Cell and Tissue Biology

Female and Male Reproductive Systems

Terms List

The key objects to concentrate on during this lab are listed below. You need to learn 1) how to recognize each object, 2) understand it's primary functions, and 3) understand how structure is related to function.

Female Reproductive System

  • Ovary, cortex, medulla, mesothelium
  • Primordial follicle, primary (unilaminar and multilaminar), secondary (antral) and Graffian follicles
  • Oocyte nucleus, cytoplasm, zona pellucida
  • Corona radiata; cumulus oophorus, antrum follicular fluid
  • Ovulating oocyte, atretic follicle
  • Granulosa cells, theca (interna and externa) cells
  • Corpus hemorrhagicum, corpus luteum, granulosa lutein cells, theca lutein cells, corpus albicans
  • Interstitial cells of stroma
  • Oviduct, mucosa, mucosa fold, fimbria, infundibulum, ampulla, isthmus
  • Ciliated and secretory cells
  • Cervix and vaginal epithelium, submucosa and smooth muscle externa
  • Uterine endometrium and myometrium, uterine glands
  • Endometrial Functionalis, spiral arteries, Basalis
  • Menstrual, proliferative and secretory phases of the endometrial cycle
  • Placenta, trophoblast cells, cytotrophoblasts, syncytiotrophoblast
  • Chorionic villi, lacunae and maternal blood
  • Fetal blood, umbilical cord, chorionic basal plate, endometrial blood vessels, the placental barrier components
  • Maternal side of placenta
  • Decidua, decidua basalis; decidual cells; spiral arteries
  • Mammary gland, inactive and active; adipose tissue
  • Lactiferous ducts; secretory lobules
  • Alveoli; alveolar epithelial cells, lipid vacuoles
  • Myoepithelial cell, immune cells

Male Reproductive System

  • Testis interstitial space, seminiferous tubules
  • Rete testis, connective tissue septa, tunica albuginea
  • Sertoli cells, Leydig cells
  • Spermatogonia, spermatocytes
  • Round spermatids, elongate spermatids, mature sperm
  • Mitosis, meiosis
  • Rete testis, efferent ductules, ciliated cells, nonciliated cells
  • Epididymis, caput versus cauda, epithelium, principle cell, narrow and basal cells, branched microvilli (also called stereocilia), ductus deferens
  • Seminal vesicle mucosal folds, epithelium, secretory cells, smooth muscle
  • Prostate, mucosa, glandular epithelium, submucosa, smooth muscle, tubule and duct
  • Prostatic urethra, transitional epithelium, mucosa, submucosa, urethral glands versus main body
  • Pelvic urethra, skeletal muscle
  • Bulbourethral glands, mucous epithelium

Although the major emphasis of this laboratory is on reproductive organs per se, slides of the hypothalamus and hypophysis are included because of the major role these glands play in regulating reproductive function.

w78d Third ventricle, monkey

The hypothalamus produces bursts of gonadotropin-releasing hormone (GnRH). GnRH in turn stimulates synthesis and release of LH and FSH from the hypophysis. Click link [4]. Identify the hypothalamic neurons. The axons from these neurons travel to the median eminence (identify) and release the GnRH into the circulation. Identify the blood vessels. Also identify the pars tuberalis, a part of the anterior pituitary.

GnRH released at the median eminence reaches the anterior pituitary via the hypothalamo-hypophyseal portal circulation.

w97a Hypophysis, chinchilla

The anterior pituitary (adenohypophysis) houses cells that produce LH and FSH. It is now known that basophils are responsible for the production of those two hormones which travel through the circulatory system to their target tissues, the ovaries and the testes. Go to link [1,1,1,1,1]. Identify the basophils some of which produce LH and FSH. Identify the acidophils. Separate acidophils release growth hormone and prolactin. Elevated prolactin levels (as in lactation) inhibit GnRH secretion. Note the close association of these polypeptide hormone secreting cells with the sinusoidal capillaries. The capillaries thus have a role both in delivering the stimulus (GnRH) for hormone production and in carrying away the resulting hormonal products (FSH/ LH).

w63 Ovary, monkey

The ovary can be roughly divided into a cortex and medulla. Identify the cortex. Click [1,1,1]. The ovary is lined with simple cuboidal epithelium (identify). The epithelium was erroneously referred to as "germinal epithelium" by earlier authors who thought that oocytes were derived from it. We now know that the primordial germ cells travel from the yolk sac to the embryonic gonad and divide mitotically.

During fetal life millions of oogonia are produced, some of which commence meiosis to yield primary oocytes. These are arrested in prophase (diplotene) of meiosis until just before ovulation. Most oocytes die during fetal and post-natal life, but up to 400,000 remain at puberty in the ovaries.

Click the thumbnail and follow [1,3]. Identify a primordial follicle which consists of an oocyte surrounded by flat follicular cells. Identify the nuclei of these cells. Most of the oocytes within the ovary are located within such primordial follicles.

