FRS - Uterus

Question 1

What is the uterus?

Function?

Answer 1

The uterus is a secondary sex organ - an organ that matures at puberty under the influence of sex hormones produced from primary sex organs (ovaries in females and testes in males).

The main role is to transport and maintain gametes.

Question 2

Anatomical structure?

Answer 2

The uterus is a thick walled muscular organ capable of expansion to accomodate a growing fetus. It is connected to the vagina distally and laterally to the uterine tubes.

The uterus has three parts:

1) Fundus - top of the uterus, above the entry point of the uterine tubes.
2) Body - usual implantation site of the blastocyst.
3) Cervix - lower part of the uterus connecting to the vagina.

Question 3

Anatomical position?

Answer 3

The exact location of the uterus varies with distension of the bladder.

In the normal adult, the uterus can be described as anteverted, with respect to the vagina and anteflexed with respect to the cervix.

Anteverted - rotated forward, towards the anterior surface of the body.

Anteflexed - flexed, towards the anterior surface of the body.

The uterus lies posterosuperior to the bladder, and anterior to the rectum.

Question 4

Clinical relevance: abnormal positioning

Answer 4

In some individuals, the uterus may not lie in an anteverted and anteflexed position. The three most common dispositions:

1) Excessively anteflexed
2) Anteflexed and retroverted
3) Retroflexed and retroverted

They do not inherently cause medical problems. However, a retroverted positioned directly superior to the the vagina, causing an increase in abdominal pressure. This may cause the uterus to prolapse into the vagina.

Uterine prolapse is particularly prevalent in those with pelvic floor damage.

Question 5

Histological structure

Layers?

Answer 5

From superficial to deep:

1) Peritoneum - a double layered membrane, continuous with the abdominal peritoneum. Also known as the perimetrium.
2) Myometrium - a thick smooth muscle layer. Cells of this layer undergo hypertrophy and hyperplasia during pregnancy in preparation to expel the foetus at birth.
3) Endometrium - inner mucous membrane lining the uterus. Can be subdivided into two layers:
i) Deep stratum basalis - Changes little throughout the menstrual cycle. Not shed in menstruation.
ii) Superficial stratum functionalis - proliferates in response to estrogens, and becomes secretory in response to progesterone. It is shed during menstruation and regenerates from cells in the deep stratum basalis.

Question 6

Ligaments of the uterus?

Answer 6

The tone of pelvic floor provides support for the uterus, but there are 5 main ligaments of the uterus too:

1) Broad ligament - this is a double layer of peritoneum attaching the sides of the uterus to the pelvis. It acts as a mesentery for the uterus and contributes to maintaining it in position.
2) Round ligament - a remnant of the gubernaculum extending from the uterine horns to the labia majora via the inguinal canal. It functions to maintain the anterverted postion of the uterus.
3) Ovarian ligament - joins the ovaries to the uterus.
4) Cardinal ligament - located at the base of the broad ligament, the cardinal ligament extends from the cervix to the lateral pelvic walls. It contains the uterine arteries and veins, in addition to supporting the uterus.
5) Uterosacral ligament - extends from the cervic to the sacrum.

Question 7

Vascular supply and lymphatics?

Answer 7

Arterial supply - uterine artery

Venous drainage - uterine veins

Lymphatic drainage - iliac, sacral, aortic, and inguinal lymph nodes.

Question 8

Clinical correleation - hysterectomy

Answer 8

A surgical removal of the uterus, usually as a result of cervical and uterine cancer.

The uterine artery crosses the ureter approximately 1cm laterally to the internal os. Care must be taken not to clamp down the ureter, damaging it, whilst trying to clamp the uterine arteries.

Water under the bridge - ureter under the artery.

Question 9

Innervation

Answer 9

Sympathetic - uterovaginal plexus - consisting of the anterior and intermediate parts of the inferior hypogastric plexus.

Parasympathetic - pelvic splanchnic nerve (S2, S3, S4)

The afferent nerve fibres mostly ascend through the inferior hypogastic plexus to enter the spinal cord at T10-T12 and L1 nerve fibers.

Question 10

Clinical correlation - disorders of the endometrium

Answer 10

1) Endometriosis - presence of ectopic endometrial tissue at sites outside the uterus. This occurs most commonly at ovaries and ligaments of the uterus. This ectopic tissue is still responsive to estrogens and can therefore proliferate and bleeding can occur, often forming a cyst. This condition is associated with dysmennorrhea and /or infertility.
2) Fibroids - benign tumours of the myometrium which affect 20% of menopausal women. They are estrogen dependent, enlarging during pregnancy and with use of the contraceptive pill but regressing after the menopause. Most fibroids are asymptomatic, but if large enough can cause menorrhagia, pelvic pain and infertility.
3) Endometrial carcinoma - most common malignancy of the female genital tract - most often found during, or after, the menopause, and characterised by abnormal uterine bleeding.