In women, when hormone levels fall towards the end of the menstrual cycle , this is sensed by nerve cells in the hypothalamus. These cells produce more gonadotrophin-releasing hormone, which in turn stimulates the pituitary gland to produce more follicle stimulating hormone and luteinising hormone, and release these into the bloodstream. The rise in follicle stimulating hormone stimulates the growth of the follicle in the ovary.
With this growth, the cells of the follicles produce increasing amounts of oestradiol and inhibin. In turn, the production of these hormones is sensed by the hypothalamus and pituitary gland and less gonadotrophin-releasing hormone and follicle stimulating hormone will be released.
However, as the follicle grows, and more and more oestrogen is produced from the follicles, it simulates a surge in luteinising hormone and follicle stimulating hormone, which stimulates the release of an egg from a mature follicle — ovulation. Thus, during each menstrual cycle, there is a rise in follicle stimulating hormone secretion in the first half of the cycle that stimulates follicular growth in the ovary. After ovulation the ruptured follicle forms a corpus luteum that produces high levels of progesterone.
This inhibits the release of follicle stimulating hormone. Towards the end of the cycle the corpus luteum breaks down, progesterone production decreases and the next menstrual cycle begins when follicle stimulating hormone starts to rise again. In men, the production of follicle stimulating hormone is regulated by the circulating levels of testosterone and inhibin, both produced by the testes.
Follicle stimulating hormone regulates testosterone levels and when these rise they are sensed by nerve cells in the hypothalamus so that gonadotrophin-releasing hormone secretion and consequently follicle stimulating hormone is decreased. The opposite occurs when testosterone levels decrease. This is known as a ' negative feedback ' control so that the production of testosterone remains steady.
The production of inhibin is also controlled in a similar way but this is sensed by cells in the anterior pituitary gland rather than the hypothalamus. Most often, raised levels of follicle stimulating hormone are a sign of malfunction in the ovary or testis. This condition is called hyper gonadotrophic- hypo gonadism, and is associated with primary ovarian failure or testicular failure. This is seen in conditions such as Klinefelter's syndrome in men and Turner syndrome in women.
In women, follicle stimulating hormone levels also start to rise naturally in women around the menopausal period, reflecting a reduction in function of the ovaries and decline of oestrogen and progesterone production. GnRH regulates release of the gonadotropins luteinizing hormone LH and follicle-stimulating hormone FSH Luteinizing hormone LH and follicle-stimulating hormone FSH The endocrine system coordinates functioning between different organs through hormones, which are chemicals released into the bloodstream from specific types of cells within endocrine ductless The hypothalamus secretes a small peptide, gonadotropin-releasing These hormones are released in short bursts pulses every 1 to 4 hours.
LH and FSH promote ovulation and stimulate secretion of the sex hormones estradiol an estrogen and progesterone from the ovaries. Estrogen and progesterone circulate in the bloodstream almost entirely bound to plasma proteins. Only unbound estrogen and progesterone appear to be biologically active. They stimulate the target organs of the reproductive system eg, breasts, uterus, vagina.
They usually inhibit but, in certain situations eg, around the time of ovulation , may stimulate gonadotropin secretion. Puberty is the sequence of events in which a child acquires adult physical characteristics and capacity for reproduction.
Circulating LH and FSH levels are elevated at birth but fall to low levels within a few months and remain low until puberty. Until puberty, few qualitative changes occur in reproductive target organs. The age of onset of puberty and the rate of development through different stages are influenced by different factors. Over the last years, the age at which puberty begins has been decreasing, primarily because of improved health and nutrition, but this trend has stabilized.
Puberty often occurs earlier than average in moderately obese girls and later than average in severely underweight and undernourished girls 1 Puberty references Hormonal interaction between the hypothalamus, anterior pituitary gland, and ovaries regulates the female reproductive system.
Such observations suggest that a critical body weight or amount of fat is necessary for puberty. Many other factors can influence when puberty begins and how rapidly it progresses. For example, there is some evidence that intrauterine growth restriction, especially when followed by postnatal overfeeding, may contribute to earlier and more rapid development of puberty. Puberty occurs earlier in girls whose mothers matured earlier and, for unknown reasons, in girls who live in urban areas or who are blind.
