12.14 Vagina

The vagina is a fibromuscular tube that functions to hold the penis during intercourse, receive and store the semen, and serve as a birth canal during parturition. It has a thick inner mucosal layer (labeled "ML" in image 12.14a) surrounding the inner cavity, the lumen (labeled "Lu" in image 12.14a), a middle muscularis layer, and an outer adventitial layer. The muscularis layer, which is not very thick and concentrated at the anterior third of the vaginal wall, consists of both circular and longitudinal smooth muscle bundles. A stratified squamous epithelium and an underlying lamina propria, containing blood vessels (labeled "BV" in image 12.14a), nerves, and lymphatics, make up the mucosal layer. Image 12.14b shows the inner epithelium of a vagina with the arrow pointing to a nucleus in one of the cells near the surface. Image 12.14c is a close-up of a normal vagina.

12.15 Uterus

The uterus is a pear-shaped organ that shows three distinct layers in cross-sectional view (see image 12.15b). The endometrium (labeled "En" in image 12.15b) is the inner layer of the uterus which surrounds the inner cavity or lumen (labeled "Lu" in image 12.15b) and consists of an epithelium of simple columnar cells and an underlying connective tissue stroma. A thick layer called the myometrium (labeled "My" in image 12.15b) consisting of smooth muscle bundles and connective tissue surrounds the endometrium. Many blood vessels (labeled "BV" in image 12.15b) are present in the the myometrium. The external surface of the uterus is covered by a serosal layer (labeled "Se" in image 12.15b) that forms the visceral peritoneum. Image 12.15b shows an intrauterine device (I.U.D.) implanted in the lumen of the uterus for contraception. Note that this coil-type I.U.D. can become impaled into the endometrium. The "T" shaped versions produce less damage, but the pointed versions (like the now infamous "Shield") can cause significant endometrial damage and produce a painful pelvic condition called endometriosis.

12.16 Endometrium

The arrows in image 12.16a point to numerous uterine glands that open onto the surface of the highly folded endometrium of the uterus. Approximately ten days after menstruation, these uterine glands regenerate under the influence of estrogen. Then, after ovulation and under the influence of progesterone, the glands begin secreting glycogen, mucus, and other substances that provide a nourishing environment that will insure the survival and successful implantation of the blastocyst in the uterus. Image 12.16b shows the endometrial lining of a uterus. Note the rich vascularity with its extensive blood supply. Image 12.16c is a more focused, higher power section of the secretory endometrium. The arrow in image 12.16c points to a coiled secretory gland of the endometrium. Image 12.16d is a higher power view into an endometrial gland. Here the arrow points at glycogen secretion droplets which will serve as food for the implanting embryo.

12.17 Fallopian Tubes

Image 12.17a shows the three layers of the wall of the fallopian tube. These include the inner mucosa (labeled "ML" in image 12.17a), an intermediate muscularis layer consisting of circularly and longitudinally arranged smooth muscle (labeled "SM" in image 12.17a) and an outer serosal layer (labeled "Se" in image 12.17a) composed of connective tissue. The highly folded inner mucosa layer consists of an epithelial layer (labeled "Ep" in image 12.17a) that covers a thin connective tissue lamina propria (labeled "LP" in image 12.17a). The numerous mucosal folds (labeled "MF" in image 12.17a) are shown projecting into the lumen of the ampulla of the fallopian tube. Image 12.17b shows the uterine portion of the fallopian tube (arrow).

12.18 Oviduct Epithelium

Image 12.18a shows the epithelium of the oviduct consists of columnar cells, many of which have cilia (labeled "Ci" in image 12.18a) on their free surfaces. The non-ciliated or secretory cells (labeled "SC" in image 12.18a) produce a secretion that serves to maintain a moist environment in the oviduct lumen. Image 12.18b is a high-powered close up of the inner epithelium of an oviduct. Note the red nuclei in the pale-blue columnar cells and especially note the cilia (arrow in image 12.18b).

