The Female Reproductive System

*Corpus luteum*

A mass of follicle cells that forms within the ovary after ovulation; secretes estrogen and progesterone. A hormone-secreting structure that develops in an ovary after an ovum has been discharged but degenerates after a few days unless pregnancy has begun.

*Cervix*

A muscular band that separates the vagina from the uterus.

*Menstrual cycle*

Along with the development of secondary sexual characteristics, puberty also initiates the menstrual cycle in females, which includes oogenesis, ovulation and the thickening and shedding of the endometrium. The menstrual cycle lasts an average of 28 days. The cycle is regulated by changes in the levels of various hormones. *The menstrual cycle can be divided into FOUR distinct phases:* 1) Flow phase 2) Follicular phase 3) Ovulatory Phase 4) Luteal Phase

*Ovum*

Egg cell. One ovum matures approximately every month.

*Fimbria*

Fingerlike projection at the end of a Fallopian tube.

*Why is ovulation important?*

For sex to result in a pregnancy, a woman has to go through ovulation. Part of the monthly menstrual cycle, ovulation happens when an egg, or ovum, becomes available for fertilization by a sperm cell. During ovulation, an egg moves from the ovaries (the organs that produce eggs) into the fallopian tubes. There, a sperm cell can fertilize the egg, which could then move into the uterus, or womb, and develop into a fetus. During ovulation, the walls of the uterus (endometrium) also thicken to prepare for a fertilized egg. But if the egg is not fertilized, the uterus sheds that lining, causing the monthly bleeding of a menstrual period.

*Fallopian tubes (oviduct)*

One of two tubes that connect the ovaries to the uterus.

*Tubal Ligation (Getting your tubes tied)*

Similar to a vasectomy in males, tubal ligation is a surgical method of female sterilization. The surgeon cuts and ties off the Fallopian tubes, keeping the secondary oocyte from entering it and possibly getting fertilized.

*Vagina*

The muscular canal extending from the cervix to the outer environment; the birth canal.

*Ovulatory Phase*

The ovulatory phase is the third phase of the female menstrual cycle, and it is the phase in which ovulation occurs. The secondary oocyte bursts from the ovary and follicular cells differentiate into the corpus luteum. Takes FOURTEEN day, 14.

*Ovulation*

The release of the secondary oocyte from the follicle held within the ovary.

*1) Flow Phase/menstruation*

The shedding of the endometrium, aka, menstruation/period, marks the *FLOW phase* or, aka, her period. This is the ONLY phase of the female reproductive cycle that can be determined EXTERNALLY. Meaning, you can actually SEE it. Which is why we use the flow phase to mark the beginning of the menstrual cycle. FIVE to SEVEN days are needed for the uterus to shed the endometrium.

*The thickness of the Endometrium*

The thickness of the endometrium increases from the beginning of the *follicular phase* to the end of the *luteal phase*. The development of blood vessels and glandular tissues helps prepare the uterus for a developing embryo. Should no embryo enter the uterus, menstruation occurs, and the menstrual cycle begins again.

*The Female Reproductive System STRUCTURES SUMMARY*

*Ovaries:* Produce the estrogen and progesterone hormones. Site of ovum (egg cell) development (oogenesis) and ovulation. *Fallopian tubes/oviducts:* Carry the ovum from the ovary to the uterus. Conception, festination usually occurs in the fallopian tubes. *Fimbria:* Sweep the ovum into the Fallopian tube following ovulation. *Uterus/womb:* Pear shaped organ in which the embryo and fetus develop. Involved in menstruation. *Cervix:* Separates the vagina from the uterus. Holds the fetus in place during pregnancy. Dilates during birth to allow the fetus to leave the uterus. *Vagina:* Extends from the cervix to the external environment. Provides a passageway for the sperm and menstrual flow. Functions as the birth canal.

*What hormone regulates ovulation?*

Pituitary hormones regulate the events of follicle deployment, ovulation, and the formation of the corpus luteum.

