•release human chorionic gonadotropin (hCG), a hormone that maintains the placenta well into the second trimester.

•secrete human chorionic mammotropin (facilitates milk production and growth), thyrotropin, corticotropin, relaxin, and estrogen.

A few months into the pregnancy, when the placenta has been well established, the corpus luteum, known as the corpus luteum of pregnancy, is no longer needed, and it also undergoes luteolysis to form the fibrotic corpus albicans.

GENITAL DUCTS

Oviduct

Each oviduct (fallopian tube) is a short muscular tube leading from the vicinity of the ovary to the uterine lumen (see Graphic 17-1). The oviduct is subdivided into four regions:

•infundibulum (whose fimbriae approximate the ovary),

•ampulla,

•isthmus, and

•intramural portion, which pierces the wall of the uterus.

The mucosa of the oviduct, composed of a simple columnar epithelium and a vascular lamina propria, is extensively folded in the infundibulum and ampulla, but the folding is reduced in the isthmus and intramural portions. The simple columnar epithelium is composed of two types of cells

•ciliated columnar, whose cilia beat toward the uterus to transport the fertilized egg into the uterus for implantation, and

•peg cells, that are also columnar but have no cilia. Their apical region is expanded and houses the secretory product that these cells release, namely:

factors for the capacitation of spermatozoa and

nutrient-rich medium that nourishes the spermatozoa as well as the fertilized ovum traveling toward the uterus.

The mucosa is surrounded by a thick smooth muscle coat composed of a poorly defined inner circular and outer longitudinal layers, which, via peristaltic action, assists the cilia to propel the fertilized egg to the uterus. The muscular coat of the oviduct is covered by a serosa, whereas its intramural portion is embedded in the uterus and is surrounded by uterine connective tissue.

Uterus

The uterus, a pear-shaped viscus, is divisible into a fundus, body, and cervix. During pregnancy, this organ houses and supports the developing embryo and fetus.

F E M A L E R E P R O D U C T I V E S Y S T E M 407

Fundus and Body of the Uterus

The uterus is composed of a thick, muscular myometrium (covered by serosa and/or adventitia) and a spongy mucosal layer, the endometrium.

•The endometrium, composed of simple cuboidal epithelium covering the lamina propria with its secretory glands, has a superficial functional layer and deep basal layer, each with its own blood supply.

The basal layer, which remains intact during menstruation, is served by short, straight arteries and is occupied by the base of the uterine glands.

The functional layer, served by the helicine (coiled) arteries, undergoes hormonally modulated cyclic changes during the menstrual cycle of a postpubertal and premenarche female.

The three phases of the endometrium during the menstrual cycle are the proliferative, secretory, and menstrual phases (see Table 17-2).

•Follicular (proliferative) phase, during which the free surface of the endometrium is reepithelialized, and the glands, connective tissue elements, and vascular supply of the endometrium are reestablished.

FSH facilitates the proliferative phase, a thickening of the endometrium and the renewal of the connective tissue, glandular structures, and blood vessels (helicine arteries) subsequent to the menstrual phase.

•Luteal (secretory) phase, occurring within a few days after ovulation, during which the glands further enlarge and become tortuous and their lumina become filled with secretory products. Additionally, the helical arteries become more coiled, and fibroblasts of the stroma accumulate glycogen and fat.

LH facilitates the secretory phase, characterized by the further thickening of the endometrium, coiling of the endometrial glands, accumulation of glandular secretions, and further coiling and lengthening of the helicine arteries.

•Menstrual phase, during which the functional layer of the endometrium is desquamated, resulting in menstrual flow, whereas the basal layer remains more or less undisturbed.

Decreased levels of LH and progesterone are responsible for the menstrual phase, which begins with long-term, intermittent vasoconstriction of the helicine arteries, with subsequent necrosis of the vessel walls as well as of the endometrial tissue of the functional layer.

It should be understood that the basal layer is unaffected because it is being supplied by the straight arteries.

During relaxation (between events of vasoconstriction), the helicine arteries rupture, and the rapid