CHAPTER 10

FEMALE REPRODUCTIVE HORMONAL CYCLES

INTRODUCTION

• During the reproductive period of life, females experience the changes that occur in the ovaries and uterus that prepare them for pregnancy.
• Each monthly cycle involves both oogenesis and preparing the uterus to implant a fertilized ovum.
• These events are controlled by the hormonal secretion of the hypothalamus, anterior pituitary and ovaries

Menarche

Menarche is the first occurrence of the menstrual cycle, the first menstrual bleeding. The average age of the menarche is 12 years whereas 8-16 years of age is considered normal. The normal cycle varies from 28-40 days.

Menopause

It is the cessation of the cyclic events in the reproductive system of the female. It signifies the end of the reproductive life.

The ovarian changes after puberty

HORMONAL REGULATION OF THE FEMALE REPRODUCTIVE CYCLE

• The ovarian and uterine cycles are controlled by Gonadotropin-releasing hormone secreted by the hypothalamus. GnRH stimulates the anterior pituitary gland to release the follicle-stimulating hormone and luteinizing hormone.
• FSH initiates follicular growth, while LH facilitates the further development of the ovarian follicles.
• Androgens are produced by the theca cells and are converted into estrogens under the influence of LH and FSH respectively. In the middle of the menstrual cycle, LH triggers ovulation and forms the corpus luteum.

• Estrogen hormone is secreted by ovarian follicles.

Its important functions are:

• It promotes the development and maintenance of female reproductive structures, secondary sexual characteristics and the breasts.
• It increases protein anabolism.
• It reduces the blood cholesterol level
• Moderate level of estrogens in the blood inhibits the hormonal secretion of both LH and FSH.

• Progesterone, secreted mainly by cells of the corpus luteum cooperates with estrogens to prepare and maintain the endometrium for the implantation of a fertilized ovum. It also prepares the mammary glands for milk secretion. High levels of progesterone also inhibit secretion of GnRH and LH.

• Relaxin: It is produced by the corpus luteum and inhibits the myometrial contraction and thus relaxes the uterus.
• Inhibin is secreted by granulosa cells of growing follicles and by the corpus luteum after ovulation. It inhibits the secretion of the FSH and LH.

PHASES OF THE FEMALE REPRODUCTIVE CYCLE

The duration of the female reproductive cycle typically ranges from 28 to 40 days, but most of the time the cycle is of 28 days. The cycle is divided into 4 phases-

1. Menstrual phase
2. Preovulatory phase
3. Ovulation
4. Post ovulatory phase

Menstrual Phase

It is also known as menstruation or menses, lasts roughly for first 5 days of the cycle (1st day of the menstruation is the first day of the new cycle). Physiologically it is the terminal phase of the reproductive cycle simultaneous with the beginning of the follicular phase (preovulatory phase) of the new cycle.

Events in the Ovaries

Under the influence of FSH, several primordial follicles develop into primary follicles and then into secondary follicles. In the beginning, the follicle begins to develop. This developmental process may take several months to occur.

Events in the Uterus

The declining levels of the progesterone and estrogens lead to the release of prostaglandins that cause the uterine spiral arterioles to constrict. Eventually, the cells get deprived of oxygen and leads to necrosis and shedding of the endometrial cells. This shedding leads to a discharge from the uterus called menstrual flow which consists of 50-150 ml of blood, tissue fluid, mucus and epithelial cells shed from the endometrium

Preovulatory Phase

The preovulatory phase is the time between the end of the menstruation and beginning of ovulation. This phase is from 6th to 13th day of a menstrual cycle.

Events in the Ovaries

Throughout the year small primordial follicles containing primary oocytes, develop into large preovulatory or Graafian follicles containing secondary oocytes in a process known as folliculogenesis (oocytes undergo mitosis prior to birth and until puberty in a process known as oogenesis).

Low levels of estrogens and progesterone stimulate the hypothalamus to produce gonadotropin releasing hormone (GnRH). This releasing hormone stimulates the anterior pituitary gland to produce the FSH and LH. FSH controls the growth and maturity of the Graafian follicles. The Graafian follicle begins to secrete oestrogen, which is comprised of oestradiol, oestrone and oestriol.The Graafian follicle continues to enlarge until it has a diameter of 20 mm and ready for ovulation.

A mature Graafian follicle

Events in the Uterus

The ovarian follicle releases the estrogen in the blood that initiates the repair of the endometrium. Stratum basalis cells divide by mitosis and produce a new layer of stratum functionalis. The endometrium thickens to double, about 4-10 mm. This preovulatory phase is known as the proliferative phase .

Ovulation Phase

The ovulation phase is the phase where the mature Graafian follicle ruptures to release the secondary oocyte into the uterine or fallopian tube for fertilization.

Post Ovulatory Phase

This phase is also known as the luteal phase, which starts after ovulation till the next mensuration. It lasts for 14 days from 15th to 28th day of the cycle.

Events in One Ovary

After the ovulatory phase, the basement membrane breaks down and the ruptured follicle forms a blood clot called corpus hemorrhagicum. Under the influence of LH, theca interna cells mixes with the granulosa cells of the follicle to form the corpus luteum. The corpus luteum is stimulated by LH to produce progesterone, estrogen, relaxin and inhibin.

If the oocyte is not fertilized, the corpus luteum whose lifespan is of 2 weeks is converted into whitish mass-like structure known as corpus albicans.

If the oocyte is fertilized and begins to divide, the embro after 8 days starts producing a hormone called human chorionic gonadotropin (hCG). the presence of hCG in maternal blood or urine is an indicator of pregnancy.

Events in the Uterus

In case of fertilization, corpus luteum produces progesterone and estrogens to promote growth and coiling of the endometrial glands, and thickens the endometrium to 12-18 mm. This phase is also known as the secretory phase of the uterine cycle as the endometrial glands secrete the glycogen.

If the oocyte is not fertilized, the corpus luteum will degenerate and will ultimately reduce the level of progesterone and estrogens. When progesterone and estrogens are withdrawn, it leads to menstruation.

MENSTRUAL HYGIENE

There are various methods used by girls and women to absorb menstrual blood. The most common methods used is a cloth. The cloth is been placed along with the undergarment.

Sanitary Napkins

The Sanitary napkin is a pad worn by females during menstruation. It is used to absorb the menstrual flow. They are disposable and for single use only.

The sanitary napkin has three layers:

• The lowest layer that lies on the underwear.
• The middle layer which soaks the blood quickly and prevents leakage.
• A surface layer that is close to the skin. It is made of perforated material that keeps the skin dry and acts as a barrier between the skin and the absorbent panel.

There are two types of napkins:

• Sanitary napkin with an adhesive (sticky) strip
• Non-adhesive sanitary napkin used with or without underwear

Advantages of Sanitary Napkins

• They are more convenient.
• They are easier to use than reusable cloth.
• They can easily absorb the menstrual fluid and thus maintain dryness.
• They can prevent infection.
• It can by all the females irrespective of their age.

Important Considerations

• The napkin should be changed as soon as it is filled with the menstrual fluid.
• Napkins should be placed in a clean and dry place
• Private parts need to be washed daily.
• Maintain hand hygiene.
• Change the underwear along with the sanitary pad if got soiled.

Other options for absorbing the menstrual blood:

• Tampons
• Menstrual cups
• Menstrual discs
• Underwear