*Follicle*

Structure in the ovary that contains the oocyte, and where oogenesis occurs. A follicle contains two types of cells: 1) A primary oocyte 2) Cells of the granulosa

*Female Reproductive System Hormones SUMMARY*

*Estrogen hormone:* Located in the follicle cells, in the ovary. Initiates secondary sexual characteristics, and causes thickening of the endometrium. *Progesterone hormone:* Located in the corpus luteum, in the ovary. Inhibits ovulation, inhibits uterine contractions, firms the cervix from fetus getting out, and stimulates the endometrium. *Follicle-stimulating hormone/ FSH:* Located in the pituitary gland. Stimulates the development of the follicle cells in the ovary, which produces estrogen. *Luteinizing hormone/ LH:* Located in the pituitary gland. Stimulates ovulation and formation and maintenance of corpus luteum, which produces progesterone and estrogen.

*The female menstrual cycle SUMMARY*

*Flow Phase:* Menstruation/period, and lasts for 1-5 days. *Follicular Phase:* Follicles develop in the ovaries, and the endometrium is restored because estrogen is produced by the follicle cells, which increases the estrogen concentration in the blood. Lasts for 6 - 13 days. *Ovulation Phase:* Oocyte bursts from ovary, and follicular cells differentiate into the corpus luteum. Lasts for 14 days. *Luteal Phase:* Corpus luteum forms and the endometrium thickens. Estrogen and progesterone are produced by the corpus luteum. Last for 15 to 28 days.

*Oocyte*

An immature ovum (egg). At birth, oocytes are already present within the ovary. As in sperm development, during its development, oocyte undergoes a type of cell division that halves the number of chromosomes, from 46 to 23.

*Menopause*

Cessation/stopping of menstrual periods owing to a lack of ovarian hormones. - is the period in a woman's life (age 45-55) when menstruation first becomes irregular and eventually stop By the time a woman reaches menopause, when ovulation ceases, few follicles remain. Older follicles are presumed to have higher genetic damage. Because female sex hormones are produced within the ovary, menopause marks the end of a girl's reproductive life and signals a drop in the production of female hormones.

*Secondary Sexual Characteristics in Females*

Enlarged breasts, less facial hair than man, softer skin, wider hips, fat around buttocks and hips, more body fat.

More information:

Estrogen levels begin to decline when the oocyte leaves the ovary, but are somewhat restored when the corpus luteum forms. *The corpus luteum secretes both ESTROGEN and PROGESTRONE*. Progesterone continues to stimulate the endometrium and prepares the uterus for an embryo. It also inhibits further ovulation, prevents uterine contractions, and firms the cervix to prevent expulsion of the fetus. The luteal phase, which occurs between days 15 - 28, prepares the uterus to receive a fertilized egg. Should fertilization of an ovum not occur, the concentrations of estrogen and progesterone will decrease, thereby causing uterine contractions. These uterine contractions make the endometrium pull away from the uterine wall. The shedding of the endometrium marks the beginning of the next flow phase, and the female menstrual cycle starts all over again.

What is the menstrual cycle? INTITIAL OVERVIEW

Hormones are released by the pituitary gland in the brain to stimulate the ovaries during the reproductive cycle. These hormones cause some of the woman's eggs, which are stored in the follicles of her ovaries, to start to grow and mature. The follicles start producing estrogen - a hormone. During this moment increased estrogen levels can be detected in a woman's blood. The increased estrogen causes the womb lining to become thicker in preparation for receiving a fertilized egg. If a woman has had sex within several days of the egg being released and sperm is present in her fallopian tube, the egg may become fertilized (she becomes pregnant). However, if the egg is not fertilized her estrogen and progesterone levels will drop and the lining of the uterus (endometrium) will start breaking down - marking the start of her period. The period consists of a small amount of blood and the endometrium. The bleeding is caused by the breaking of fine blood vessels within the womb as the lining detaches itself. A period generally lasts about five days. Bleeding is more profuse during the first two days.

