Female genital physiology

2021-06-15 05:02 PM

The germinal epithelium covers the outer surface of the ovary and relates to the mesothelial layer that covers the ovarian mesentery.

The female reproductive organs include (1) ovaries, (2) fallopian tubes, (3) uterus, (4) vagina and (5) vulva. (6) The mammary gland is also considered part of the female reproductive organs (figure).

Structure and function

Ovary

The ovaries are considered female gonads. Each woman has 2 ovaries, located in front of the pelvic cavity, and on either side of the uterus. On the ovary, there is a point for the entrance of blood vessels and nerves called the ovary hilus.

Each ovary consists of the following parts:

The germinal epithelium covers the outer surface of the ovary and is connected with the mesothelial layer covering the ovarian mesentery. Although called germinal epithelium, their job is not to produce eggs.

The white sheath (tunica albuginea) is composed of dense and irregular connective tissue located just below the germinal epithelium.

The stroma is an area of ​​connective tissue beneath the white crust consisting of a shallow, dense layer called the cortex and a deeper, looser layer called the medulla.

The follicles are in the white shell with egg cells at different stages of development and surrounded by cells. At first, these surrounding cells have only one layer, then they grow in number to form many layers of cells and are called granulosa cells. These granulosa cells nourish the developing egg cell and secrete oestrogen as the follicle develops.

Mature follicle (Graaf cyst): is a large fluid-filled follicle that ruptures and releases a grade II oocyte during ovulation.

Corpus luteum: contains the remains of an egg after ovulation. The corpus luteum produces progesterone, oestrogen, relaxing, and inhibin. When the corpus luteum degenerates, it becomes a fibrous tissue called the corpus luteum.

Figure: The stages of development of follicles in the ovary.

Egg production process

Oocytes must undergo meiosis to produce eggs that carry a haploid set of chromosomes (n=23).

Right from the early foetal stage, primordial germ cells have migrated from the endoderm of the yolk sac to the ovary and differentiated into oogonia bearing a diploid set of chromosomes (2n = 46). ). These cells divide by mitosis to form about 6 to 7 million oocytes around the fifth month of pregnancy, and then mitosis stops.

Right before birth, many oocytes degenerate, and only a few of them develop into primary oocytes with duplicated diploid chromosomes entering the first phase of meiosis. stage of meiosis and stops there until puberty.

 

Figure: Structure of a mature follicle.

Before birth, each primary follicle is surrounded by a layer of granulosa cells to form primary follicles, which degenerate into those that fail to form follicles.

At birth, each girl has only about 2 million grade I follicles left. By puberty, this number is reduced to about 400,000, and of those, only about 400 will mature and be released during a person's reproductive life. female, the rest will be degraded.

Each month, about 1,000 follicles begin to develop. These follicles will begin to develop at different times, those that develop at the time with the most favourable hormonal conditions will continue to develop and the follicles that develop at less favourable times. more likely to degenerate. In each cycle, in each ovary, only 6 to 10 follicles will develop to the antrum stage, and of these, only one will mature.  

As the follicle grows (Figure 7) an inner glycoprotein layer is formed between the primary oocyte and the granulosa cells called the zone pellucida. The innermost layer of granulosa cells is firmly attached to the opacity and is called the corona radiata. The outermost layer of granulosa cells lies on the basal membrane separating them from the stroma of the ovary, this layer is called the cortex of the follicle (theca foliculi). When the granulosa cells begin to secrete, the follicular fluid collects in the antrum located in the centre of the follicle. The primary follicle then becomes a secondary follicle.

During adolescence, the primary and developing follicles continue to degenerate and no oocytes and follicles are formed.

The primary oocyte carrying the 2n set of chromosomes completes the first division of meiosis to produce two cells that carry the double haploid (n) set but are not the same size, the smaller cells are called secondary polar bodies The first polar body contains only the nucleus, while larger cells called secondary oocytes receive most of the cytoplasm.

After puberty, under the influence of hormones FSH and LH of the anterior pituitary gland, each month there is a grade II follicle that continues the process of meiosis until the middle of meiosis II and stops there. The follicle then becomes a mature follicle ready to burst and release the secondary oocyte.

