Fertilization and Life

The entry of the sperm stimulates the second meiotic division to resume in the oocyte, creating a polar body which is pushed to the side, and a large ovum with all the cytoplasm and 23 single-stranded chromosomes (Applegate, 2000, 421). The sperm then moves to the center of the egg, their nuclear membranes disintegrate, and the chromosomes combine, completing the fertilization process. The zygote now has a full complement of chromosomes, and is the first cell of the future fetus. The effects of fertilization are the creation of a cell with a new combination of chromosomes, half of which came from the sperm, and half of which came from the egg. This will result in a unique individual if

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ific purposes of producing a blastocyst for implantation and development into an embryo. Mitosis after birth results in two cells of comparable size; cleavage results in progressively smaller cells as the number of cells increases. They are contained in a limited space, bound by the zona pellucida. 12.3 Ovulation is prompted by luteinizing (LH) hormone from the anterior pituitary gland, and occurs when a mature follicle at the ovary surface ruptures and releases a secondary oocyte into the peritoneal cavity (Applegate, 2000, 406). The ovulated secondary oocyte is ready for fertilization, and is surrounded by the zona pellucida and the zona radiata. The portion of the follicle that remains in the ovary enlarges and is transformed into a corpus luteum. A corpus luteum is a glandular structure, and it secretes progesterone and some estrogen. If fertilization does not take place, the corpus luteum only remains functional for about 10 days, and then degenerates into a corpus albicans, which is mainly composed of scar tissue and does not produce any hormones. If fertilization of the secondary oocyte does occur, the corpus luteum remains active and secretes progesterone, which stimulates the develop0ment of the uterus a
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Approximate Word count = 1220
Approximate Pages = 5 (250 words per page)

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