S uterine tubes

The uterine tubes are paired tubes that extend bilaterally from the uterus toward the ovaries (see Fig. 22.1). Also commonly referred to as the Fallopian tubes, the uterine tubes transport the ovum from the ovary to the uterus and provide the necessary environment for fertilization and initial development of the zygote to the morula stage. One end of the tube is adjacent to the ovary and opens into the peritoneal cavity; the other end communicates with the uterine cavity.

Each uterine tube is approximately 10 to 12 cm long and can be divided into four segments by gross inspection:

• The infundibulum is the funnel-shaped segment of the tube adjacent to the ovary. At the distal end, it opens into the peritoneal cavity. The proximal end communicates with the ampulla. Fringed extensions, or fimbriae, extend from the mouth of the infundibulum toward the ovary.

• The ampulla is the longest segment of the tube, constituting about two thirds of the total length, and is the site of fertilization.

• The isthmus is the narrow, medial segment of the uterine tube adjacent to the uterus.

• The uterine or intramural part, measuring about 1 cm in length, lies within the uterine wall and opens into the cavity of the uterus.

The wall of the uterine tube is composed of three layers

The uterine tube wall resembles the wall of other hollow viscera, consisting of an external serosal layer, an intermediate muscular layer, and an internal mucosal layer. However, there is no submucosa.

• The serosa or peritoneum is the outermost layer of the uterine tube and is composed of mesothelium and a thin layer of connective tissue.

• The muscularis, throughout most of its length, is organized into an inner, relatively thick circular layer and an outer, thinner longitudinal layer. The boundary between these layers is often indistinct.

• The mucosa, the inner lining of the uterine tube exhibits relatively thin longitudinal folds that project into the lumen of the uterine tube throughout its length. The folds are most numerous and complex in the ampulla (Fig. 22.15) and become smaller in the isthmus.

The mucosal lining is simple columnar epithelium composed of two kinds of cells, ciliated and nonciliated (Fig. 22.15b). They represent different functional states of a single cell type.

• Ciliated cells are most numerous in the infundibulum and ampulla. The wave of the cilia is directed toward the uterus.

• Nonciliated, peg cells are secretory cells that produce the fluid that provides nutritive material for the ovum.

The epithelial cells undergo cyclic hypertrophy during the follicular phase and atrophy during the luteal phase in response to changes in hormonal levels, particularly estrogens. Also, the ratio of ciliated to nonciliated cells changes during the hormonal cycle. Estrogen stimulates ciliogenesis, and progesterone increases the number of secretory cells. At about the time of ovulation, the epithelium reaches a height of about 30 /jlm and is then reduced to about one half that height just before the onset of menstruation.

Bidirectional transport occurs in the uterine tube

The uterine tube demonstrates active movements just before ovulation as the fimbriae become closely apposed to the ovary and localize over the region of the ovarian

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