INTERNAL ACCESSORY ORGANS

of female secondary sexual characteristics. See section titled “Endocrine System” for listing of secondary female sexual characteristics. The ovaries are also the primary source of progesterone (in a nonpregnant female). This hormone promotes changes that occur in the uterus during the female reproductive cycle. In addition, progesterone stimulates the enlargement of mammary glands and ducts, and increases fat deposits in female breasts during puberty. INTERNAL ACCESSORY ORGANS The internal accessory organs of the female reproductive system include a pair of fallopian tubes, the uterus, and the vagina (fig. 1-61). Fallopian Tubes The fallopian tubes, also known as uterine tubes, serve as ducts for the ovaries, providing a passageway to the uterus. The fallopian tubes are composed of three tissue layers. These tissue layers include an inner mucosal layer, a middle muscular layer, and an outer serous layer, and they are continuous with the layers of the uterus. The fallopian tubes are in contact with the ovaries but are not continuous 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. Once the ovum enters the fallopian tubes, it is transported to the uterus by peristalsis and gravity. Fertilization of an ovum normally takes place in the fallopian tubes. Uterus The function of the uterus is to receive the embryo that results from the fertilization of an egg cell, and to sustain its life during development. The uterus, or womb, is a hollow, pear-shaped organ with thick, muscular walls. The uterus is divided into two main regions, the body and cervix (fig. 1-61). The body of the uterus consists of the upper two-thirds of the uterus. The cervix is the lower one-third portion of the uterus that projects into the upper part of the vagina. The cervical opening into the vagina is called the external os. The uterine wall is composed of three layers: the endometrium, the myometrium, and the perimetrium. The inner lining consists of specialized epithelium, called endometrium, which undergoes partial destruction approximately every 28 days in the n o n p r e g n a n t f e m a l e . T h e m i d d l e l a y e r, t h e myometrium, consists of bundles of interlaced muscular fibers. The muscular layer produces powerful rhythmic contractions that are important in the expulsion of the fetus at birth. The perimetrium consists of an outer serosal layer that covers the body of the uterus and part of the cervix. The uterus also has three openings: superiorly and laterally, two openings connect the fallopian tubes to the uterus, and inferiorly, an opening leading to the vagina. 1-61 FOLLICULAR FLUID OOCYTE FOLLICULAR CELLS OVARY PRIMORDIAL FOLLICLE TIME OVULATION FALLOPIAN TUBE HM3F0162 Figure 1-62.—Ovulation process.