Uterus – Structure and Function of the Uterus

The uterus is essential for reproduction in humans and mammals. Fertilized eggs implant in the uterus during their early embryonic stage. The fetus remains there until it is developed enough to leave the mother’s body. The uterus serves to protect and nourish the fetus during its development.

The uterus is a muscular organ. During labor, it plays a key role in enabling the baby to pass through the mother’s pelvis and exit her body.

Where is the uterus located?

In the human body, the uterus is located in the center of the female lower abdomen. The front part rests on the bladder, and the back part borders the rectum.

The uterus and these two neighboring organs are entirely covered by the peritoneum. This creates peritoneal recesses between the individual organs. The exact position of the uterus depends on how full the rectum and bladder are at any given time.

To prevent the uterus from slipping downward due to gravity, it is anchored in the pelvis. This is achieved by

• the round ligaments,
• a ligament extending toward the pelvic wall, and
• the so-called parametrium.

The parametrium is a frontal plate consisting of connective tissue. It is reinforced by several ligaments, including those extending toward the sacral hố. These ligaments hold the uterus in a flexible, suspended position, which is supported by the pelvic muscles.

What does the uterus look like, and how is it structured?

The uterus is a hollow organ shaped like an upside-down pear. The weight of the uterus ranges from 30 to 120 grams. There are also considerable variations in size. Typically, the uterus is about seven centimeters long, three centimeters thick, and five centimeters wide.

During pregnancy, its dimensions change dramatically. Shortly before birth, it is comparable in size to two small soccer balls. The weight of the muscle mass alone increases to approximately 500 grams. No other human organ is capable of such a massive transformation.

The anatomical structure of the uterus is roughly divided into two parts:

• the body of the uterus (corpus uteri) with the uterine cavity and
• the cervix (cervix uteri) with the cervical os.

The body of the uterus, accounting for about two-thirds of the total volume, is by far the largest part of the uterus. At its upper end, the corpus uteri terminates at the fundus uteri and transitions into the fallopian tubes. The fallopian tubes connect the uterus to the ovaries.

The uterine wall consists of three layers. The outer layer is surrounded by the peritoneum and connective tissue. The middle layer consists of strong muscle tissue. The inner layer is a mucous membrane, the endometrium. This is where fertilized eggs implant.

The endometrium is constantly renewing itself. If pregnancy does not occur, the endometrium is shed during menstruation.

However, if a fertilized egg has implanted, the uterine lining contributes to the formation of the placenta. In this case, it is expelled after birth along with the placenta as the afterbirth.

Between the cervix and the body of the uterus lies the isthmus, which is approximately five to ten millimeters long. It is also particularly narrow.

The lower part of the organ is formed by the cervix (cervix uteri). It encloses the cervical canal, the canalis cervicis. This canal begins at the external os, which protrudes into the vagina. It ends at the internal os. The os is the inner part of the cervical canal. With a diameter of about three millimeters, it is by far the narrowest point of the canalis cervicis.

Size of the uterus in a woman in late pregnancy © turhanerbas | AdobeStock

About 70 percent of all women experience a uterine condition—usually benign—at some point in their lives. Fibroids and polyps are the most common.

Fibroids and polyps

Fibroids develop from the muscle tissue of the uterus. The hormones estrogen and progesterone have a major influence on the growth of these tumors. For this reason, tumors generally do not form before the onset of puberty.

Fibroids are most common in women over 30. In many cases, they shrink with the onset of menopause. Often, fibroids go undetected because they do not cause any symptoms. In such cases, treatment is not necessary.

Sometimes, however, fibroids do cause symptoms, such as

• menstrual problems,
• difficulty urinating,
• pain in the lower abdomen or during sexual intercourse,
• impaired fertility, and
• a deficiency in red blood cells.

Polyps develop from the lining of the uterus or the cervix. In this case as well, doctors attribute their growth to the influence of hormones.

Polyps usually occur before the onset of menopause and during menopause. Between 3 and 16 percent of women are affected by polyps. If you experience heavy bleeding or cramp-like pain, polyps may be the cause.

Uterine and Cervical Cancer

Unlike benign fibroids and polyps, carcinomas are malignant.

They most often develop in the cervix (cervical cancer) and, less commonly, directly in the uterine body (endometrial cancer).

Depending on the stage of the cancer, it can also spread to other organs. These metastases require complex treatments, such as

• surgery,
• radiation therapy, or
• chemotherapy.

Regular participation in screening exams is therefore very important.

Functional Cysts

Cysts are cavities in the tissue that become encapsulated. These cysts may contain tissue fluid, pus, or blood. As long as they do not rupture, cysts do not usually cause any health problems.

Problems can arise if the cysts form on the ovaries or in other sensitive areas. Ovarian cysts can also twist on their stalk, which can cause severe abdominal pain. In such cases, as well as in the event of a cyst rupture (when the cyst bursts), an urgent laparoscopy is required. Cysts are usually detected via ultrasound.

Often, a disruption in the hormonal cycle is the trigger for their development. This explains why cysts occur exclusively in women of reproductive age. In addition to menstrual irregularities, functional cysts can also cause pain during certain movements, depending on their location.

PCOS

Polycystic ovaries, also known as PCOS, are a hormonal disorder. They are caused by structural abnormalities and impaired function of the ovaries. They occur in up to 12 percent of all women of childbearing age. 

The cause is a disorder that leads to elevated levels of androgen hormones. This results in fertility problems and menstrual cycle irregularities.

Symptoms of PCOS include

• excessive hair loss,
• acne, and
• a lack of ovulation.

At the same time, numerous small cysts develop on the ovaries, which can be detected by ultrasound.

Endometriosis and Adenomyosis

Endometriosis is also one of the more common conditions affecting the internal reproductive organs. Up to 15 percent of all women are affected by this often painful condition.

Endometriosis is defined as the growth of the endometrium outside the uterine cavity. The endometrium spreads to the peritoneum, the intestines, or the ovaries. In some cases, the vaginal wall is also affected by this uncontrolled growth of the endometrium. In rare cases, other organs outside the abdominal cavity may also be affected. 

Endometriosis often progresses without any symptoms. However, many women with the condition suffer from

• cramps and
• persistent pain in the lower abdomen

during menstruation. In addition, there may occasionally be back pain and pain during sexual intercourse. The unchecked growth of the endometrial tissue can lead to reduced fertility.

Endometriosis is often accompanied by a condition known as adenomyosis. This involves the ingrowth of endometrial-like tissue into the muscular wall of the uterus. This often results in particularly painful menstrual bleeding or breakthrough bleeding. If endometriosis is suspected, an early laparoscopy is recommended.

The uterus is a central organ and part of the female reproductive system; it is a pear-shaped, muscular, hollow organ. Its structure and function show that the uterus consists of various sections, such as the body of the uterus and the cervix, which forms an important connection to the vagina.

The fertilized egg implants inside the uterus, where the fetus develops during pregnancy, and the uterus provides optimal conditions for this process. During pregnancy, the organ grows significantly, even though the uterus weighs only a few grams in its initial state. The position of the uterus describes its location within the pelvis; it is usually tilted slightly forward relative to the cervix, although the uterus may shift downward.

Anatomically, the upper two-thirds of the uterus constitute the main body, while variations such as a bicornuate or bicollis uterus may occur, and the uterus exhibits individual differences. In addition, the uterus and the ovaries are functionally connected, with part of the uterus working closely with other structures and regressing after childbirth. Uterine disorders can cause symptoms ranging from mild discomfort to severe pain, which is why, in some cases, a hysterectomy may be necessary if problems cannot be treated otherwise.