Corpus: Uterus

The uterus, or womb, is the female reproductive organ in which the fertilised eggs mature into an embryo or foetus before birth. All female mammals have a uterus.
The following discussion is limited to humans.

The uterus arises developmentally from two ducts (Müllerian duct) that fuse together. If this fusion is not complete, the uterus may have a more or less pronounced septum or, in rare cases, even be double (see anomalies).

The uterus is relatively small before puberty, then becomes approx. 5-10 cm in size and expands strongly upwards and to the sides during pregnancy. It can then extend above the navel. After childbirth, the muscles of the uterus contract strongly within a short period of time, causing the organ to shrink rapidly. After the menopause, the uterus becomes even smaller.

The shape of the uterus resembles an upside-down pear. At the upper end of the uterus, the fundus uteri, there are two lateral extensions, the fallopian tubes. The uterus is a muscular hollow organ approx. 7 cm long, 5 cm wide and weighing 30-120 g. Size and weight can understandably vary considerably depending on previous pregnancies.

The uterus can be divided anatomically into the following sections:

• Fundus uteri (uterine fundus)
• Corpus uteri (body of the uterus)
• Isthmus uteri (uterine isthmus)
• Cervix uteri (neck of the womb)
• Portio (cervix)

The inside of the uterus is called the uterine cavity or cavum uteri. It contains the lining of the uterus, the so-called endometrium.

Topographical anatomy[Bearbeiten]

Lagevarianten[Bearbeiten]

The position of the uterus in the pelvis depends on its supporting apparatus and the size and filling status of the rectum and bladder. The position of the uterus can be described using three terms:

• Flexio uteri: angle between the uterine body and the cervix
• Versio uteri: angle between the cervical canal and the longitudinal axis of the vagina
• Positio uteri: Position of the uterus on the imaginary connecting line through the two ischial spinae

The position of the uterus can vary greatly from person to person. If the uterus is bent forwards in relation to the cervix, this is referred to as "anteflexion". If the uterus is bent backwards, this is referred to as "retroflexion". Other positional variants are "anteversion" and "retroversion". The most common positional variant (normal variant) is anteversion-anteflexion.

Nachbarstrukturen[Bearbeiten]

The uterus has a topographical relationship to the following structures:

• ventral: Urinary bladder
• dorsal: intestine (rectum)
• lateral: pelvic vessels, the ovaries and the psoas major muscle
• caudal: pelvic floor

Peritoneal relationships[Bearbeiten]

The peritoneum extends from the urinary bladder to the anterior wall of the uterus, covers most of it and extends from the posterior wall of the uterus to the rectum. In the centre of these three organs, two peritoneal cavities are formed, which are known as the ventral vesicouterine cavity and the dorsal rectouterine cavity. The latter peritoneal cavity also forms the deepest point of the female peritoneal cavity (Douglas space) and protrudes directly above the posterior vaginal vault - formed by the vaginal portio with the vagina. It should be noted that the portio vaginalis uteri is free of peritoneum.

Containing apparatus[Bearbeiten]

The supporting apparatus of the uterus includes the connective tissue structures surrounding the uterus, which are summarised under the term "parametria", as well as the pelvic floor muscles caudally. The retaining ligaments (ligamenta) in the parametrium suspend the uterus from the pelvis.

• ventral: by the ligamentum teres uteri and the ligamentum vesicouterinum
• lateral: through the ligamentum latum uteri or the ligamentum cardinale
• dorsal: through the sacrouterine ligament and the rectouterine ligament

The pelvic floor muscles essentially ensure that the uterus does not descend. The levator ani muscle plays the most important role in this.

Vascular pathways[Bearbeiten]

Arterial supply[Bearbeiten]

The arterial supply is via the uterine artery, which arises as a visceral branch from the internal iliac artery. In the ligamentum latum it approaches the uterus at the level of the cervix and gives off branches to the vagina (vaginal rami). It then runs along the lateral lower edge with strong tortuosity and the release of numerous branches (arteriae helicinae), which are also tortuous, upwards to the fundus. Once there, it gives off a ramus tubarius to the uterine tube on both sides and an additional ramus ovaricus to the ovary. The latter anastomoses between the uterine artery and the ovarian artery. The tortuosity of the uterine artery makes it possible to adapt to changes in the size of the uterus during pregnancy.

