Wheater's (6th ed.), Ch 19, Female Reproductive System

Stevens and Lowe's (4th ed.), Ch 17, Female Reproductive System

Overview:

The goal of this lab is to examine the microscopic anatomy of the female reproductive system and associated structures.  Remember that this system is dynamic.  The histology reflects this feature, so there is not one view of these organs, but a cycling continuum.

Slide Descriptions

Webslide 0069_I:  Ovary and oviduct, monkey, Masson  [DigitalScope]  

At low magnification note the general features of the ovary at the bottom of the section: the wide outer cortical region containing follicles, the central medulla, and the hilus (on the left).

In the cortex, locate primordial follicles, primary follicles, and secondary (antral) follicles, most of which are atretic.  Notice the organization of the granulosa cells in the various types of follicles and try to find intact oocytes.  The zona pellucida around each oocyte is not as well preserved on this slide as on the next Webslide 0068.  Also find the large corpus luteum and the much smaller corpus albicans.  What are the differences in their respective structures and function?  Some cells of the connective tissue stroma assemble around developing follicles and differentiate into the theca interna (rounded cells directly under the granulosa cells) and theca externa (more elongated cells).  Describe the mesothelium covering the ovarian cortex.   How does it differ in structure from the mesothelium that you have seen covering other organs?  (This ovarian mesothelial layer used to be called the “germinal epithelium” because it was once believed to give rise to the germ cells.  Now it is known that the germ cells migrate into the ovary early in development.)

The medulla contains large blood vessels and is continuous with the hilus on the left side of the section.  Large arteries and veins can be observed in the hilus, which is covered by a simple squamous mesothelium.

Next examine the infundibulum of the oviduct near the top of this section. Observe the extensive folding of its surface and the presence of fimbriae that extend toward the ovary and are sectioned at various angles.  What is the function of these fimbriae? Cilia can be observed on some of the simple columnar cells.

Webslide 0068_I:  Ovary follicles, monkey, H&E  [DigitalScope]

In this thin section look for the same structures that you identified in the previous slide.  Although the hilus is not present in this slide, you should be able to distinguish cortex from medulla by the presence of follicles in the cortex and large blood vessels in the medulla.  In this thin section it is often possible to see the zona pellucida between the oocyte and the granulosa cells, particularly in large secondary follicles.   Around the secondary follicles note the theca externa and theca interna, with the some of the cells in the latter distinguished by the presence of lipid droplets in their cytoplasms.  You should also be able to find nests of primordial follicles near the outside of the cortical region.  Multiple corpora albicans are present in this section.

Webslide 236a (courtesy of UMich):  Ovary with corpus luteum, human, H&E  [DigitalScope]

This is a functional corpus luteum.  What are the differences in appearance of theca lutein and granulosa lutein cells?  Are there blood vessels in the corpus luteum?  How did they get there?

Webslide 198 (courtesy of UMiss):  Fallopian tube (oviduct, isthmus), primate, cross section, H&E  [DigitalScope]

Find the three layers of the oviduct wall, mucosa, muscularis, and serosa.  Focus on identifying the ciliated and secretory (“peg”) cells of the mucosal epithelium, which is well preserved in this slide.   Note the inner circular and outer longitudinal smooth muscle layers in the muscularis, as well as the simple squamous mesothelium covering the serosa.  Observe the major structural differences between the isthmus (this slide) and the infundibulum of the oviduct (Webslide 0069).

The next four sections are from the uterus at different phases of the menstrual cycle.  In comparing the proliferative and secretory phases note the thickness of the endometrium (thicker in the secretory phase) and the shapes of the glands (more coiled or “corkscrew” regions in the secretory).

Webslide 0066_I:Uterus, monkey, proliferative, H&E  [DigitalScope]

This is a cross section of the uterus in the proliferative phase.  At low power identify the different layers of the uterus (endometrium, myometrium and perimetrium).   Note that the endometrial glands are relatively straight and lined with columnar epithelium. Occasional mitoses can be seen.  The stroma is a highly cellular connective tissue. Although textbooks say that the uterus has three muscle layers, these layers are not as distinct as the layers found in the GI or urinary tracts.  Rather swirls or whorls of muscle cells are seen.   The perimetrium consists of connective tissue covered by a simple squamous mesothelium.

