Lecture # 17: The Female Reproductive System

The Female Reproductive System (Chapter 28)

Objectives

3- To describe the changes in the ovarian follicles in relation to oogenesis.

4- Describe the hormonal events that regulates the ovarian cycle.

5- Describe how the uterus changes during the menstrual cycle.

Ovulation

1- To describe the structure and functions of the principal organs of the female reproductive system.

2- To describe the oogenesis.

The Female Reproductive System

Main Reproductive Organs or Gonads

Duct system Accessory Glands and Organs

External Genitalia

Ovaries Uterus

Vagina

Uterine tubes Clitoris

Labia minora

Internal Genitalia External Genitalia

Labia mayora

Bartolini’s or greater vestibular glands

Paraurethral glands

The Female Reproductive System

Ovary

Uterine tubes

Uterus

Vagina

Labia minora

Labia mayora

Clitoris

Paraurethral glands

Bartolini’s or greater vestibular

glands

The Female Reproductive System is more complex than that of the male because it serves more purposes:

1- It produces and delivers gametes.

2- It provides nutrition and safe harbor for fetal development.

3- It gives birth, and nourishes the infant.

The OvariesThey are the female gonads which produce egg cells (ova) and sex hormones.

Tunicaalbuginea

It is where germ cells develop.

Cortex

MedullaIt is occupied by major arteries and veins.

The egg develop in their own fluid-filled follicles

Follicle bursting and releasing the egg (ovulation).

The Ovarian Ligaments

Ovarian ligament

It attaches the ovary to the uterus.

Suspensory ligament

It attaches the ovary to the pelvic wall and contains ovarian artery, vein and nerves.Broad

ligament

Broad ligament:

Mesosalpinx

Mesometrium

MesovariumIt attaches the ovary to the broad ligament.

IsthmusAmpulla

The Uterine Tubes

Infundibulum

Fimbriae

Functions:They receive and transport the egg to the uterus. It is the site where fertilization generally occurs.

Uterine tubes are lined by a simple columnar epithelium with ciliated cells and a smaller number of secretory cells.

The cilia beat toward the uterus and, with the help of muscular contraction of the tube, convey the egg in that direction.

Once it has been released, the oocyte begins a slow journey to the uterus through the uterine tubes (fallopian tubes).

Ovulation

While within the tube, the oocyte may encounter sperm and become fertilized prior to entering the uterus.

Implantation DAYS 7-10

The UterusIt is a thick muscular chamber that opens into the roof of the vagina.

2- It expels the fetus at the end of its development.

Functions:

1- It harbors and provides a source of nutrition for the fetus.

Body

Fundus

Vagina

Cervix

Cervical canalExternal os

Lateral fornix

It is the external serosa layer.

It constitutes most of the uterine wall, and is composed mainly of smooth muscle. It produces labor contractions and expels the fetus.

Internal os

It is a simple columnar epithelium, compound tubular glands, and a stroma populated with leukocytes, macrophages, and other cells.

Stratum basalis: The deep layer, stays behind and regenerates a new stratum functionalis with each menstrual cycle.

Stratum functionalis: The superficial half, shed each menstrual period.

Perimetrium

During pregnancy, the endometrium is the site of attachment of the embryo and forms the maternal part of the placenta from which the fetus is nourished.

Myometrium

Endometrium

The VaginaIt is a distensible muscular tube (8-10 cm).

1- It is a passageway for menstrual flow.

2- It receives the penis and semen.

3- It is a passageway for delivery.

Functions:

Urinary bladder

Uterus

Vagina

Urethra

Urethral orifice

Vaginal orifice

Rectum

Anus

Bacteria ferment glycogen rich cells producing acidic pH in vagina, which inhibits the grow of pathogen.

The vaginal epithelium is simple cuboidal in childhood, but the estrogens of puberty transform it into a stratified squamous epithelium (vaginal metaplasia).

Posterior fornix

Anterior fornix

Bartolini’s or greater vestibular gland

Paraurethral gland

They keep the vulva moist, and provide lubrication during sexual excitement.

External GenitaliaMons pubis

Labia majora

Labia minora

Glans or clitoris

Prepuce

Urethral opening

Vaginal entrance

Hymen (torn)

Perineum

The Mammary GlandsThey produce milk to nourish the baby.