Venous supply[Bearbeiten]

Venous drainage takes place via the highly developed uterine venous plexus. It often absorbs the blood draining from the vagina and then flows via the uterine veins into the internal iliac veins. An additional outflow into the ovarian plexus is also possible.

Nervous supply[Bearbeiten]

The inferior mesenteric plexus, together with the inferior hypogastric plexus, provides the sympathetic supply to the uterus. The fibres that originate from these nerve plexuses run to the organ via the large uterovaginal plexus (Frankenhäuser plexus, pelvic ganglion).

The parasympathetic fibres originate from S2-S4 and also reach the uterus via the uterovaginal plexus.

The parasympathetic nervous system is responsible for the contraction of the uterus, whereby it also has a vasodilating effect. The effect of the sympathetic nervous system is hormone-dependent and leads to contraction or relaxation depending on the situation.

Histologically, the uterus is made up of several layers. From the outside to the inside:

• Perimetrium (tunica serosa, peritoneal covering)
• Myometrium or tunica muscularis (muscle layer of smooth muscle)
• Endometrium (tunica mucosa, nidation mucosa)

The part of the uterus that protrudes into the abdominal cavity is surrounded by peritoneum, which is called the perimetrium in this area.

Outside of pregnancy, the muscle cells of the myometrium have a length of around 50 μm. The influence of pregnancy hormones and foetal growth lead to hyperplasia and hypertrophy of the smooth muscle cells, which can then reach a length of up to 800 μm.^[1]

The uterus provides the space for the development of the embryo or foetus. The uterine lining is built up and broken down in the monthly cycle under hormonal control. If fertilisation does not occur during this period, menstruation takes place.

If the egg cell (zygote) is fertilised and the embryo successfully implants (nidation), the uterine lining continues to grow and, together with the trophoblast, forms the placenta, which ensures that the growing embryo is nourished. It is expelled after birth as the so-called afterbirth.

During the complex processes of organogenesis for the development of a new life, malformations of the uterus can occur.

These anomalies can also affect the development of the other female reproductive organs. The uterus is formed by the fusion of the so-called Müller ducts (paramesonephric duct). An abnormal fusion can result in anomalies of the uterus:

• Uterus arcuatus - dented uterine fundus with a cavum uteri
• Uterus septus - The uterine cavity is divided into 2 parts by a septum
• Uterus didelphys - Double attachment of uterus, cervix and vagina
• Uterus bicornis unicollis - double uterine body with one cervix
• Uterus bicornis bicollis - Double uterus with fusion of the medial wall, double cervix, rarely also double vagina
• Uterus unicornis - Due to the absence of one of the two Müller ducts, only one horn of the uterus develops. A second horn may be rudimentary.

The examination of the uterus is the domain of gynaecology. A variety of methods are used.

• Palpation
  • Vaginal palpation of the cervix
  • Palpation of the uterus through the abdominal wall
• Colposcopy: examination of the cervix
• Sonography: examination using ultrasound
• Computed tomography
• Magnetic resonance imaging
• Laparoscopy

• Abnormal uterine bleeding (AUB)
  • Absent, too light or too infrequent menstruation
  • Menstruation that is too heavy, too frequent, too long or irregular
• Malformations (aplasia and dysplasia)
• Uterine fibroids
• Corpus carcinoma
• Cervical cancer ("cervical carcinoma")
• Prolapse

The ICD codes of some common diagnoses relating to the uterus are listed below:

• N85.0 Glandular endometrial hyperplasia
• N85.1 Adenomatous endometrial hyperplasia
• N85.2 Uterine hypertrophy
• N85.3 Uterine subinvolution
• N85.4 Positional anomaly of the uterus
• N85.5 Inversion of the uterus
• N85.6 Intrauterine synechiae
• N85.7 Haematometra
• N85.8 Other specified non-inflammatory diseases of the uterus
• N85.9 Non-inflammatory diseases of the uterus, unspecified
• N86 Erosion and ectropion of cervix uteri
• N87 Dysplasia of the cervix uteri

• Podcast image source: © Susan Wilkinson / Unsplash