Some primordial follicles start developing for no apparent reason. The flat follicular cells divide and become cuboidal. The follicle is then called a unilaminar primary follicle (identify). The follicular cells multiply further and become stratified. They are often referred to as the granulosa layer. The oocyte itself becomes bigger.

In addition, the size of the entire follicle increases due to frequent mitoses in the granulosa layer. The follicle is now termed a multilaminar primary follicle. Zoom out once. Then click [4]. The zona pellucida (identify) appears between the oocyte and the granulosa cell layer, being very likely produced by both. The ovarian stromal cells surrounding the follicle arrange to form the theca interna (identify). The follicle is now under the control of FSH and starts producing estrogen.

Click link [1]. The oocyte has almost reached its final size. (Compare the size of the oocyte to the granulosa cells surrounding it.) Note the large, eccentric nucleus of the oocyte. The cytoplasm is replete with RNA, Golgi complexes, mitochondria, and precursors of cortical granules (identify). LH stimulates the theca interna to produce an androgen which is then converted (aromatized) to estrogens by the adjacent granulosa cells. Granulosa cells also produce polypeptide hormones (for example, inhibin and follistatin). A basal lamina separates the theca from the granulosa cells although it cannot be seen in this view.

Click the thumbnail and follow [1,5]. This shows a portion of a preovulatory, mature (Graafian) follicle. (You may see the entire structure by zooming out once, but don't forget to come back.) In humans (unlike many other mammalians that produce litters) only one follicle ovulates during each cycle. Somehow this dominant follicle inhibits the development of competing follicles in both ovaries. The follicle has become enlarged primarily due to the accumulation of fluid (liquor folliculi). Identify the highly vascularized theca interna.

The fate of most of the follicles in the ovary is death (atresia). The atresia can occur at any stage of follicular development. Small follicles are phagocytosed by macrophages and disappear without a trace. All structures of the larger follicles disappear except for remnants of the hyalinized basal lamina, referred to as the glassy membrane. Identify such an atretic follicle.

Click link [1]. In the mature follicle the oocyte is protected by an accumulation of granulosa cells called the cumulus oophorus (identify). The cells immediately surrounding the oocyte are called the corona radiata (identify). These cells will continue surrounding the oocyte even after ovulation. Just before ovulation the primary oocyte finishes meiosis I, triggered by a surge of LH, resulting in the production of the secondary oocyte and the first polar body. The secondary oocyte retains almost all of the cytoplasm. Notice the mitotic figures visible in the granulosa cells.

Click link [1] and note the labeled structures. Zoom out once and click link [2]. Notice the mitotic figures. The granulosa cells are still actively dividing at this point, but will stop dividing after ovulation. Click links [1] and [2] to see higher-power views of mitotic figures.

Click the thumbnail and follow [1,5,2] to see a higher-power view of the granulosa cell layer, the theca interna and the theca externa. Note the rich capillary bed in the theca interna. The theca externa is composed of stromal cells resembling fibroblasts. There are also some smooth muscle cells intermingled, but those are not evident in this view. The smooth muscle cells are thought to aid in the ovulation process.

Click the thumbnail and follow [2]. This provides a review of the structures described above. Pay particular attention to the abundance of atretic follicles.

Click the thumbnail and follow [4]. This corpus luteum (identify) is regressing but is still actively producing estrogen, progesterone and inhibin. Note the abundant vasculature. Click [1] to see a higher magnification view.

Click the thumbnail and follow [3,1,1] to see active corpus luteum cells at higher magnification. Notice the abundance of lipid droplets containing cholesterol, the precursor of sex steroids. These cells also have a highly developed SER, necessary to carry out the many hydroxylation reactions involved in sex hormone syntheses.

b62 Corpus luteum, human

The slide shows a portion of one corpus luteum with a small amount of surrounding ovarian tissue. After ovulation the follicle collapses. The basal lamina between the theca interna and granulosa cells breaks down. Blood vessels grow into granulosa cells from the theca interna. The theca and the granulosa cells luteinize. This involves enlargement of cell size along with a decrease in RER and an increase in SER and lipid content. Luteinized cells become more specialized toward synthesis and secretion of progesterone and estrogen instead of the predominantly estrogenic and polypeptide products of the follicular phase. Progesterone, however, is the major hormone produced by the corpus luteum.

Click link [2]. In this thick paraffin section one can only identify granulosa lutein cells, theca lutein cells, and connective tissue in the center. Notice the folded surface of the corpus luteum, resulting from collapse of the follicle. Zoom out once and click [1], identifying the same three components. Links [1] and [2] give higher-power views of the same structures.

