Lesson 27 Female reproductive system text.pdf

_____________ LESSON 27 _____________ FEMALE REPRODUCTIVE SYSTEM The female reproductive system consists of the ovaries, uterine tubes (oviducts), uterus, cervix, vagina, vestibule, vulva and associated glands. I. OVARY The ovary is a combination of an exocrine gland since it generates oocytes and...

_____________ LESSON 27 _____________ FEMALE REPRODUCTIVE SYSTEM The female reproductive system consists of the ovaries, uterine tubes (oviducts), uterus, cervix, vagina, vestibule, vulva and associated glands. I. OVARY The ovary is a combination of an exocrine gland since it generates oocytes and an endocrine gland since it produces hormones such as estrogens and progesterone. It is a parenchymal organ surrounded by a thick layer of connective tissue, the tunica albuginea, surrounded, in turn, by a simple cuboidal epithelium called the germinal epithelium, which is a specialized mesothelium (serosa) that comes from the peritoneum. The ovarian parenchyma is divided into an outer cortex and an inner medulla (except in the mare where these areas are inverted). The cortex is a wide peripheral zone that contains the follicles and the corpora lutea, between which loose connective tissue is observed. The medulla is the inner area and is made up of highly vascularized loose connective tissue and smooth muscle fibers. In this area are located the ovarian rete that are formed by networks of irregular channels lined by a cubical epithelium or by solid cellular cords and that can give rise to follicular cells. Figure 2. Ovary of a bitch. Yellow corpus luteum. 2 Figure 1. Ovary of a bitch. Tertiary follicle. 1 1 1. Ovarian follicles They are made up of a primary oocyte (occasionally two or three) surrounded by follicular cells. A primary oocyte is considered to be the cell that comes from the maturation of the oogonia, during the embryonic stage, and that has not completed its first meiotic division. According to their state of maturity, the following are distinguished: 1. Primordial follicle (unilaminar, preantral and resting). It is made up of a primary oocyte surrounded by a simple squamous epithelium of follicular cells that rest on a basement membrane. They arise prenatally, although in the bitch they can also appear postnatally. The primary oocyte measures about 20 µm in diameter, has a central and spherical nucleus with a prominent nucleolus and few organoids. 2. Primary follicle (unilaminar, preantral and growing). It is made up of a primary oocyte surrounded by cubical or columnar follicular cells. 3. Secondary follicle (multilaminar, preantral and growing). It is made up of a primary oocyte surrounded by a stratified epithelium of polyhedral follicular cells, called granulosa cells. In addition, the zona pellucida appears, a glycoprotein layer that is located around the plasma membrane of the oocyte. In this area there is a penetration of microvilli of the oocyte on the one hand and cytoplasmic extensions of the granulosa cells on the other, differentiating communicating junctions between the two that serve to nourish the oocyte. The zona pellucida is formed by the secretions of the granulosa cells and the oocyte. As the development of the follicle continues, the granulosa cells secrete a protein-like liquid and pour it out, forming small fissures between them. Towards the end of the second phase, a multilaminar vascularized layer of spindle cells, the theca cells, begins to appear around the granulosa cells . 4. Tertiary follicle (multilaminar, antral and growing). Also called Graafian follicle. When mature, it can measure up to 7 cm in the mare and up to 2 cm in the cow. The primary oocyte measures 150–300 µm in diameter. It has, as in previous states, a central and spherical nucleus with a prominent nucleolus, but the cytoplasmic organoids are more developed. Thus, it presents a very evident Golgi complex, numerous rough endoplasmic reticulum cisterns, mitochondria and lipid vacuoles in the cytoplasm. Surrounding the oocyte is the zona pellucida already described. The granulosa cells in contact with the oocyte acquire a columnar shape and are arranged radially, constituting the corona radiata, with a nutritional function. The follicular antrum is formed when the fluid-filled fissures secreted by the granulosa cells fuse to form a large cystic cavity that contains the follicular fluid and displaces the oocyte. 2 The granulosa cells are polyhedral and completely surround the follicular antrum. In large tertiary follicles, granulosa cells have the structural characteristics of protein-secreting cells, with numerous rough endoplasmic reticulum cisternae. Before ovulation, the granulosa cells acquire the characteristics of steroid-secreting cells (numerous vesicles of smooth endoplasmic reticulum and mitochondria with tubular cristae). These cells secrete estrogens, a hormone responsible for the development of the reproductive system and sexual receptivity. The stratum granulosum is surrounded by theca, differentiating between theca interna and theca externa. The first, highly vascularized, is made up of spindle cells that in mature follicles become steroid (androgen) secreting cells. The theca externa is a thin layer of loose connective tissue. 3 Figure 3: Two tertiary follicles showing all its components. The primary oocyte completes the first meiotic division to become a secondary oocyte, producing the first polar body. This occurs before ovulation, except for the bitch and the mare who can ovulate a primary oocyte. The maturation of the ovarian follicles is induced by the follicle-stimulating hormone or FSH, produced in the adenohypophysis. 