At ovulation, a secondary oocyte, along with the first polar body and the coronal layer, is released into the pelvis and collected into the Fallopian tube. If not fertilized, the oocyte will degenerate and if fertilized, it will continue to complete the second division of meiosis to form 2 cells with haploid chromosomes of irregular size. The larger cell is called the ovum and the other is called the second polar body.

The nucleus of the ovum (n = 23) combines with the nucleus of the sperm (n = 23) through fertilization to form a diploid zygote (2n = 46). The first polar body can also continue to divide to form two microscopic bodies, which will degenerate.

Fallopian tubes (fallopian tubes)

Each woman has 2 fallopian tubes located on either side of the uterus, responsible for catching and transferring the oocyte after ovulation to the uterus. Each fallopian tube is about 10cm long, the part close to the ovary is funnel-shaped with tentacles, one of which will attach to the ovary. The bulbous part of the fallopian tube that occupies about two-thirds of the outside of the fallopian tube is the widest and longest, followed by the shorter, narrower, thicker waist that attaches to the upper lateral side of the uterus.

The wall of the fallopian tube has three layers, the innermost layer is covered with hairy columnar epithelial cells and secretory cells with microcapillaries that provide nutrients to the egg, the middle layer is a bilayer ceramic smooth muscle layer. : the inner layer is thicker, running around and the outer layer is thinner, running vertically. The peristaltic activity of this muscle layer and of the hairy cells in the lumen of the fallopian tube will help the secondary oocyte to move gradually towards the uterine lumen. The outermost layer is the serosa surrounding the fallopian tube.

Usually, fertilization occurs in about the outer 2/3 of the fallopian tube, about 24 hours after ovulation. The zygote will undergo several divisions and reach the uterus about 7 days after ovulation. At this point, it is called a blastocyst.

Uterus

 

Figure: Fallopian tubes and uterus.

The uterus participates in a menstrual activity, is the place of implantation of an egg if fertilized, the place of embryo development, participates in parturition and is the way for sperm to enter to fertilize a secondary oocyte.

In a non-pregnant woman, the uterus is about 7cm long, 5cm wide, and 2cm5 thick. The uterus is larger in pregnant women and smaller in women with low levels of female sex hormones such as in menopause or in women who use oral contraceptives.

The uterus is divided into three parts: the base at the top, the body in the middle, and the neck that opens towards the vagina. Secretory cells in the cervical mucosa secrete cervical mucus which is a mixture of water, glycoproteins, serum proteins, lipids, enzymes, and inorganic salts.

Each female of reproductive age excretes between 20 and 60ml of cervical mucus per day. During ovulation, the fluid is more dilute and alkaline (pH = 8.5) creating favourable conditions for sperm activity, outside this period the fluid is more viscous. This mucus also plays a role in providing energy for sperm.

The part of the cervix and its mucus act as a reservoir for sperm, helping them avoid the unfavourable environment of the vagina and avoid phagocytosis. They may also play a role in altering the sperm's ability to fertilize an oocyte.

Histologically, the uterus is divided into three layers, the outermost layer is the serosa, the middle is the muscular layer consisting of three layers of smooth muscle with the middle layer running around, the inner layer running along and the outer layer running diagonally, the innermost layer is the inner layer. The endometrium is rich in blood vessels, consisting of a single layer of columnar epithelium with hairy and secretory cells on the inside of the uterus, below is a rather thick layer of connective tissue and deeply developed endometrial glands. into the epithelial layer and extend the winch near the muscle layer.

The endometrial layer is divided into two layers: (1) the functional layer, located on the side of the uterine cavity, which is shed during menstruation, (2) the basal layer, which lies below the functional layer, which helps this layer to heal after each period. menstruation times.

The uterus is supplied with blood by the uterine arteries. The arcuate arteries originating from this artery will arrange around the uterus in the muscular layer and form radial branches that go deep into this layer, before entering the endothelium they divide into 2 types of arteries: (1) ) the straight arteries supply blood to the basal layer and (2) the spiral arteries supply blood to the functional layer, which has significant changes during the menstrual cycle.