The age of onset of puberty also varies among ethnic groups eg, tending to be earlier in blacks and Hispanics than in Asians and non-Hispanic whites [ 2 Puberty references Hormonal interaction between the hypothalamus, anterior pituitary gland, and ovaries regulates the female reproductive system. Physical changes of puberty occur sequentially during adolescence see figure Puberty—when female sexual characteristics develop Puberty—when female sexual characteristics develop Precocious puberty is onset of sexual maturation before age 8 in girls or age 9 in boys.
Diagnosis is by comparison with population standards, x-rays of the left hand and wrist to assess skeletal Breast budding see figure Diagrammatic representation of Tanner stages I to V of human breast maturation Diagrammatic representation of Tanner stages I to V of human breast maturation Hormonal interaction between the hypothalamus, anterior pituitary gland, and ovaries regulates the female reproductive system.
Then, pubic and axillary hair appear see figure Diagrammatic representation of Tanner stages I to V for development of pubic hair in girls Diagrammatic representation of Tanner stages I to V for development of pubic hair in girls Hormonal interaction between the hypothalamus, anterior pituitary gland, and ovaries regulates the female reproductive system.
Menarche the first menstrual period occurs about 2 to 3 years after breast budding. Menstrual cycles are usually irregular at menarche and can take up to 5 years to become regular.
The growth spurt is limited after menarche. Body habitus changes and the pelvis and hips widen. Body fat increases and accumulates in the hips and thighs. Central influences that regulate release of GnRH include neurotransmitters and peptides eg, gamma-aminobutyric acid [GABA], kisspeptin.
Such factors may inhibit release of GnRH during childhood, then initiate its release to induce puberty in early adolescence. Early in puberty, hypothalamic GnRH release becomes less sensitive to inhibition by estrogen and progesterone. Estrogen stimulates development of secondary sexual characteristics. Pubic and axillary hair growth may be stimulated by the adrenal androgens dehydroepiandrosterone DHEA and DHEA sulfate; production of these androgens increases several years before puberty in a process called adrenarche.
Archives of Disease in Childhood —, ; used with permission. Pediatrics 1 , Pediatrics —, Arch Dis Child —, A female is born with a finite number of egg precursors germ cells. Germ cells begin as primordial oogonia that proliferate markedly by mitosis through the 4th month of gestation.
During the 3rd month of gestation, some oogonia begin to undergo meiosis, which reduces the number of chromosomes by half. By the 7th month, all viable germ cells develop a surrounding layer of granulosa cells, forming a primordial follicle, and are arrested in meiotic prophase; these cells are primary oocytes. Beginning after the 4th month of gestation, oogonia and later oocytes are lost spontaneously in a process called atresia; eventually, In older mothers, the long time that surviving oocytes spend arrested in meiotic prophase may account for the increased incidence of genetically abnormal pregnancies 1 Ovarian follicular development reference Hormonal interaction between the hypothalamus, anterior pituitary gland, and ovaries regulates the female reproductive system.
FSH induces follicular growth in the ovaries. During each menstrual cycle, 3 to 30 follicles are recruited for accelerated growth. Usually in each cycle, only one follicle achieves ovulation. This dominant follicle releases its oocyte at ovulation and promotes atresia of the other recruited follicles. Collecting a sample of blood is only temporarily uncomfortable and can feel like a quick pinprick. Afterward, there may be some mild bruising, which should go away in a few days.
The blood sample will be processed by a machine. The results usually are available after a day or two. The FSH test is considered a safe procedure. However, as with many medical tests, some problems can occur with having blood drawn, like:.
Having a blood test is relatively painless. Still, many kids are afraid of needles. Explaining the test in terms your child can understand might help ease some of the fear. Allow your child to ask the technician any questions he or she might have.
Tell your child to try to relax and stay still during the procedure, as tensing muscles and moving can make it harder and more painful to draw blood.
It also may help if your child looks away when the needle is being inserted into the skin.
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