Practice with this virtual slide: 006 Ovary Mammalian. I think this is dog, so that is why there are 3 Corpus Luteums (multiple ovulations). This is good for some follicles but the oocyte is missing in all but one Graafian follicles and then the nucleus is missing. Also, the theca lutein is not well developed and mostly at the edge of the CL. Can you find: Primordial follicle, Primary follicle, Primary Unilaminar follicle, Primary Multilaminar follicle, Secondary follicle and Antral follicle, Follicular cells, oocyte, Zona pellucida, Antrum, Graafian follicle, Corona radiata, Cumulus oophorus, Granulosa cell layer, Theca cells (interna and externa), Atretic follicle, Corpus luteum, Theca luteum, Granulosa luteum, Interstitial gland cells.

w62 Ovary and uterine tube, monkey

Identify the ovary and uterine tube (including fimbriae).

Click link [5,1]. The ovarian stroma forms a layer called tunica albuginea (rich in collagen) just underneath the ovarian epithelium. Identify these. Notice also the primary follicle.

Click the thumbnail and follow link [4]. Identify the regressing corpus luteum and the interstitial gland. Click link [1,1]. Identify the interstitial gland. This is thought to develop from the theca interna of some atretic follicles, and is particularly prominent in the macaque monkey, the source of this specimen. Interstitial glands are also found in humans, especially in late pregnancy. The function of the gland is unknown, although the presence of lipid droplets suggest that it might be involved in steroid metabolism.

Go to the thumbnail and follow [4,2,1]. Even though the corpus luteum is regressing, some of the cells are still active.

Go to the thumbnail and click link [6]. Notice the cross-sections of the ovarian artery in the mesovarium.

Click the thumbnail. The uterine tube (oviduct, Fallopian tube) is curled. Therefore several cross-sections of it are seen. Click link [1]. Notice the irregular shape of the uterine tube lumen due to infoldings of mucosa. The muscle layer (much thinner than in humans) surrounds the mucosa.

Click link [1]. Notice that the arteries have an unusual arrangement of smooth muscle, with an elastic lamina appearing in the middle of the muscle layer. Notice the abundance of lymphatic vessels. During ovulation the blood vessels and lymphatics become engorged. These together with smooth muscle aid in movement of the oviduct toward the ovary.

Click the thumbnail and follow [2]. This shows another cross-section of the oviduct. Pay particular attention to the abundance of blood and lymphatic vessels.

Click the thumbnail. Follow [3,1,1]. Identify the smooth muscle. The presence of mast cells (identify) in the oviduct is important because the oviduct provides part of a pathway from the "outside world" to the peritoneal cavity. The mast cells function as "sentinels" of the body by initiating the inflammatory response.

Click the thumbnail and go to link [7]. The mouth of the uterine tube has fingerlike processes called fimbriae (identify). Follow [1,2]. The uterine tube is lined with columnar epithelium (identify). Note also the abundance of blood vessels. Click link [1] and identify all the structures, paying particular attention to the intraepithelial lymphocyte and the ciliated cells. The cilia are thought to beat towards the uterus and aid in the transport of the oocyte and/or the fertilized ovum. Beating of the cilia in this diretion also helps prevent bacteria from outside the body entering the peritoneal cavity.

Click link [1]. The main cells types in the epithelium are the ciliated cells and the secretory cells. The secretory cells (identify) produce nutrients for the oocyte and the fertilized ovum. They also elaborate substances leading to "capacitation" of the spermatozoan. Note the basal cell. Basal cells are stem cells from which all other cell types of the epithelium derive. This specimen demonstrates another cell type which resembles enteroendocrine cells of the intestine. Identify these endocrine cells. Notice the presence of lymphocytes (another line of defense) in the lamina propria and inside the epithelium.

Practice with this virtual slide: 089 Ovary/Oviduct. This slide shows the oviduct very well, even the fimbria. However, the ovary is not very well preserved but it does show some things other slides do not, such as atretic follicles and corpus albicans. You can still find most stages of follicle development from Primordial to the beginning of secondary follicle. Can you find: Follicles, growing follicle with granulosa cells in mitosis, Atretic follicle scars, Large Corpus luteum, Corpus albicans, Oviduct, Fimbriae, Ciliated and nonciliated secretory epithelial cells. Why would the Fimbria have mostly ciliated cells and the ampulla an increase in the secretory cells?

Practice with this virtual slide: 62 Ovary and uterine tube - Monkeyt. This tissue is stained with Toluidine blue so somewhat dark but the resolution is excellent. It is good for seeing the Theca lutein cells the invade the corpus luteum. Cellular detail of the follicles is also very good, even showing the nucleolus in the very large nucleus of the oocytes. Can you find: Ovary- Corpus luteum (Aging/regressing), Fimbriae, Oviduct, Ciliated and secretory epithelial cells, basal bodies, enteroendocine cells (at the base of the epithelium and have a somewhat halo around them.