Areola

Nipple

Lobules

Lactiferous duct

Lactiferous sinus

Suspensory ligament

Pectoralis major

Pectoral fat pad

By the end of the six month of pregnancy the mammary glands are fully developed (prolactin hormone produced by the adenohypophysis).

After birth

Lobes

Puberty and Menopause

It is triggered by rising levels of Gonadotropin releasing hormone (GnRH) produced by the hypothalamus.

Puberty begins at age 8-10 for most girls in US.

GnRH stimulates the anterior lobe of pituitary to produce gonadotropins:

Follicle-stimulating hormone (FSH)

Luteinizing hormone (LH)

FSH stimulates developing ovarian follicles and they begin to secrete estrogen, progesterone, and inhibin.

Estrogens are feminizing hormones with widespread effects on the body. The principal estrogens are : Estradiol (the most abundant), estriol, and estrone.

Gonadotropin releasing hormone (GnRH)

Luteinizing hormone

(LH)

Follicle-stimulating hormone

(FSH)

Estrogens

Progesterone

Inhibin

Effects of the Estradiol:

2- It stimulates growth of ovaries and secondary sex organs.

3- It stimulates growth hormone secretion.

4- It produces an increase in height and widening of the pelvis.

5- It is responsible for feminine physique because it stimulates the deposition of fat.

6- It makes a girl’s skin thicker, but remains thinner, softer, and warmer than males of the corresponding age.

Estradiol is the most abundant estrogen (feminizing hormones).

Estradiol (estrogen)

1- It stimulates vaginal metaplasia.

The vaginal epithelium changes from simple cuboidal to stratified squamous.

Feminizing Hormones

Oogenesis and Sexual Cycle

Reproductive Cycle Sexual Cycle

The events that recur every month when pregnancy does not intervene.

It consists of two interrelated cycles controlled by shifting patterns of hormone secretion:

Ovarian cycle(The events in the ovaries)

Menstrual cycle(The parallel events in the uterus)

The sequence of events from fertilization to giving birth.

Follicular phase

Ovulation

Luteal phase

Proliferative phase

Secretory phase

Menstrual phase

Premenstrual phase

Events that Occur in the Ovaries1- Oogenesis (production and development of oocytes).

2- Folliculogenesis (development of the follicles).

Like spermatogenesis, it produces haploid gametes by means of meiosis.

1- Oogenesis

Oogenesis

Spermatogenesis 1- Males produce sperm continually.

1- It is a cyclic event that releases one egg per month.

2- Spermatogonia and spermatocytes are produce continually during fertile period of life.

2- Oogonia and primary oocyte are produce only before birth.

3- Oogonia multiply until the fifth month reaching 5 to 6 million in number. Then go into a state of arrested development until shortly before birth.

4- Shortly before birth oogonia transform into primary oocyte.

5- Most of primary oocytes undergoes degeneration before the girl is born and during childhood.

6- By puberty, only about 400, 000 remains (even if a woman ovulates every 28 days from 14 to 50, she would ovulate 480 times.

OOGENESIS

MITOSIS

OogoniaDiploid

Diploid

Before birth

MEIOSIS I

After puberty

It stops inprophase

MEIOSIS ICompleted

Primaryoocyte

Haploid

Secondaryoocyte

It stops inmetaphase Before ovulation

First polarbody

After ovulationSecondpolarbody

MEIOSIS IICompleted Haploid

Secondaryoocyte

If fertilizationoccurs

MEIOSIS II

1-Oogenesis

Primary oocytes (diploid) in prophase I of MEIOSIS I.

FSH triggers the start of the ovarian cycle.MEIOSIS I is completed to form one secondary oocyte (haploid) and the first polar body.

Between the third and seventh month of fetal life:

Primary oocytes (diploid) begin MEIOSIS I but it is stopped in prophase I.

During reproductive life: Every month one secondary oocyte begins MEIOSIS II that is stopped in metaphase II. Ovulation occurs, and if the secondary oocyte is fertilized, MEIOSIS II is completed to form the ovum and the second polar body.

At birth:

At puberty:

Oogonia undergo mitosis and produce primary oocytes (diploid).

Primordial follicles

Primary follicles

Secondary follicles

Tertiary follicles

Ovulation

2- Folliculogenesis As the egg undergoes oogenesis, the follicle around it undergoes developments called folliculogenesis

They consist of a primary oocyte in early meiosis, surrounded by a single layer of squamous follicular cells. They are concentrated in the cortex of the ovary.

