Special Histology and Embryology: Practical Course - V. K. Naphpanyuk 2001

Reproductive System
Female Reproductive System
Ovaries

The FEMALE Reproductive System (organa genitalia feminina) consists of the Gonads (ovaries) and accessory reproductive Organs (fallopian tubes, Uterus, Vagina, and external genitalia).

The ovaries (ovarium) are female gonads that produce Female Germ Cells (ova/eggs) and Female Sex Hormones (estrogens and progesterone).

The Ovary is a paired organ located near the lateral wall of the lesser pelvis. Ovaries are oval-shaped, measuring approximately 4×2×1.5 cm, with the right ovary being slightly larger. They are attached to the broad ligament of the uterus by a peritoneal fold (mesovarium).

Externally, the organ is enclosed by a tunica albuginea, which is formed by dense Fibrous Connective Tissue covered by mesothelium. The free surface of the mesothelium bears microvilli.

Beneath the capsule lies the cortex, and deeper still is the medulla.

The cortical substance (cortex ovarii) consists of stroma and parenchyma.

The stroma of the cortex is formed by connective tissue containing Collagen fibers and a small amount of elastic fibers. This connective tissue is exceptionally rich in fibroblasts that resemble smooth myocytes, known as interstitial cells. They are capable of hormone synthesis.

The parenchyma of the cortex comprises primordial, primary, secondary (vesicular), and mature follicles (tertiary follicles or Graafian follicles), corpora lutea, corpora albicantia, atretic follicles, and atretic bodies.

The primordial follicle (folliculus ovaricus primordialis) is formed by a primary oocyte (15–25 µm in diameter) arrested in the diplotene stage of meiotic prophase, surrounded by a single layer of follicular epithelial cells and a basement membrane. The nuclei of the epithelial cells are elongated, with Cell diameters up to 9 µm. The follicles are roughly spherical, about 50 µm in diameter, and located in the superficial layers of the cortex (micrograph 47).

Primary follicles (folliculus ovaricus primarius). Follicular growth is accompanied by an enlargement of the germ cell itself. A secondary zona pellucida appears around the oolemma, external to which lie 1–2 layers of cuboidal follicular cells resting on a basement membrane. The Cell surface features Two Types of microvilli: the first penetrate the zona pellucida, while the second establish contact between folliculocytes. Similar microvilli are also present on the oolemma of the oocyte. During maturation divisions, these microvilli become shorter and eventually disappear. Follicles consisting of a growing oocyte, a forming zona pellucida, and several layers of follicular epithelium are termed primary follicles.

Secondary follicles (folliculus ovaricus secundarius) (vesicular, antral) possess a Stratified Epithelium and a cavity—the follicular antrum—filled with fluid produced by follicular cells. The follicular fluid contains female sex hormones (estrogens). Such follicles begin to form during Puberty. Meanwhile, the oocyte, along with its surrounding zona pellucida and follicular cells forming the cumulus oophorus, is displaced toward one pole of the follicle. Subsequently, numerous Blood capillaries grow into the outer tunic, which differentiates into two layers: internal and external. In the theca interna, numerous interstitial cells homologous to the interstitial Cells of the Testis (glandulocytes) are located around branching capillaries. The theca folliculi externa is formed by Cytology/practical/45.html">Dense connective tissue.

The mature follicle (tertiary) (folliculus ovaricus tertiaricus) is a follicle ready for ovulation. The oocyte, surrounded by a layer of follicular cells called the corona radiata, is pushed toward the upper pole of the growing follicle. The cells of the corona radiata directly adjacent to the growing oocyte have long, branching processes that penetrate through the zona pellucida and reach The surface of the oocyte. Through these processes, nutrients are supplied from the follicular cells to the oocyte, which utilizes them to synthesize yolk Lipoproteins and other substances in its Cytoplasm.

The tertiary follicle reaches such a size that it bulges On the surface of the ovary, with the cumulus oophorus and oocyte positioned within the protruding part of the vesicular Structure.