2. Ovulation When the tertiary follicle is fully developed, it makes prominence on the surface of the ovary. LH (luteinizing hormone), produced in the adenohypophysis, stimulates the release of prostaglandins, including prostaglandin F2α (PGF2α). 3 This prostaglandin is believed to cause collagenases to be released from follicular cells, causing digestion of the follicular wall and its distension at the site of rupture, called the stigma. The pressure of the follicular fluid causes the exit of the oocyte surrounded by the corona radiata of granulosa cells. 3. Atresia This is the name given to the regression of the follicles that begin to develop in the ovary but do not undergo ovulation. 4. Corpus luteum At ovulation the follicle ruptures and becomes the corpus hemorragicum as blood fills the antrum. After ovulation, the stratum granulosum is vascularized by the theca interna vessels. The granulosa cells and those of the theca interna luteinize due to the action of the hormone LH. Luteinization is the process by which granulosa and theca interna cells transform into lutein cells and includes hypertrophy and hyperplasia of both cell types and the production of different hormones. A yellow pigment, lutein, appears in the lutein cells of the cow, mare and bitch (yellow corpus luteum). Large lutein cells come from granulosa cells, which is why they are also called granulosa-lutein cells. They measure about 40 µm, are polygonal, with a large spherical nucleus and lipid inclusions in their cytoplasm (synthesizing steroids) and produce progesterone, which is the hormone responsible for promoting nesting and maintaining pregnancy. The small lutein cells come from the cells of the theca which is why they are also called theca-lutein cells. They measure about 20 µm and have more lipids but fewer steroid-synthesizing organoids than the previous ones. They produce small amounts of androgens, estrogens, and small amounts of progesterone. The first regression sign of the corpus luteum occurs at the end of the diestrus and is characterized by condensation of the lutein pigment, which appears reddish (red corpus luteum), followed by fibrosis. The connective tissue scar that persists after the regression is called the corpus albicans (or white). 4 4 Figure 4: Atretic tertiary follicle. 5 Figure 5: Corpus albicans. II. UTERINE TUBES (OVIDUCTS) They are bilateral and tortuous structures that extend from the ovary to the uterine horns and carry the oocytes, spermatozoa and zygotes. They consist of: 1. Infundibulum (funnel shape). 2. Ampulla. 3. Isthmus (narrow segment that joins the uterus). Structure 1) Mucosa/submucosa: lined by a simple columnar or pseudostratified columnar epithelium (depending on the species), with cilia in most cells. Both cell types, ciliated and non-ciliated, have microvilli, but only non-ciliated cells have secretory activity, whose function is nutrition. Loose connective tissue with many plasma cells, mast cells and eosinophils is disposed under this epithelium. The tubes show a very narrow lumen because the mucosa and submucosa have numerous folds, as well as finger-like projections called fimbriae. 2) Muscularis: made up of a layer of smooth muscle fibers arranged circularly, although there are also longitudinal bundles. 3) Serosa. 5 Figure 6: Cross section of the infundibulum. Figure 7: Detail of the fimbriae and the epithelium that covers them. Function 1. The infundibulum collects the oocytes that are expelled from the ovary. The fimbriae present highly vascularized loose connective tissue inside. At the time of ovulation, these vessels become congested causing the fimbriae to be turgid and, as a result of rhythmic contractions of the smooth muscle fibers, to move above the surface of the ovary. 2. Fertilization occurs in the caudal portion of the ampulla. III. UTERUS The uterus is the implantation site of the fetus and its sheaths and undergoes changes during the ovarian and reproductive cycle. In most animal species it consists of: 1. Horns (two). 2. Body. 3. Cervix (joins the vagina). Structure of the uterine horns and body 1. Tunica mucosa/submucosa or endometrium. The endometrium is made up of two areas that differ in both structure and function. The superficial layer or functional zone is the zone that totally or partially degenerates during a reproductive cycle and can be lost in some species. The deep layer or basal area is thin, persists throughout the cycle and regenerates the functional area. The epithelium is simple columnar in the mare and carnivores and pseudostratified columnar in the sow and ruminants. It rests on loose connective 6 tissue, highly vascularized and innervated with numerous fibroblasts, macrophages and mast cells. Many melanocytes can be seen in sheep. Simple branched tubular glands lined by a simple columnar epithelium are found throughout the endometrium. In ruminants, caruncles are seen, which are circumscribed thickenings of the endometrium. They are rich in fibroblasts and have a wide blood supply. Caruncles are the places of attachment of the maternal placenta to the fetal placenta. 2. Tunica muscularis or myometrium: consists of a thick inner layer of smooth muscle fibers arranged in a circular way and a longitudinal layer. These fibers increase in size and number during pregnancy. Between these layers are large arteries, veins and lymphatics. 