Obstetrics and Gynecology - A. M. Gromova 2000

Anatomical and physiological features of the female body
Menstrual cycle

The menstrual cycle refers to the cyclic changes that occur within a woman's body, particularly in her reproductive Organs, which prepare the body for Pregnancy.

The duration of the menstrual cycle is calculated from the first day of the previous menstruation to the first day of the next. It most commonly lasts 28 days, though a range of 21 to 35 days is also normal. Menses typically lasts from 3 to 7 days. Menstrual Blood is dark, non-clotting, and mixed with mucus; the total volume lost during a single period ranges from 50 to 150 ml. While mild cramping in the lower abdomen or lower back may occur during menstruation, a woman's capacity for work should not be impaired.

The primary hallmark of a healthy, fully functioning menstrual cycle is its biphasic nature, meaning it consists of two distinct phases: Phase I (the follicular phase) and Phase II (the luteal phase), without which pregnancy cannot occur.

The first menstruation (menarche) typically occurs at ages 12 to 14, after which cycles should remain regular throughout a woman's reproductive years (ceasing only during pregnancy and Lactation).

Regulation of the Menstrual Cycle

The FEMALE Reproductive System is organized hierarchically into five levels. The first level comprises the target Tissues—the sites of hormone action. These include the reproductive organs, Mammary Glands, as well as Hair follicles, Skin, and adipose tissue. The Cells of these tissues and organs possess specific receptors for Sex Hormones.

The second level is represented by the Ovaries, where complex processes of steroid synthesis and follicular development take place. Folliculogenesis is a continuous process in the Ovary that begins during the antenatal period and ends in postmenopause. In humans, a single follicle typically matures during each cycle. By the first days of the menstrual cycle, the dominant follicle already has a diameter of 2 mm and grows to an average of 21 mm by the time of ovulation. Over this period, the volume of follicular fluid increases 100-fold. The follicular fluid shows a sharp rise in prostaglandin and estrogen concentrations. Elevated levels of prostaglandin E₂ stimulate the surge of luteinizing hormone and trigger ovulation. Ovulation itself involves the rupture of the basal membrane of the dominant follicle, accompanied by bleeding from the disrupted capillaries surrounding the theca cells. Following the release of the oocyte into the follicular cavity, capillaries rapidly invade the area, and the cells undergo luteinization, accumulating Cytoplasm and lipid droplets. This process leads to The formation of the corpus luteum, the cells of which produce progesterone. Additionally, the human corpus luteum secretes small amounts of estradiol and androgens.

The steroid-producing Tissues of the ovary include the granulosa cells lining the follicular cavities, the internal theca cells, and, to a much lesser extent, the stromal cells. Gonadotropins (FSH and LH) play an essential role in steroid synthesis.

The third level of the reproductive system is the Pituitary Gland, specifically its anterior lobe, the adenohypophysis, which synthesizes gonadotropic hormones: follitropin (follicle-stimulating hormone - FSH), lutropin (luteinizing hormone - LH), and prolactin (PRL), which regulate the function of the ovaries and mammary glands.

FSH stimulates follicular growth and the proliferation of granulosa cells, and induces the formation of LH receptors On the surface of granulosa cells. Working in synergy with FSH, LH promotes ovulation and, together with prolactin, stimulates progesterone synthesis. Prolactin exerts diverse effects on the female body, with its primary biological role being The Development of mammary glands and The regulation of lactation.

The fourth level of the reproductive system is the hypophysiotropic area of the Hypothalamus. It consists of clusters of Neurons that form the ventromedial, dorsomedial, and arcuate nuclei. The Nerve Cells of these nuclei possess neurosecretory activity, producing hypophysiotropic hormones (releasing hormones) known as liberins, which are chemically classified as decapeptides.

Releasing hormones travel via the axons of these nerve cells to terminal endings that closely abut the capillaries of the median eminence of the hypothalamus, forming the portal Circulatory system that links the Hypothalamus and Pituitary gland. A unique feature of this system is bidirectional blood flow—both toward the hypothalamus and toward the pituitary—which is crucial for feedback mechanisms. The release of releasing hormones occurs in a circhoral rhythm that is established during Puberty and serves as an indicator of the maturity of hypothalamic neurosecretory structures.

Thus, circhoral secretion of releasing hormones initiates the hypothalamic-pituitary-ovarian axis, though its Organization cannot be considered entirely autonomous, as it is modulated by impulses from extrahypothalamic structures.

