Asia Under Girls 026

Biology and gender

The human female reproductive system

In terms of biology, the female sex organs are involved in the reproductive system, whereas the secondary sex characteristics are involved in nurturing children or, in some cultures, attracting a mate. The ovaries, in addition to their regulatory function producing hormones, produce female gametes called eggs which, when fertilized by male gametes (sperm), form new genetic individuals. The uterus is an organ with tissue to protect and nurture the developing fetus and muscle to expel it when giving birth. The vagina is used in copulation and birthing (although the word vagina is often colloquially and incorrectly used for the vulva or external female genitalia, which also includes the labia, the clitoris, and the female urethra). The breast evolved from the sweat gland to produce milk, a nutritious secretion that is the most distinctive characteristic of mammals. In mature women, the breast is generally more prominent than in most other mammals; this prominence, not necessary for milk production, is probably at least partially the result of sexual selection. (For other ways in which men commonly differ physically from women, see Man.)

Spectral karyotype of a human female. The XX combination is formed at the 23rd week of gestation. - National Human Genome Resource Institute

An imbalance of maternal hormonal levels and some chemicals (or drugs) may alter the secondary sexual characteristics of fetuses. Most women have the karyotype 46,XX, but around one in a thousand will be 47,XXX, and one in 2500 will be 45,X. This contrasts with the typical male karotype of 46,XY; thus, the X and Y chromosomes are known as female and male, respectively. Unlike the Y chromosome, the X can come from either the mother or the father, thus genetic studies which focus on the female line use mitochondrial DNA.

Biological factors are not sufficient determinants of whether a person considers themselves a woman or is considered a woman. Intersexed men and women, who have mixed physical and/or genetic features, may use other criteria in making a clear determination. There are also women who have, or have had prior to surgical intervention, a typically male physiology (trans, transgendered or transsexual women; there are varying social, legal, and individual definitions with regard to this issue). (See gender identity.)

Although fewer females than males are born (the ratio is around 1:1.05), due to a longer life expectancy there are only 81 men aged 60 or over for every 100 women of the same age, and among the oldest populations, there are only 53 men for every 100 women.^{[citation needed]} Women have a lower death rate than men, and on average, live five years longer.^{[citation needed]} This is due to a combination of factors: genetics (redundant and varied genes present on sex chromosomes in women); sociology (such as not being expected in most countries to perform military service); health-impacting choices (such as suicide or the use of cigarettes, and alcohol); the presence of the female hormone estrogen, which has a cardioprotective effect in premenopausal women; and the effect of high levels of androgens in men. Out of the total human population, there are 101.3 men for every 100 women (source: 2001 World Almanac).

Most women go through menarche and are then able to become pregnant and bear children.^[1] This generally requires internal fertilization of her eggs with the sperm of a man through sexual intercourse, though artificial insemination or the surgical implantation of an existing embryo is also possible (see reproductive technology). The study of female reproduction and reproductive organs is called gynaecology. Women generally reach menopause in their late 40s or early 50s, at which point their ovaries cease producing estrogen and they can no longer become pregnant.

To a large extent, women suffer from the same illnesses as men.^{[citation needed]} However, there are some diseases that primarily affect women, such as lupus. Also, there are some sex-related illnesses that are found more frequently or exclusively in women, e.g., breast cancer, cervical cancer, or ovarian cancer. Women and men may have different symptoms of an illness and may also respond differently to medical treatment. This area of medical research is studied by gender-based medicine.

During early fetal development, embryos of both sexes appear gender neutral; the release of hormones is what changes physical appearance male or female. As in other cases without two sexes, such as species that reproduce asexually, the gender-neutral appearance is closer to female than to male.

Source from : http://en.wikipedia.org/wiki