Webslide 0041_I:  Uterus, human, early proliferative,  H&E  [DigitalScope]

Again note the presence of relatively straight glands lined by simple columnar epithelium in the endometrium and whorls of smooth muscle in the myometrium.  Although the epithelium of the uterus is the same as in the oviduct, it is difficult to distinguish secretory and ciliated cells in this slide.  However, careful examination will allow detection of basal bodies in the ciliated cells, with no basal bodies in the secretory cells. 

 

 

Webslide 0067_I:  Uterus, human, early secretory,  H&E   [DigitalScope]

Compare at low magnification the glands in this secretory uterus to what you observed in the previous slides.  Note the obvious difference in their height and the length of the coiled regions of the glands.   Simple columnar epithelium covers the uterine surface and lines the glands.  At high power, ciliated and secretory cells can be observed in the surface epithelium but not in the glands.

 

 

 

Webslide 0305_I:  Uterus, human, early secretory,  H&E   [DigitalScope]

This slide is similar to Webslide 67 above; quickly note the BASAL location of the glycogen in the cells of the glands indicating that this sample was obtained while in the early secretory phase of the uterine cycle.

Webslide 249 (courtesy of UMich):  Human Cervix, H&E   [DigitalScope]

This slide spans the boundary between the uterine cervix and the vagina. 

First, scan at low power the cervix on the lower edge of the section and observe the cervical glands in the endometrium.  Notice that the large, branched glands differ in shape from the glands in most of the uterus (previous slides). Unlike in the rest of the uterus, the endometrium in the cervix changes little in thickness during the menstrual cycle.  Much of the cervical surface epithelium is not present in this slide, but you should be able to identify the simple columnar epithelium cells lining the cervical glands that secrete mucus serving to lubricate the vagina.  The myometrium contains bundles of smooth muscle, and the simple squamous mesothelium covering the perimetrium is evident in your slide.

Although the epithelium at the boundary of the cervix and vagina is not preserved, the non-keratinized stratified squamous epithelium of the vagina is present at the right hand surface of the slide.  The outer layers of these epithelial cells are filled with glycogen giving them an empty appearance, characteristic of this vaginal epithelium.  The vaginal mucosa is highly vascularized, but contains no glands.  The ill-defined muscle layers contain bundles of smooth muscle. The muscle layers grade into an adventitia.

Weblide 250-1 (courtesy of UMich): Human vagina, H&E  [DigitalScope]
Webslide 250-2 (courtesy of UMich): Human vagina, trichrome  [DigitalScope]

The vagina connects the female reproductive system to the exterior of the body. At low magnification, note its three-layered structure: the mucosal lining, smooth muscle layer, and outer adventitial layer. The epithelium that lines the vagina is stratified squamous, which appears slightly vacuolated due to the presence of glycogen in these cells, which is removed during fixation.

The connective tissue of the thick lamina propria contains many elastic and collagen fibers throughout and many small veins in the deeper region. The subjacent smooth muscle layers are arranged in poorly defined inner circular and predominant outer longitudinal layers; it may be easier to discern the smooth muscle from the surrounding connective tissue in the trichrome-stained section. The connective tissue (seen particularly well in sections stained with trichrome) of the outer adventitial layer also contains many elastic fibers, thus contributing to the overall distensibility of this region. Also evident in the adventitia in both H&Eand trichrome-stained sections are parasympathetic ganglia that innervate the erectile tissue (i.e. the numerous small veins) of the lamina propria.

Webslide 259 (courtesy of UMich) Mammary gland, inactive (nulliparous), H&E  [DigitalScope]
Webslide 258 (courtesy of UMich) Mammary gland, active (pregnant), H&E  [DigitalScope]

The mammary gland contains multiple lobules separated by connective tissue septa that often contain fat.  Each lobule contains tubuloalveolar glands and intralobular ducts, whereas larger interlobular ducts can be seen in the CT septa.  A key structural feature is that the glands and intralobular ducts are lined by simple cuboidal epithelium, whereas the interlobular ducts are lined by stratified cuboidal epithelium (similar to the ducts of sweat glands).  Remember that this is a changing scene and the relative sizes of the lobules and septa can change; when the glands are distended the interlobular tissue can appear as thin septa between the lobules.  In this lactating mammary gland some of the alveoli and ducts contain red-staining secretory product.

