EMBRYOLOGY AND ANATOMY OF FEMALE GENITAL TRACT

EMBRYOLOGY AND ANATOMY OF FEMALE GENITAL TRACT

EMBRYOLOGY
Development of the genital organs
Following fertilization, the normal embryo contains 23 sets of chromosomes, including 22 autosomes and one sex chromosomes from each parent.
46xy embryo will develop as a male
46xx embryo will develop as a female.
Its the presence or absence of the y chromosome which determines whether the undifferentiated gonad becomes a testis or an ovary. Although genetic sex is determined at fertilization, gender is not apparent untill approximatly the 12th week of embryonic life.


Both the genital organs and urinary tract develop from the intermediate cell mass mesoderm. The pronephros and mesonephros develop to form the primitive kidney but disappears subsequently and finally the metanephros appears to form the definitive kidney. The duct of the pronephros and mesonephros persist as the Wolfian duct, which runs caudally to join the urogenital sinus. On the medial aspect of the mesonephros, the genital ridge appears as a swelling in which a gonad is to be developed. On the lateral side of the mesonephros develops the Mullerian duct from which the female genital tract develops.

By the 5th week of embryonic life, both male and female embryos start to develop the following structures on either side of the midline. as in fig.1
1-genital ridge (proliferation of coelomic epithelium) .
2-mesonephric (wolffian) duct (lateral to the genital ridge).
3-para meso-nephric (Mullerian) duct.

Fig.1 Cross-sectional diagram of the posterior abdominal wall showing the genital ridge


Development of the ovary
Differentiation of the gonad:
Gonads appear as a pair of longitudinal ridges called: the genital ridges formed from proliferation of the coelomic epithelium and condensation of underlying mesenchyme over the ventral surface of the mesonephros. The primordial germ cells appear among the endodermal cells in the wall of yolk sac, they migrate by amoeboid movement along the dorsal mesentery of the hindgut reaching the genital ridge by the beginning of the 5th week. If there is no Y-chromosome, the primitive gonads start to become ovaries.
The primitiv gonad is first evident in embryos at 5 weeks. It forms as a bulb on the medial aspect of the meso-nephric ridge and is of triple origin. See fig.2.


*Coleomic epithelium of the genital ridge
*The underlying mesoderm
*The primitive germ cells.


If no y chromosome, the gonads, forms an ovary and the oogonia begin to develop within follicles The next stage involves the primitive germ cells (now known as oocytes) becoming surrounded by a ring of pregranulosa cells, stromal cells. Mitotic division,by which the germ cells have been increasing in numbers, then csases and they enter the 1st stage of meiosis & prophase arrest. Approximately 7million germ cells are present at 5 months, but at birth this has fallen to 2 million. At the same time, as the ovary descends into the abdominal cavity, two ligaments develop to help control its descend.

Fig.2 Development of ovary



Testis:

In genetically male embryo (Y-chromosome), at 7 weeks the primitive sex cords continue to proliferate and penetrate deep into the medulla to form medullary cords. Toward the hilum of the gonad the cords break into network of tiny cell strands giving rise of rete testis and they loss contact with the surface epithelium, the cords are composed of primitive germ cells and the sustentacular cells of Sertoli that are derived from the surface epithelium, while Leydig cells derived from the underlying mesenchyme and they lie between the cords.
By 8weeks these cells begin to produce testosterone, which in turn influences the development of the genital ducts and the external genetalia. Medullary cords form seminiferous tubules when acquire a lumen at puberty.

Development of the uterus and Fallopian tubes

In the absence of functioning testis, the Mullerian system develops into the fallopian tubes, uterus and vagina. The Wolfian ducts begin to degenerate and subsequently disappear.
The development of the genital ducts and external genetalia are under the influence of hormones circulating in the fetus. In male fetus, Sertoli cells of the fetal testis produce a non-steroidal substance: Mullerian inhibiting substance (MIS) or anti Mullerian hormone causing regression of the duct. Fetal testis produces also testosterone, which promotes the development of mesonephric duct and virilizes the external genetalia. So in male fetus under the hormones mentioned above, The Mullerian duct regress and the mesonephric duct (Wolfian) will develop into ductus deference, ejaculatory duct. While in the female fetus because of the lack of these hormones, the Mullerian duct will develop into main female genital ducts.

The lower end of the Mullerian ducts come together in the mid line, fuse and develop into the uterus & cervix. At first there is a septum separating the lumina of the 2 ducts, but later this disappears and a single cavity is formed, i. e. the uterus.
The upper parts of both ducts form the Fallopian tube .The lower end of the fused Mullerian ducts beyond the uterin luman remains solid forms a cord. As in fig.3.


