Physiology of the female reproductive system

What is meant by the physiological nature or physiology?

The nature and the functioning of an organ of the body, and the term physiological means physiology.

What is the menstruation?

It is a monthly menstrual bleeding, also called “menstrual cycle”, and this blood is caused by the fall of the endometrium in the absence of pregnancy, and it should be noted that menstrual bleeding is not a separate event in itself, but is caused by hormonal changes and its impact on the endometrium, that is, in the case of amenorrhea, the problem is not the absence of menses, but we must look for the reason for amenorrhea, starting from the possibility of pregnancy to hormonal disorders and other reasons.

What is ovarian cycle?

It is the process of growth and production of eggs and hormonal changes that occur during this process to the end of the process of ovulation

What is meant by the cycle of the uterus or endometrial cycle?

It means changes in the endometrium during the menstrual cycle in preparation for the reception of the embryo and the occurrence of pregnancy, which ends with the flow of menstrual blood in the absence of pregnancy

What is an egg or ovum?

It is the female sex cell, that is, the feminine gamete that is produced in the ovary. Gradually evolved to form an embryo after fertilization by sperm.

What is an egg vesicle or follicle?

A vesicle that grows in the ovary and contains a fluid within which the egg or ovum is located.

The female reproductive system works under the influence of a hormone secreted from a part of the brain called the hypothalamus, which stimulates the secretion of a group of hormones from the pituitary gland in the brain, which in turn stimulates the ovary for the growth of the egg and the process of ovulation. Other hormones that affect the feminine qualities and endometrium to produce the so-called menstrual cycle

What is meant by the cycle of hormones of the hypothalamus and pituitary gland?

There is a part of the brain called “hypothalamus” that secretes hormones stimulating the pituitary gland, namely:

The pituitary gland in turn responds to “hypothalamus” hormones, secreting many hormones that affect many body functions.

The pituitary gland is divided into two parts:

The anterior lobe of the pituitary gland secretes the following hormones:

The posterior lobe of the pituitary gland: The posterior lobe does not secrete hormones, but it stores two types of hormones produced from the hypothalamus:

Ovarian cycle

The ovary works under the influence of two types of hormones that are secreted from the pituitary gland, namely hormone FSH & LH.

FSH stimulates the growth of eggs before ovulation, which in turn produces estrogen during the growth process.

LH stimulates ovulation, which results in a rise in progesterone.

Length of the menstrual cycle:

The length of the menstrual cycle is calculated in days from the first day of menstrual blood flow to first day of menstrual blood flow of the next cycle.

The length of the menstrual cycle of a woman varies from one cycle to another.

The ovarian cycle is divided into three parts:

  • Follicular phase
  • Ovulation process
  • Luteal phase

Follicular phase

Since the birth of the female ovary contains a large number of primitive follicles, which contain immature eggs. At the beginning of each cycle, a number of these follicles begin to grow during the first half of the cycle (the duration of the first half of the cycle varies depending on the length of the menstrual cycle) and begins to form a liquid inside it containing the developing egg, and by the sixth day of the cycle, the rest of the follicles become atretic while only one follicle continues to grow and is called the dominant follicle, until it reaches the appropriate size, of 18-20 millimeters and this vesicle contains liquid inside with only one full-grown egg, called It has a “Graafian follicle”.

During this stage of growth of eggs, some cells surrounding the egg secrete estrogen of the type of Estradiol and is symbolized by E2.

The follicular phase coincides with menstruation and reproductive phase in the uterine cycle (endometrial cycle)


It is the second phase of the ovarian cycle, and its occurrence coincides with the end of the reproductive phase and the beginning of the secretory phase in the endometrium cycle, after the end of the vesicular stage and the growth of the egg, ovulation occurs under the influence of the sudden rise of the hormone LH secreted from the pituitary gland on the 12th day of the cycle, and the Grave vesicle explodes and the egg towards the fallopian tube.

Some minor drops of blood can occur in the abdominal cavity as a result of ovulation with can cause little pain of ovulation.

The vesicle casing remains inside the ovary and is filled with a yellow fluid that turns into a “corpus luteum”

The egg remains in the fallopian tube for about one day (24 hours) after ovulation and then begins to decay if not fertilized with sperm

Ovulation time according to the length of the menstrual cycle

The second half of the menstrual cycle or post-ovulation period (luteal phase) is always a fixed period in all menstrual cycles and is two weeks, and the difference is only in the first half of the menstrual cycle (follicular phase), and therefore ovulation time varies depending on the length of the menstrual cycle,

The day of ovulation is:

The seventh day of the 21-day cycle, the 14th day of the 28-day cycle, and the 21st day of the 35-day cycle

Luteal phase

Is the last phase, and its occurrence coincides with the secretory phase of the uterine cycle (endometrial cycle)

The vesicle shell remains inside the ovary, which is filled with a yellow fluid and turns into a “corpus luteum” which produces the hormone “progesterone”, which reaches its highest rate after 8 days of ovulation (day 21 of the 28-day cycle), and continue secretion until the placenta is formed in case of pregnancy.

In the absence of fertilization of the egg, the corpus luteum begins to decompose on the tenth day after ovulation and progesterone production stops.

In the case of fertilization of the egg and the occurrence of pregnancy, the corpus luteum continues to secrete progesterone until the end of the ninth week of pregnancy to maintain the endometrium in the most appropriate status for the continuation of pregnancy, then the placenta secretes progesterone as one of its functions.