Finally, consider the organizational differences between the thyroid, prostate, and mammary glands (sometimes classified as “look-alikes in histology”).

Pathology Correlate:

Slide 33  [DigitalScope]

This slide contains a biopsy of the uterus from a 38-year-old woman who presented with irregular menstruation and intesne, episodic uterine cramping. Grossly, the myometrium was distorted by numerous circumscribed nodules ranging in size from 2 to 6 centimeters. As you inspect this slide at low magnification, you will note a roughly circular area in the center of the tissue section that stains more deeply than the surrounding myometrium. This area is not really encapsulated, but it looks different, and seems to be separated from the adjacent myometrium along at least part of its circumference.

• Note that this circumscribed area is more densely cellular, with a higher concentration of nuclei and a bluer color.

• Note the structure of the surrounding normal myometrium -- interlacing bundles of spindle-shaped cells that run in fascicles. Some of these fascicles are cut longitudinally, and others in cross-section.

• You will see that the neoplasm is also composed of interlacing bundles of spindle shaped cells. While not actually encapsulated, the nodule is easily distinguished from its surroundings by its denser cellularity and darker color.

• Compare the nuclei in the neoplasm with those in the normal myometrium and note that they are essentially identical (although more closely packed).

Extra Slides

I. OVARY

Slide 239 (ovary, monkey, H&E)  [DigitalScope]
Slide 269 (ovary, monkey, PAS)  [DigitalScope]
Slide 269-2 (ovary, monkey, PAS)  [DigitalScope]
Slide 235 (ovary, human, H&E)  [DigitalScope]
Slide 234 (ovary, human, H&E)  [DigitalScope]
Slide 234-2 (ovary, human, trichrome)  [DigitalScope]
Slide 236a (ovary, human, H&E)  [DigitalScope]

Overview: The ovaries are paired organs situated on either side of the uterus. They are attached on one edge, the hilus, to the broad ligament of the uterus by a fold of peritoneum, the mesovarium. Using slide 239, examine the overall topography of the ovary and note the numerous vessels which enter it via the broad ligament. The inner medulla (present in most slides) is highly vascular and composed of a loose connective tissue core. Examine the outer cortex of the ovary which is composed of stroma and numerous follicles in various stages of development. In slide 239, note the layer of collagenous connective tissue, the tunica albuginea [example] just below the surface epithelium (mesothelium/serosa often misleadingly referred to as “germinal epithelium”) that covers the ovary.

Examine the stroma of the cortex in slide 239 and note the whorls of closely-packed, spindle-shaped fibroblasts. The cortex also contains many oocytes (300,000- 400,000 at birth) embedded in this cortical stroma. Because of the variation in sectioning, age and stage of the cycle, you will have to study several slides in order to study all aspects of follicular development, atresia and corpus luteum formation.

Primordial & Primary Follicles: Examine several primordial follicles [example] using slide 239 or 269 and note that they consist of a large oocyte surrounded by a layer of flattened follicular cells. Next examine the appearance of primary follicles [example] in which the large oocyte is surrounded by a layer of cuboidal follicular cells (also good in slide 238). These follicular cells proliferate to form a loose multi-layer, the granulosa cell layer. A rim of neutral glycoprotein, the zona pellucida (clear zone), surrounds the oocyte separating it from the surrounding granulosa cells. Slide 269 has been stained with PAS, so that carbohydrates and connective tissue are highlighted. Using this slide, examine the zona pellucida [example] of several smaller follicles. Stromal cells form a dense sheath (theca) around the follicle.

Secondary Follicles: Examine the structure of several secondary follicles [example] and observe that between the stratified granulosa cells there are large lacunae that coalesce to form the follicular antrum. The stromal cells surrounding the follicle have differentiated to form an inner layer (theca interna) of plump cells that secrete steroid precursors and an outer layer (theca externa) composed of concentrically arranged stromal cells that provide support for the developing follicle. Slide 235 also has good theca layers (see below).