Practice with this virtual slide: Uterine tube - ampulla. This section is a little too thick so the staining is too dark. However, it is good to see the oviduct epithelium and to note that in this region where fertilization is to take place there are a lot of secretory cells. Can you find: Submucosa, uterine tube epithelium, ciliated epithelial cells, secretory epithelial cells, lamina propria.

b66 Uterus, human (proliferative phase)

The uterus is composed of three layers, an innermost endometrium, myometrium, and perimetrium (peritoneum). The perimetrium is not visible in this view. Identify the other two structures.

Click [1] and again identify the endometrium and myometrium. Click [1]. The uterus is lined by low columnar epithelium that continues into the glands (identify). The uterine stroma (identify) is composed of loose connective tissue. During this proliferative phase the glands are straight with narrow lumina. Zoom out once and click [2] to see the bases of the glands. Note the presence of blood vessels in the uterine stroma.

Go to the thumbnail and follow [2,1]. Since this is an oblique section we see bases of the uterine glands mostly in cross sections. Notice the narrow lumina of the glands.

Zoom out once and click link [2]. The myometrium (identify) is composed of smooth muscle. Notice the presence of arteries.

Practice with this virtual slide: Uterus-human, proliferative phase. Fixation of human uterus is not easy and it shows in these slides. Also, the phases involve progressive changes in the mucosa so it is not an all or none event. In this slide, the base of the gland show the lumen is a bit open but at the top opening to the lumen the gland is still young and not secretory yet. Can you find: Endometrium, uterine epithelium, uterine glands, endometrial stroma, myometrium, smooth muscle bundles.

b65 Uterus, human (secretory phase)

Identify the endometrium and myometrium. Notice that the endometrium is considerably thicker than that of the previous slide. (Go back to b66, compare the relative thickness of the endometrium and return.)

Click link [2]. Notice that the uterine glands (identify) are coiled in the secretory phase. The lumina are wider than in the proliferative phase. Follow link one for a higher magnification view. Zoom out once and click [2]. Identify the uterine epithelium, uterine gland and the blood vessels. In the secretory phase the uterine stroma is edematous. So there has been an increase in cell number and the size of the interstitium.

Click the thumbnail and follow [1,1]. Identify the endometrium and myometrium.

Practice with this virtual slide: Uterus - human secretory phase. Although the tissue is overstained due to the difficulty in fixing human uterus, it still clearly shows the basic structures and illustrates the gland during secretory phase. Note the wider lumen and secretory material in the lumen. Can you find: Endometrium, uterine epithelium, uterine glands, secretory lumen, spiral arteries (high magnification, you can see the smooth muscle), myometrium, smooth muscle bundles, at top of myometrium you can see cross section of the arcuate arteries that feed the radial arteries in the basalis.

b69 Vagina, human

The vagina is a fibroelastic tube composed of mucosa, muscular layer, and adventitia. Click [1]. Identify the nonkeratinized epithelium and the underlying connective tissue (lamina propria). Click [1]. Notice the thickness of the epithelium (which is estrogen-dependent) and the presence of blood vessels in the lamina propria. Zoom out once and click [2]. Notice the abundance of blood vessels. Most of these vessels are veins and resemble those of the erectile tissue of the penis. The vagina is devoid of glands and gets its lubrication primarily from these blood vessels, but some comes from the cervix as well. The connective tissue is rich in elastic fibers, although that is not evident in this slide.

Practice with this virtual slide: Vagina - human. This is mostly folded skin mucosa with a thick external muscle layer. Note the abundance of immune cells in the lamina propria/submucosa area and even in the epithelium. Can you find: Non-keratinized stratified squamous epithelium, mucosa, lamina propria, connective tissue, blood vessels, muscular layer, adventitia.

b70 Mammary gland (inactive) human

This is a section of mammary gland from a non-pregnant woman of fertile age. Click link [1]. The gland is composed mostly of adipose tissue with a few duct systems, typical of the inactive state. Click link [1] and identify the adipocytes and duct system.

Practice with this virtual slide: 095 Mammary Gland Inactive. This is an immature mammary gland tissue with some of the nipple and even hair follicles. Because it is from an immature animal, the gland tissue is similar to inactive gland. Do not confuse hair follicle glands with their sebaceous glands for the mammary gland, which is deeper in the tissue surrounded by the fat cells. Gland alveoli are very small, but the ducts are open, although small, too. Can you find: Adipocytes, collagen bundles.

b71 Mammary gland (active) human

This is a section of a mammary gland of a pregnant woman. Click link [1]. During pregnancy estrogen induces growth of the duct system. Progesterone stimulates the proliferation of the lobulo-alveolar system (identify). Click [1] for a higher-power view.

b71a Mammary gland (lactating) human

This section is from the mammary gland of a lactating woman. Click link [1,1]. In response to prolactin, milk production begins in the alveolar cells. Note the large lumina and the presence of milk.