Primordial follicles

They have larger oocytes and follicular cells that still form a single layer.

They have still larger oocytes and follicular cells are now stratified (granulosa cells).Zona pellucida: It is a layer of glycoprotein gel secreted by granulosa cells around the oocyte.Theca folliculi: It is a fibrous husk of connective tissue around the granulosa cells.

Granulosa cells begin secreting follicular fluid, which accumulates in little pools in the follicular wall - this defines the tertiary follicles

As they enlarge, the pools merge forming a single fluid-filled cavity, the antrum.

Normally only one follicle from each month’s cohort becomes a mature follicle destined to ovulate while the rest degenerate.

Primary follicles

Secondary follicles

Tertiary follicles

Mature (Graafian) follicles

Ovarian cycle

Menstrual cycle

Ovarian cycle

(The events in the ovaries)

Menstrual cycle

(The parallel events in the

uterus)

Follicular phase

Ovulation

Luteal phase

Proliferative phase

Secretory phase

Menstrual phase

Premenstrual phase

Oogenesis and Sexual Cycle

Luteal phaseFollicular phase

GonadotropinsFollicle Stimulating Hormone (FSH)

They are produced by the anterior pituitary.

It stimulates the development of the follicles and the secretion of estradiol.

Luteinizing Hormone (LH)

It stimulates ovulation.

Estradiol It is produced by the maturing follicles and stimulates secretion of LH and FSH by the anterior pituitary

Gonadotropin releasing hormone (GnRH)

Estradiol

LHProgesterone

It has a crucial role in preparing the uterus for the possibility of pregnancy.

The Ovarian Cycle

EstrogensFSH

Pituitary

Ovarian Cycle

Follicular phase

Ovulation

Luteal phase

It is characterized by growing follicles.

It is governed by follicle stimulating hormone (FSH) from the pituitary gland and estrogens from the ovarian follicles.

It is triggered by luteinizing hormone (LH) from the pituitary gland (released in response to estrogen secretion for the follicles).

It is governed by the luteinizing hormone (LH) from the pituitary gland, and progesterone and estrogen produced by ovarian corpus luteum.

Stratum basale

The Menstrual CycleProliferative phase

(6 to 14 day)

At the end of the menstruation, the endometrium consists only of the stratum basale.

Estrogen stimulates mitosis in the stratum basalis and the prolific regrowth of blood vessels regenerating the functionalis, By day 14 is 2 to 3 mm thick.

As new cohort of follicles develop in the ovaries, they secrete more and more estrogen.

Stratum functionalis

Secretory phase ( 15 to 26)

The endometrium thickens still more in response to progesterone from corpus luteum.

The endometrium thickens as a result of secretion and fluid accumulation rather than mitosis.

Progesterone stimulates endometrial glands to secrete glycogen. Glands grow wider, longer and more coiled.By the end of this phase, the endometrium is 5 to 6 mm thick- a soft, wet, nutritious bed available for embryonic development.

Premenstrual phase ( 27 and 28 days)

The corpus luteum atrophies and progesterone levels fall sharply, triggering spasmodic contractions of spiral arteries.

It causes endometrial ischemia and brings about tissue necrosis and menstrual cramps

Pools of blood accumulate in stratum functionalis and necrotic endometrium mixes with blood and serous fluid and forms the menstrual fluid.

When enough menstrual fluid accumulates in the uterus, it begins to be discharged by the vagina.

Menstrual phase (1 to 5 day)

Spiral artery

Proliferative phase

Proliferative phase Estrogen stimulates mitosis in the stratum basalis and the prolific regrowth of blood vessels regenerating the stratum functionalis.

Estradiol

Progesterone

Secretory phase The endometrium thickens still more in response to progesterone from corpus luteum.

Premenstrual phase Corpus luteum atrophies and progesterone levels fall sharply. This causes endometrial ischemia with tissue necrosis and menstrual cramps.

Secretory phase Premenstrual

phase

Menstrual Cycle:

Necrotic endometrium mixes with blood and serous fluid and produce the discharge of menstrual fluid from the vagina.

Menstrual phase

Menstrual phase

The first day of discharge is day 1 of the new cycle