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Female Reproductive System |
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| Atlas (Wheater's 6th ed.): | ||
| Text (Junquiera's 15th ed.): | ||
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
I. OVARY and OVIDUCTWebslide 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).
II. UTERUSThe 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).
III. UTERINE CERVIXWebslide 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.
IV. VAGINAWeblide 250-1 (courtesy of UMich): Human vagina, H&E [DigitalScope] 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&E and trichrome-stained sections are parasympathetic ganglia that innervate the erectile tissue (i.e. the numerous small veins) of the lamina propria.
V. MAMMARY GLANDWebslide 259 (courtesy of UMich) Mammary gland, inactive (nulliparous), 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 irregular 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 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 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. These plasma cells are the source of secretory IgA in the milk. Finally, consider the organizational differences between the thyroid, prostate, and mammary glands (sometimes classified as “look-alikes in histology”).
VI. PLACENTASlide 253 Placenta, early, H&E [DigitalScope] With the implantation of a zygote into the uterus, a number of changes take place in the endometrium. Cells from the embryonic trophoblast invade the uterine mucosa, secretions from these cells coalesce to form lacunae in the endometrium, which is now termed the decidua. These spaces also contain maternal blood. The trophoblast rapidly invades the decidua forming primary chorionic villi, that contain only trophoblast cells (outer syncytiotrophoblast and inner cytotrophoblast). Mesenchyme and blood vessels form the core of the secondary villi. During the second half of pregnancy the cytotrophoblast cells disappear and the capillary basal lamina fuses with that of the syncytiotrophoblast to improve exchange. Begin with slide 253, which is early placenta. The entire field is filled with chorionic villi cut predominantly in cross section. Mesenchymal tissue and fetal blood vessels (filled with fetal RBCs, which, in the early stages of fetal hematopoiesis, still have nuclei) make up the core of each villus which is covered by a trophectoderm shell of inner, cytotrophoblast and outer syncytiotrophoblast cells. The syncytiotrophoblast cells are more eosinophilic and have smaller nuclei. As the name implies, these cells result from the fusion of many cells and thus have many nuclei per cell and no discernable lateral boundaries. In contrast, cytotrophoblast cells are clearly demarcated, have a single, large nucleus and basophilic cytoplasm. Notice that there is almost a complete ring of cytotrophoblast cells covering each villus in early placenta --these cells function largely as progenitor cells for the formation of the syncytiotrophoblast, and they become less numerous as the pregnancy continues. Study slide 255, which is a late placenta. Although you will be able to see an occasional cytotrophoblast cell, you will not be able to see forming villi in this late placenta. Examine the trophectoderm shell, which now consists of multinucleated syncytiotrophoblast cells located on the outer surface of the villi as well as an occasional residual underlying cytotrophoblast cell. The nuclei of the syncytiotrophoblast cells often form aggregates of so-called "syncytial knots" that may look like specks of dirt when viewed at lower magnification. Syncytiotrophoblast cells that are bathed in maternal blood have apical surfaces specialized for absorption (microvilli), pinocytosis, and exocytosis and an appearance typical of secretory cells. The syncytiotrophoblast cells also convert DHEA from the fetal adrenal glands to progesterone to replace the function of the corpus luteum in maintaining the uterine endometrium during the remainder of the pregancy after the corpus luteum degenerates. Large quantities of an amorphous eosinophilic substance, fibrinoid, may also be deposited in the intervillus space in this older placenta. This material clings to the villus surface and may bind several villi together. The amount of fibrinoid in combination with the appearance of the connective tissue in the villi can be used to stage the placenta.
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.
DO THIS AFTER YOU HAVE DONE EVERYTHING ELSE Webslide 0314_I: Ovary, ovulating, cat [DigitalScope] This slide shows a set of serial sections from an ovary. In the top left hand corner of the bottom set of sections, is a follicle that is in the process of rupturing.
Practice Questions 1. Which structure in the ovary contains a fully developed oocyte surrounded by cumulus cells and a large, fluid-filled antrum?
2. The corpus luteum primarily secretes which hormone to maintain the endometrium?
3. The epithelial lining of the oviduct is best characterized by which feature?
4. The secretory phase of the uterine cycle is histologically characterized by:
5. Active mammary glands are primarily characterized by the presence of:
6. Which cells in the placenta produce human chorionic gonadotropin (hCG)?
7. A 28-year-old woman in the late proliferative phase of her menstrual cycle undergoes an endometrial biopsy. The histological report describes straight tubular glands and a dense stroma. Which hormone is most responsible for these changes?
8. A 29-year-old woman presents with irregular menstrual cycles. A biopsy of the endometrium shows a thin functional layer and an intact basal layer. What phase of the menstrual cycle does this indicate?
Organ Review OSU_044 [DigitalScope] Identify as specifically as possible the organ shown in the slide AND provide at least FOUR specific or characteristic features (e.g. specific cell types and/or arrangements of cells/tissues in the organ) supporting your identification. For EACH feature listed, provide a brief explanation regarding its functional significance and/or how that feature is helpful in terms of distinguishing the organ. [ANSWER]
Extra Slides I. OVARYSlide 239 (ovary, monkey, 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] 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. UTERUSSlide 244 (uterus, proliferative 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.
IV. UTERINE CERVIXSlide 249 (cervix, H&E) [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. VAGINASlide 250-1 (vagina, H&E) [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 Gland259 Mammary gland, inactive, nulliparous, 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.
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