The uterus needs to be supplied with a large amount of blood in order to re-grow the functional layer after menstruation, to serve the implantation of the egg after fertilization and the development of the placenta.

Vagina

The vagina with a length of about 10cm is the place to receive the penis and semen during intercourse, through the vagina sperm will enter the uterine cavity through the cervix. Menstruation also passes here to come out.

The vaginal mucosa is continuous with the uterine mucosa; after puberty, the vagina is lined with non-keratinized stratified squamous epithelial cells and sparse connective tissue forming transverse wrinkles. vagina. The vaginal mucosa contains a large amount of glycogen, when broken down, it will form organic acids, creating a low pH environment that inhibits the growth of bacteria, but this also affects the viability. and sperm activity. The alkaline nature of semen contributes to neutralizing the acidity of the vagina and increases sperm viability.

The muscular composition of the vagina consists of 2 layers of smooth muscle, a layer running around on the outside, a layer running along the inside, they give the vagina a great ability to stretch, this property is essential for childbirth. and intercourse.

In the lower part of the vagina, where the opening is the vaginal opening, there may be a thin perfused mucous membrane called the hymen that forms a border around the vaginal opening that partially closes the opening.

Vulva

The vulva is a female's external genitalia.

(1) Mu: located above the vagina and urethral opening, formed by the protrusion of fatty tissue above the public joint and covered by a layer of skin and pubic hair.

(2) Large lips: like the male scrotum, also covered with a layer of pubic hair, containing a lot of fatty tissue, sweat and sebaceous glands.

(3) Baby lips: have many sebaceous glands but no sweat glands and fat organization

(4) The clitoris: is a small cylindrical mass of erectile tissue and nerves, located at the superior junction of the two labia minora. This is a structure like a penis in men and can erect when stimulated. The clitoris has a definite role in creating sexual arousal in the female.

(5) Vestibular: The vestibule is the part between the two labia minora, inside it is the hymen, the vaginal opening, the external urethral orifice, and many holes of the ducts. Each side of the external urethral orifice is the foramen of the Sken's glands, and each side of the foramen is the foramen of the Bartholin's glands, the secretions of which lubricate the vagina during intercourse. Running along the bottom of the baby's lips is the vestibular ball consisting of two erect organs, located on both sides of the vaginal opening. This organ will erect when filled with blood, narrowing the vaginal opening and exerting pressure on the penis during intercourse.

Perineum (perineum)

The perineal region is the rhombus-shaped region between the groin and buttocks folds containing the external and anal genitalia. A straight line running across the perineum divides the perineum into an anterior urogenital triangle with the external genitalia and an anal triangle posteriorly with the anus.

Mammary glands

The mammary glands are modified sweat glands located above the pectoralis major and serratus anterior muscles and attached to these muscles by a deep fascia.

Each breast consists of a protruding pigmented papilla called a nipple, on the nipple there are many small holes next to each other, these are the outer openings of the milk ducts. The pigmented skin surrounding the nipple is called the areola, and the areola is rough because it contains many sebaceous glands.

Chains of connective tissue called suspensory ligaments of the breast or Cooper's ligaments run between the skin and the deep fascia to support the breast. These ligaments loosen with age or due to excessive stretching, causing the breasts to sag.

Within each breast, the mammary gland consists of 15 to 20 lobes, separated by fatty tissue. The amount of this fatty tissue determines the size of the breast. Each lobe is further subdivided into several lobules, each consisting of many cysts, which are milk-secreting glands linked together by connective tissue. Surrounding the follicles are spindle-shaped cells called myoepithelial cells, which, when contracted, help release milk toward the nipple. The milk produced is poured into the lactiferous sinuses, where milk is stored before being discharged through the milk ducts.

Ovarian hormones

The oestrogens

Synthesis and transformation:

There are three types of oestrogens: (1) 17(-oestradiol; (2) estrone and (3) estriol, all of which are C18 steroids secreted by the granulosa cells and the inner cortex (theca internal) of the follicles. egg, corpus luteum and placenta.

oestrogen is also formed in the circulatory system through the aromatization of androstenedione. Under the catalysis of the enzyme aromatase androstenedione to estrone and testosterone to oestradiol.

