VET 313 Lecture Module 2024 Female Reproductive System PDF
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2024
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This document provides an overview of the female reproductive system, focusing on the different organs, their histology, and associated structures. It also covers the various species differences and the functions of the organs. This is part of a veterinary science lecture module.
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The Female Reproductive System The female reproductive system consists of bilateral ovaries and uterine tubes (oviducts), a usually bicornuate uterus, cervix, vagina, vestibule, vulva, and associated glands. It is concerned with the production and transport of ova, the transport of spermatoz...
The Female Reproductive System The female reproductive system consists of bilateral ovaries and uterine tubes (oviducts), a usually bicornuate uterus, cervix, vagina, vestibule, vulva, and associated glands. It is concerned with the production and transport of ova, the transport of spermatozoa, fertilization, and the accommodation of the conceptus until birth. Objectives a) Recall and name the different organs comprising the female reproductive system of the body b) Identify and describe histologically the different organs and its associated structures belonging to female reproductive system c) Enumerate and recognize differences among organs among mammalian species d) Enumerate and recognize differences among organs in mammalian and avian species e) Relate structures present as to the functions of the organs. The female reproductive system consists of organs that are involved in the production of female gametes or ova and also the site of in vivo fertilization and in mammals, of pregnancy. The mammalian female reproductive system (Fig. 225) consists of two (2) ovaries, two (2) sets of excretory or genital ducts (2), accessory gland, external genitalia and placenta. The ovaries are the site of development and maturation of female germ cells. In addition, the ovaries function as endocrine glands, synthesising several sex hormones including oestrogen, progesterone, testosterone and other androgens. At certain stages of the reproductive cycle, and during pregnancy, a hormone-producing corpus luteum (or several corpora lutea, in multi- ovulatory species) is (are) formed in the ovary. The uterine tubes transport germ cells, including the ova of the female and the spermatozoa of the male. Union of the two haploid germ cells (fertilization) occurs in the proximal segment of the uterine tubes. This gives rise to the zygote from which the embryo forms. The newly formed embryo passes through the uterine tube into the uterus, where it becomes implanted in the mucosa (nidation, implantation) and continues its embryonic and fetal development. During pregnancy, the mucosa of the uterus undergoes species-dependent modifications and contributes to the formation of the placenta (refer to embryology texts). The cervix, vagina, vestibule and vulva constitute the birth canal. The vagina and labia of the vulva represent the external genitalia and copulatory organs. In sexually mature animals, the organs of the female reproductive tract undergo cyclic changes in structure. These are most pronounced in the parenchyma of the ovary and in the mucosa of individual organs. VET 313 Lecture Module 2024 Ovary ✓ Female counterpart of the testis. ✓ From exterior to interior, the ovary is composed of: – mesovarium (ligamentum latum uteri) – part of the supportive apparatus of the female reproductive organs, – germinal epithelium – simple cuboidal epithelium, – tunica albuginea surrounding the cortex and medulla ✓ Both exocrine (ova production) and endocrine (hormone secretion) functions. ✓ Parenchymatous organ: in sexually mature animal changes in structure according to the species, age and stage of estrous cycle of the animal. ✓ Oval shaped except in mare where it is bean-shaped due to the presence of the ovulation fossa (fossa ovarii), an indentation at the attached border of the ovary. ✓ Appears lobulated in sow because of many follicles and corpora lutea protruding from the ovarian surface. ✓ Surface is covered by germinal epithelium, a modified visceral peritoneum that in embryonic ovary is simple cuboidal and in mature animals, simple squamous. ✓ Presents a cortex and a medulla (Fig. 226). ❖ Cortex » Functional part of the ovary. » Peripheral location; in mare it has a deep central location and only remains on the surface at the ovulation fossa (site of all ovulation). » Stroma - highly cellular loose CT with a "swirly" appearance (cells and fibers run in various directions. – Bitches: stroma contains prominent cortical tubules (narrow channels lined by simple cuboidal epithelium that may continue with the germinal epithelium). – Rodents, queens and bitches: stroma contains cords of polyhedral interstitial endocrine cells/epitheloid cells. VET 313 Lecture Module 2024 – Capsule (tunica albuginea) an irregular DWFCT with collagen fibers arranged parallel to the ovarian surface is located beneath the germinal epithelium. » Parenchyma - composed of ovarian follicles in various stages of development or atresia, corpus hemorrhagicum, corpus luteum and corpus albicans. ✓ Ovarian Follicles – Composed of an oogenic cell surrounded by follicular cells. – Decreases progressively with age: more numerous in younger animals. – Growth of ovarian follicles and corpora lutea disrupts the continuity of the tunica albuginea and the latter appears inconspicuous during the height of ovarian activity. – Five developmental stages of ovarian follicles: » primordial follicles » primary follicles, » secondary follicles, » growing follicles, » mature follicles » atretic follicles. ❖ Primordial follicles ▪ Earliest and most numerous stage Oocytes in suspended state o First meiotic prophase Only a few progress beyond this stage ▪ Form a thick layer in the peripheral cortex immediately beneath the germinal epithelium. ▪ Formed in “nests” from a single oogonium ▪ Consist of a large round primary oocyte (young oogenic cell enclosed by vitelline membrane) surrounded by a single layer of flat or squamous follicular cells. ❖ Primary follicles ▪ Older than the primordial follicles. At puberty, some begin to develop Follicular epithelium becomes simple cuboidal without an antrum. ▪ Oocyte is still quiescent but may enlarge later in this stage VET 313 Lecture Module 2024 As follicular epithelium grows, oocyte produces more cytoplasm ▪ Follicle as a whole enlarges ▪ Epithelial cells in vicinity begin to develop as theca ▪ As they grow they gradually move deeper towards the medulla (except in the horse) for nourishment. ❖ Secondary follicles ▪ A transitional stage ▪ Follicular epithelium stratifies and becomes secretory; produces follicular fluid ▪ May become very large and stratified ▪ Late in this stage oocyte develops a ZONA PELLUCIDA around it Zona pellucida o An amorphous glycoprotein coat formed by follicular epithelial cells closest to oocyte o Essentially a thickened basement membrane ▪ Secretory activity of follicular cells is continuing ❖ Tertiary/Antral/Growing/Graafian follicle ▪ Small to large in size; definitely larger than primary follicles. ▪ Oval or round in shape and located deeper in the cortex. ▪ A single ANTRUM has formed ▪ Presents several layers of follicular cells, a primary oocyte and an antrum (space that separates the primary oocyte from the surrounding follicular cells). ▪ Parts of the growing follicle from the center outward: primary oocyte, zona pellucida, corona radiata, cumulus oophorus, antrum, membrana granulosa and theca folliculi. Zona pellucida - refractile homogenous material located external to the vitelline membrane. Corona radiata - single layer of follicular cells located external to the zona pellucida. Cumulus oophorus - several layers of follicular cells that surround the corona radiata and form a stalk that anchors the primary oocyte to the membrana granulosa. Antrum - cavity that separates the cumulus oophorus from the membrane granulosa. o Created by the reorganization of follicular cells. o Filled with estrogen-containing fluid, the liquor folliculi. Membrana granulosa - several layers of estrogen-secreting follicular cells that surround the antrum and form the wall of the ovarian follicle. o Basal layer of follicular cells rests on a basal lamina that demarcates the follicle from its capsule. VET 313 Lecture Module 2024 Theca folliculi - follicular capsule formed by CT stroma of the cortex that lies external to the basal lamina. o Two layers: theca interna, an inner cellular (fibroblasts) layer and theca externa , an outer fibrous (collagen) layer. ❖ Mature follicles ▪ The largest follicles in the ovary. ▪ As they approach their maximum size they