Puberty begins at age 8 to 10 for most girls in the United States. It is triggered by rising levels of GnRH, stimulates anterior lobe of pituitary to produce: FSH and LH. FSH stimulates developing ovarian follicles and they begin to secrete estrogen, progesterone, inhibin, and a small amount of androgen. Thelarche is the onset of breast development is the earliest noticeable sign of puberty. Pubarche is the appearance of pubic and axillary hair, sebaceous glands, and axillary glands. Menarche is the first menstrual period, which requires about 17% body fat in teenagers and 22% in adults. Estradiol stimulates vaginal metaplasia, growth of ovaries and secondary sex organs, growth hormone secretion, responsible for feminine physique because it stimulates the deposition of fat, and makes a girl’s skin thicker. Progesterone, primarily acts on the uterus preparing it for possible pregnancy in the second half of the menstrual cycle. Estrogens and progesterone suppress FSH and LH secretion through negative feedback. Inhibin selectively suppresses FSH secretion. Hormone secretion is distinctly cyclic and the hormones are secreted in sequence. Oogensis
Oogensis is egg development. Oogensis produces haploid gametes by means of meiosis, distinctly cyclic event that normally releases one egg each month, accompanied by cyclic changes in hormone secretion, and cyclic changes in histological structure of the ovaries and uterus. Egg development resumes in adolescence. Embryonic development of ovary: female germ cells arise from yolk sac, colonize gonadal ridges the first 5 to 6 weeks of development, differentiate into oogonia and multiply until the fifth month, transform into primary oocytes: early meiosis I, most degenerate (atresia) by the time the girl is born, egg or ovum: any stage from the primary oocyte to the time of fertilization, by puberty, 400,000 oocytes remain. FSH stimulates monthly cohorts of oocytes to complete meiosis I. Each oocyte divides into two haploid daughter cells of unequal size and different destinies. It is important to produce an egg with as much cytoplasm as possible. If fertilized, it must divide repeatedly and produce numerous daughter cells. Folliculogenesis
Folliculogenesis is the development of the follicles around the egg that undergoes oogenesis. Primordial follicles: consists of a primary oocyte in early meiosis, surrounded by a single layer of squamous follicular cells, follicular cells connected to the oocyte by fine cytoplasmic processes for passage of nutrients and chemical signals, concentrated in the cortex of the ovary, most wait 13 to 50 years before they develop further, and adult ovary has 90% to 95% primordial follicles. Primary follicles have larger oocytes and follicular cells that still form a single layer. Secondary follicles still have larger oocytes and follicular cells now stratified (granulosa cells). Zona pellucida is a layer of glycoprotein gel secreted by granulosa cells around the oocyte. Theca folliculi is the connective tissue around the granulosa cells condenses to form a fibrous husk. Mature (graafian) follicles are normally only one follicle from each month’s cohort becomes a mature follicles destined to ovulate and remainder degenerate. Ovulation
Ovulation is the rupture of the mature follicle and the release of its egg and attendant cells, typically around day 14. Estradiol stimulates a surge of LH and a lesser spike of FSH by anterior pituitary. Ovulation takes only 2 to 3 minutes: Nipplelike stigma appears on ovary surface over follicle, seeps follicular fluid for 1 to 2 minutes, follicle bursts and remaining fluid oozes out carrying the secondary oocyte and cumulus oophorus, and normally swept up by ciliary current and taken into uterine tube. Uterine tube prepares to catch the oocyte when it emerges, it swells the edema, its fimbriae envelop and caress the ovary in synchrony with the woman’s heartbeat, cilia create gentle current in the nearby peritoneal...