What is female reproductive endocrinology?
The hormonal interaction between the hypothalamus, the anterior pituitary gland, and the ovaries regulate the female reproductive endocrinology system. The hypothalamus secretes a small peptide, gonadotropin-releasing hormone (GnRH), also recognized as a luteinizing hormone-releasing hormone.
GnRH regulates the release of gonadotropins, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) from specialized (gonadotropic) cells in the anterior pituitary gland (see figure The CNS-hypothalamic-pituitary-gonadal target organ axis). These hormones are released in short bursts (pulses) every 1 to 4 hours. LH and FSH promote ovulation and stimulate the secretion of the sex hormones estradiol (an estrogen) and progesterone from the ovaries.
Estrogen and progesterone circulating in the bloodstream almost completely bound to plasma proteins. Only free estrogen and progesterone appear to be biologically active. They stimulate the target organs of the reproductive system (eg, breasts, uterus, vagina). They are usually inhibitory, but in certain situations (eg, around ovulation), they can stimulate gonadotropin secretion.
Puberty is the order of events in which a child acquires adult physical characteristics and reproductive volume. Circulating levels of LH and FSH are elevated at birth, but drop to low levels within a few months and remain low until puberty. Until puberty, few qualitative variations occur in reproductive target organs.
Age of onset of puberty: The age of onset of puberty and the rate of development through diverse stages are influenced by different factors. Over the past 150 years, the age at which puberty begins has been decreasing, primarily due to better health and nutrition, but this trend has stabilized. Puberty often occurs earlier than average in moderately obese girls and later than average in underweight and malnourished girls.
Such explanations suggest that critical body weight or amount of fat is essential for puberty. Many other factors can influence the onset of puberty and how quickly it progresses. For example, there is some evidence that intrauterine growth restriction, especially when followed by postnatal overfeeding, can contribute to earlier and faster 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 between ethnic groups (eg, it tends to be earlier in blacks and Hispanics than in Asian and non-Hispanic whites).
Physical changes of puberty: The physical changes of puberty occur consecutively during adolescence (see figure Puberty, when female sexual characteristics progress). Mammary budding (see figure Schematic representation of Tanner stages I to V of human mammary maturation) and the onset of the growth spurt are generally the first recognized changes.
Subsequently, pubic and axillary hair appear (see figure Schematic representation of Tanner’s stages I to V for pubic hair development in girls), and accelerated growth peaks.
Menarche (the first menstrual period) occurs about 2 to 3 years after the breast buds. Menstrual cycles are typically irregular at menarche and can take up to 5 years to become regular. The growth spurt is limited after menarche. Body habit changes and the pelvis and hips widen. Body fat increases and accumulates on the hips and thighs.
Mechanisms that initiate puberty: The mechanisms that initiate puberty are unclear.
Central influences that regulate GnRH release include neurotransmitters and peptides (eg, gamma-aminobutyric acid [GABA], kisspeptin). These factors can inhibit GnRH release during childhood and then initiate its release to induce puberty in early adolescence. In early puberty, hypothalamic GnRH release becomes less sensitive to inhibition by estrogen and progesterone.
The resulting increase in GnRH release promotes the secretion of LH and FSH, which stimulates the production of sex hormones, primarily estrogen. Estrogen stimulates the development of secondary sexual characteristics.
The growth of pubic and axillary hair can be enthused by the adrenal androgens dehydroepiandrosterone (DHEA) and DHEA sulfate; the manufacture of these androgens increases several years before puberty in a process called adrenarche.
The Hypothalamic Pituitary Gonadal (HPG) Axis of Amphibians
Reproductive endocrinology has been characterized mainly in anurans (frogs, toads) with some corroborative data from urodeles (salamanders, newts). Gymnophionid amphibians (caecilians or apodans) are similar to urodeles, although endocrine details are not well understood.
The hypothalamus controls gonadotropin secretion through the release of GnRH (see Tsai (2011)). Amphibian FSH stimulates spermatogenesis in males, as well as follicle development and estrogen secretion in females.
What regulates the female reproductive endocrinology cycle?
The menstrual cycle is regulated by hormones. Luteinizing hormone and follicle-stimulating hormone, which are bent by the pituitary gland, promote ovulation and kindle the ovaries to produce estrogen and progesterone.
What are the two female reproductive endocrinology cycles?
A fertile woman exhibits two periodic cycles: the ovarian cycle, which occurs in the cortex of the ovary, and the menstrual cycle, which occurs in the endometrium of the uterus. The phases of the menstrual cycle are under the control of the hormones unseen during the different phases of the ovarian cycle.
What are the 2 main female reproductive endocrinology hormones?
The two main feminine sex hormones are estrogen and progesterone. Although testosterone is considered a male hormone, women also produce and need a small amount of it as well.
What are the 5 main functions of the endocrine system?
- Endocrine system function
- Growth and development
- sexual function and reproduction
- heart rate
- blood pressure
- sleep and wake cycles
- body temperature
How does the endocrine system touch the female reproductive endocrinology system?
The endocrine glands release hormones into the bloodstream. This allows hormones to travel to cells in other parts of the body. Endocrine hormones help control mood, growth, and development, the way our organs function, metabolism, and reproduction. The endocrine system regulates the amount of each hormone that is released.