12.19 Ovaries

The ovary (as seen in image 12.19a) is divided into a central medulla (labeled "Me" in image 12.19a) and outer cortex (labeled "Co" in image 12.19a). The medulla is principally composed of loosely packed connective tissue containing many blood vessels (labeled "BV" in image 12.19a), lymphatic vessels and nerves. The outer surface of the ovary is a cuboidal epithelium, called the germinal epithelium, which is continuous with the peritoneum at the mesovarium (labeled "Mo" in image 12.19a). The cortex of the ovary contains many primordial follicles (germ cells surrounded by a single layer of follicle cells), but these are too small to be seen in this low power view. When these primordial follicles are stimulated by pituitary hormone (FSH), the enlarge and proliferate new cells to become secondary follicles (labeled "SF" in image 12.19a). Also visible are corpus lutea (labeled "CL" in image 12.19a), which have formed from the follicular cells remaining after the egg is ovulated. Image 12.19b is a light microscope slide of an ovary showing numerous developing follicles (labeled "b" in image 12.19b), stromal blood vessels (labeled "c" in image 12.19b), and a developing corpus luteum (labeled "a" in image 12.19b).

12.20 Follicles

Image 12.20a shows a close-up view of the ovarian cortex which contains numerous ovarian follicles in various stages of development. The connective tissue stroma (labeled "St" in image 12.20a) in the cortex of the ovary contains primordial and primary follicles (labeled "PF" in image 12.20a) as well as larger secondary follicles (labeled "SF" in image 12.20a). The secondary follicle will ultimately mature to a very large Graafian follicle. Image 12.20b is the ovarian cortex showing a close-up of primordial follicles (labeled "b" in image 12.20b) which have been generated by the germinal epithelium (labeled "a" in image 12.20b). Note the large amount of connective tissue stroma around the follicles and under the epithelium.

12.21 Graafian Follicles and Corpus Luteum

Image 12.21a shows the zona pellucida (labeled "ZP" in image 12.21a) surrounding the oocyte. The zona pellucida is locally folded due the removal of the germ cell. The antrum, the central cavity, is filled with liquor folliculi and is surrounded by follicle cells, which are collectively called the membrana granulosa (labeled "MG"in image 12.21a). The follicle cells that invest the germ cell and suspend it into the antrum collectively constitute the discus proligerus (labeled "DP" in image 12.21a), and the follicle cells immediately surrounding the zona pellucida constitute the corona radiata (labeled "CR" in image 12.21a).

Image 12.21b shows a secondary follicle. The zona pellucida (arrow in image 12.21b), the coronal radiata (labeled "a"in image 12.21b), the follicle cells of the membrana granulosa layer (labeled "b" in image 12.21b), and an outer theca layer (labeled "c" in image 12.21b). Toward the end of the menstrual phase days (4 to 5) about 20 of the primary follicles develop into secondary follicles. The secondary follicle contains a secondary oocyte. Image 12.21c shows a ruptured bloodied follicle called the corpus hemorrhagicum. Image 12.21d is a closer view of this post-ovulatory follicle. Following ovulation the ovarian follicle partially collapses and blood within it forms a clot. Image 12.21e shows the transformation of the corpus hemorrhagicum into a corpus luteum. The clot is being absorbed by the remaining follicular cells and there is enlargement to form the corpus luteum (labeled "a" in image 12.21e).

12.22 Mammary Glands

The diagram in image 12.22a is of the human breast. Image 12.22a shows the many glandular secretion elements. This glandular tissue (compound tubulo-alveolar glands) functions to produce milk and then the milk passes into the lactiferous ducts. Each duct has a dilated region called the ampulla in which the milk is stored. The milk is then ejected by a hormonal trigger (oxytocin). Image 12.22b shows a close-up view of an alveolus of a mammary gland and image 12.22c is an even more magnified view of the glandular tissue. Image 12.22d shows a highly magnified view of the inner epithelium of the alveolus of an active mammary gland.