Mature/Graafian Follicle: With continued development, the follicle becomes a Graafian or ovulatory follicle [example] [CAVEAT]. The granulosa zone now consists of many layers of cuboidal follicular epithelial cells located at the periphery of the large, well-formed follicular antrum. The oocyte has attained its full size, is located eccentrically within the follicle in a small hillock, the cumulus oophorus which protrudes into the antrum. The zona pellucida is surrounded by a continuous layer of follicular cells, the corona radiata. Because of its size, the oocyte will not be present in every section of the follicle, but examine the other components of a tertiary follicle. The theca interna is separated from the granulosa cells by a distinct basement membrane. Theca externa cells are densely packed, spindle-shaped cells which blend with the theca interna cells and with the surrounding stroma. Note that the theca interna has a rich capillary vascular supply, particularly well demonstrated in slide 235 [example] (see the diagram in R pg 779, 23.7a).

Atretic Follicles: Because the contents of only one follicle are usually ovulated at a time in humans, other follicles which have been stimulated to develop must degenerate, or undergo atresia [example]. Atresia is not limited to mature follicles, but may begin at any stage in follicular development. Early atretic alterations include: clumping of the nuclear chromatin (pyknosis) and shrinkage and lysis of the cytoplasm of the oocyte, granulosa or follicular cells. Examine the pyknotic granulosa cells [example], which are sloughed into the follicular antrum. The basement membrane that separates the granulosa cells from the theca interna may also thicken considerably to form a so-called “glassy membrane.” These changes are especially well illustrated in H&E slide 234 [example] and trichrome-stained slide #234-2 [example]. Make sure you are able to differentiate atretic changes from artifacts related to shrinkage due to fixation. Macrophages may eventually invade the center of the larger atretic follicles that are finally replaced by loose connective tissue.

Corpus Luteum: After ovulation, the follicle which housed the ovum collapses and becomes highly infolded and invaded by vessels, forming the corpus luteum [example] (yellow body). Examine slide 236a and observe that the corpus luteum appears pale and very folded. If the egg is fertilized and implants, the corpus luteum enlarges to become the corpus luteum of pregnancy. Examine the inner granulosa lutein cells [example] (formed from the remaining granulosa cells) and the outer theca lutein cells [example] which come from the remaining theca interna cells. Both cell types are polyhedral and filled with lipid droplets and have centrally located nuclei. The theca lutein cells are, however, considerably smaller, more darkly staining and have fewer lipid filled vacuoles than the granulosa lutein cells. They are found most prominently in the infoldings right up against the granulosa lutein layer. Granulosa lutein cells contain a pigment, lipochrome, which produces the yellowish color of the corpus luteum in an unfixed ovary. A central blood clot may be present in recently ovulated follicles.

Corpus Albicans: If the egg is not fertilized, the corpus luteum degenerates, and is gradually infiltrated with collagen and a few (if any) fibroblasts, forming the corpus albicans (white body) particularly evident in slide 234 stained with H&E [example] and trichrome [example]. The corpus albicans is also formed during the later half of pregnancy when the placenta takes over steroid secretion from the corpus luteum. Excellent examples of corpus albicans can be best observed in slides 234 or 236. 

II. OVIDUCTS (FALLOPIAN or UTERINE TUBES)

Slide 240-1 (oviduct, infundibulum, H&E)  [DigitalScope]
Slide 240-2 (oviduct, ampulla, H&E)  [DigitalScope]
Slide 241even (oviduct, isthmus, H&E)  [DigitalScope]
Slide 241odd (oviduct, uterine segment, H&E)  [DigitalScope]

The oviduct conducts the ovulated egg from the peritoneal cavity to the uterus over a period of approximately three days, during which fertilization and segmentation of the zygote occurs. There are striking regional variations in the oviducts that reflect:

1) the trapping of the egg, 2) a region where fertilization takes place, and 3) a region simply for transport to the uterus.

