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Origin of the gamets

الكلية كلية طب حمورابي     القسم الكلية ذات القسم الواحد     المرحلة 3
أستاذ المادة سلام عبد الامير يحيى الموسوي       25/10/2019 16:49:10
Formation of Gametes
Gametes form from diploid germ cells. Germ cells separate off from the other cells of the body – somatic cells - very early in development and find their way to the primordial gonads, which develop into the ovaries in the female and the testes in the male. In a complex interaction with somatic cells of the gonad the germ cells first multiply by mitosis, then undergo meiosis to form haploid gametes. (The primordial germ cells are formed in the epiblast during the second embryonic week.)
The Female
The necessity to nurture the embryo and fetus limits the number of female gametes that can be produced. Unless pregnant, a woman of reproductive age will produce 12-14 ova per year, a total of about 400 over a reproductive life-span of nearly 40 years from puberty to the menopause.
Ova are capable of fertilisation by sperm for about 36 hours after they are released from the gonad (‘ovulation’), so in practice a woman is fertile for only a few days a year. To maximise the chance of conception and the survival of the conceptus, each ovulation is embedded in a reproductive cycle of events in the gonads, reproductive tract, and the rest of the body.
The female internal genitalia provide an environment within which sperm may travel to and fertilise the ovum, the conceptus can implant to form a placenta, and the embryo can develop to term.
The female external genitalia provides a means of introducing sperm to the female reproductive tract and the formation of a birth canal through which the fetus may be delivered. Secondary sexual characteristics develop at puberty to facilitate sexual interaction.
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المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .