OVARIES The ovaries (female gonads) are two almond- shaped glands suspended by ligaments in the up- per pelvic cavity, one on either side of the uterus, posterior  and  inferior  to  the  fallopian  tubes.  Their prime  function  is  to  produce  the  ova  and  the female   hormone   estrogen   and   progesterone. Although  these  hormones  are  manufactured  by the ovaries, their production is controlled by the anterior  pituitary  gland.  These  hormones  play essential  roles  in  the  development  of  secondary sex characteristics, the reproductive cycle, gesta- tion,  and  lactation. The graafiau follicles are microscopic pockets in the ovaries. One a month, under hormonal in- fluence,  a  follicle  matures,  ruptures,  and  expels its  ovum  into  the  uterus.  Each  ovary  normally releases an ovum every 56 days, the right and left ovary alternately discharging an ovum every 28 days.  The  menstrual  cycle  in  most  women  is therefore  28  days  in  length. FALLOPIAN  TUBES The fallopian (uterine) tubes are composed of internal   mucous,   middle   muscular,   and   outer serous coats that are continuous with the layers of the uterus. They serve as ducts of the ovaries, providing a passageway to the uterus. These tubes are in contact with the ovaries, but are not con- tinuous  with  them.  Their  funnel-shaped  openings, called free openings, are fringed with fingerlike processes that pick up an ovum and draw it into the fallopian tubes, where it is transported to the uterus by peristalsis and gravity. Fertilization of an  ovum  normally  takes  place  in  the  fallopian tubes. UTERUS The uterus (womb) is a hollow, pear-shaped organ with thick, muscular walls. It is lined with a  specialized  epitheliums,  called  endometrium, which undergoes partial destruction about every 28  days  in  the  nonpregnant  woman. The uterus averages 7 cm in length and 5 cm in width. It has three openings: the openings of the fallopian tubes laterally and the opening into the vagina. The parts of the uterus are the body, which is the large upper portion, and the cervix, which  is  the  smaller  portion  that  projects  into  the upper  part  of  the  vagina.  The  cervical  opening into the vagina is called the external os. The walls of  the  uterus  arc  highly  flexible  and  are  composed of three layers that are continuous with the respec- tive  layers  of  the  fallopian  tubes. In addition to being the focal point of the en- dometrial (menstrual) cycle, the uterus is the site of implantation, growth, and development of the fertilized ovum. The muscular walls of the uterus produce powerful rhythmic contractions that are important in the expulsion of the fetus at birth. VAGINA The vagina is a musculomembranous, collap- sible tube capable of great distention. It is lined with mucous membrane that extends from the cer- vix to the vulva. The canal is about 7.5 cm long, and its lining membrane, which is greatly folded, is continuous with the inner lining of the uterus. The  vagina  is  the  organ  that  receives  the  male sperm during intercourse. It also forms the lower portion of the birth canal, stretching widely dur- ing  delivery.  In  addition,  it  serves  as  an  excretory duct  for  uterine  secretions  and  menstrual  flow. RECURRING CYCLES When females reach puberty, they begin to ex- perience  the  two  recurring  female  cycles,  the ovarian  and  endometrial. As  previously  mentioned,  each  ovary  produces a mature ovum every 56 days. They expel their ova  on  an  alternating  basis,  approximately  one every 28 days. The length of this cycle may vary markedly  from  individual  to  individual  and  be- tween cycles of the same individual. On the first days   of   menstruation,   several  ova  within  the graafian follicles begin to mature, and normally one  will  be  expelled  14  days  before  the  next menstrual  flow.  This  is  the  ovarian  cycle. The  endometrial  cycle  centers  around  the periodic development and breakdown of the en- dometrial lining of the uterus. The first phase of the cycle is the menses, or menstruation. It begins when the endometrial lining starts to slough off from the walls of the uterus, and it is characterized by bleeding from the vagina. This is day 1 of the cycle, and this phase usually lasts through day 5. The time between the last day of the menses and ovulation is known as the postmenstrual phase. It lasts from day 6 through day 13 or 14 and is characterized  by  proliferation  of  endometrial  cells in the uterus, which develop under the influence of  the  hormone  estrogen.  Ovulation  is  the  rup- ture  of  a  graafian  follicle  with  the  release  of  a mature  ovum  into  the  fallopian  tubes.  It  usu- ally  occurs  on  day  14  or  15  of  the  cycle.  The 3-50