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Oogenesis in the Marketplace. Patents on Oogenesis. List of terms related to Oogenesis. Editor-In-Chief: C. Michael Gibson, M. It is the female process of gametogenesis. It involves the various stages of immature ova. In mammals , oogenesis occurs in the ovarian follicle of the ovary.
It is interesting to note that such an important process in animal life cycles is done completely without the aid of spindle -coordinating centrosomes. It consists of several processes: oocytogenesis , ootidogenesis and the final maturity to form an ovum. Folliculogenesis is a separate process during ootidogenesis.
The creation of oogonia traditionally doesn't belong to oogenesis, but to the common path of gametogenesis together with spermatogenesis.
The number of ciliated cells in the epithelium of the fimbriae increase increase in ciliation. Sperm are deposited in the upper vagina and must overcome several obstacles to reach an egg in the ampulla of one of the uterine tubes. The egg itself is viable for only about 24 hours.
Table 1 - Obstacles to Sperm Transport. The alkaline seminal fluid temporarily neutralizes the normal acidity pH 4. The composition of cervical mucus changes during menstrual cycle. Sperm can most easily penetrate the thinner E-mucus that predominates during the last few days before ovulation, as opposed to the thicker G-mucus.
Two modes of transport:. Slow — the rest of the sperm swim their way up the last part of the cervical tube, are stored in cervical crypts folds of the cervix , and are slowly released into the uterus over days.
Table 2 - Karyotypes of Germ Cells and Gametes. Primordial germ cell. Primary oocyte. Secondary oocyte. Mature oocyte. Type A spermatogonium. Type B spermatogonium. Primary spermatocyte. Secondary spermatocyte. Aneuploidy is an abnormal number of chromosomes that can result from either unbalanced chromosomal translocations or nondisjunction during meiosis II.
Most chromosomal abnormalities are incompatible with life, however, some combinations do result in live offspring, and trisomies involving chromosomes 13, 14, 15, 21 and 22 groups D and G chromosomes are relatively common birth defects. Oogenesis occurs in the outermost layers of the ovaries. As with sperm production, oogenesis starts with a germ cell, called an oogonium plural: oogonia , but this cell undergoes mitosis to increase in number, eventually resulting in up to one to two million cells in the embryo.
The cell starting meiosis is called a primary oocyte. This cell will begin the first meiotic division, but be arrested in its progress in the first prophase stage.
At the time of birth, all future eggs are in the prophase stage. At adolescence, anterior pituitary hormones cause the development of a number of follicles in an ovary. This results in the primary oocyte finishing the first meiotic division.
The cell divides unequally, with most of the cellular material and organelles going to one cell, called a secondary oocyte, and only one set of chromosomes and a small amount of cytoplasm going to the other cell. This second cell is called a polar body and usually dies. A secondary meiotic arrest occurs, this time at the metaphase II stage. At ovulation, this secondary oocyte will be released and travel toward the uterus through the oviduct.
If the secondary oocyte is fertilized, the cell continues through the meiosis II, completing meiosis, producing a second polar body and a fertilized egg containing all 46 chromosomes of a human being, half of them coming from the sperm.
Spermatogenesis occurs in the wall of the seminiferous tubules, with stem cells at the periphery of the tube and the spermatozoa at the lumen of the tube.
Immediately under the capsule of the tubule are diploid, undifferentiated cells.
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