Practice with this virtual slide: 096A Mammary gland active. This is a very large piece of tissue so not fixed really well but it does show an accurate appearance of the gland that is very active. On the outside (upper) is normal skin structure with even hair follicles. In the gland tissue you will see large ducts that contain milk and the ducts are surrounded by a lot of connective tissue that helps to give it structure. Milk contains an abundance of lipid and because that is extracted during processing for histology it appears as empty vacuoles, and there are many here at the epithelial cell/alveolar lumen surface. Can you find: Active alveoli (mammary duct), Mammary duct (active), luminal milk lipid and protein (pink staining with eosin), some cells in the milk are immune cells.

w68 Umbilical cord, human

The umbilical cord connects the fetus to the placenta. It is composed of two umbilical arteries (identify) carrying deoxygenated blood from the fetus to the placenta, and an umbilical vein carrying oxygenated blood from the placenta to the fetus. These blood vessels are surrounded by fetal connective tissue (Wharton's jelly) which protects the vessels from collapsing due to movement of the fetus.

Click [1,1] and identify the fetal fibroblasts in the Wharton's jelly. Zoom out once and click link [2]. Note that the lumen of this specialized vein is open although filled with blood. The thick wall is composed of several layers of smooth muscle and elastic laminae.

Click the thumbnail and follow link [2]. Notice that the lumen of the umbilical artery is closed, preventing exsanguination of the fetus after the cord is cut. Click [1] to see a higher-magnification view of this specialized artery. The wall of the artery is composed of smooth muscle and very few elastic laminae.

Practice with this virtual slide: 68 Umbilical cord - human. Two umbilical Arteries (adjacent) and one large umbilical vein.

w67a Placenta, human

This section is from the maternal side of a full-term placenta. Identify the maternal side and the villi.

Click link [1]. Identify the maternal side. Click [1,1]. Not much is known about the fibrinoid layer. It is thought to be part of the system preventing the mother from rejecting the fetus. Notice also the cross-sections of the fetal villi and the clumped nuclei of the syncytiotrophoblast, typical of term placenta.

Click the thumbnail and follow [1,3]. The decidual cells are of maternal origin and are highly-modified endometrial stromal cells.

Click the thumbnail and then link [2]. Notice that the placenta is composed mostly of villi, a few of which are identified. Click link [1]. Notice the syncytiotrophoblast, the outermost portion of the villus. Click link [1]. Identify the maternal-fetal barrier which is composed of (1) the syncytiotrophoblast, (2) the basal lamina, and (3) the fetal capillary endothelium. Where do you think maternal blood would appear in this picture?

Click the thumbnail and follow [1,2]. Identify placental villi surrounded by maternal blood. Click [1,1]. Look at all the identified structures in this view. Macrophages in the villi are also known as Hofbauer cells.

Practice with this virtual slide: 67a Placenta decidua -Human. Placenta is very difficult to preserve and embed for cutting. However, this one is quite good and provides high resolution of all the major cell types. Can you find: Maternal side, Umbilical arteries, Umbilical vein (larger), endometrial blood vessels, Decidua basalis, decidual cells, Fibrinoid layer, Fetal side, Chorionic villi, lacunae and maternal blood, fetal blood and capillaries and endothelium, syncytiotrophoblast, cytotrophoblast cells, fetal connective tissue and fibroblasts, blood-placenta barrier.

w72 Testis, epididymis, vas deferens; rat

Identify the three major structures present in this low-power view.

Click link [2]. Each testis is surrounded by a capsule composed of three layers. The outermost layer is called tunica vaginalis, a detached diverticulum from the peritoneum. It has been removed from this specimen and is therefore not visible. The innermost layer, the tunica vasculosa (identify) contains blood vessels. The middle layer, the tunica albuginea (identify), is a thick connective tissue capsule. The testis per se is composed of two compartments, seminiferous tubules and the interstitial connective tissue. The convoluted seminiferous tubules (identify) are the site where spermatozoa develop. The interstitium (identify) contains Leydig cells that synthesize the androgens. Although the two compartments are structurally separated they are functionally interdependent.

Click link [3]. The combined length of the seminiferous tubules in one human testis is about 250 m. The seminiferous tubules (identify) are lined by seminiferous (germinal) epithelium. Mature spermatozoa are seen in vortex-like whorls (identify) in the lumen. The interstitium (identify) contains blood vessels and a large lymphatic space (in rat) and Leydig cells. In the rat Leydig cells are far less numerous than in humans and seem to "float" in the lynphatic space.

Click the thumbnail and follow [2,2]. The germinal epithelium (like all epithelia) rests on a basal lamina (identify). Outside the basal lamina is the peritubular tissue containing myoid cells (identify). Myoid cells are contractile and may have a role in moving spermatozoa along the lumen. Oxytocin may stimulate contraction of the myoid cells.

In the adult the seminiferous epithelium is composed of two cell lines: (1) a nonproliferating population (do not divide after puberty) of Sertoli cells (identify), and (2) a proliferating population of germ cells whose daughter cells, while differentiating, migrate continuously toward the lumen. In humans it takes about 70 days for spermatogonia to differentiate into spermatozoa. The two testes together may produce 1000 new spermatozoa every second. Spermatogenesis involves genetic reshuffling and packaging of the resulting haploid sets of chromosomes in a parcel suitable for effective delivery to the oocyte.