Development of the vagina
 After the caudal tip of the paramesonephric ducts has reached the urogenital sinus, two solid evaginations grow out from the sinus, they are called: sino-vaginal bulbs. They proliferate to form a solid vaginal plate which proliferates cranially increasing the distance between the uterus and the urogenital sinus. By the 5th month the vagina is completely canalized.
The vagina has a double origin: most of the upper vaginal portions (fornices) are Mullerian in origin while the lower portion derived from the urogenital sinus. The lumen of the vagina remain separated from that of the urogenital by a thin tissue layer called: hymen. fig.3



Development of external genitalia
Male fetus:
Under the influence of androgens secreted by fetal testis, the external genetalia develop with rapid elongation of the genital tubercle to form the phallus. The phallus forms the shaft of the penis and glans; the genital swelling will form the scrotum. The phallus pulls the urethral folds forward which then fuse to from penile urethra.

Differential stage:

Female fetus:
In the absence of androgens and presence of estrogen, the genital tubercle elongate only slightly to form the clitoris, the urethral folds do not fuse but develop into labia minora. The genital swellings enlarge to form labia majora.
The female development is a simple progression from these structures ;
*genital tubercle_______clitoris
*genital folds_______labia minora
*genital swellings________labia majora.

ANATOMY

EXTERNAL GENITALIA
The female external genitalia (the vulva) include
1-The mons pubis
2- The labia majora
3- The labia minora
4- The clitoris


5- The vestibule and the vestibular orifice
6- The greater vestibular glands .

1- The mons pubis

Is composed of fibrofatty tissue, which covers the body of pubic bones. Inferiorly it divides to become continuous with the labium majus.

2- The labia majora

Are two folds of skin with underlying adipose tissue bounding either side of the vaginal opening. They contain sebaceous and sweat glands and a few specialized apocrine glands

3- The labia minora

Are two thin folds of skin that lie between the labia majora . Anteriorly they divide into two to form the prepuce & frenulum of the clitoris. Posteriorly they fuse to form a fold of skin called fourchette. They contain sebaceous glands but have no adipose tissue.

4- The clitoris.

Is a small 1cm erectile structure , it covered by ischiocavernosus muscle and it had highly developed nerve supply.

5- The vestibule

Is the cleft between the labia minora. The urethra, the ducts of the Bartholin's glands & the vagina open in the vestibule. The vestibular bulbs are two masses of erectile tissue that lie on either side of the vaginal entrance. They contain rich plexus of veins.
Bartholin's glands, each about the size of a small pea, lie at the base of each bulb & open via a 2 cm duct . into the vestibule between the hymen & the labia minora. Some times the ducts of this gland obstruct leading to Bartholin cyst & if infection develop it may lead to Bartholin abscess.
The vaginal orifice is surrounded by the hymen which is a thin fold of mucous membrane across the entrance to the vagina . There are usually openings in it to allow menses to escape.

The perineal body

Is a perineal mass of muscular tissue that lies between the anal canal & the lower third of the vagina. Its apex is at the lower end of the rectovaginal septum & its base is covered with skin & extends from the fourchette to the anus.


The urethral orifice
Is immediately anterior to the vaginal orifice, about 2- 3 cm beneath the clitoris. It is about 4 cm in length.

INTERNAL REPRODUCTIVE ORGANS

1-The vagina
2-The uterus
3-The fallopian tubes
4-The ovaries
See fig.6

Fig.6 Internal female reproductive organs

1-The vagina
It is a fibromuscular canal lined with stratified squamous epithelium that leads from the uterus to the vulva. It is longer in the posterior wall ( around 9 cm) than anteriorly (approximately 7 cm). The vault of the vagina is divided into 4 fornices ; posterior, anterior & two lateral. The vaginal walls are rugose with transverse folds allowing it to distend during the process of labour.The vagina is kept moist by secretions from the the uterine and cervical glands & by some transudation from its epithelial lining. It has no glands. The epithelium is thick and rich in glycogen, the growth of Doderlein's bacillus a normal commensal of the vagina that breaks down the glycogen to form lactic acid, producing a PH of around 4.5.This has a protective role for the vagina against pathogens.
Age changes
#At birth, the vagina is under the influence of maternal oestrogens, so the epithelium iswell developed. After a couple of weeks, the effects of oestrogen disappear and the PH rises to 7 and the epithelium atrophies.
# At puberty, the reverse occurs.
# At the menopause,the vagina tends to shrink and the epithelium atrophies.

2- Uterus

It is a fibromuscular organ shaped like an inverted pear, tapering inferiorly to the cervix, and in non-pregnant state is situated entierly within the pelvis. Its hollow organ and has thick muscular walls.
Pre-pregnancy; 7*5*3 cm; weight 70 g.
Full term; 30*25*20 cmcm; weight 1000 g.
It consist of ....the corpus (body) & the cervix
The corpus
Its the upper part of the uterus consist of
1-the fundus, the upermost part.
2-cornu, which is the site of insertion of the Fallopian tube.
3-the isthmus, when uterus tapers to a small central constricted area, ends by attaching to the cervix.
The constriction at the isthmus where the corpus joins the cervix is the anatomical internal os. Uterus is in anteflexion & anteversion position.