The cells of the inner cortex of the follicle have many LH receptors. LH acts through cyclic AMP to increase the conversion of cholestenone to androstenedione. Some androstenedione is converted to oestradiol which enters the circulation.

The inner coat of the follicle also supplies androstenedione to the granulosa cells to form oestradiol that is secreted into the follicular fluid.

Granulosa cells have many FSH receptors. FSH promotes oestradiol secretion via the cyclic AMP pathway to increase aromatase enzyme activity. Mature granulosa cells also have LH receptors, and LH also stimulates the production of oestradiol.

17(-oestradiol is excreted in the circulation in the same amount as estrone. is then converted to estriol mainly in the liver. Of the three types of oestrogens, oestradiol is the most potent and etriol the weakest.

In the circulatory system, only about 2% is free, the rest is bound to proteins. In the liver the oestrogens are oxidized to glucuronides and sulphate complexes which are then excreted into the bile and reabsorbed into the blood. There are at least 10 different metabolites of oestradiol in the urine.

Excretion and mechanism of action:

Most oestrogens are produced by the ovaries, which have two peaks: (1) Just before ovulation and (2) mid-luteal phase, during the second half of the menstrual cycle.

Oestradiol is excreted in amounts of 36 mg/day (133 mmol/day) during the early follicular phase (early menstrual cycle, 380 mg/day just before ovulation and 250 mg/day in the mid-luteal phase (table). .

After menopause, oestrogen secretion is greatly reduced and remains at very low levels.

In men, oestradiol production is 50 mg/day (180 (mmol/day).

Like other steroids, oestrogen combines with intracellular receptor proteins to form complexes that combine with DNA to promote the transcription of genes to synthesize new proteins that change cell function.

Table: 24-hour production rates of steroid hormones at different phases of the menstrual cycle.

Sex steroids

Early follicular phase

Before Ovulation

The middle stage of the corpus luteum

Progesterone (mg)

1,0

4,0

25,0

17-Hydroxyprogesterone (mg)

0,5

4,0

4,0

Dehydroepiandrosterone (mg)

7,0

7,0

7,0

Androstenedione (mg)

2,6

4,7

3,4

Testosterone (mg)

200,0

240,0

170,0

Estrone (mg)

50,0

350,0

250,0

Oestradiol (mg)

36,0

380,0

250,0

Effects on female genitalia:

The oestrogens promote the development of the follicles and increase the motility of the fallopian tubes.

During the menstrual cycle oestrogen causes cyclical changes in the endometrium, cervix, and vagina, as discussed below.

oestrogen increases blood flow to the uterus and has an important role in the smooth muscle system of the uterus.

In prepubertal and oophorectomy women, the uterus is small, and the uterine muscles are atrophied and inactive. oestrogen increases the number of uterine muscles and contractile proteins in muscle cells.

Under the influence of oestrogen, the uterine muscles become more active and more excitable. The uterus that is already under the influence of oestrogen is more sensitive to oxytocin.

Long-term treatment with oestrogen will enlarge the endometrium, when treatment stops, it will shed the endometrium causing vaginal bleeding. Bleeding sometimes occurs during the treatment when oestrogen is used for a long period of time.

Effects on endocrine organs:

oestrogen reduces FSH secretion. In some cases, oestrogens inhibit LH secretion (negative feedback) and in other cases, they increase LH secretion (positive feedback). The oestrogens can increase the size of the pituitary gland.

Effect on personality:

oestrogen induces oestrous expression in animals and increases libido in humans. This effect is caused by the direct action of oestrogens on certain neurons in the hypothalamus.

Effects on the mammary glands:

Oestrogen promotes the development of the duct system of the mammary glands and causes the breasts to develop in women during puberty.

oestrogen also increases pigmentation in the areola, but this is more pronounced in the first pregnancy

Impact on secondary sex characteristics:

The changes to a woman's body during puberty along with breast, uterine, and vaginal development are partly because of oestrogen and partly due to simply the absence of androgens in the testes.

The woman's narrow shoulders and wide hips along with the distribution of fat in the chest and buttocks create a characteristic female figure.