Spermatogonia (identify) are stem cells that rest on the basal lamina. They divide mitotically. Some of them maintain the stem cell population. Others are stimulated to differentiate. There are several categories of spermatogonia. It is the type B spermatogonia that will give rise to primary spermatocytes. However, only experts can distinguish among the categories of spermatogonia.

Spermatogonia divide and give rise to the primary spermatocytes (identify). Primary spermatocytes duplicate their DNA content and then move into the adluminal compartment by disrupting transiently the tight junctions between adjacent Sertoli cells. In this new microenvironment they enter the (long) first prophase of meiosis I. Primary spermatocytes are the largest cells in the spermatogenic line and usually show coarse chromatin. Thus they are easily identified. Look at them.

Meiosis I ends with the formation of two daughter cells, the secondary spermatocytes, each containing 23 chromosomes( with two sister chromatids). The secondary spermatocytes are short-lived and soon divide into haploid spermatids. Due to their short life secondary spermatocytes are usually not seen in sections. Spermatids (identify), however, are easily identified. They are located closer to the lumen and have round nuclei. Spermatids do not divide. Instead they differentiate into spermatozoa through spermiogenesis. Spermiogenesis involves considerable differentiation of all cellular structures: (1) condensation of the nucleus into heterochromatin, (2) acrosome formation from Golgi, (3) formation of flagellar tail, and (4) discarding of extra cytoplasm. This view shows spermatids during acrosome formation. Identify the acrosomes and the spermatozoan head. (The "pointed head" is typical of rodents, but not of humans.)

The acrosome (identify) eventually covers the head of the spermatozoan like a swimming cap. It can be seen in the maturing spermatids like a quarter-moon next to the nucleus. The acrosome contains several enzymes, for example, hyaluronidase, which will disperse the granulosa cells of the corona radiata, and proacrosin, which will later yield acrosin to digest the zona pellucida, thus facilitating the sperm head entry into the oocyte. When spermatozoa are fully differentiated morphologically they are released from, and by, the Sertoli cells to the lumen of the seminiferous tubule. At this point however, they are immotile and incapable of fertilization.

Sertoli (supporting, sustentacular, nurse) cells are large cells extending from the basal lamina to the lumen of the seminiferous tubule. Their outline is difficult to see in LM sections because they embrace the germ cells with many extensions. Their nucleus (identify) is homogenously staining with a prominent nucleolus located close to the basal lamina.

Go to the thumbnail and follow [1,4] and identify Sertoli cell nuclei. Although it cannot be seen in LM, the neighboring cells communicate with numerous gap junctions. Near the basal part of the cell the neighboring Sertoli cells have elaborate junctional complexes with multiple tight junctions. These tight junctions form the blood-testis barrier: the spermatogonia are outside the barrier in the basal compartment, primary spermatocytes and their daughter products are located in the adluminal compartment inside the barrier. The Sertoli cells are able to maintain a controlled microenvironment within the adluminal compartment that is especially favorable for germ cell differentiation. The blood-testis barrier also prevents leakage of spermatozoal substances into the systemic circulation where they could elicit an immune response. Sertoli cells have many other functions perhaps the most important being the production of androgen-binding protein (ABP) which concentrates testosterone. FSH stimulates ABP production. Identify all the other structures in the picture.

Click the thumbnail and follow [1,2]. Identify all the objects. Then click link [1]. Leydig cells are responsible for testosterone production under the stimulus of LH. The Leydig cells are typical steroid-secreting cells with abundant SER and lipid droplets. Testosterone is released into the circulation, but, more importantly, it diffuses into the Sertoli cells where it binds to ABP. Local seminiferous tubule concentrations of testosterone are 50 to 100 times higher than in the peripheral blood. These high concentrations are required for spermatogenesis. Notice the presence of macrophage and a lymphocyte, common components of interstitial tissue.

Click the thumbnail and follow [1,3] to see more Leydig cells. The rat has far fewer Leydig cells than humans. Identify other labeled structures in this view.

w73 Testis, dog

Identify testis, rete testis, and ductuli efferentes. Follow [1,1]. By now you should recognize the primary spermatocytes by their coarse chromatin pattern. (Stare at them.) This specimen has abundant Sertoli cells. Their perikarya are easily identified by the homogenous pale-staining nucleus and the prominent nucleolus (identify). Even though this specimen is not well fixed, or maybe because of it, one can actually see the Sertoli cell cytoplasm reaching toward the lumen (identify). In addition to the fuctions mentioned before, the Sertoli cells provide nutrients to the germ cells, they provide the fluid that drives the immotile spermatozoa through the ducts to the epididymis, and they phagocytose residual cytoplasm from spernatozoa. They synthesize and secrete inhibin and estradiol. Notice the presence of Leydig cells and lymphatics in the interstitium. Recognize the mitotic figures.

