Tag: oestrogens

The female reproductive system consists of the following organs:

• ovaries – produce secondary oocytes and hormones (progesterone, oestrogens, relaxin, and inhibin)
• fallopian tubes – the sites where fertilisation normally occurs; additionally assist in transporting a secondary oocyte to the uterus
• uterus – cavity in which a fertilised ovum implants, and develops into a fetus for pregnancy and labour
• vagina – the site which receives the penis during sexual intercourse, and which acts as a passageway during childbirth
• external organs / vulva / pudendum

The Ovaries

The ovaries are a pair of irregularly scarred surfaced pale white glands measuring between 2.5 to 3.5cm long, 2cm wide, and 1.25cm thick. They produce gametes, which are secondary oocytes that develop into mature ova following fertilisation, and the hormones oestrogen, progesterone, inhibin, and relaxin.

The ovaries are held in place by 3 types of ligaments, namely the broad ligament of the uterus, which is part of the parietal peritoneum that attaches to the ovaries by the mesovarium; the ovarian ligament, which anchors the ovaries to the uterus; and the suspensory ligament, which attaches the ovaries to the pelvic walls.

Each ovary consists of:

GERMINAL EPITHELIUM – a layer of simple epithelium which covers the ovary’s surface and is continuous with the mesothelium that covers the mesovarium. The germinal epithelium does not give rise to ova.

TUNICA ALBUGINEA – a whitish capsule of dense irregular connective tissue found right beneath the germinal epithelium.

OVARIAN CORTEX – consists of ovarian follicles which are surrounded by dense irregular connective tissue containing scattered smooth muscle cells. The ovarian cortex can be found right beneath the tunica albuginea.

OVARIAN MEDULLA – consists of loose connective tissue which contains blood vessels, lymphatic vessels, and nerves.

OVARIAN FOLLICLES – consist of oocytes in various developing phases and surrounding cells which provide nourishment to the oocytes and secrete oestrogens throughout the follicle’s growing phase; single-layered surrounding cells are referred to as follicular cells, while multiple-layered surrounding cells are referred to as granulosa cells.

GRAAFIAN FOLLICLE – large follicle full of fluid in a close-to-being-ruptured state.

CORPUS LUTEUM – contains the remnants of the mature follicle, following ovulation; the corpus luteum produces progesterone, oestrogens, relaxin, and inhibin, before turning into fibrous scar tissue referred to as the corpus albicans.

The Fallopian Tubes

The fallopian tubes are two hollow fibromuscular cylinders lined by epithelium which extend outwards and backwards around 10cm from the uterine cornu to the ovaries. Each fallopian tube is divided into the following parts:

1. interstitial (approx. 0.7mm x 2.5cm)
2. isthmus (approx. 1mm x 2.5cm)
3. ampulla (approx. 6mm x 5cm)
4. infundibulum (approx. 10mm wide)

The fallopian tubes are made up of 3 layers:

INTERNAL MUCOSA – contains ciliated columnar epithelial cells that help move the fertilised ovum along the tube.

MUSCULARIS – is the middle layer. It is composed of an inner circular ring of smooth muscle and an outer thin region of longitudinal smooth muscle; peristaltic contractions of the muscularis along with the ciliary action of the mucosal cells assist the oocyte or fertilised ovum to move towards the uterus.

SEROSA – the outer layer of the fallopian tubes.

The Uterus

The uterus is a pear-shaped hollow organ that projects anteriorly and superiorly over the urinary bladder, measuring about 7.5cm x 5cm at the fundus, and 2.5cm from front to back. The uterine wall thickness measures around 1 to 2cm.

The uterus features the following anatomical subdivisions:

• fundus – dome-shaped portion superior to the fallopian tubes
• body – tapering entral portion
• cervix – inferior narrow portion which opens into the vagina; projects inferiorly and posteriorly, and enters the vaginal wall at almost a right angle
• isthmus – constricted region measuring around 1cm long found between the body and the cervix

The uterine cavity is the uterine body’s inferior. The cervical canal is the interior of the narrow cervix. The cervical canal opens into the uterine cavity at the internal os into the vagina at the external os.

The uterus is made up of 3 layers:

PERIMETRIUM – the outer layer of the uterus becomes the broad ligament laterally, covers the urinary bladder and forms the vesicouterine pouch anteriorly, and covers the rectum and forms the rectouterine pouch a.k.a. pouch of Douglas posteriorly.

MYOMETRIUM – the middle layer of the uterus is thickest and circular in the fundus area and the thinnest and longitudinal in the cervix area; the myometrium responds to oxytocin released by the pituitary during labour and childbirth through contraction coordination which help in expelling the fetus from the uterus.

ENDOMETRIUM – the inner layer of the uterus is highly vascular. It is divided into two layers: the stratum functionalis lines the uterine cavity and sloughs off during menstruation, and the stratum basalis, which is a permanent layer, gives rise to a new stratum functionalis following each menstruation.

