Uterus

The uterus is approximately the size and shape of a pear with a central cavity and thick muscular walls (Fig. 1.12).

The serosal surface is the closely applied peritoneum beneath which is the myometrium which is a smooth muscle supported by connective tissue. The myometrium is made up of three layers of muscle, external, intermediate and internal layers. Clinically this is important as fibroids leave the layers intact and removal through a superficial incision leaves the three layers intact. The three layers run in complimentary directions which encourage vascular occlusion during contraction, an important aspect of menstrual blood loss and postpartum haemostasis. The mucous membrane overlying the myometrium to line the cavity is the endometrium. Glands of the endometrium pierce the myometrium and a single layer of columnar epithelium on the surface changes cyclically in response to the menstrual cycle.

The uterus consists of a fundus superiorly, a body, an isthmus (internal os) and inferiorly the cervix (external os). The cervix is a cylindrical structure which is muscular in its upper portions but this gives way to fibrous connective tissue as the cervix sits at the top of the vagina. The cervix is lined by columnar epithelium, which secretes alkaline mucus neutralizing the effects of vaginal acidity.

The cervix and uterus do not always sit in the same plane and when the uterine body rotates anteriorly it is referred to as anteflexed and posteriorly as retroflexed. The axis of the entire uterus can be anteverted or retroverted in relation to the axis of the vagina (Fig. 1.13).

The uterus is supported by the muscles of the pelvic floor together with three supporting condensations of connective tissue. The pubocervical ligaments run from the cervix anteriorly to the pubis, the cardinal ligaments pass laterally from the cervix and upper vagina to the lateral pelvic side walls and the uterosacral ligaments from the cervix and upper vagina to the sacrum. These uterosacral ligaments can be clearly seen posterior to the uterus in the Pouch of Douglas and are a common site for superficial and deep infiltrating endometriosis.

The uterine blood supply is derived mainly from the uterine artery, a branch of the anterior division of the internal iliac artery. An anastamosis occurs with the blood supply delivered through the ovarian ligament and derived direct from the ovarian artery.

The round ligament is the remains of the gubernacu-lum and extends from the uterus laterally to the pelvic side wall and then into the inguinal canal before passing down into the labia majora. It holds the uterus in anteversion, although it is a highly distensible structure in pregnancy. It is usually the first structure divided at hysterectomy allowing the surgeon to open the overlying folds of peritoneum known as the broad ligament.

Fundus

Infundibulum

Intramural part Isthmus

Fimbriae

Fig. 1.12 Uterus and fallopian tubes.

Ureter Lateral fornix Vagina

Uterine tube

Infundibulum

Intramural part Isthmus

Fimbriae

Anteversion Uterus

Ureter Lateral fornix Vagina

Cavity of uterus Body

Internal os Supravaginal cervix Cervical canal Vaginal cervix External os

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