The fifth level of the reproductive system comprises extrahypothalamic cerebral structures that receive sensory input from the external environment and interoreceptors, transmitting these signals via Neurotransmitters to the neurosecretory nuclei of the hypothalamus.

A woman's menstrual function is influenced by numerous factors, including: physical and psychological stress, Developmental anomalies of the reproductive organs, infantilism, extragenital and endocrine disorders, nutritional imbalances,

exposure to environmental hazards, genetic pathology, Diseases of the FEMALE REPRODUCTIVE ORGANS (such as inflammation or tumors), and others.

The Ovarian Cycle

The ovaries are paired oval organs measuring 30-40 mm in length and weighing 4-5 g. Each ovary consists of two distinct layers: an inner and an outer layer. The inner layer (medulla) is composed of bundles of Cytology/cytology/32.html">Smooth Muscle tissue, spindle-shaped and oval cells, and a stroma, and is richly vascularized by the outer cortical layer. The outer surface of the ovary is covered by a cuboidal germinal epithelium, beneath which lies a compact layer known as the tunica albuginea. Closer to The surface of the cortex are primary follicles (each containing an immature egg—a primary oocyte surrounded by small follicular cells). By puberty, their total number reaches approximately 38,000–40,000, of which only about 400 are utilized over a lifetime. Follicular maturation begins with the intensive growth of follicular cells. The follicle increases in size and shifts closer to the ovarian surface. The follicular cells multiply into multiple layers surrounding the oocyte to form the granulosa layer. These cells secrete a fluid, liquor folliculi, which creates spaces within the granulosa layer. Some of these cells migrate to the periphery (forming a thin lining) to constitute the membrana granulosa, while others accumulate tightly around the oocyte to form the cumulus oophorus. Within the cumulus, the oocyte is enclosed by the zona pellucida. The Cells of the follicular layer provide nutritional support to the oocyte. The follicle is surrounded by a layer of Connective Tissue cells varying in shape and size, which differentiate into two layers: the theca interna and theca externa. The theca interna is separated from the follicle by a basal membrane, borders the ovarian stroma, and lies adjacent to the granulosa cells. The follicular fluid and the oocyte are pushed toward the periphery by the granulosa cells (at this stage, the follicle reaches a diameter of 2-4 mm). Following the rupture of the Graafian follicle, blood escaping from the ruptured theca folliculi accumulates at the base, forming a clot. Subsequently, the cells of the membrana granulosa proliferate and turn yellow due to the accumulation of lutein, giving rise to the corpus luteum, which is about the size of a cherry. If pregnancy does not occur, the corpus luteum persists for 12 to 14 days before undergoing regression.

The ovary secretes estrogens, progesterone, and androgenic hormones. Estrogens are produced by the granulosa cells and interstitial cells. Over a 24-hour period, both ovaries secrete about 0.5 mg of estrogens, the primary forms being estradiol, estrone, and estriol, with estradiol being the most potent. Estrogenic hormones are also secreted by the Placenta and Adrenal Glands. These hormones exert vegetative, generative, and systemic effects on the body.

Progesterone is secreted by the corpus luteum, placenta, and adrenal glands, with a total output of 150-200 mg per cycle. Progesterone prepares the uterine lining (endometrium) for the implantation of a fertilized egg (secretory phase) and suppresses uterine contractions.

Selection/3.html">Stages of development of the Corpus Luteum:

1. Stage of proliferation – the rapid multiplication of granulosa cells.

2. Stage of vascularization – Blood Vessels grow inward toward the center of the corpus luteum. A lipid substance, lutein, appears in the cytoplasm of the granulosa cells, transforming the corpus luteum into an endocrine gland.

3. Stage of peak development (occurring on days 26–27 of a 28-day menstrual cycle) – the corpus luteum grows to be 1.5 to 2 times larger than a mature follicle.

4. Stage of regression – the degeneration of lutein cells, which gradually undergo fibrosis. The corpus luteum loses its color and decreases in size.

The first stages last 4–5 days, the third takes 10 days, and the fourth lasts from 8 to 10 weeks. If pregnancy occurs, the corpus luteum reaches its peak development by the 11th–14th week of pregnancy, occupying almost the entire ovary (about 3 cm in diameter).

The ovarian cycle consists of 2 phases: the follicular and the luteal phase. During their functional activity, both the follicle and the corpus luteum act as Endocrine glands.