Cervical Mucus

Cervical mucus is a secretion produced by the secretory cells of the cervix’s mucosa. It consists of water, glycoprotein, lipids, enzymes, and inorganic salts. Females in their fertile years secrete between 20-60ml of cervical mucus daily, which is more hospitable to sperm at or close to ovulation, when it is less viscous and increasingly alkaline with a pH of 8.5. Viscous mucus forms the cervical plug which stops sperm penetration.

The Vagina

The vagina is a long tubular fibromuscular canal measuring approximately 10cm long which extends from the exterior of the body to the cervix. It acts as a receptacle for the penis during sexual intercourse, an outlet for menstruation, and a passageway during childbirth.

The vaginal mucosa, which is continuous with the uterine mucosa, contains large glycogen stores that, upon decomposing, produce organic acids, which lead to a resulting acidic environment which retards microbial growth.

The Vulva

The vulva a.k.a. pudendum, is the female’s external genitalia. It consists of the following:

• mons pubis
• labia majora
• labia minora
• clitoris

Mammary Glands

The mammary glands, which lie over the pectoralis major and the serratus anterior, are modified sweat glands which produce milk.

Functions of the breast in relation to lactation include:

• milk synthesis
• milk secretion
• milk ejection

NIPPLE – pigmented projection.

LACTIFEROUS DUCTS – closely spaced duct openings which allow milk ejection.

AREOLA – circular rough-looking pigmented area surrounding the nipple which contains modified sebaceous glands.

SUSPENSORY LIGAMENTS OF THE BREAST A.K.A. COOPER’S LIGAMENTS – strands of connective tissue found between the skin and the deep fascia that provides support for the breast.

MILK – following production, milk passes from the milk-secreting alveoli into secondary tubules, and then into mammary ducts. Mammary ducts close to the nipple expand and form lactiferous sinuses, where milk is stored, and is eventually drained into the lactiferous ducts, which drain into the exterior.

Hormones Related to the Female Reproductive System

Follicle-Stimulating Hormone (FSH)

• in females initiates the development of an ova every month, and stimulates cells within the ovaries to secrete oestrogens
• in males stimulates the testes to produce sperm
• secretion depends on the hypothalamic regulating factor gonadotropin releasing factor (GnRF), which is released in response to oestrogens in females, and to testosterone in males through a negative feedback system

Luteinizing Hormone (LH)

• along with oestrogens, in females it stimulates the release of an ovum within the ovary, prepares the uterus for the implantation of the fertilised ovum, stimulates the formation of the corpus luteum in the ovary to secrete progesterone, and prepares the mammary glands for milk secretion
• in males it stimulates the interstitial endocrinocytes in the testes to develop and secrete testosterone
• secretion is controlled by GnRF, which works through a negative feedback system

Prolactin (PRL)

• requires priming of the mammary glands through oestrogens, progesterone, corticosteroids, growth hormone, thyroxine, and insulin
• initiates and maintains milk secretion by the mammary glands (amount of milk is determined by oxytocin)
• has an inhibitory and an excitatory negative control system
• level rises during pregnancy, falls right after delivery, and rises again during breastfeeding, which is why in the 1st two days following birth, mothers do not produce milk but colostrum

NOTE: women on oral contraceptives may experience lack of milk production due to their hormonal effect.

Pituitary Gland Posterior Lobe

The posterior lobe of the pituitary gland a.k.a. neurohypophysis, does not synthesise hormones. It releases hormones to the circulation via the posterior hypophyseal veins to be distributed to target cells in other tissues. The cell bodies of the neurosecretory cells produce Oxytocin (OT) and Antidiuretic Hormone (ADH) / Vasopressin.

Oxytocin (OT)

• is released in high amounts just before birth
• stimulates contraction of smooth muscle cells in the pregnant uterus
• stimulates the contractile cells around the mammary gland ducts
• affects milk ejection
• works through a positive feedback cycle which is broken following birthing
• is inhibited by progesterone, but can work in conjunction to oestrogens

The Female Reproductive Cycle

The female reproductive cycle a.k.a. menstrual cycle demonstrates regular cyclic changes seeming as periodic preparations for fertilisation and pregnancy, which, if unsuccessful, results in menstruation where the uterine mucosa (stratum functionalis portion of the endometrium) is shed.

The ovarian cycle features a series of events related to the maturation of an ovum which usually occurs on a monthly basis.