Examine its open end near the ovary, the infundibulum [example], in slide 240-1 and note the funnel shape and ridges of mucosa that extend as a fringe of finger-like projections known as fimbriae. Note the ciliated cells that cover the fimbria that help sweep the egg into the oviduct. Move on to slide 240-2 to trace the passage of the egg from the infundibulum through the numerous longitudinal folds of the ampulla [example] recalling that this is where fertilization usually occurs. Next is the isthmus region in slide 241even [example] that is characterized by tall branching ridges of mucosa which project into and partially fill the lumen of the oviduct. Note the numerous non-ciliated secretory (peg) cells and the ciliated cells that line the lumen. The isthmus contains tall folds and few ciliated cells, while the interstitial (or intramural because it’s within the uterine wall) segment, shown in slide 241odd, [example] has low ridges and a preponderance of secretory cells. Observe that as you progress from the infundibulum where there is a large lumen filled with many mucosal folds toward the uterus, the overall luminal diameter decreases, as does the number of ciliated cells, while the proportion of smooth muscle in the muscular layer gradually increases.

Examine the loose connective tissue of the lamina propria using slide 241even. Next, study the muscularis organized roughly into circular, oblique, and sparse longitudinal layers of smooth muscle. It has been suggested that this muscle may play a two-fold role; first, in distending the oviduct toward the ovary to aid in “capturing” the ovum; and second, in producing peristaltic waves which help propel the ovum toward the uterus. The outermost layer of the oviduct, the serosa, is highly vascular and is composed of mesothelium and thin underlying connective tissue that is continuous with the broad ligament.

III. UTERUS

Slide 244 (uterus, proliferative phase, H&E)  [DigitalScope]
Slide 243 (uterus, early secretory phase, H&E)  [DigitalScope]
Slide 245-1 (uterus, secretory phase, H&E)  [DigitalScope]
Slide 245-2 (uterus, menstrual phase, H&E)  [DigitalScope]

The uterus is a pear-shaped, hollow organ partially covered by peritoneum. Examine the overall topographical organization of the uterus from its outer serosal or adventitial covering, through the thick muscular layer (myometrium) to the mucosa (endometrium) in slide 243 (this slide is actually at a stage between proliferative and secretory).

The myometrium [example] of the uterus is composed of interwoven bundles of smooth muscle supported by dense connective tissue. Examine their arrangement into indistinct bundles, with several bundles running roughly parallel to the long axis of the body of the uterus. During pregnancy, the muscle fibers elongate, proliferate and produce collagen in response to hormonal stimulation.

The endometrium [example] is divided into two layers or strata and consists of a simple columnar epithelium and an underlying stroma that contains tubular glands that may branch near the myometrium. The stratum functionale or functional layer is the thicker, outer layer that is sloughed off with menstruation. The underlying stratum basale or basal layer is retained throughout the menstrual cycle and serves as the regenerative source of the stratum functionale. The endometrium undergoes striking cyclical modifications that depend on sequential hormonal alterations. Compare specimens from proliferative and secretory phases with the menstrual phase.

1. Proliferative Phase (days 5-14): In slide 244 [DigitalScope], the proliferative phase is underway and glands have proliferated and cover the surface. Although difficult to see in these sections, spiral arteries [example] are elongated and convoluted, and extend from the basal layer into the functional layer.
2. Secretory Phase (days 15-28): In slide 245-1 [DigitalScope], observe that the glands of the secretory phase endometrium appear convoluted. Toward the end of this phase, apical tissues become ischemic and glands take on a characteristic “saw tooth” appearance [example]. The endometrium reaches its maximal thickness during this period, and spiral arteries continue to grow and extend into the superficial regions of the functional layer. There is also considerable leukocyte infiltration in the stroma.
3. Menstrual Phase (days 1-4): In slide 244-2 [DigitalScope], much of the stratum functionalis has sloughed away, and amongst the debris are numerous blood cells (RBCs and leukocytes). Notice that the stratum basalis remains intact.

IV. UTERINE CERVIX

Slide 249 (cervix, H&E)  [DigitalScope]
UCSF slide 405 (cervix, trichrome)  [DigitalScope]

The uterine cervix shown in slide 249 is continuous with both the body of the uterus and the upper portion of the vagina. Note that the wall has considerable smooth muscle and much dense connective tissue. Note also the number of collagen fibers in the stroma.

