The Uterus

The Uterus

The uterus is a thick walled pear shaped hollow, muscular organ lying in the pelvis

Functions

·              Prepares for pregnancy each month

·              Shelters the baby

·              Expels the uterine contents after pregnancy

Position - the uterus is situated in the cavity of the true pelvis , behind the bladder and in front of the rectum. It leans forward which is kown as anteversion; It bends forwards on itself which is known as anteflexion. When the woman is standing this result in an almost horizontal position with the fundus resting on the bladder .

Relations

Anterior :  in front of the uterus lie the uterovesicalpouch and bladder

Posterior : behind the uterus are the rectouterine pouch of Douglas and the rectum.

Lateral : on either side of the uterus are the broad ligaments, the uterine tubes and the ovaries.

Superior :  above the uterus lie the intestines Inferior below the uterus is the vagina

Supports

The uterus is supported by the pelvic floor and maintained in position by several ligaments, of which those at the level of the cervix are the most important The Transverse Cervical Ligaments these fan out fromthe sides of the cervix to the side walls of the pelvis. They are sometimes known as the ‘cardinal ligaments’ or ‘Mackenrodt’s ligaments’

The uterosacral ligaments these pass backwards fromthe cervix to the sacrum

The pubocervical ligaments these pass forwards fromthe cervix, under the bladder, to the pubic bones.

The broad ligaments these are formed from the folds ofthe peritoneum which are draped over the uterine tubes. They hang down like a curtain and spread from the sides of the uterus to the sides walls of the pelvis

The round ligaments. Thesehave little value as asupport but tend to maintain the anteverted position of the uterus. They arise from the cornua of the uterus in front of and below the insertion of each uterine tube and pass between the folds of the broad ligament, through the inguinal canal, to be inserted into each labium majus.

The ovarian ligament.These also begin at the cornuaof the uterus but behind the uterine tubes and pass down between the folds of the broad ligament to the ovaries. It is helpful to note that the round ligament, the uterine tube and the ovarian ligament are very similar in appearance and arise from the same area of the uterus. This makes careful identification important when tubal surgery is undertaken.

Structure

The non- pregnant uterus is a hollow muscular pear-shaped organ situated in the true pelvis. It is 7.5cm long, 5cm wide and 2.5 cm in depth. The cervix forms the lower one third of the uterus and measures 2.5cm in each direction.

The uterus consists of the following parts :

The Body or Corpus  : This makes the upper two thirds ofthe uterus and is the greater part.

The Fundus  : This is the domed upper wall between theinsertions of the uterine tubes.

The Cornua :  These are the upper outer angles of theuterus where the uterine tubes join.

The Cavity. :  This is a potential space between theanterior and posterior walls. It is triangular in shape, the base of the triangle being uppermost

The Isthmus  : this is a narrow area between the cavityand the cervix which is 7cm long. It enlarges during pregnancy and labour to form part of the lower uterine segment

The Cervix or Neck. : This protrudes into the vagina, theupper half being above the vagina, is known as the supravaginal portion while the lower half is the infravaginal portion.

The Internal Os (Mouth) this is the narrow openingbetween the isthmus and the cervix.

The External Os. : This is a small round opening at thelower end of the cervix. After childbirth it becomes a transverse slit with an anterior and a posterior lip.

The Cervical Canal lies between these two and is acontinuation of the uterine cavity. This canal is shaped like a spindle, narrow at each end and wider in the middle.

Layers

The uterus has three layers, of which the middle muscle layer is by far the thickest.

The Endometrium this layer forms a lining of ciliatedepithelium(mucous membrane ) on a base of connective tissues or stroma

In the uterine cavity this endometrium is constantly changing in thickness throughout the menstrual cycle. The basal layer does not alter, but provides the foundation from which the upper layers regenerate. The epithelial cells are cubical in shape and dip down to form glands that secrete alkaline mucus.

The cervical endometrium does not respond to the hormonal stimuli of the menstrual cycle to the same extent. Here the epithelial cells are tall and columnar in shape and the mucus-secreting glands are branching racemorse glands. The cervical endometrium is thinner than that of the body and is folded into a pattern known as the ‘arbor vitae’ (tree of life). This is though t to assist the passage of the sperm. (the portion of the cervix that protrudes into the vagina is covered with squamous epithelium similar to the squamo-columnar junction and it is known as the intravaginal cervix ,about 1.5 cm.

The Myometrium or muscle coat. This layer is thick inthe upper part of the uterus and is more sparse in the isthmus and cervix. Its fibers run in all directions and interlace to surround the blood vessels and lymphatics that pass to and from the endometrium. It is this arrangement that facilitate the arrest of haemorrhage after delivery of the baby-“living ligament” The ou ter layer is formed of longitudinal fibers that are continuous in those of the uterine ligaments and the vagina

In the cervix the muscles fibers embedded in collagen fibers, which enable it to stretch in labor.

The Perimetrium.This is a double serous membrane ,and extension of the peritoneum, which is draped over the uterus, covering all but a narrow strip on either side and the anterior wall of the supravaginal cervix from where it is reflected up over the bladder

Blood supply

Uterine artery which is a branch of internal iliac artery. Ovarian artery a branch of abdominal aorta supply ovary and fallopian tube ad join with uterine artery

Lymphatic drainage

Lymph is drained from uterine body to internal iliac glands mainly

Nerve supply

Mainly  from autonomic, sympathetic  and parasympathetic nervous system via Lee Frankenhauser’s plexus or pelvic plexus