Click the thumbnail and go to link [2]. The seminiferous tubules empty via straight ducts (not seen here) into rete testis (identify), a meshwork of anastomosing channels. Click link [1]. The rete is lined by simple cuboidal epithelium. The spermatozoa pass through the tubuli recti and rete testis very rapidly. Note that the lumen is therefore empty. Note also the abundance of lymphatic vessels.

Click the thumbnail, follow link [3] and identify the ductuli efferentes. Click link [1]. Ductuli efferentes (about twelve in number in the human) connect the rete testis to the epididymis. Identify the ciliated epithelial cells of the ductuli. These cells absorb nearly 90% of the seminiferous fluid. Without this reabsorption the sperm remains diluted and incapable of normal maturation in the epididymis. This process is under the influence of estrogen, one of the few presently known functions of estrogen in human males. Notice the thin smooth muscle layer. Smooth muscle contraction and ciliary beating aid in movement of the contents toward the epididymis.

w72 Testis, epididymis, vas deferens; rat

We return to this slide to continue the journey down the duct system of a typical spermatozoon. Click link [1] and identify the epididymis. It is 6 m long and highly tortuous in humans. Click link [5] for a higher-power view. Then click link [1]. The spermatozoa pass through the epididymis slowly (12 days) and when they have arrived at the tail of the epididymis they have acquired motility. The epithelium is pseudostratified columnar with giant microvilli (identify). This epithelium is both secretory and absorptive. It provides the spermatozoa with a glycoprotein coat and it absorbs most of the remaining fluid. Thus spermatozoa become concentrated in the lumen (identify). The epididymis is the main storage site for spermatozoa. Most of the unused spermatozoa are phagocytosed here.

Go to the thumbnail and click [3,1]. The epididymis straightens out at the tail and is continuous with the ductus deferens, a muscular duct 35 to 50 cm long in humans. Identify each of the structures in this view. The epithelium is pseudostratified. In humans the muscle coat is thick and is composed of three distinct smooth muscle layers. The inner and outer layers are longitudinal and the middle, thick, layer is circular. This smooth muscle contracts rhythmically during ejaculation and is the main mover of stored sperm.

Practice with this virtual slide: 071 Testis Plastic-Mouse PAS. This tissue was fixed by vascular perfusion, so the capillaries will lack RBCs and appear white. However, this permits very good resolution of the cell types and PAS staining of the carbohydrates, such as the glycosylated enzymes in the Golgi and Acrosome of spermatids. Can you find: Tunica albuginea, seminiferous tubules, lumen, interstitium, Sertoli cell nucleus and nucleolus, Leydig cell, peritubular myoid cell, capillaries, spermatogonia, pachytene spermatocytes, mitosis (along basement membrane) versus meiotic cell division (in one stage and throughout the epithelium), round spermatids, spermatid nucleus, acrosome, elongated spermatids, mature sperm.

Practice with this virtual slide: 085 Testis & rete testis-Dog. Very good because rete testis and seminiferous tubules are somewhat similar to human testis. Fixation and staining is more like that of pathology slides, but more difficult to understand. Can you find: Tunica albuginea, seminiferous tubules, interstitium, rete testis, septa, Sertoli cell, Leydig cell, peritubular myoid cell, spermatogonia, pachytene spermatocytes, round spermatids, spermatid nucleus, elongated spermatids, mature sperm.

Practice with this virtual slide: 082 Epididymis -Dog. This is head of the epididymis and is similar to that in man. On the lower side are the efferent ductules (smaller in diameter and having a shorter epithelium) and on the upper side is the epididymis, having wider lumens and a much taller epithelium. Note that the efferent ducts are not created equal. Some have vacuoles, while others have apical proteinaceous cytoplasm. Some are tiny in diameter but others have wider lumens. There are many (maybe 15 efferent ducts) but only one epididymal tube. Identify the following: ductuli efferentes, ciliated cells (fixation is not perfect so the cilia look like tangled fingers extending from some cells), non-ciliated cells (just short microvilli and no long cilia), epididymis, tall columnar principal cells, long branched microvilli (also called stereocilia), narrow cell (nucleus near lumen), basal cell, peritubular smooth muscle, spermatozoa in lumen (head and tail).

Practice with this virtual slide: 084 Epididymis, cauda Dog. This shows larger lumens of cauda epididymis and at one end (left) shows the beginning of vas deferens (one cross section). Identify the following: ductus epididymis, concentrated sperm in lumen, epithelium is shorter than in caput epididymis, principal cells, basal cells, peritubular smooth muscle, vas deferens (one section), thick wall of muscularis.

b76a Seminal vesicle, human

The seminal vesicle is a tortuous diverticulum off the ductus deferens. Click link [1]. The wall has two smooth muscle coats and an elaborately folded mucosa. Click link [1] and identify the smooth muscle and the mucosal folds. Zoom out once and click link [2]. Identify all the structures highlighted. The vesicles secrete and store a viscous component of the seminal fluid rich in fructose, prostaglandins, and coagulating proteins. The fructose serves as an energy source for spermatozoa. Prostaglandins stimulate contractions of the female genital tract. About 60% of the seminal fluid is derived from the seminal vesicles.