The mucosa is lined by a tall columnar mucus-secreting epithelium in its uterine portion, but note the abrupt change to stratified squamous epithelium at its vaginal face. This stratocolumnar junction which should be readily identifiable in both slide 249 [example] and UCSF slide 405 [example] is frequently the site of pre-neoplastic and neoplastic (cervical cancer) changes. The mucosa is thrown into deep irregular folds known as plicae palmitae (palmate folds). During the majority of the uterine cycle these glands secrete a highly viscous mucus forming a barrier to microorganisms, while at mid-cycle (ovulation) the mucus becomes more hydrated, which facilitates sperm entry. Blockage of the openings of the cervical mucosal glands frequently results in the accumulation of secretory products within the glands, leading to the formation of dilated Nabothian cysts which may be seen in USCF slide 304 [example]. These cysts are generally benign; however, they can become clinically relevant should they become enlarged enough to cause obstruction of the cervical canal.

V. VAGINA

Slide 250-1 (vagina, H&E)  [DigitalScope]
Slide 250-2 (vagina, trichrome)  [DigitalScope]

The vagina connects the female reproductive system to the exterior of the body. At low magnification, note its three-layered structure: the mucosal lining, smooth muscle layer, and outer adventitial layer. The epithelium that lines the vagina is stratified squamous, which appears slightly vacuolated due to the presence of glycogen in these cells, which is removed during fixation.

The connective tissue of the thick lamina propria [example] contains many elastic and collagen fibers throughout and many small veins in the deeper region. The subjacent smooth muscle layers [example] are arranged in poorly defined inner circular and predominant outer longitudinal layers; it may be easier to discern the smooth muscle from the surrounding connective tissue in the trichrome-stained section [example]. The connective tissue (seen particularly well in sections stained with trichrome) of the outer adventitial layer also contains many elastic fibers, thus contributing to the overall distensibility of this region. Also evident in the adventitia in both H&E [example] and trichrome-stained sections [example] are parasympathetic ganglia that innervate the erectile tissue (i.e. the numerous small veins) of the lamina propria.

VI. Mammary Gland

259 Mammary gland, inactive, nulliparous, H&E   [DigitalScope]
258 mammary gland, active, (pregnant) H&E   [DigitalScope]

Like the other tissues in the female reproductive system, alterations in circulating hormone levels result in histologically demonstrable changes in the mammary gland. Compare the examples of an inactive and active glands, noting the differences in the amount of glandular tissues. In slide #259 (inactive gland) note the dense irrengular interlobular connective tissue found between quiescent glandular lobules that consist of only a few clusters of small ducts surrounded by a mass of less dense intralobular connective tissue. Many ducts appear to be composed of 2 layers of cuboidal epithelium. The inner layer are the actual ductal epithelial cells whereas the outer layer of cells is, in fact, a layer of myoepithelial cells. 

In slide #258 (active gland), you can see that the amount of the glandular tissues has increased, while that of the connective tissue has decreased.  This increase involves the numbers of both the epithelial cells and myoepithelial cells.   The proliferation of these cells lead to the formation of secretory alveoli. Note also the increased cellularity (especially, the plasma cells) of the intralobular connective tissue. This tissue was probably taken from an individual before the last trimester. When compared with the inactive mammary gland, you can see that the intralobular ducts have proliferated to form additional secretory regions. Both the epithelial cells and myoepithelial cells increase in number. Alveoli [example] have formed, their epithelial cells have large, clear areas of apical cytoplasm, a region occupied by glycogen and lipid. Note the increased cellularity of the intralobular connective tissue. Note also that not all lobules within the gland have proliferated to the same degree. In many sections, portions of a large excretory, lactiferous ducts [example] are present. The epithelial lining is again two layered, the bottom layer being principally myoepithelium. Compare the morphology of the inactive and active gland. Observe the intralobular connective tissue and note the abundance of plasma cells [example]. These plasma cells are the source of secretory IgA in the milk.