Oestrogen

• Oestrogen assists in the development and maintenance of the endometrial lining of the uterus, secondary sex characteristics, and breasts
• Oestrogen helps keep fluid and electrolyte balance
• Oestrogen increases protein anabolism (process in which amino acids are transformed into proteins) and is synergistic with the Growth Hormone a.k.a. Somatotropin
• Oestrogen helps in keeping a low blood cholesterol level

NOTE: Moderate levels of oestrogens in the blood inhibit GnRF (Gonadotropin-Releasing Hormone) release by the hypothalamus. This causes the inhibition of FSH (Follicle Stimulating Hormone) secretion by the anterior pituitary gland.

pROGESTERONE

• Progesterone works in conjunction with Oestrogen in preparing the endometrium for implantation of a fertilised ovum, and in preparation of the mammary glands for milk secretion

NOTE: High levels of progesterone inhibit GnRF (Gonadotropin-Releasing Hormone) and LH (Luteinizing Hormone).

Inhibin

• Inhibin inhibits the secretion of FSH (Follicle Stimulating Hormone) and LH (Luteinizing Hormone). This happens so as to inhibit multiple ovum maturation following the release of a mature ovum following ovulation.

Relaxin

• Relaxin helps relax the uterus through the inhibition of myometrium contractions
• Relaxin is produced by the placenta during pregnancy to help increase relaxation of the uterine smooth muscle
• Relaxin increases the flexibility of the pubic symphysis near the end of pregnancy, and may also help in the cervix dilation process in preparation for childbirth

The Menstrual Cycle

The menstrual cycle can be divided into 3 phases:

THE MENSTRUAL PHASE – the periodic discharge of 25ml to 65ml of blood, tissue fluid, mucus and epithelial cells, caused by a sudden reduction in oestrogens and progesterone. This phase usually lasts for around 5 days.

1. During this phase, 20 to 25 primary follicles start to produce small amounts of oestrogens.
2. By the end of menstruation, around 20 of these primary follicles develop into secondary follicles, while surrounding cells increase in number, differentiate, and secrete follicular fluid.
3. The follicular fluid forces an immature ovum to the edge of the secondary follicle and fills the follicular cavity, whilst secondary follicles produce oestrogens, leading to an elevation of oestrogen levels in the blood.
4. Ovarian follicle development results from GnRF secretion by the hypothalamus, which then stimulates high FSH production by the anterior pituitary.

THE PREOVULATORY PHASE – the second phase of the menstrual cycle which covers the phase between menstruation and ovulation.

1. FSH and LH stimulate ovarian follicles to increase oestrogen production, which stimulates the rebuilding of the endometrium, which by the end of this phase doubles to up to 6mm.
2. With the thickening of the endometrium, short straight endometrial glands develop, and arterioles coil and lengthen whilst penetrating the functionalis.
3. LH is secreted in increasing quantities as this phase starts to near its end.
4. A secondary follicle matures into a vesicular ovarian a.k.a. graafian follicle, ready for ovulation. At this time, just before ovulation occurs, the vesicular ovarian starts producing small amounts of progesterone.

OVULATION – the immature ovum in the vesicular ovarian follicle is released into the pelvic cavity around the middle of the menstrual cycle.

1. Immediately prior to ovulation, high levels of oestrogen inhibit GnRF production by the hypothalamus, which in turn inhibits FSH secretion by the anterior pituitary via a negative feedback effect.
2. At the same time, high levels of oestrogen work through a positive feedback effect, causing the anterior pituitary to release a high amount of LH which triggers ovulation.
3. Following ovulation, the vesicular ovarian follicle collapses, the follicular cells enlarge, change, and form the corpus luteum.

THE POSTOVULATORY PHASE – represents the time between ovulation and onset of upcoming menses. This phase is consistent in duration.

1. Following ovulation, LH secretion stimulates the development of the corpus luteum.
2. The corpus luteum secretes increasing quantities of oestrogens and progesterone.
3. FSH secretion increases gradually whilst LH secretion decreases.
4. During this phase, progesterone becomes the most dominant ovarian hormone.

SEQUELAE

1. If fertilisation and implantation do not occur, the increasing progesterone and oestrogen levels secreted by the corpus luteum inhibit GnRF and LH secretion.
2. The corpus luteum degenerates, which causes decreased secretion of progesterone and oestrogens.
3. The corpus luteum becomes the corpus albicans, whilst the decrease in progesterone and oestrogens trigger another menstrual cycle to begin, along with increased output of GnRF by the hypothalamus and a new output of FSH.

Conditions & Operations Related to the Female Reproductive System

Hysterectomy

Hysterectomy is the most common gynaecological operation, commonly indicated in endometriosis, pelvic inflammatory disease, recurrent ovarian cysts, excessive uterine bleeding, and cancer of the cervix, uterus, or ovaries.

There are 3 types of hysterectomies:

1. Total Hysterectomy – removal of the uterine body and cervix
2. Partial Hysterectomy – removal of uterine body only (cervix is left in situ)
3. Radical Hysterectomy – removal of uterine body, cervix, fallopian tubes (and possibly the ovaries), the vagina’s superior portion, the pelvic lymph nodes, and supporting structures

Cystocoele

Cystocoele is a herniation of the bladder wall into the vaginal cavity.

Rectocoele

Rectocoele is a herniation of the rectum into the vaginal wall.

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