Editing Human sexuality (section)

=====Internal female anatomy=====
{{main|Female reproductive system}}

The female internal reproductive organs are the [[vagina]], [[uterus]], [[Fallopian tube]]s, and [[ovary|ovaries]]. The vagina is a sheath-like canal that extends from the vulva to the cervix. It receives the penis during intercourse and serves as a depository for sperm. The vagina is also the [[birth canal]]; it can expand to {{convert|10|cm|inch|abbr=on}} during labor and delivery. The vagina is located between the [[bladder]] and the [[rectum]]. The vagina is normally collapsed, but during [[sexual arousal]] it opens, lengthens, and produces lubrication to allow the insertion of the penis. The vagina has three layered walls; it is a self-cleaning organ with natural bacteria that suppress the production of yeast.<ref name="ReferenceA"/>{{page needed|date=February 2016}} The [[G-spot]], named after the [[Ernst Gräfenberg]] who first reported it in 1950, may be located in the front wall of the vagina and may cause orgasms. This area may vary in size and location between women; in some it may be absent. Various researchers dispute its structure or existence, or regard it as an extension of the clitoris.<ref name=Hines>{{cite journal |author=Hines T |date=August 2001 |title=The G-Spot: A modern gynecologic myth |journal=Am J Obstet Gynecol |volume=185 |issue=2 |pages=359–362 | doi=10.1067/mob.2001.115995  |pmid=11518892|s2cid=32381437 |url=https://semanticscholar.org/paper/59ac3e423b824c8b64b2359c10a496730cd2a656 }}</ref><ref name="Balon, Segraves">{{cite book|first1=Richard |last1=Balon |first2=Robert Taylor |last2=Segraves|title=Clinical Manual of Sexual Disorders |publisher= [[American Psychiatric Association|American Psychiatric Pub]]|year=2009|access-date=24 January 2014|page=258|isbn=978-1-58562-905-3|url={{Google books |plainurl=yes |id=YuP3Hb0TMLQC |}} }}</ref><ref name="Kilchevsky">{{cite journal|title=Is the Female G-Spot Truly a Distinct Anatomic Entity?|journal=[[The Journal of Sexual Medicine]]|volume= 9|date=January 2012 |pmid=22240236|doi=10.1111/j.1743-6109.2011.02623.x|lay-url=http://www.huffingtonpost.com/2012/01/19/g-spot-does-not-exist_n_1215822.html|lay-source=[[The Huffington Post]]|lay-date=19 January 2012 |last1=Kilchevsky |first1=A |last2=Vardi |first2=Y |last3=Lowenstein |first3=L |last4=Gruenwald |first4=I |issue=3|pages=719–726}}</ref>

The uterus or womb is a hollow, muscular organ where a fertilized egg (ovum) will implant itself and grow into a fetus.<ref name="ReferenceA"/>{{page needed|date=February 2016}} The uterus lies in the pelvic cavity between the bladder and the [[bowel]], and above the vagina. It is usually positioned in a 90-degree angle tilting forward, although in about 20% of women it tilts backwards.<ref name="innerbody.com"/> The uterus has three layers; the innermost layer is the [[endometrium]], where the egg is implanted. During ovulation, this thickens for implantation. If implantation does not occur, it is sloughed off during menstruation. The cervix is the narrow end of the uterus. The broad part of the uterus is the [[fundus (uterus)|fundus]].<ref name="ReferenceA"/>{{page needed|date=February 2016}}

During [[ovulation]], the ovum travels down the Fallopian tubes to the uterus. These extend about {{convert|4|inch|cm|spell=in}} from both sides of the uterus. Finger-like projections at the ends of the tubes brush the ovaries and receive the ovum once it is released. The ovum then travels for three to four days to the uterus.<ref name="ReferenceA"/>{{page needed|date=February 2016}} After sexual intercourse, sperm swim up this funnel from the uterus. The lining of the tube and its secretions sustain the egg and the sperm, encouraging [[fertilization]] and nourishing the ovum until it reaches the uterus. If the ovum divides after fertilization, [[identical twins]] are produced. If separate eggs are fertilized by different sperm, the mother gives birth to non-identical or [[fraternal twins]].<ref name="innerbody.com"/>

The ovaries (female gonads), develop from the same embryonic tissue as the [[testicles]]. The ovaries are suspended by ligaments and are the source where ova are stored and developed before ovulation. The ovaries also produce female hormones [[progesterone]] and [[estrogen]]. Within the ovaries, each ovum is surrounded by other cells and contained within a capsule called a primary follicle. At puberty, one or more of these follicles are stimulated to mature on a monthly basis. Once matured, these are called [[Graafian follicles]].<ref name="ReferenceA"/>{{page needed|date=February 2016}} The female reproductive system does not produce the ova; about 60,000 ova are present at birth, only 400 of which will mature during the woman's lifetime.<ref name="innerbody.com"/>

Ovulation is based on a monthly cycle; the 14th day is the most fertile. On days one to four, menstruation and production of estrogen and progesterone decreases, and the endometrium starts thinning. The endometrium is sloughed off for the next three to six days. Once menstruation ends, the cycle begins again with an FSH surge from the pituitary gland. Days five to thirteen are known as the pre-ovulatory stage. During this stage, the pituitary gland secretes [[follicle-stimulating hormone]] (FSH). A negative feedback loop is enacted when estrogen is secreted to inhibit the release of FSH. Estrogen thickens the endometrium of the uterus. A surge of [[Luteinizing Hormone]] (LH) triggers ovulation.

On day 14, the LH surge causes a Graafian follicle to surface the ovary. The follicle ruptures and the ripe ovum is expelled into the abdominal cavity. The fallopian tubes pick up the ovum with the [[Fimbriae of uterine tube|fimbria]]. The cervical mucus changes to aid the movement of sperm. On days 15 to 28—the post-ovulatory stage, the Graafian follicle—now called the [[corpus luteum]]—secretes estrogen. Production of progesterone increases, inhibiting LH release. The endometrium thickens to prepare for implantation, and the ovum travels down the Fallopian tubes to the uterus. If the ovum is not fertilized and does not implant, menstruation begins.<ref name="ReferenceA"/>{{page needed|date=February 2016}}