Ovulation is the bridging process between the follicular and luteal phases. It typically occurs on the 14th–16th day of the menstrual cycle. Occasionally (very rarely), polyovulation may occur, involving two ovulations within a single menstrual cycle.

It was previously believed that follicular rupture and the release of the egg occurred solely due to mechanical factors (increased pressure within the oocyte) or trophic disturbances in the follicle, meaning the rupture took place in an avascular zone. Today, however, it is known that ovulation is the result of complex neurohumoral regulation. It is believed that the rupture of the follicular wall involves Enzymes linked to the hyaluronic acid-hyaluronidase system. As pressure rises within the mature follicle, impulses are triggered that stimulate the secretion of oxytocin (in the posterior pituitary gland). Oxytocin causes the contraction of the smooth muscle cells in the follicular wall. Consequently, the follicular wall thins and ruptures in the avascular region.

Follicular growth and maturation are stimulated by FSH. The synthesis of estrogenic hormones is driven by the combined action of FSH and LH, while LH stimulates the formation and Development of the corpus luteum. Progesterone is produced under the control of LH and LTH.

In addition to gonadotropic hormones, oxytocin and serotonin also participate in the regulation of the menstrual cycle. Oxytocin induces uterine contractions and influences both ovulation and lactation, whereas serotonin helps reduce uterine bleeding during mensis.

A feedback loop exists between the ovary and the pituitary gland. Gonadotropic hormones stimulate The production of high levels of estrogens, which in turn act on the pituitary gland to suppress The excretion of trophic hormones. Conversely, high levels of progesterone inhibit the production of LH and LTH while disinhibiting FSH stimulation.

High concentrations of LTH (prolactin) stimulate Mammary Gland Function while inhibiting the release of FSH and LH, thereby halting follicular development (which explains why nursing mothers do not menstruate).

Uterine Cycle

The uterine cycle is characterized by the cyclical onset of uterine bleeding under the regulatory control of the pituitary gland.

The following changes take place within the Uterus:

1. Desquamation phase (days 1 to 6): the functional layer breaks down and shedding begins. The withdrawal of progesterone causes ischemia in the endometrial Vascular System, leading to the destruction and detachment of its functional layer, thereby initiating menstruation.

2. Regeneration and proliferation phase: from the end of mensis until the 14th day of the cycle. This phase occurs under METABOLISM/18.html">The Influence of estrogens (with the pituitary secreting FSH and LH during this time). The endometrial layer is restored, reaching a thickness of 4–5 mm.

3. Secretory phase (days 15–25): endometrial glands secrete fluid. The functional layer reaches a thickness of 8–10 mm and differentiates into a compact and a spongy layer. This phase is stimulated by progesterone, while the pituitary produces LH and LTH.

Parameters of normal menstruation include a blood loss of 100–150 ml (the blood does not clot), the absence of pathological subjective symptoms, a cycle duration of 21–35 days, and menstrual bleeding lasting 3–5 days.

Changes in the Vagina

Cyclical changes occur within the vaginal mucosa, which can be identified through periodic cytological and morphological examinations. These changes affect all layers of the mucosal membrane. A smear is collected from the posterior vaginal fornix, then fixed and stained.

There are 4 distinct layers within the mucosa:

- basal layer, located on the basement membrane (the deepest layer), consisting of single-layered cells of cylindrical or cuboidal shape, characterized by very large nuclei and basophilic cytoplasm;

- parabasal layer, composed of multi-layered polygonal cells connected by intercellular bridges, featuring large nuclei and basophilic cytoplasm;

- intermediate layer, consisting of spindle-shaped cells with peripherally stained, flattened nuclei connected by intercellular bridges; the nuclei are somewhat smaller, showing signs of degeneration, and perinuclear vacuoles occasionally appear;

- superficial layer, comprising large, flat, polygonal cells with small pyknotic nuclei. These cells undergo keratinization as they approach the surface.

The mucosa accumulates Glycogen and undergoes surface keratinization, which serves a protective function. Vaginal cells continuously change in shape and size. Basal cells pass through all stages to reach the outermost epithelial layer, where they are eventually shed. Consequently, cells corresponding to each respective layer appear in the vaginal content.

During the period of follicular growth and high estrogen levels, the cytological smear is characterized by an Abundance of superficial epithelial cells, peaking just before ovulation. In the second phase of the cycle, the number of superficial cells decreases, and intermediate-layer cells with folded edges and acidophilic protoplasm become predominant.