move toward the ovarian surface and eventually bulge from the free surface of the ovary. ▪ Structurally similar to the growing follicles except that they have very large antrums. ▪ OVULATION: Can occur anywhere on the surface of the ovary o OVULATION FOSSA in mares o NOT due to pressure o Necrotic patch (stigma) forms & autolyses o Oocyte and corona released o Follicular fluid released o Follicle collapses Thecal and granulosa cells form CORPUS LUTEUM in the emptied follicle VET 313 Lecture Module 2024 ▪ Corpus hemorrhagicum Remnant of a mature follicle in the ovary after ovulation. Presents a collapsed wall and folded membrana granulosa (due to escape of liquor folliculi during ovulation), blood in the antrum and absence of primary oocyte. Short lived ▪ Corpus luteum Develops from the corpus hemorrhagicum. Made up of Thecal cells and granulosa cells. Produce estrogen and progesterone Maintains pregnancy In most animals persists to parturition Eventually will disappear and form a scar Young corpus luteum o Highly folded theca interna and membrana granulosa. o Follicular cells of membrana granulosa and the thecal cells undergo luteinization (enlargement and lipid accumulation) and are transformed into granulosa lutein cells and theca lutein cells, respectively. ▪ Granulosa lutein cells Large (approximately 40 mm in diameter), plump, pale staining, polygonal cells that fill up the antrum. Large spherical vesicular nucleus. Contains many lipid granules, mitochondria and smooth ER, indicating steroid synthesis during metestrus and diestrus. Hormones secreted: o Estrogens (particularly estradiol – 1,7B), secreted under the influence of FSH, which elicits receptive sexual behaviors' in females during estrus. o Folliculostatin (protein hormone) with negative feedback influence on FSH secretion o Progesterone which assists estrogen in eliciting sexual behaviors during estrus and promotes endometrial development in preparation for pregnancy. o Relaxin (polypeptide hormone) which relaxes the ligaments of the symphysis pubis before parturition. VET 313 Lecture Module 2024 ▪ Theca lutein cells Minor population of small luteal cells occupying the trabecular and peripheral areas of the corpus luteum. Contain more lipids but fewer mitochondria and smooth ER than the large luteal cells. Under the influence of LH theca luteal cells secrete androstenedione and testosterone. Mature corpus luteum o Round yellow body (because lutein cells contain a yellow lipid pigment, lutein). o Lutein does not accumulate in the luteal cells of sows and ewes. o Cow: the corpus luteum reaches maximum diameter of 25 mm on day 12 after ovulation. o Without pregnancy the corpus luteum (corpus luteum of ovulation) regresses or involutes in late diestrus. o Signs of regression or involution ▪ Fibrosis – scarring of connective tissue ▪ Changes in lutein cell: condensation of lutein pigments, accumulation of large lipid droplets and crystalloid inclusions. ▪ Regression is complete 1 to 2 days after estrus. o With pregnancy the corpus luteum persists as the gravid corpus luteum (corpus luteum of pregnancy). o Bitch: corpus luteum persists throughout a period equal to the normal gestation period whether pregnancy occurs or not. ▪ Corpus albicans Scar tissue formed from involuted corpus luteum. A small glistening body of collagen fibers in the cortex. A remnant of an old follicle o Always formed after ovulation and passing of the CL o More obvious in some species, e.g, primates o May form from non-ovulated follicles as well VET 313 Lecture Module 2024 ❖ Atretic follicles ▪ Most follicles never develop ▪ ATRESIA is terminated development ▪ Almost all destined to become atretic ▪ Control/selection unclear ▪ May contain glassy remnants of zona pellucida ▪ Size & nature depend on stage reached ▪ Degenerating, collapsed, irregular follicles. ▪ Present a shrinking, pyknotic or vacuolated primary oocyte, a membrana granulosa that may detach from the basal lamina and a collapsed antrum. ❖ Medulla » Vascular central region of the ovary that contains loosely arranged CT with nerves, lymphatics and many large blood vessels. » Arteries enter at the hilus and are arranged in coils within the medulla. » At the junction with the cortex, they form a plexus that supplies the cortical tissue. » These capillary networks are subject to cyclic structural changes regulated by specialized arteries (‘barrier arteries’) and