In females, the larynx still maintains the same structure as in pre-puberty, so the voice is still high. Less body hair but more hair than men. Pubic hair grows flat on top. The growth of pubic and axillary hair in women is mainly because of androgens, which are mainly secreted by the adrenal glands rather than by oestrogen.

Other effects:

Normal women-only retain water and salt and gain a little weight before menstruation. Water and salt retention is caused not only by oestrogen but also by increased secretion of androsterone during the luteal phase.

Oestrogen causes the sebaceous glands to secrete more fluid, which contrasts with the effects of testosterone and prevents acne from developing.

Oestrogens significantly reduce plasma cholesterol and thereby inhibit the process of atherosclerosis thereby increasing the rate of myocardial infarction and other complications of atherosclerotic disease in premenopausal women.

Progesterone

Synthesis and transformation:

Progesterone is a C21 steroid secreted by the corpus luteum, placenta and to a small extent by the follicles. It is an important mediator in steroid synthesis in all steroid hormone-secreting tissues, so a small amount of progesterone enters the bloodstream from the testes and adrenal cortex.

In the circulation only 2% of progesterone is in the free state, the rest is bound to proteins.

Progesterone has a short half-life and is converted to pregnanediol in the liver, which binds to glucuronic acid and is excreted in the urine.

Excrete:

In men, progesterone levels are about 0.3 ng/mL (1 nmol/L). In women, this concentration is about 0.9 ng/mL (3 nmol/L) during the follicular phase of the menstrual cycle. This difference is due to the secretion of small amounts of progesterone by cells in the follicles. Cells in the cortex (theca) of the follicle supply pregnenolone to the granulosa cells, which then convert this substance to progesterone. At the end of the follicular phase, progesterone secretion begins to increase.

During the luteal phase, the corpus luteum secretes large amounts of progesterone and the ovary increases its secretion of progesterone by a factor of 20 leading to an increase in serum progesterone concentrations, peaking at 18 ng/mL. (60 nmol/L).

Impact:

Progesterone is responsible for changes in the endometrium for pregnancy and cyclical changes in the cervix and vagina. This hormone has an estrogenic antagonistic effect on the uterine muscle, reducing its excitability and reducing the sensitivity of the uterine muscle to oxytocin. Progesterone also reduces the number of oestrogen receptors in the endometrium and accelerates the conversion of 17(-estradiol) to a less active estrogenic.

In the breast, progesterone stimulates the growth of lobules and follicles. It differentiates ductal tissues previously prepared by oestrogen and supports the secretory function of the breast during lactation.

The feedback effect of progesterone is quite complex, it acts on both the hypothalamus and the pituitary gland. Large amounts of progesterone will inhibit LH secretion and potentially inhibit the effects of oestrogen. Progesterone injections can prevent ovulation in humans.

Progesterone is thermogenic and raises body temperature at the time of ovulation. Progesterone also stimulates respiration, so alveolar CO2 pressure in the luteal phase is lower than in men.

High-dose progesterone increases urine sodium (natriuresis), presumably by inhibiting aldosterone's effect on the kidneys. This hormone has no role in the anabolic process.

Substances that have progesterone-like effects are called gestagens or progestins or pregestational agents. They are used with synthetic oestrogen’s to make oral contraceptives.

Relaxing

Relaxing is a polypeptide hormone that relaxes the pubic and other joints of the pelvis. This hormone also dilates and softens the cervix during pregnancy and thus facilitates delivery. It also inhibits uterine contractions to facilitate egg implantation and probably also has a role in mammary gland development.

In nonpregnant women, relaxing is found in the corpus luteum and endometrium during the secretory phase of the menstrual cycle. In men relaxing is found in semen secreted by the prostate gland.

During pregnancy the placenta secretes more relaxing to further relax uterine smooth muscle, dilate the public joint and may also contribute to cervical dilation during delivery.

Menstrual cycle

Each menstrual cycle consists of two parallel cycles: (1) the ovarian cycle, in which the development and degeneration of oocytes take place, and (2) the uterine cycle, which includes changes in the lining of the uterus. endometrial lining.

Changes in the menstrual cycle are affected by the action of the anterior pituitary hormones FSH and LH under the influence of the hypothalamic GnRH.