*Uterus/womb*

Is a hallow, pear-shaped organ located between the bladder and the anus in females. Is the largest organ in the female reproductive system. The embryo and fetus develop in the uterus. The uterus/womb is composed of TWO major tissues: 1) A muscular outer lining, myometrium 2) and a glandular inner lining of the uterus, know as the *endometrium.*

*How oogenesis happens*

Oogenesis begins when nutrient follicle cells surrounding the primary oocyte begin to divide. As the primary oocyte undergoes cell division, the majority of cytoplasm and nutrients move to one of the end poles and form a secondary oocyte. The secondary oocyte contains 23 chromosomes. The remaining cell, referred to as the first polar body, receives little cytoplasm and dies. As the follicle cells surrounding the secondary oocyte multiply, a fluid-filled cavity forms. Eventually, the dominate follicle pushes outward, ballooning the outer wall of the ovary. Constriction of blood vessels weakens the ovarian wall above the follicle, while enzymes weaken the wall of the follicle from the inside. The outer surface of the ovary wall bursts and the secondary oocyte is released. This process is referred to as *ovulation.* Surrounding follicle cells remain within the ovary and are transformed into the corpus luteum, which secreted hormones essential for pregnancy. If pregnancy does not occur, the corpus luteum degenerates after about 10 days. After its release from the ovary, the secondary oocyte is swept into the funnel-shaped end of the Fallopian tube by the fimbria. The secondary oocyte is moved along the Fallopian tube by cilia where, if healthy sperm are present, it will become fertilized. The secondary oocyte will then undergo another unequal division of cytoplasm and nutrients and develop into the fertilized ovum. The cell that retains most of the cytoplasm and nutrients becomes the ovum, and the other cell become the second polar body, which deteriorates. If the secondary oocyte is not fertilized, it will deteriorate within 24 hours and die. When this occurs, the female will undergo a menstrual cycle (aka, have her period.)

*Luteal Phase*

The development of the corpus luteum marks the beginning of the LUTEAL phase. Occurs between days 15 - 28, and prepares the uterus to receive a fertilized egg by thickening the endometrium.

*2) Follicular Phase*

The follicular phase is characterized by the development of follicles within the ovary before ovulation. *As follicles develop, the hormone ESTROGEN is secreted, increasing the estrogen concentration in the blood.* *The increased estrogen causes the womb lining to become thicker in preparation for receiving a fertilized egg.* The follicular phase takes SIX to THIRTEEN days. Follicular phase- Follicular growth and production of E

*Oogenesis*

The formation and development of mature ova. -In the male, the formation of sperm is spermatogenesis. In female humans, oogenesis occurs in specialized cells in the ovaries, called the follicles.

*Granulosa*

The granulosa is the layer of cells that forms the follicle wall. These cells provide nutrients for the developing oocytes.

*Feedback Control of the Menstrual Cycle:*

The hypothalamus and pituitary complex *regulates the production of estrogen and progesterone*, like the way it regulated sperm count and testosterone in males. In females, the gonadotropins *follicle-stimulating hormone (FSH)* and *luteinizing hormone (LH), regulate the control of hormones produced by the ovaries: *estrogen* and *progesterone.* *FSH in females:* a gonadotropin that promotes the development of the follicles in the ovary. *LH in females:* a gonadotropin that promotes ovulation and the formation of the corpus luteum.

Feedback loop

The onset of female puberty is signaled by the release of GnRH from the hypothalamus. GnRH activates the pituitary gland, which is the production and storage site of FSH and LH. During the follicular phase of the menstrual cycle, the blood carries FSH secretions to the ovary, where follicle development is stimulated. The follicles within the ovary secrete estrogen, which initiates the development of the endometrium. As estrogen levels rise, a negative feedback message is sent to the pituitary gland to turn off secretions of FSH. The follicular phase of the menstrual cycle has ended. Simultaneously, the rise in estrogen stimulates the LH producing cells of the pituitary gland. LH secretion rises dramatically and ovulation occurs. After ovulation, the remaining follicular cells, under the influence of LH, are transformed into functioning corpus luteum. The luteal phase of the mistral cycle has begun.

*Estrogen*

is a hormone that activates development of female secondary sex characteristics, and increased thickening of the endometrium during the menstrual cycle. The lining of the uterus, the endometrium, thickens in response to estrogen stimulation during the menstrual cycle, then sheds at the times of menses. Estrogen causes the lining to grow and thicken to prepare the uterus for pregnancy. Estrogen is to women like testosterone is to men. Testosterone, remember, stimulates the maturation of the testes, spermatogenesis, and penis.