arteriovenous anastomoses. » Medullary lymph vessels and veins leave the ovary at the hilus. » Predominantly autonomic nerve fibres innervate the follicles and smooth muscle cells of the blood vessel walls. ❑ Cyclic Changes in the Ovary – Refers to the periodic changes in the ovarian structure in direct relation to the proestrus, estrus, metestrus, diestrus and anestrus stages of the estrous cycle – Influenced by the hormones FSH and LH secreted by the pars distalis of the pituitary gland. ❑ Proestrus Accelerated growth of primordial follicles as influenced by FSH. ❑ Estrus Ovarian follicle ovulates (ruptures and releases the primary oocyte into the fallopian tube). Ruptured follicle is now called the corpus hemorrhagicum. During or after ovulation, the primary oocyte undergoes meiosis to give rise to a secondary oocyte and a first polar body. ❑ Metestrus Development of corpus luteum. ❑ Diestrus Maximum development of corpus luteum and maximum secretion of progesterone. Without pregnancy, the later part of diestrus is characterized by involution of corpus luteum and formation of corpus albicans. ❑ Anestrus Occurs in wild animals. Period of long quiescence between breeding periods. VET 313 Lecture Module 2024 Ovarian follicles do not undergo further development. Corpus luteum continues to involute. Excretory or Genital Ducts – Ducts that transport the ovum from the ovary to the outside. – Consist of the: fallopian tube, uterus, vagina and vulva. ❑ Fallopian tubes, Uterine tubes or Oviducts » Two small bilateral tortuous tubular organs that receive the ovulated ovum from the ovary and the spermatozoa from the uterine horn. » Divided into four regions: infundibulum, ampulla, isthmus and interstialis (intramural part). ❑ Infundibulun: – Large funnel-shaped portion of the oviduct that presents finger-like projections called fimbria. ❑ Ampulla – The longest thin-walled portion of the oviduct. – Caudal part is the site of fertilization. ❑ Isthmus – Short narrow muscular part of the oviduct near its connection with the uterus. ❑ Interstialis (intramural part) – Short terminal part of the oviduct, which extends to the uterus. » The fallopian tube presents the following features in its wall: ❑ T. mucosa – Extensively folded: tubal lumen presents' a labyrinthine system of narrow spaces. – LE - simple columnar intermittently ciliated with the non- ciliated secretory cells showing apical blebs. – LP - loose CT without glands. – MM - absent. ❑ T. submucosa – Loose CT without glands. ❑ T. muscularis – Inner circular or spiral and outer longitudinal smooth muscle fibers. – Isthmus: three layers (inner longitudinal, middle circular and outer longitudinal smooth muscle layers). ❑ T. serosa—typical. VET 313 Lecture Module 2024 ❑ Uterus » Changes in thickness in relation to stages of the estrous cycle. » Ruminants: endometrium presents caruncles, the elevated areas of lamina propria that are highly vascularized, devoid of uterine glands and the eventual sites of contact of the foetal cotyledons. » Walls of the horns and body present three layers: endometrium, myometrium and perimetrium. ❑ Endometrium – Innermost layer that corresponds to the t. mucosa and t. submucosa of a typical tubular organ. – LE - simple columnar epithelium. – LP - loose CT with simple or branched straight tubular uterine glands (endometrial glands). – MM - absent. ❑ Myometrium – Corresponds to the t. muscularis of a typical tubular organ. – Two layers of smooth muscle fibers arranged into a thick inner circular layer and a thin outer longitudinal layer. – Between the two layers is the stratum vasculare, a layer of large blood vessels. ❑ Perimetrium – Corresponds to the t. serosa of a typical tubular organ – Similar in structure to t. serosa except that a large number of lymphatic vessels may be present. VET 313 Lecture Module 2024 ❑ Cervix » The wall of the cervix (cervix uteri) has the same layers as the typical tubular organ. ❑ T. mucosa – Presents primary, secondary and tertiary folds, giving the impression of the presence of glands although true uterine glands are absent in the cervix. – LE - simple columnar with non-secretory ciliated cells, mucous- secretory cells and goblet cells. In the bitch, however, it is stratified squamous. ❑ Mucus secretion by the secretory cells increases during estrus and pregnancy. ❑ During pregnancy the mucus thickens to form the cervical seal or cervical plug. ❑ Ruminants: