FERTILIZATION - Preparation of Endometrium (Review) The...

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Preparation of Endometrium (Review) The endometrium has two main parts relating to oocyte binding, the strata basalis and strata functionalis. The endometrium has three main phases: proliferating phase, the secretory phase, and the menstrual phase. The phases correspond with the ovarian cycle. The ovarian cycle actually drives the menstrual cycle through estrogen and progesterone. The menstrual phase occurs when the corpus luteum of the ovarian cycle dies. As a result, progesterone and estrogen is no longer present to support the strata functionalis. Additionally, the proliferative phase of the strata functionalis is initiated by a spike in estrogen by the secondary follicle and mature follicle. The combination of the oocyte and sperm could only occur at mid-cycle when the strata functionalis is at the secreting phase and the cervical mucous is thin enough to let sperm pass. Fertilization At ovulation, meiosis is finished and the secondary oocyte is ready. The sperm begins to swim towards the oocyte and their acrosome ends get ready to digest the zona pellucida. The corona radiata is passed via the pecking-like motion of the sperm as they move towards the egg. After the zona pellucida has been breached by the digestive enzymes of the acrosome, the sperm is able to inject it's genetic material into the egg. As soon as the sperm touches the oocyte, depolarization of the oocyte membrane occurs. This prevents other sperms from binding to the egg. Only one sperm is able to bind to the egg due to this depolarization (fast block to polyspermy).
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Additional barriers to sperm-egg interaction include the hardening of the zona pellucida. The acrosome is unable to digest through this hardened zona pellucida. One sperm-cell interaction has been confirmed, meiosis must finish and the secondary nucleus of the oocyte must turn into haploid female pronucleus (pronucleus refers to the fact that this stage is before the true nucleus has been produced). The male pronucleus and the female pronucleus combine to produce a diploid proper nucleus. Early development - Egg to Blastocyst Egg released from the ovary Near the ovary is the infundibulum which contain finger-like projections known as the fimbriae. The fimbriae directs the egg to the uterine tube where they meet the sperm. The sperm and egg meet at the ampulla (isthmus) of the uterine tube.
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FERTILIZATION - Preparation of Endometrium (Review) The...

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