Uterus

Menstrual cycle

A follicle begins a period of development in the ovary during the first days of the cycle, it matures and ruptures to release a secondary oocyte. The wall of the follicles transforms into the corpus luteum that secretes progesterone (luteal phase). 10 days later after ovulation the corpus luteum regresses until ceasing to function and is replaced by fibrous tissue. The breakdown of the endometrium reduces progesterone and oestrogen levels as the corpus luteum degenerates. Changes that occur in the endometrium during the menstrual cycle can be divided into three phases: - Proliferative phase - Secretory phase - Menstrual phase

Menstrual phase

As the corpus luteum regresses the stroma changes and the endometrium thickness diminishes. Blood escapes from superficial vessels of the endometrium forming small haematomata beneath the surface of the epithelium. The stratum functionalis is shed gradually leaving the stratum basalis. Blood and necrotic endometrium appear in the uterine lumen and is discharged from the uterus via the vahina for 3-6 days.

Broad ligaments

Extends from the sides of uterus to the lateral walls and floor of pelvis; made of mesosalpinx (encloses uterine tube), mesovarium (carries ovarian vessels and nerves), mesometrium (contains part of transverse cervical ligament. They don't provide support to the uterus.

Lymphatic drainage

Lymphatic vessels drain lymph from the body and cervix of the uterus to the external and internal iliac lymph nodes, as well as the obturator lymph nodes. In turn, the fundus is drained to the para-aortic lymph nodes.

Secretory phase

Steroid receptors in the endometrium activate a sequence a gene expression that produces a sequences of events that prepare the tissue for blastocyst implantation. This phase coincides with the luteal phase. In the early secretory phase, glandular secretory activity (glycogen) increases. In the late secretory phase, glandular secretory activity declines. glycogen is need to feed the blastocyst during its implantation in the endometrium

Squamocolumnar junction

The SJ is located at the internal os of cervix before puberty. As oestrogen levels rise during puberty, the cervical os opens, exposing the endocervical columnar epithelium on to the ectocervix. -This area of columnar cells on the ectocervix is called an ectropion (cervical erosion). -It is then exposed to the acidic environment of the vagina and, through a process of squamous metaplasia, transforms into stratified squamous epithelium. -This area is thus known as the 'transformation zone'. -This area is the most usual site of cervical intraepithelial neoplasia (CIN), which may progress to malignancy. -In postmenopausal women, the squamocolumnar junction recedes into the endocervical canal.

Myometrium

The body of the uterus has four layers (inside out): - Submucosal (innermost) layer - composed of longitudinal and oblique muscle fibres. Where the lumen of the uterine passes through the uterine wall a circular muscle coat is formed. - Vascular layer - rich in blood vessels and longitudinal muscle. - Supravascular layer - circular muscle for stabilising the uterine wall. - Longitudinal muscle layer - subserosal layer adjacent to the serosa

Cervix histology

The cervical canal is lined by a deeply folded mucosa with a surface epithelium of columnar mucous cells. There are branched tubular glands that secrete clear alkaline mucus. The surface of the intravaginal part of the cervix (ectocervix) is covered by non-keratinised stratified squamous epithelium. The columnar secretory epithelium of the endocervical canal meet the ectocervix at the squamocolumnar junction at the external os.

Endometrium

The endometrium is the inner, mucous membrane lining of the uterus it is lined with simple columnar epithelium, some have cilia and some microvilli. The endometrial stroma contains numerous tubular glands that secrete glycogen and glycoproteins. It is followed by a cell-rich connective tissue layer (lamina propria). There is a transition to squamous non-keratinized epithelium at the squamocolumnar junction. Physiologically the endometrium is divided into the functional layer (stratum compactum and spongiosum ) and basal layer (stratum basale). The functional layer has more hormonal responsiveness, the basal doesn't vary morphologically during the menstrual cycle.

Proliferative phase

The epithelium from the persisting basal parts of the uterine glands grown over the surface of the endometrium which was shed by menstruation. The endometrium thickens as cell divide in response to an increase of oestrogen produced by the ovary. The glands become tortuous and the lining epithelium become tall columnar.

Mesometrium

The mesometrium is the most inferior and largest part of the broad ligament. It extends from the pelvic floor to the ovarian ligament and the body of the uterus. It encloses the uterine artery, the suspensory ligament of the ovary and the proximal part of the round ligament of the uterus. Ovarian nerves and vessels travel through the suspensory ligament of the ovary.

Mesovarium

The mesovarium is the posterior extension of the broad ligament, containing the ovary. It attaches to the hilum of the ovary, carrying the ovarian vessels and nerves.

Innervation

The nerves derive from the inferior hypogastric plexus. The branches supply the uterine body and tubes and connect tubal nerves from the inferior hypogastric plexus and the ovarian plexus. Sympathetic innervation originates from the T12 and L1 spinal segments, while the parasympathetic nervous supply is provided by the S2 to S4 spinal segments. All vessels and nerves run through the lateral ligaments (ligamentum latum uteri), a broad duplication of the peritoneum connecting the lateral wall of the uterus with the pelvic wall.