intraepithelial and simple tubular glands may be present. ❑ Sows: 90% of the cervix is lined by stratified squamous nonkeratinized epithelium that undergoes cyclic changes like the vaginal epithelium. – LP - irregular DWFCT, which becomes loose and edematous during estrus. – MM - absent. ❑ T. submucosa - same structure as the lamina propria. ❑ T. muscularis – Well developed; consists of inner circular and outer longitudinal smooth muscle layers. VET 313 Lecture Module 2024 – Inner circular layer presents prominent elastic fibers, which together with the smooth muscles reestablish the structure of the cervix after parturition. ❑ T. serosa - is typical. ❖ Cyclic Changes in the Uterine Endometrium » Proestrus ❑ LE hypertrophies and begins to be invaded by neutrophils. ❑ LP becomes highly vascular and congested with occasional hemorrhage. » Estrus ❑ LE continues to proliferate and become invaded by lymphocytes and monocytes. ❑ LP remains congested, edematous and hemorrhagic. ❑ Uterine glands start to proliferate and the secretory activity of the glandular cells is increased. ❑ A thick endometrium and highly developed glands are characteristic of the estrous uterus. » Metestrus ❑ Continued proliferation and coiling of uterine glands and continued secretory activities of epithelial and glandular cells. ❑ Disappearance of edema in the lamina propria. » Diestrus ❑ Maximum proliferation and extensive coiling of uterine glands. ❑ If fertilization occurs, the maximum secretory activity of epithelial and glandular cells is maintained. ❑ If there is no fertilization, vascularity of the lamina propria decreases, secretory activity ceases and the lining and glandular cells involute. » Anestrus ❑ Endometrium is thin, lined by simple cuboidal epithelium and presents few simple straight uterine glands. ❑ Vagina » Muscular tube that communicates with the cervix of the uterus dorsally and opens ventrally to the vestibule of the vulva. » Site of deposition of the semen. » During estrus the vagina contains increased amounts of mucus secreted by the cervical epithelium. » Wall presents the following features: ❑ T. mucosa – Presents flat longitudinal folds and in cows, prominent circular folds in the cranial portion of the vagina. – LE - stratified squamous non-keratinized. ❑ Cow: isolated foci of goblet cells are present in the cranial portion. ❑ Bitch: intraepithelial glands have been observed during the estrus stage. – LP - loose to dense irregular CT with lymph nodules in the caudal part of the vagina. – MM - absent. VET 313 Lecture Module 2024 ❑ T. submucosa – presents lymphatic nodules. ❑ T. muscularis – Two to three layers of smooth muscle fibers (inner longitudinal, middle circular and outer longitudinal). – The inner longitudinal layer is of variable occurrence. ❑ T. serosa/t. adventitia. – T. serosa - present in the cranial portion of the vagina and replaced by t. adventitia caudally. – Typical loose CT with large blood vessels, nerves and ganglia. ❖ Cyclic Changes in Vagina o It is very evident in the bitch where they are used to determine the best period for mating. o Proestrus ▪ Superficial cell layer of the stratified squamous epithelium becomes cornified with pyknotic nuclei. ▪ Third day of the proestrus: ▪ Cornification extends to the lower layers of cells where the nuclei may eventually disappear. ▪ Erythrocytes proliferate in the vaginal epithelium due to diapedesis from the underlying vascular bed. ▪ Leukocytes are absent by the middle of proestrus while various types of bacteria may be present on or within the epithelial cells. o Estrus ▪ Lining epithelial cells are cornified with pyknotic nuclei. ▪ Late estrus: Epithelial cells are without nuclei. Erythrocytes become fewer while bacteria are still present. Cellular debris becomes abundant. ▪ One to two days before diestrus: neutrophils reappear. o Diestrus ▪ Abundant neutrophils. ▪ Many small, round, noncornified, round to oval epithelial cells with large, distinct and uniform nuclei. o Anestrus ▪ Many noncornified, round to oval epithelial cells which contain large, distinct and uniform nuclei. ▪ Few neutrophils and minimal cellular debris. VET 313 Lecture Module 2024 ❖ Vaginal cytology o Vaginal cytology provides a way of determining stages of the estrous cycle of the bitch or queen and therefore can be helpful to the practitioner who is trying to determine the best time to breed an animal o In the