Oocyte development in embryonic stage & nutrition of oocyte.

What Do you mean by Carnegie stages 8 and 9 of embryo?? . ABC of oogenesis :-Oogenesis: from the yolk sac in human embryos, ancient germ cells migrate into the indifferent gonadal streak. These ancient germ cells can be found in humans in the yolk sac in the Carnegie stages 8 and 9.

What is the importance of autosomes in the development of gonads & primordial gem cells in either sex?  Do members  believe that “ The differentiation of germ cells to oogonia does not depend  on sex chromosomes of the germ cells but is regulated by somatic cells in the gonads.” :   The germ cells of the ovaries, the oogonia, reproduce meiotically. In human embryos, primordial germ cells reach the genital ridges from the yolk sac endoderm 5-6-week post-fertilisation. These primordial germ cells or primor­dial follicles form the basic reproductive unit of the ovary.

At five months of embryonic development, the oogonia inside the ovaries enter the first meiosis and differentiate to primary oocytes. At this stage, there are about seven million oocytes in the ovary. They decrease until delivery to two million. As primordial follicles such oocytes they remain quiet until puberty, when, due to abortive growth, any primordial follicles deteriorate resulting at the beginning of puberty in only 40,000 primary oocytes. About 400-500 of these mature during the following ovarian cycles into mature oocytes from menarche to menopause. There is evidence that those preovulatory follicles which are destined to develop dominat follicles are already selected from the pool of germ cells at 24 weeks gestation. Do you believe this??

 In each primordial follicle, an immature oocyte is surrounded by a single epithelial cell layer composed of granulosa cells. These are surrounded by a basal lamina creating a microenvironment that does not directly interact with oocyte.

Summary of the development of primordial germ cells, oogonia, oocytes and primor­dial follicles
Stage	Oocyte development
6 weeks	Primordial germ cells reach the genital ridges from the yolk sac endoderm
9-10 weeks	Differentiation into oogonia, migration of stroma cells from the medulla, morphologically distinguishable ovary
12 weeks	Oocytes as germ cells in meiosis and interstitial cells appear
20-24 weeks	Formation of primordial follicles
24 weeks	Gemt cells reach a peak of approximately 6-7 million
Birth	Two million primordial follicles are present
Birth to menarche	The number of primordial follicles decreases from several million to several hundred thousand
Reproductive years	Only 350-400 of oocytes will develop into full maturity, reach ovulation and corpus luteum formation. After recruitment 99.9 % become atretic
Menopause	Few if any primordial follicles are remaining, menopause is the permanent cessation of menstruation resulting from the loss of ovarian follicle activity

the surrounding cells. As all primordial follicles are formed before birth, only a few survive until menopause. The development of the oocytes and ovary is summarised in

Isolated oocytes do not grow in culture without their companion somatic cells, the granulosa cells, attached. Their intimate and complex relationship extends from follicle formation to ovulation and affects the development and function of both cell types. Details of the interaction and nature of this intimate relationship are just beginning to emerge. Knowledge comes primarily from in vitro experiments. Cutting-edge knowledge will come from trials of artificial oocyte production of pluripotent somatic or embryonic stem cells However, data in this field are still limited. Human oocytes spontaneously complete nuclear maturation when they are released from antral follicles and cultured in vitro for up to 48 h. Germinal vesicle breakdown (GVBD) occurs after 12 h, but this does not happen simulta­neously and in some oocytes GVBD does not begin until 24 h after the beginning of in vitro culture. The molecular mechanism involved in human oocyte maturation is very interesting. Ovulation

After menarche, in every ovulatory cycle, one recruited follicle grows during the follicular phase up to a diameter of approximately 22 mm, ruptures and, depending on the stimulus of follicle-stimulating hormone (FSH) and luteinising hormone (LH) at the time of ovulation, releases the oocyte for fimbrial pick-up and fertilisation or for digestion by macrophages. Healing mechanisms of cytokines immediately close the follicular defect and help to form the corpus rubrum or, in cases of pregnancy, the corpus luteum graviditatis. The pre-ovulatory phase is characterized by an oestrogen rise, low progesterone values and the direct initiation

There is evidence that those preovulatory follicles which are destined to develop dominat follicles are already selected from the pool of germ cells at 24 weeks gestation. Do you believe this ??