3. Tunica serosa or perimetrium: it is a serous membrane that includes smooth muscle fibers. Uterine changes during the ovarian cycle During the ovarian cycle, the uterus, particularly the endometrium, undergoes profound changes in its structure induced by hormones produced in the ovary and adenohypophysis. In general, during the estrogenic phase (proestrus and estrus) the endometrium thickens, becomes swollen, and blood vessels become congested. In cows and carnivores there are small endometrial hemorrhages during ovulation (metrorrhagia). During the predominance of progesterone (metestrus and diestrus), the endometrial glands develop a lot (hyperplasia), adopting a spiral shape. 8 Figure 8: Endometrium with spiral-shaped glands. The uterine lumen is observed (*). Figure III. 9: Endometrium and myometrium (arrow). ÚTERO: CÉRVIX O CUELLO. 7 9 IV. CERVIX UTERI Structure The cervix presents a sinuous lumen, with folds that vary in number and arrangement according to the species, and which must be taken into account when performing artificial insemination. The histological structure consists of: 1. Mucosa/submucosa: it is divided into an endocervix and an exocervix. The endocervix is lined by a columnar epithelium with many goblet cells. During estrus and pregnancy, large amounts of mucus are secreted. During pregnancy, the mucus thickens to form the cervical plug that prevents the entry of bacteria and protects the fetus from infections. Simple tubular glands are observed in ruminants. The exocervix is lined by a squamous stratified epithelium that undergoes the same cyclical transformations as that of the vagina. Under this epithelium there is a dense and irregular connective tissue that during estrus suffers edema and acquires a loose areolar structure. 2. Muscularis: made up of two layers of smooth muscle fibers; an internal circular and an external longitudinal. Elastic fibers stand out in the circular layer. Muscle and elastic fibers are necessary to restore the structure of the cervix after farrowing. 3. Serosa. V. VAGINA. folds. It extends from the cervix to the vestibule, presenting several longitudinal Structure 1. Mucosa/submucosa: lined by a squamous stratified epithelium that increases in thickness and keratinizes during proestrus and estrus. Underlying the epithelium is a loose connective tissue. Mucosa-associated lymphoid tissue is observed in the caudal area. 2. Muscularis: made up of two layers of smooth muscle fibers; an internal circular and an external longitudinal. 3. Cranially a serosa and caudally an adventitia. 8 Figure 10: Cervix: on the left the exocervix is observed, lined by a stratified epithelium and on the right the endocervix, lined by a simple epithelium and with tubular glands. Figure 11: Vagina: lined by squamous stratified epithelium and lymphoid follicle in lamina propria-submucosa. VI. VESTÍBULE It is located between the vagina and the vulva. 1. The mucosa / submucosa is similar to the caudal area of the vagina but with more subepithelial lymphoid nodules. In the vestibular wall there are abundant vessels, venous plexuses, cavernous tissue and small lymphatic vessels that become congested during estrus. In addition, in the mucosa of the vestibule the major vestibular glands are distinguished. They are branched tubuloalveolar glands with mucous secretion and only appear in the cow, sheep and cat. The minor vestibular glands are branched tubular glands with mucous secretion that lubricates the surface and are present in all species. 2. The tunica muscularis is made up of an inner longitudinal layer of striated skeletal muscle formed by the vulvar constrictor and vestibular constrictor muscles and a circular outer layer of smooth muscle. 3. Adventitia. VII. VULVA It has two lips lined by a thin skin with numerous mast cells and apocrine glands. VIII. CLITORIS Constituted by a corpus cavernosum similar to that of the penis. 9 IX. PARTICULARITIES OF THE AVIAN FEMALE REPRODUCTIVE SYSTEM OVARY In adult birds only the left ovary remains. The ovarian cortex and medulla are distorted by the presence of large follicles in various stages of development or atresia, each of these follicles being attached to the trunk of the ovary by a peduncle. In the avian ovary there are no true tertiary follicles since an antrum does not form. In the avian follicle, the oocyte is surrounded by one or more layers of granulosa cells and these are in turn surrounded by theca interna and theca externa cells. Granulosa cells shed with the oocyte at ovulation, while theca cells remain in the ovary to form a temporal corpus luteum. AVIAN OVIDUCT In birds, the term oviduct is used for the entire reproductive duct of the female. In adults only the left side develops. It presents five different regions: 1. Infundibulum: it is the place where the fertilization of the oocyte occurs. It is lined by a simple ciliated columnar epithelium. 2. Magnum: in it the albumin is produced. It has the same anterior epithelium with numerous goblet cells and subepithelial glands. 3. Isthmus: the inner membranes of the shell are produced there. It is lined by a simple ciliated columnar epithelium. 4. Uterus: the inorganic part of the eggshell is produced in it. It presents a ciliated columnar pseudostratified epithelium and tubular glands in the submucosa. 5. Vagina: spermatozoa are stored in it for up to 21 days. It is lined by a ciliated columnar pseudostratified epithelium and has tubular glands in the submucosa. Cloaca. Vagina, large intestine and ureters flow into the cloaca, which has a simple columnar epithelium with numerous goblet cells. 10