bitch, proestrus, estrus, diestrus, and anestrus are stages of the estrous cycle. The formation of the corpus luteum occurs during late estrus in the bitch. Therefore, there is no metestrus. o Proestrus lasts an average of 9 days and is characterized by a watery, bloody discharge and swollen vulva. o Estrus is evidenced when a bitch is willing to stand for mating, and ordinarily lasts about 9 days. A clear or bloody discharge is present. o Diestrus lasts for about 2 months and begins on the day when the bitch no longer tolerates a male's advances. o Anestrus follows diestrus and may last from two to ten months. o Various types of epithelial cells are found in vaginal smears taken during the estrous cycle. ▪ Parabasal cells are the smallest. They are round cells with round nuclei, and have the highest nucleocytoplasmic ratio of any of the sloughed cells. ▪ Intermediate cells are larger than parabasal cells. Their nuclei are similar in size and shape to those of the latter. The corners of intermediate cells are rounded. ▪ Superficial intermediate cells (transitional cells) are bigger than intermediate cells and have angular edges. Their nuclei resemble those of parabasal and intermediate cells. ▪ Superficial cells are similar in size to superficial intermediate cells. Their edges are angular and may be folded. Their nuclei are pyknotic, faded, or lacking. o Smears taken during proestrus (early to mid) may contain erythrocytes and neutrophils as well as parabasal, intermediate, superficial intermediate, and superficial cells. During late proestrus, superficial intermediate and superficial cells are the most numerous, and neutrophils decline. o The vast majority (90% or more) of cells found in smears taken during estrus are superficial cells. During late proestrus, similar smears may be obtained. Ordinarily, during estrus, neutrophils are not observed. Erythrocytes show a reduction in number, but in many bitches they can be found throughout estrus and into early diestrus. Bacteria may be found in estrous smears. o During diestrus, superficial cells decrease by a minimum of twenty percent. Parabasal and intermediate cells, which may have been absent or very sparse, increase to more than 10% and frequently rise to more than 50%. Although neutrophils reappear during diestrus, smears from some bitches contain few or none. Because erythrocytes may be present in smears from early diestrus, it is not possible to distinguish proestrus from diestrus without taking more than one smear. o During anestrus, parabasal and intermediate cells predominate in smears. Bacteria may be found, but will be less abundant than in proestrus or VET 313 Lecture Module 2024 estrus. Neutrophils may occur, but are ordinarily less abundant than in early diestrus. External genitalia – The mammalian female external genitalia is the vulva, which consists of the vestibule, clitoris and labia. Vestibule – Cavity of the vulva. – Contains the clitoris and the external urethral orifice, the opening of the female urethra. – Structurally similar to the caudal portion of the vagina. – Wall presents the following features: – T. mucosa – LE - stratified squamous non-keratinized epithelium with extensive lymphocytic infiltration. – LP - loose and dense CT rich in elastic fibers and with vestibular glands. – Cows, ewes and queens: major vestibular glands - compound tubuloalveolar mucous glands embedded within the constrictor muscle in the lateral walls of the vestibule. – Other species: minor vestibular glands - simple branched tubular mucous glands scattered throughout the vestibule but in the cow they are concentrated near the clitoris. – MM - absent. – T. submucosa - same as the LP. – T. muscularis - inner longitudinal and outer circular smooth muscle layers. – The outer circular layer consists of the constrictor vestibuli and constrictor vulvae. – T. advetitia - is typical. Clitoris – Homologue of penis. – Consists of body, glans and prepuce, but these are not as developed as in the penis. – DWFCT capsule. – Contains erectile tissue. – Structurally similar to vestibule except that the lamina propria-t. submucosa contains erectile tissue. Labia (Lips) – Folds of integument that form the wall of the vestibule. – Only one pair is developed in domestic animals - the labia minora. – Outer surface is covered by skin with hairs. – Inner surface is covered by stratified squamous nonkeratinized epithelium. VET 313 Lecture