The role of hormones

Uterine and ovarian cycles are controlled by GnRH (gonadotropin-releasing hormone) of the hypothalamus.

GnRH stimulates the release of FSH (follicle-stimulating hormone) and LH (luteinizing hormone) hormones from the anterior pituitary.

FSH favours the development of the follicles and initiates the secretion of oestrogens by the follicles.

LH stimulates the follicles to develop further, enhances oestrogen secretion, controls ovulation, forms the corpus luteum and stimulates the secretion of progesterone, oestrogen, relaxing and inhibin from this organization.

Moderate levels of oestrogens in the blood inhibit the release of GnRH by the hypothalamus and the anterior pituitary gland from releasing FSH and LH. This inhibition is the basis of the action of the oral contraceptive pill.

Progesterone is secreted mainly by the corpus luteum, which works in concert with oestrogens to prepare the endometrium for implantation of the fertilized egg and to prepare the mammary glands for the synthesis and secretion of milk. High concentrations of progesterone also inhibit GnRH and LH secretion.

Inhibin is secreted by the granulosa cells of the developing follicles and the corpus luteum. Has an inhibitory effect on both FSH and LH secretion, but weaker?

Phases of the menstrual cycle

The menstrual cycle is counted from the first day of menstruation and lasts from 24 to 35 days, with an average of 28 days, divided into 4 phases: (1) menstrual period, (2) pre-ovulation phase, (3) the ovulatory phase and (4) the post-ovulatory phase.

Menstrual period:

Lasts from the first to the fifth day. During this stage in the 2 ovaries, there are about 20 grade II follicles that begin to grow. Follicular fluid secreted by granulosa cells and exuded from capillaries collects in the cavernous cavity and enlarges while the oocyte remains close to the edge of the developing follicle.

In the uterus, the functional layer of the endometrium is shed, bleeding, this phenomenon occurs because the amount of progesterone and oestrogen drops sharply, causing constriction of the torsion arteries of the functional layer in the endometrium, leading to the destruction of the endometrium. element of this class.

Menstrual fluid about 50 - 150 ml including blood, mucus, epithelial cells, and tissue fluid from the endometrium will pour from the uterine cavity through the cervix and vagina to exit. At this point, the endometrium is very thin because only the stroma remains.

Pre-ovulation period:

Lasting from the 6th to the 13th day of the 28-day cycle, this is the period with the most change in the 4 phases of the menstrual cycle and thereby makes the menstrual cycle longer or shorter. compared to 28 days.

In the ovary under the influence of FSH, the follicles continue to grow and begin to secrete oestrogen and inhibin, around day 6, one follicle will outgrow the other follicles, the amount of oestrogen and inhibin produced by the follicle. This secretion will reduce the amount of FSH thereby causing the less developed follicles to degenerate. The remaining follicle will develop into a mature follicle (Graaf cyst) and continue to grow until about 20mm in diameter, blistering on the surface of the ovary and ready for ovulation.

Oestrogen secretion is increasing under the influence of increasing LH concentration. Oestrogen is the primary hormone in this phase, but a small amount of progesterone is secreted by the mature follicle within a day or two before ovulation.

Figure: Changes of hormones, follicles, endometrium, and body temperature during the menstrual cycle.

In the uterus, oestrogen released in the blood will stimulate the regeneration of the endometrium, the cells of the basal layer will undergo mitosis to create a new functional layer when the endometrial layer thickens, the endothelial glands The short and straight fascia begins to develop, the arterioles coil and extend to the functional layer. The thickness of the endothelium is then about 4 to 6 mm. With these changes in the uterus, the pre-ovulatory phase is also called the proliferative phase.

Ovulation phase:

Occurs on day 14 of a 28-day cycle. Graaf's cyst is disrupted, releasing grade II oocytes into the pelvic cavity and then into the fallopian tubes. During shedding, the secondary oocyte maintains the opacity and the coronal layer. Thus, it takes almost 20 days for a grade II follicle to become a mature follicle.