Fig.7 Coronal section of the uterine cavity
The longitudinal axis of the uterus is at right angle to the vagina & normally tilts forwards is called anteversion & its usually flexed forwards on itself at the isthmus is called anteflexion. As in fig.7 .In around 20% of women, this tilt is not forwards but backwards-retroversion & retroflexion.
The uterus consists of 3 layers
*peritoneum; the outer serous layer; which covers the body of the uterus anteriorly & posteriorly, laterally it spreads out to form the leaves of the broad ligament.
*myometrium; the middle muscular layer; forms the main bulk of the uterus .
*endometrium; the inner mucous layer; has tubular glands that dip into the myometrium & covered by a single layer of columnar epithelium. This epithelium is under go cyclical changes & lost due to effects of pregnancy & menstruation.
Increase the size during pregnancy is mostly due to hypertrophy of existing cells rather than increase in number.
Uterus is supported by ligaments (fig.8)
1-transverse cervical (cardinal ligaments)
2-round ligament
3-uterosacral ligaments.

Fig.8 The ligamentous supports of the uterus

(a) Frontal view. (b) Lateral view. 1-transverse cervical lig.; 2-round lig.; 3-uterosacral lig.

The cervix

Is a narrower than the body of the uterus approximately 2.5-3 cm in length. It consist of two parts :
* supra vaginal part :lies in continuation with isthmus, lined with columner ep.
*vaginal part :protruding into the vagina, lined with stratified sequamous epithelium.
The squamocolumner junction is also known as the transformation zone, which is an area of rapid cell division, therefore, It is the common site of cervical carcinoma (90%). The begining & the end of the endocervical canal are called the anatomical internal & external os respectively.
Age changes of uterus
* After birth, the disappearance of maternal oestrogens causes the uterus to decrease in length by around one third & cervix is then twice the length of the uterus.
*At puberty, the corpus grows much faster and the size ratio reverses.
*After menopause, the uterus atrophied, the mucosa becomes very thin, the glands almost disappear & the wall becomes less muscular.


3-The Fallopian tubes (oviducts)
Each tubeis about 10 cm long & extended outwards from the uterine cornu to end near the ovary. The tubes convey the ovum from the ovary towards the uterus & its the site of fertilization which provides oxygenation & nutrition for sperm, ovum and zygote.

It is distiguished in to 4 parts;

1-interstitial part
2-the isthmus
3-ampulla
4-infundibulum
The Fallopian tube run in the upper margin of the broad ligament, part of which, known as mesosalpinx.The epithelium of the tubes contains two functioning cell types, the ciliated cells & the secretory cells.

4-The ovaries

In the young adult, they are almond shaped, solid, a greyish pink & approximately 3 cm long, 1.5 cm wide & 1 cm thick 10g weights. It has a twin functions both steroid production & gametogenesis. It has a central vascular medulla & an outer thick cortex.
The ovary is the only intra-abdominal structure not to be covered by peritonum.
The ligaments of the ovaries ;1-the ovarian ligaments 2-the suspensory ligaments 3-the mesovarian carry the blood supply to the ovary.

Age changes

*In the child, they are small structures, 1.5 cm long. They have a smooth surface & at birth contain between 1 & 2 million primordial follicles.
*At puberty, the ovaries increase in size as a result of proliferation of the stromal cells.
*After the menopause, no active follicles are present & the ovary becomes a small, shrunken with a wrinkled surface.

The blood supply

1-Ovarian A.: the cheif source of the blood for ovaries .
2-Uterine A.: corpus branch, cervical-vaginal branch.
3-Vaginal A.: main source of blood for the middle part of vagina.


4-Internal pudendal A.: supply superficial perineum, labia majora, labia minora, lower part of the vagina & clitoris. See fig.



The lymphatic drainage

***Vulva, lower⅓ of vagina.___superficial inguinal & femoral LN
***Uterus, cervix and upper⅔ of vagina____internal iliac, obturator & external iliac LN, common iliac & para aortic LN.
***Ovaries and tubes_______para aortic LN. See fig.

lymphatic drainage

The nerve supply of pelvis
Nerve supply of vulva and perineum.
*Pudendal nerve (S2,3,4) divide into perineal n. supply the vulva.The dorsal n. of the clitoris.
Sensory fibres from the mons and labia also pass in the ilioinguinal and genitofemoral n. to the 1st lumber root.
*Posteriofemoral cutaneous n. carries sensation from perineum to the S1, 2, 3.
Nerve supply of the pelvic viscera
*Sympathetic n.fibers of the pre aortic plexus are continuous with those of the superior hypogastric plexus. Below, the superior hypogastric plexus divides, and on each side its fibres are continuous with fibres passing beside the rectum to join the utero vaginal plexus.
*Para sympathetic fibers from S2, S3, S4 join the utero vaginal plexus. Fibres from (or to) the bladder, uterus, vagina & rectum join the plexus.











PAGE1