Function

Reproductive function

The reproductive function of the uterus is to accept a fertilized ovum which passes through the utero-tubal junction from the fallopian tube. It implants into the endometrium, and derives nourishment from blood vessels which develop exclusively for this purpose. 

The fertilized ovum becomes an embryo, attaches to a wall of the uterus, creates a placenta, and develops into a fetus (gestates) until childbirth. Due to anatomical barriers such as the pelvis, the uterus is pushed partially into the abdomen due to its expansion during pregnancy. Even during pregnancy the mass of a human uterus amounts to only about a kilogram (2.2 pounds). 

Blood flow

The uterus is essential in sexual response by directing blood flow to the pelvis and to the external genitalia, including the ovaries, vagina, labia, and clitoris.

Menstrual cycle

The series of changes in which the uterine lining is shed, rebuilds, and
prepares for implantation.The timing of the menstrual cycle starts with the first day of menses, referred to as day one of a woman’s period. Cycle length is determined by counting the days between the onset of bleeding in two subsequent cycles. Because the average length of a woman’s menstrual cycle is 28 days, this is the time period used to identify the timing of events in the cycle. However, the length of the menstrual cycle varies among women, and even in the same woman from one cycle to the next,typically from 21 to 32 days. 

Just as the hormones produced by the granulosa and theca cells of the ovary “drive” the follicular and luteal phases of the ovarian cycle, they also control the three distinct phases of the menstrual cycle. These are the menses phase, the proliferative phase, and the secretory phase.

Development

Bilateral Müllerian ducts form during early fetal life. In females, these ducts give rise to the Fallopian tubes and the uterus. In humans the lower segments of the two ducts fuse to form a single uterus, however, in cases of uterine malformations this development may be disturbed. The different uterine forms in various mammals are due to various degrees of fusion of the two Müllerian ducts.

Anatomical structure

The uterus is located inside the pelvis immediately dorsal (and usually somewhat rostral) to the urinary bladder and ventral to the rectum (Pic. 1). The human uterus is pear-shaped and about three inches (7.6 cm) long. A nonpregnant adult uterus weighs about 60 grams. The uterus can be divided anatomically into four segments:

  • the fundus
  • corpus
  • cervix 
  • internal os

The uterus consists of a body and a cervix (Pic. 2). The cervix protrudes into the vagina. The uterus is held in position within the pelvis by condensations of endopelvic fascia, which are called ligaments. These ligaments include the:

  • pubocervical
  • transverse
  • cervical ligaments
  • cardinal ligaments
  • uterosacral ligaments

 It is covered by a sheet-like fold of peritoneum, the broad ligament.

Histological structure

Endometrium

The endometrium (Pic. 3) consists of a single layer of columnar epithelium plus the stroma on which it rests. The stroma is a layer of connective tissue that varies in thickness according to hormonal influences. Simple tubular uterine glands reach from the endometrial surface through to the base of the stroma, which also carries a rich blood supply of spiral arteries. In a woman of reproductive age, two layers of endometrium can be distinguished. These two layers occur only in endometrium lining the cavity of the uterus, not in the lining of the uterine (Fallopian) tubes.

The functional layer is adjacent to the uterine cavity. This layer is built up after the end of menstruation during the first part of the previous menstrual cycle. Proliferation is induced by estrogen (follicular phase of menstrual cycle), and later changes in this layer are engendered by progesterone from the corpus luteum (luteal phase). It is adapted to provide an optimum environment for the implantation and growth of the embryo. This layer is completely shed during menstruation.

The basal layer, adjacent to the myometrium and below the functional layer, is not shed at any time during the menstrual cycle, and from it the functional layer develops.
In the absence of progesterone, the arteries supplying blood to the functional layer constrict, so that cells in that layer become ischaemic and die, leading to menstruation.

Myometrium

The myometrium (Pic. 4), is located between the endometrium (the inner layer of the uterine wall), and the serosa or perimetrium (the outer uterine layer).

Myometrium has 3 layers:

  • outer made of longitudinal smooth muscles
  • middle from crisscrossing muscle fibres act as living ligature during involution of uterus and prevent blood loss
  • inner circular fibres 

The inner one-third of the myometrium (termed the junctional or sub-endometrial layer) appears to be derived from the Müllerian duct, while the outer, more predominant layer myometrium appears to originate from non-Mullerian tissue, and is the major contractile tissue during parturition and abortion. Also, the junctional layer appears to function like a circular muscle layer, capable of peristaltic and anti-peristaltic activity, equivalent to the muscular layer of the intestines.

Perimetrium

The perimetrium (or serous coat of uterus) is the outer serosa layer of the uterus (Pic. 5), equivalent to peritoneum. It is embrionically derived from visceral peritoneum. Perimetrium consists of superficial mesothelium, and a thin layer of loose connective tissue beneath it. Posterior surface of the uterus is completely covered by the perimetrium, but anterior surface only partially.

Endometriosis

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Sources

Anatomy of the Female Reproductive System ―sourced from Lumen licensed under CC BY 4.0
Uterus ―sourced from Wikipedia licensed under CC BY-SA 3.0
Female Reproductive Anatomy ―sourced from Boundless licensed under CC BY-SA 4.0
Endometrium ―sourced from Wikipedia licensed under CC BY-SA 3.0
Myometrium ―sourced from Wikipedia licensed under CC BY-SA 3.0
Perimetrium ―sourced from Wikipedia licensed under CC BY-SA 3.0
Gray1167 ―by Mysid licensed under CC0 1.0
Endometrium ocp use3 ―by Nephron licensed under CC BY-SA 3.0
Uterus (myometrium) ―by Jpogi licensed under CC0 1.0
Illu cervix ―by unknown licensed under CC0 1.0
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