Endometrial cycle (also called uterine cycle)

The endometrial cycle, called menstrual cycle, as we said earlier, should be known to be a product and not a separate event, meaning that the occurrence or non-occurrence of menstruation is not in itself a problem because it is caused by the effect of hormones secreted during the growth of ova and the process of ovulation under the influence of the pituitary gland hormones, so if you have a disorder in menstruation should look for the cause.

Endometrial function

It prevents adhesions between the inner walls of the uterus and thus remains hollow.

The lining of the uterus grows during the menstrual cycle in terms of thickness, density of blood vessels and glands so that it is the optimal environment for receiving embryo implantation if fertilization has already occurred.

Endometrium is divided into two layers:

Basal layer (STRATUM BASALIS):

It is the layer attached to the muscular layer (MYOMETRUM) and is the main layer from which the most esoteric layer is renewed every month.

Functional layer (STRATUM FUNCTIONALIS):

It is the layer that grows with each menstrual cycle and then breakdown in the period of the menstrual period “menstruation” in the absence of pregnancy, and then reproduced again.

Stages of the endometrial cycle: The endometrial cycle is divided into three stages:

  • Menstruation period
  • Proliferative Endometrium
  • Secretory Endometrium

Changes in the phases of the endometrial cycle occur under the influence of ovarian hormones (estrogen and progesterone) in addition to the luteinizing hormone (LH).


Menstruation is the first phase of the uterine cycle, called menstruation, and the first day of the menstrual flow is the first day of the new cycle and it coincides with the start of the follicular phase

The exit of menstrual blood is the collapse of the endometrium formed in the previous uterine cycle, and this collapse is caused by a decrease in the level of progesterone in the blood after the decomposition of the corpus luteum as a result of no pregnancy.

Therefore, the delay of menstruation is one of the initial signs of pregnancy because it reflects the fertilization of the egg and the implantation of embryo in the lining of the uterus and secretion of the hormone hCG, which maintains the survival of the corpus luteum, which continues to secrete the hormone progesterone, which keeps the endometrium in its secretory status to maintain pregnancy

The menstrual flow usually lasts from two days to a week (3-5 days on average). In each menstruation, a women lose 20 to 80 milliliters of blood, and the larger the amount of blood, the greater the risk of iron deficiency anemia.

2 – Reproductive endometrium

The reproductive phase is the second stage in the uterine cycle, and its occurrence coincides with the follicular phase (the stage of growth of eggs) in the ovary cycle immediately after the end of menstruation, in which the endometrium grows and reproduces under the influence of estrogen secreted by the developing egg, and increase the thickness and blood vessels

3- Secretory phase

The secretory phase is the last phase of the uterine cycle, and its occurrence coincides with the luteal phase (the stage of the corpus luteum) in the ovarian cycle after ovulation, in which the proliferative endometrium turns into a secretory uterine lining to form the most suitable climate for embryo implantation in the event of pregnancy.

Progesterone functions

  • Transformation of the endometrium from the proliferative uterine lining to the secretory uterine lining, where the endometrium grows in terms of thickness and density of blood vessels and glands to form the optimal climate to receive embryo implantation in the event of fertilization
  • Effect on the normal secretions of the cervix to become more viscous and less in quantity in order to prevent the ascend of any infection or any more sperms in next intercourse
  • The effect on the breast glands in the breast, the breast becomes more congested, which is the natural change that is accompanied by some pain before the menstruation, and then subsides after the descent of menstruation.
  • Progesterone helps to relax uterine smooth muscles during pregnancy.

Estrogen functions

  • The growth of female secondary sexual characters like the growth of breast and sound changes
  • Uterine growth and the growth of endometrium in the proliferative phase (first half of the menstrual cycle)
  • Softening and durability of the vaginal wall
  • Maintain skin freshness and vascular integrity
  • Maintain the bone integrity
  • Stimulate the liver to produce proteins
  • Increase the production of coagulation factors in the blood and reduce the proportion of antithrombin III
  • Increased platelet adhesion
  • Increased triglycerides and high-density lipoproteins (HDL) (healthy lipoproteins).
  • Reduce the proportion of low-density lipoproteins (LDLs)
  • Stimulate the storage of water and salts in the body
  • Increased cortisol in the blood
  • High estrogen level stimulate the secretion of LH from the pituitary gland to stimulate the process of ovulation after the completion of egg growth
  • Help androgenic hormones stimulate sexual desire


During the life of the fetus, the ovaries contain about 7 million cells called germ cells, which are the mother cells of the eggs. When the female is born, this number has shrunk to about 2 million. This number has been reduced to about 300,000 to 500,000 follicles in the ovaries, but only about 50 follicles are urged to grow from puberty to menopause, while atrophy of the remaining follicles occurs.

Definition of puberty Menarche:

It is the age at which the first menstrual cycle (menstruation) occurs and is known as the start of menstruation, the last stage in adulthood

Definition of puberty:

Puberty is a group of natural organic changes resulting from hormonal changes, after which the reproductive system becomes capable of reproduction

Timing of puberty: puberty occurs in females in the period between 11 to 13 years, while in males occurs between the ages of 9 to 14 years

Stages of puberty

Puberty begins with breast growth under the influence of female hormones secreted from the ovaries (estrogen and progesterone)

Then hair growth in the armpit and pubic area, which is determined by the effect of male hormones secreted from the adrenal gland

And then finally the first menstruation, which is also caused by the effect of estrogen and progesterone on the endometrium

The menstrual cycle at the onset of puberty is non-ovulatory (i.e without ovulation) and ovulation is usually organized within a year