Practice with this virtual slide: Seminal vesicle-human . This is human organ but in this case not very active (heavily folded mucosa without filling with secretory fluids). Identify the following: Epithelium of seminal vesicle, secretory cells, area of luminal fluids, mucosal folds, smooth muscle muscularis.

Practice with this virtual slide: 079 Seminal Vesicle Rat. This shows very active secretions and filling of the lumen with fluid. Identify the following: Epithelium of seminal vesicle, secretory cells, mucosal folds, smooth muscle muscularis.

w76 Prostate, human

The prostate gland is about the size of a horse chestnut; it encircles the urethra near the neck of the bladder and is composed of 30 to 50 small glands that open into the prostatic urethra. Click link [1] and identify the prostatic glands. Go to the thumbnail and follow [2]. The glands are in three groups, arranged concentrically around the urethra, although this configuration is not apparent in this view. The glands are embedded in a connective tissue stroma that contains abundant smooth muscle. Identify the prostatic gland lumen. Click link [1] and identify the prostatic gland (alveolus) and the smooth muscle. Click link [1] for a higher-power view of the glandular epithelium and stroma.

Go to the thumbnail and follow [1,1]. The gland epithelium is low columnar. Prostatic concretions are often found in lumina of the glands. Identify all the labeled structures, paying particular attention to the smooth muscle. The function of the prostate is not quite clear. It contributes approximately 20% of the seminal fluid and adds acid phosphatase and zinc to the semen.

b76 Prostate, human

Click link [1] and identify the labeled structures. Click link [1]. The smooth muscle seems more pronounced in this view. (Perhaps the patient from whom this specimen was taken suffered from prostatic hypertrophy, a very frequent condition in human males.)

Practice with this virtual slide: 76 Prostate-human-stained. This slide is very thin and give excellent resolution of the cells. However, the toluidine blue stain provides little contrast. So, focus on the prostate gland epithelium, the secretory cells with vacuoles, prostate smooth muscle, prostatic concretions, prostatic alveolus, prostate stroma.

Practice with this virtual slide: 081A1 Prostate Dog. This slide his H&E staining and give the required contrast between connective tissue and the prostate glandular mucosa and secretory epithelium. Also seen is the prostatic urethra and the opening of the glands onto the transitional epithelium. Identify the following: prostate epithelium, glandular lumen and opening, prostate smooth muscle, prostatic alveolus, prostate stroma, urethra, transitional epithelium, blood sinuses, urethral prostate glands versus the main body.

Practice with this virtual slide: 081B Prostate & Urethra. This slide is very good because it shows 3 sections of the male urethra: urethra outside and pre-prostate (left), inside or prostatic urethra (middle), and pelvic or post-prostatic urethra (right). Trichrome stain shows muscle (red) versus connective tissues (blue green).

Pre-prostate urethra (Far left side). Identify the following: transitional epithelium, lamina propria/submucosa, collagen bundles, blood sinusoids, urethral crest, muscle circular versus longitudinal, innervation of the muscle wall with wavy nerve fiber bundles. What type of muscle is found here?

Prostatic urethra (Central section). The center tissue shows two lobes of the prostate, main glands, periurethral glands and opening onto the transitional epithelium. There are also 2 ejaculatory ducts. Identify the following: transitional epithelium, lamina propria/submucosa, urethral crest, collagen bundles, blood sinusoids, periurethral prostate gland, glandular opening, main prostate gland, ejaculatory ducts (with pseudostratified columnar epithelium with short microvilli).

Pelvic urethra (Far right side). This part of the urethra enters the penis and is under voluntary control for urination. Identify the highly stretched transitional epithelium, the thick wall of muscle the external urethral sphincter (can you identify the type of muscle?). Identify the vast supply of innervation to control the contraction of this tissue during urination. There is also a small portion of the bulbourethral gland present in the submucosa of this tissue. Identify the gland and its epithelium.

Semen

Semen consists of spermatozoa in seminal plasma, a mixture of the secretions of the auxiliary glands. Normal ejaculate is 2 to 5 ml in volume and contains 20 to 150 million spermatozoa per ml. At the beginning of the erection the mucus from the bulbourethral glands and glands of Littre lubricate the urethra. At the beginnning of the ejaculation the prostatic secretions are discharged first. Next the bulk of the spermatozoa accumulated in the epididymis are expelled. The final portion of the ejaculate is the thick secretion of the seminal vesicles.