This process occurs because the high levels of oestrogens at the end of the pre-ovulatory phase act as positive feedback back to the hypothalamus to secrete GnRH and the anterior lobe to secrete LH. The anterior pituitary gland secretes FSH and further secretes LH. The sudden elevation of LH levels disrupts the mature follicle and releases the second-grade oocyte.

Signs of ovulation include (1) an increase in body temperature (about 0.2 - 0.3oC, corresponding to 0.4 to 0.6oF) due to a slight increase in progesterone levels before ovulation, (2) cervical fluid is thinner, (3) cervix is ​​slightly dilated and soft, sometimes there is pain in the ovary.

The reverse stimulating effect of oestrogen on the hypothalamus and anterior pituitary gland would not occur if progesterone was also present at the same time.

After ovulation, the follicle collapses and the blood flowing from the tear of the follicle into the follicle will form a blood clot, this clot will be absorbed by the remaining cells of the follicle, the follicle will then increase in size, change shape to form corpus luteum under the influence of LH. Under the stimulating effect of LH, the corpus luteum will secrete some progesterone, oestrogen, relaxing and inhibin.

Post-ovulation period:

Lasting 14 days from the 15th to the 28th day of a 28-day cycle, this is the most constant cycle, lasting from ovulation to the start of the next menstrual period. After ovulation, the secretion of LH stimulates the rest of the follicles to develop into the corpus luteum.

If grade II oocytes are not fertilized after 2 weeks, the corpus luteum will degenerate into a scar called the white body. The drop in progesterone and oestrogen due to the degeneration of the corpus luteum leads to menstruation.

A drop in the hormone’s progesterone, oestrogen, and inhibin stimulates the release of GnRH, FSH and LH, which stimulates the follicles to grow and start a new menstrual cycle.

Because of the role of the corpus luteum in the post-ovulatory phase, this phase is also known as the luteal phase.

In the uterus, under the influence of progesterone and oestrogen, the corpus luteum secretes the endometrium, thickening with the development and coiling of the endometrial glands, increasing glycogen secretion, and developing the vascular system on the surface of the uterine lining. endothelium, increasing the amount of organizational fluid. These changes reach their maximum one week after ovulation in preparation for implantation of the fertilized egg, which corresponds to the time it takes for the egg to travel through the fallopian tube from ovulation to arrival. The womb. Due to changes in the uterus, this phase of the menstrual cycle is also known as the secretory phase.

Puberty and menstruation start

In females, the levels of LH, FSH, and oestrogen in the prepubertal phase are very low. Between the ages of 7, and 8, girls experience an increased secretion of androgens by the adrenal glands leading to pubic and axillary hair growth.

Puberty is initiated with an increase in LH and FSH during sleep. During the next phase of puberty, LH and FSH are secreted throughout the day. Increased levels of these hormones stimulate the ovaries to secrete oestrogen leading to the development of female secondary sexual characteristics.

At birth, the breasts of both boys and girls are underdeveloped. During puberty, under the influence of oestrogen and progesterone, the female breasts begin to develop. Breast engorgement is the first outward manifestation of puberty. The ductal system begins to develop, fat accumulation occurs, and the areola and nipples grow and darken.

oestrogen and progesterone also stimulate the growth of the fallopian tubes, uterus, and vagina. The first period (menarche) occurs around the age of 12.

Menopause

In women between the ages of 40 and 50, the ovaries begin to respond poorly to the sex hormones of the anterior pituitary gland, causing progesterone and oestrogen levels to decrease so that the follicles do not undergo normal development. often lead to menopause.

Changes in GnRH release and a decreased response to GnRH by the anterior pituitary cells in LH secretion also contribute to menopause.

Some women experience flushing, sweating, headache, hair loss, muscle pain, vaginal dryness, insomnia, weakness, weight gain, mood swings.

After menopause, the ovaries, fallopian tubes, uterus, vagina, external genitalia, and breasts shrink. The drop in oestrogen levels during this period also leads to osteoporosis. However, female libido does not decrease with these changes due to the influence of adrenal androgens.

A woman's reproductive activity only takes place during a certain period from the start of menstruation until menopause. The ability to fertilize also decreases with age, perhaps over time ovulation is no longer regular, the service capacity of the fallopian tubes and uterus for the development of young embryos also decreases.