Further expansion of the vesicular cavity, overcrowded with follicular fluid, leads to stretching and thinning of both the external capsule and the tunica albuginea at the site where the follicle abuts the surface, culminating in its rupture and ovulation.

Atretic bodies (corpus atreticum) are occasionally found among follicles. They develop from follicles that ceased their development at various stages.

The medullary substance (medulla ovarii) is formed by connective tissue containing Blood Vessels, nerves, and epithelial cords, which are remnants of the pronephros/mesonephros (primitive Kidney).

Oogenesis

Oogenesis (ovogenesis) is The process of development of female germ cells from oogonia to a mature ovum.

Oogenesis proceeds similarly to Spermatogenesis, yet possesses its own distinct features and consists of three stages.

The First stage (multiplication period) takes place during intrauterine development from the second to the fifth month and consists of the mitotic division of oogonia and The formation of primordial follicles.

The Second Stage (growth period) occurs in the functioning ovary and involves the transformation of the primary oocyte within a primordial follicle into a primary oocyte within a mature follicle. In the Nucleus of the growing oocyte, chromosome conjugation and tetrad formation take place, while yolk inclusions accumulate in the cytoplasm.

The Third Stage (maturation period) begins with the formation of a secondary oocyte and concludes with the release of the mature egg from the ovary during ovulation. The maturation period, much like in spermatogenesis, includes two divisions; notably, the Second Division follows the first without an interkinesis, leading to a reduction of the chromosome number by half, resulting in a haploid set.

During the first maturation division, the primary oocyte divides, producing a secondary oocyte and a small polar body (reduction body). The secondary oocyte receives almost the entire mass of accumulated yolk and therefore remains as large in volume as the primary oocyte. The polar body is a small cell with scant cytoplasm that receives one dyad from each tetrad of the primary oocyte nucleus. During the second maturation division, the division of the secondary oocyte yields one ovum and a second polar body.

Unlike spermatogenesis, oogenesis lacks stage IV—the spermiogenesis/formation stage.

Preparation 5. Section of a young cat's ovary (Fig. 75).

Low magnification. Examine and draw the slide. It is visible that the ovary is externally covered by the tunica albuginea and superficial epithelium. Beneath the ovarian capsule in the cortical substance, A large number of small primordial follicles are located. The oocyte of a primary follicle is surrounded by the zona pellucida and a single layer of cuboidal or columnar follicular cells. Vesicular follicles are frequently encountered in which the section passed above or below the oocyte, and therefore the oocyte is not visible within the follicle. It is necessary to find a follicle where the section passed through the cumulus oophorus and study it at high magnification.

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Fig. 75. Section of a young cat's ovary. Hematoxylin-eosin staining. x 40:

1 — cortical substance of the ovary; 2 — medullary substance of the ovary; 3 — superficial epithelium; 4 — tunica albuginea; 5 — primordial follicles; 6 — vesicular follicle (Graafian follicle) with the cumulus oophorus; 7 — primary oocyte; 8 — corona radiata; 9 — follicular cells of the granulosa layer; 10 — theca interna of the vesicular follicle; 11 — theca externa of the vesicular follicle; 12 — atretic bodies; 13 — corpus luteum; 14 — blood vessels; 15 — growing follicles

High magnification. The Nucleus and cytoplasm surrounding the oocyte are visible within the oocyte. With a slightly lowered condenser, the zona pellucida appears as a strongly light-refracting rim on the surface of the oocyte. This is followed by the corona radiata formed by follicular epitheliocytes. The follicle is filled with follicular fluid. The granulosa layer is located on the basal membrane of the follicle. External to the basal membrane lies the connective tissue theca interna with capillaries and thecal endocrinocytes. The theca externa consists of tightly packed fibers and spindle-shaped cells.

An atretic body can be recognized by the preserved deformed zona pellucida of the destroyed oocyte. The corpus luteum in its peak functional stage is best drawn from a demonstration slide. The medullary substance contains blood vessels, Lymphatic vessels, and surrounding loose connective tissue.

