CHAPTER 25The Gonads: Development & Function of the Reproductive System 411THE FEMALE REPRODUCTIVE
SYSTEM
THE MENSTRUAL CYCLE
The reproductive system of women (Figure 25–21), unlike
that of men, shows regular cyclic changes that teleologically
may be regarded as periodic preparations for fertilization and
pregnancy. In humans and other primates, the cycle is a men-
strual cycle, and its most conspicuous feature is the periodic
vaginal bleeding that occurs with the shedding of the uterine
mucosa (menstruation). The length of the cycle is notoriously
variable in women, but an average figure is 28 days from the
start of one menstrual period to the start of the next. By com-
mon usage, the days of the cycle are identified by number,
starting with the first day of menstruation.Ovarian Cycle
From the time of birth, there are many primordial follicles
under the ovarian capsule. Each contains an immature ovum
(Figure 25–21). At the start of each cycle, several of these fol-
licles enlarge, and a cavity forms around the ovum (antrum
formation). This cavity is filled with follicular fluid. In hu-
mans, usually one of the follicles in one ovary starts to growFIGURE 25–21 Functional anatomy of the female reproductive tract. The female reproductive organs include the ovaries, the uterus and the
fallopian tubes, and the breast/mammary glands. The sequential development of a follicle, the formation of a corpus luteum and follicular atresia are
shown.
VaginaUrethraBladderRectumOvaryUterine tubeUterusVaginaUterine cavityCervixBroad ligamentOvaryUterine tube
Ligament of the ovary
FundusOvarian arteryInterstitial
cell massAntral
follicleTheca externaTheca internaGranulosa
Follicular fluidMature
follicleAntrumCorpus
hemorrhagicumOvulated
oocytePrimordial
Germinal follicle
epitheliumOvarian
stromaAtretic
follicleYoung
corpus luteumMature
corpus luteumRegressing
corpus luteumCorpus
albicansBlood
vessels