Peritoneal folds

The parietal peritoneum is reflected over the upper genital tract to produce anterior (uterovesical), posterior (rectovaginal) and lateral peritoneal folds (broad ligaments).

Uterosacral, transverse cervical, and pubocervical ligaments

The pubocervical, transverse cervical and uterosacral ligaments are condensations of the visceral connective tissue that connect the pelvic visceral, they radiate outwards from the cervix towards the pelvic side walls, like the spokes of a wheel. Uterosacral ligaments - contains fibrous tissue and smooth muscle. The two ligaments pass back from the cervix and uterine body and attach to the anterior aspect of the sacrum. Transverse cervical ligaments - the two ligaments run from the lateral walls of the pelvis to the supravaginal part of the cervix and the lateral parts of the vaginal fornix. They are traversed by the ureters and pelvic blood vessels. Pubocervical ligaments - the two ligaments extend from the anterior aspect of the cervix and upper vagina to the posterior aspect of the pubic bones.

True ligaments

The true ligaments are fibromuscular bands that fix the uterus to the bones of the pelvis. They provide support to the uterus. The ligaments of the pelvis consist of the: - Round - Uterosacral - Transverse cervical - Pubocervical ligaments

Mesosalpinx

The upper portion of the broad ligament it is attached superiorly to the uterine tube and posteroinferiorly to the mesovarium. The fibrous suspensory ligament of the ovary is attached superolaterally and the ovarian ligament is attached medially. The mesosalpinx encloses and suspends the uterine tube within the pelvic cavity. In addition, it encloses anastomoses between the uterine and ovarian vessels.

Serosa

The uterine body is covered by peritoneal serosa, which continues downwards posteriorly to cover the supravaginal cervix. The anterior cervix and the lateral surfaces of the uterine body and cervix are not covered by peritoneum.

Venous drainage

The uterine veins extend laterally in the broad ligaments, running adjacent to the arteries and passing over the ureters. They drain into the internal iliac veins. The uterine venous plexus anastomoses with the vaginal and ovarian venous plexuses.

Uterovesical and rectovaginal folds

The uterovesical fold consists of peritoneum reflected on the bladder from the uterus at the junction of its cervix and body. The rectovaginal fold extends lower and consists of peritoneum reflected from the posterior vaginal fornix onto the from of the rectum. It is bounded anteriorly by the uterus, supravaginal cervix, and posterior vaginal fornix; posteriorly by the rectum; and laterally by the uterosacral ligaments.

Body of the uterus histology

The uterus is composed of three main layers. From the lumen out: - Endometrium (mucosa) - Myometrium (smooth muscle) - Serosa (advnetitia)

Arterial supply

The uterus is supplied by the uterine artery, a branch of the anterior division of the internal iliac artery. One branch travels within the broad ligament of the uterus until the region close to the ovarian hilum, where it forms an anastomosis with the uterine branches of the ovarian artery. The second branch supplies the cervix and anastomoses with several branches of the vaginal artery. The uterine artery also gives several perforating branches within the uterine wall that form two surrounding systems around the uterus called the posterior and anterior arcuate arteries.

Round ligament

There are two in total, each extending from the lateral cornu of the uterus, through the broad ligament, enters the inguinal canal through the deep inguinal ring and ends in the connective tissue of the labium majus in the perineum. This structure helped the descent of the ovaries during embryonic development from the posterior abdominal wall. The closer to the uterus the more the smooth muscle within the ligament, becoming purely fibrous at the edges. The round ligament contains vessels, nerves and lymphatics draining the uterine region around the entry of the uterine tubes into the superficial inguinal lymph nodes.

Position of the uterus

When the bladder is empty, typical uterus is - Anteverted - the long axis of the uterus is inclined towards the vagina 90° - Anteflexed - bent forward against the cervix at the isthmus (internal os) 170° When bladder is fully distended, the uterus is retroverted and retroflexed The shape and size however may vary depending on age, number of pregnancies and hormonal status.

Cervix

Inferior portion of the uterus that extends from the isthmus to the vagina. The upper end is pens into the uterine body at the internal os, and the lower end opens into the vagina at the external os. The external end of the cervix enters the upper end of the vagina, thereby dividing the cervix into supravaginal and vaginal parts. In nulliparous women, the external os is usually a circular aperture, whereas, after childbirth, it is a transverse slit.

Body of the uterus

It has an inverted pear-shape and extends from the fundus to the cervix. Fundus is the rounded portion of the uterus superior to the attachment of the uterine tubes. The body ends at a constriction known as the isthmus. The round and ovarian ligaments are inferoanterior and inferoposterior, respectively, to each cornu. The anterior surface of the uterine body is covered by peritoneum reflected on to the bladder at the uterovesical fold. The peritoneum covering posterior surface of the uterus continues down to the cervix and upper vagina, and is then reflected back to the rectum along the surface of the recto-uterine pouch.

Uterus overview

It is a thick-walled muscular organ in the pelvis between the bladder & uterovesical space and the rectum & recto-uterine pouch. The broad ligaments are lateral. The uterus is divided structurally and functionally into the muscular body of the uterus (corpus uteri) and the fibrous cervix (cervix uteri).