Label on the figure: 1) cortical substance of the ovary; 2) medullary substance of the ovary; 3) superficial epithelium; 4) tunica albuginea; 5) primordial follicle; 6) vesicular follicle (Graafian follicle) with the cumulus oophorus; 7) primary oocyte; 8) corona radiata; 9) follicular cells of the granulosa layer; 10) theca interna of the vesicular follicle; 11) theca externa of the vesicular follicle; 12) atretic bodies; 13) corpus luteum; 14) blood vessels; 15) growing follicles.

Ovulation

Ovulation (ovulatio) is the rupture of the mature ovarian follicle wall and the release of the primary oocyte into the Abdominal cavity under the Influence of the luteinizing hormone (lutropin) when the Pituitary Gland dramatically increases its secretion.

At this time, the oocyte is in metaphase of the second maturation division.

In the preovulatory stage, pronounced hyperemia of the ovary occurs, along with an increase in the permeability of the hematofollicular barrier accompanied by The Development of interstitial edema and infiltration of

the follicular wall by segmented neutrophils. During this time, the volume of the follicle and the pressure within it increase very rapidly, and the follicular wall sharply thins. In addition, a high concentration of catecholamines is detected in nerve fibers and endings during this period. Besides the factors listed above, Proteolytic Enzymes, as well as the interaction of hyaluronic acid and hyaluronidase contained in its capsule, contribute to the thinning and loosening of the follicle.

Oxytocin plays a significant role in ovulation. Before the onset of ovulation, oxytocin secretion increases in response to The stimulation of nerve endings caused by the increase in intra follicular pressure.

The secondary oocyte, surrounded by the follicular epithelium, passes from the abdominal cavity into the infundibulum and further into the lumen of the Uterine tube, where the very rapid second maturation division takes place and a mature egg cell, ready for Fertilization, is formed.

Corpus Luteum

The corpus luteum is a temporary auxiliary endocrine gland within the ovary that forms from the remnants of a mature follicle.

The excess of luteinizing hormone that led to ovulation causes Changes in the elements within the wall of the ruptured mature follicle and the Formation of the corpus luteum.

Blood from the Vessels of the internal layer, whose integrity is disrupted at the moment of ovulation, pours into the cavity of the emptied vesicle. The blood clot is rapidly replaced by connective tissue in the center of the developing corpus luteum.

The process of Development of the corpus luteum consists of four stages:

1. The stage of proliferation and vascularization is accompanied by the multiplication of epithelial cells from the former granulosa layer, among which capillaries actively grow inward from the internal layer.

2. The stage of glandular metamorphosis is a process accompanied by marked Hypertrophy of the follicular epithelium cells and the accumulation of yellow pigment (lutein) within these cells. They are called lutein cells.

3. The stage of peak development is accompanied by an increase in the newly formed corpus luteum and the initiation of progesterone hormone synthesis. The duration of this stage varies. If fertilization does not occur, the peak period of the corpus luteum lasts 12-14 days and is referred to as the menstrual corpus luteum. If Pregnancy occurs, this body persists for a longer period and is called the corpus luteum of pregnancy.

4. The stage of regression is accompanied by Atrophy of the glandular cells, proliferation of the connective tissue of the central scar; a corpus albicans — a connective tissue scar — is formed in place of the former corpus luteum.

Uterine Tubes

The uterine tubes, or oviducts (tuba uterina, salpinx), are paired tubular organs that originate from the Fundus of the uterus, extend within the broad ligament toward the lateral surface of the lesser pelvis, and terminate near the ovaries.

The wall of the uterine tube is formed by three layers: 1) the mucous membrane (mucosa), lined with a simple columnar epithelium consisting of two cell types — ciliated and secretory (micrograph 48). The mucosa also includes the lamina propria, formed by loose fibrous connective tissue; 2) the muscular layer (myosalpinx), consisting of an inner circular or spiral layer and an outer longitudinal layer; 3) the serous membrane (serosa), which covers the fallopian tubes externally.