotrophoblast secretes enzymes that degrade the uterine wall (eg. matrix metalleoproteinases), and actively pulls the entire blastocyst into the wall of the uterus via adhesion and migration
- Uterine wall has been prepared by hormones and responds to trophoblast invasion by decidual reaction (accumulation of glycogen and lipids that are engulfed by trophoblast to nourish embryo)
- Uterine wall responds by angiogenesis and endometrial gland secretion for nourishment of embryo
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