Module 2024 Avian Female Reproductive System The avian female reproductive system consists of one (1) ovary, one (1) excretory or genital duct or oviduct or fallopian tube and a cloaca. Ovary (Left ovary) During embryonic development the female chick embryo has two ovaries. As development progresses the right ovary degenerates and only the left ovary is retained. Membranous organ with finger-like projections suspended like a pendulum from the dorsal body wall by the mesovarium. Like a bunch of grapes due to the presence of many round follicles of various sizes projecting from the ventral surface of the organ. Presents an outer thick peripheral cortex and a centrally located vascular medulla. – Cortex Covered by a germinal epithelium (simple squamous or simple cuboidal type), just like the mammalian ovary. Underneath the germinal epithelium is the tunica albuginea made up of dense connective tissue. In Philippine native hens, collagen fibers were not observed in the periphery of the cortex indicating the absence of tunica albuginea in this breed. Stroma consists of loose CT and regressing postovulatory follicles. Regressing postovulatory follicle consists of a cluster of pale-staining vacuolated cells with pyknotic nuclei and many fat vacuoles in the cytoplasm. Parenchyma consists of ovarian "follicles" in various stages of development or atresia. True ovarian follicles are not present because avian follicles have no antrum. Corpus luteum is not formed from the ruptured ovarian follicle. Grossly, the ovarian follicles are of four (4) types based on their diameters: large yellow follicles (greater than 10mm), medium yellow follicles (6-10 mm), small yellow follicles, (4-6 mm) and large white follicles (2-4 mm). Histologically, there are five (5) types of follicles in the avian cortex: primary, growing, mature, atretic and discharged follicles. VET 313 Lecture Module 2024 ✓ Primary follicle The smallest follicle; located superficially in the cortex. Round: contains a relatively large primary oocyte (mean diameter = 21.1 µm) with a centrally located nucleus and a small amount of yolk. Enclosed by a distinct perivitelline membrane (PM) with fine elastic fibers. External to PM is a single layer of cuboidal follicular cells, the membrane granulosa. External to membrana granulosa is a thin basal lamina (BM) that consists of condensed fine elastic fibrils. Peripheral to BM is a single layer of spindle-shaped cells, the cellular theca interna. No theca externa. ✓ Growing follicles The second most numerous (mean number = 29.6) follicles. Located deeper in the cortical stroma. Round but larger (mean diameter 244 µm) than the primary follicle. Morphologically similar to the primary oocyte of the primary follicle except that it contains a larger amount of yolk and has a larger size (mean diameter = 215.1 µm). Yolk contains lipids, such as lecithin, cholesterol and carotene, arranged in concentric layers. Well defined perivitelline membrane. Membrana granulosa is pseudostratified columnar epithelium. Basal lamina - condensed CT fibrils. Theca interna - like in the primary follicle Theca externa - indistinct. Pale vacuolar interstitial luteal endocrine cells present. ✓ Mature follicles Structurally similar to growing follicles but larger. Suspended from the ovary by a pedicle of cortical tissue or follicular stalk. ✓ Atretic follicles The least numerous (mean number 11.5). Wide range of diameters from 12 to 100 µm and a mean diameter of 56 µm. Irregular in size and shape: vacuolations in the follicular cells or primary oocyte, proliferation of follicular and thecal cells and detachment of the follicle from the theca interna. – Medulla Occupies the fibrous core of the avian ovary. Diffuse: not as well developed as in mammals. Made up of collagen fibers and with numerous blood vessels. Excretory or Genital Duct or Oviduct Ducts that transport and add investments to the ovum. o Investments of the ovum are the albumen, shell membrane and shell. o Investments are added to the ovum while it passes through the different regions of' the excretory duct on its way to being laid as the egg. VET 313 Lecture Module 2024 The right oviduct also degenerates like the right ovary thus only the left oviduct is retained. Form a muscular, long and tortuous tubular organ that is divided into infundibulum, magnum, isthmus, uterus or shell gland and vagina. VET 313 Lecture Module 2024 o Infundibulum ▪ Funnel-shaped with dilated end, the fimbria, which catches the ovum upon its release from the ovary. ▪ Usual site of fertilization. ▪ Secretes the chalaza. ▪ Thin wall, narrow irregular lumen. ▪ Wall presents the following layers: T. mucosa o Extensively folded with primary folds. o Primary folds may give off secondary folds that result in the narrow irregular appearance of the infundibular lumen. o LE - simple or pseudostratified columnar ciliated with occasional goblet cells. o LP - typical. o MM - absent. T. submucosa - typical. T. muscularis - loosely arranged inner circular and outer longitudinal smooth muscle layers. ▪ In some regions of infundibulum a stratum vasculare or vascular layer separates the two layers of smooth muscles. o Magnum ▪ The longest portion of the oviduct ▪ Very thick wall and very narrow labyrinthine lumen. ▪ Wall is similar to that of the infundibulum except that: ▪ Folds of t. mucosa-submucosa are taller and wider with many branched tubular glands that secrete egg white or albumen. VET 313 Lecture Module 2024 ▪LE - pseudostratified columnar predominantly secretory with apical blebs, and a few ciliated cells. ▪ Folds of t. mucosa-submucosa are taller and wider with many branched tubular glands that secrete egg white or albumen. ▪ LE - pseudostratified columnar predominantly secretory with apical blebs, and a few ciliated cells. o Isthmus ▪ Shortest portion of the oviduct. ▪ Structurally similar to the magnum except that: T. mucosa presents narrow longitudinal mucosal ridges that present secondary folds. o LE - simple or pseudostratified columnar predominantly ciliated with very few secretory cells. o LP - mucosal glands secrete the shell membrane (thick outer and thin inner layer of protein, mainly keratin). o Uterus or shell gland ▪ Unlike its mammalian counterpart, is not designed for the implantation of fertilized ovum. ▪ Responsible for the production of eggshell. ▪ Expanded portion of the oviduct ▪ Not divided into regions. ▪ Presents a wall and a labyrinthine lumen. ▪ Wall presents the following features: T. mucosa or endometrium- presents leaf-shaped longitudinal folds. o LE - pseudostratified columnar ciliated. o LP - loose CT with extensive coiled tubular shell-producing glands. o MM - absent. T. submucosa - blends with lamina propria to form the endometrium. T. muscularis or myometrium - presents an inner circular and a well developed outer longitudinal smooth muscle layers separated by a stratum vasculare. T. serosa or perimetrium - typical. o Vagina ▪ Short narrow duct with a thick wall and a labyrinthine lumen. ▪ Opens into the urodeum of cloaca. ▪ Wall presents the following features: T. mucosa - presents slender leaf-shaped primary folds that give off secondary folds. o LE - pseudostratified columnar predominantly ciliated with a few goblet cells; simple columnar epithelium in sperm- host glands. o LP - loose CT without glands except in the uterovaginal junction where sperm- host glands are present. ▪ Sperm-host glands - tubular glands that store sperms. ▪ Sperms remain functional for up to 21 days. o MM - absent T. submucosa - typical. T. muscularis VET 313 Lecture Module 2024 o Very thick inner circular and thin outer longitudinal smooth muscle layers. o Contraction of this tunic propels the egg to the cloaca for expulsion outside. T. serosa - is typical in the cranial portion of the vagina and replaced by t. adventitia caudally. o Cloaca ▪ Corresponds to the external genitalia of mammals. References: Aughey, E. and Frye, F.L. 2001. Comparative Veterinary Histology with Clinical Correlates. Manson Publishing Ltd Bacha, W.J. and Bacha, L.M. 2012. Color Atlas of Veterinary Histology, 3rd Edition. John Wiley & Sons, Ltd. Banks, W.J. 1993. Applied Veterinary Histology. 3rd Edition. Mosby Inc. Caceci, T. 2015. Doctor C's On-Line Histology. https://www.doctorc.net/ De Ocampo, G.D. 2008. Lecture Notes in Veterinary Histology. 6th Ed. UPCVM, UPLB Dellman, H.D. and Eurell, J.A. 1998. Textbook of Veterinary Histology. 5th Ed. Baltimore: Lippincott, Williams and Wilkins Eurell, J.A. and Frappier, B.L. 2006. Dellmann’s Textbook of Veterinary Histology. 6th Edition. Blackwell Publishing Konig H.E. and Liebich H.G. 2004. Veterinary Anatomy of Domestic Animals: Textbook and Color Atlas. Schattauer GmbH. Liebich, H.G. 2019. Veterinary Histology of Domestic Mammals and Birds. 5th Edition. 5m Publishing VET 313 Lecture Module 2024