The endometrium, or lining of the uterus, lines the inside of the uterus. It takes on an important role in the female cycle and in conception. From the first onset of menstruation until the end of menopause, its structure and function are influenced by hormones such as estrogen and progesterone.
What is a uterine lining?
The endometrium is the innermost layer of the uterus, which consists of glands, interstitial tissue and covering tissue. While the uterus is the organ in which the embryo develops and grows, the actual implantation of the fertilized egg takes place in the endometrium. Through processes that have not yet been fully elucidated, the cells of the endometrium interact with the outer cell layer of the fertilized egg, leading to implantation and thus the beginning of pregnancy. In addition, the placenta, egg membrane and umbilical cord are formed by these processes taking place at the cellular level. The activity of the endometrium is controlled by hormones that influence its formation and degradation. If no implantation of a fertilized egg has occurred during the fertile days, the built-up endometrium is shed and menstruation occurs. During pregnancy, the implantation of the embryo and the remodeling of the uterus result in a different anatomical division of the endometrium. This is then called the “decidua” and is divided into four areas.
Anatomy and structure
The endometrium consists of
- Tubular, mucus-forming glands called the glandulae uterinae
- From the interstitial tissue (stroma), which is located between the glandulae uterinae and functions as a supporting tissue.
- And from the single-layered covering tissue, the epithelium , which serves to protect the mucosa both from external pressure and bacteria.
The endometrium is divided into two parts, the stratum basale and the stratum functionale . Only the latter is built up during the menstrual cycle by the influence of the hormone estrogen and is shed with menstruation. During pregnancy, the areas of the endometrium are defined as follows: The decidua basalis is located near the fusion point of the embryo and endometrium. Its outer edge is called the decidua marginalis. The decidua capsularis envelops the embryo in the egg membrane and at the beginning of pregnancy is still separated from the decidua paterialis , the rest of the endometrium, by free space in the uterus. After a while, however, the embryo is large enough to completely fill the uterus. Then the decidua capsularis and decidua parietalis are adjacent to each other.
Function and tasks
The implantation of the fertilized egg takes place at the endometrium. This process is also called nidation. The endometrium is prepared for nidation during the cycle by estrogen produced by the fallopian tube during what is called the proliferation phase. Once fertilization has occurred, the fertilized egg approaches the endometrium, which is highly built up at this point in the cycle. Upon contact, the outer part of the zygote, called the trophoblast, begins to develop into two layers of cells. The inner one begins to form the placenta, which will later provide nutrition for the embryo. The outer one invades the endometrium, beginning its transformation into the decidua. The trophoblast also begins to form the amniotic sacs after implantation. Thus, the endometrium serves to “receive” the fertilized egg and is the point where the zygote connects with the mother’s organism. Here, in addition to the placenta, the umbilical cord is formed, which ensures the supply of the embryonic metabolism and its oxygen supply. With the complete enclosure of the germ by the endometrium and thus the formation of the egg cavity, the implantation process is completed. Since the function of the endometrium is to accommodate the embryo and connect the maternal organism with the embryonic organism, it is no longer subject to any changes due to hormonal influences before puberty and after menopause, since conception cannot occur at these times.
Complaints and diseases
Endometritis is the term used to describe inflammation of the endometrium caused by vaginally invading bacteria. Symptoms of endometritis include fever and pressure pain. It can usually be treated with broad-spectrum antibiotics.The causative germ transmission for endometritis usually occurs during delivery or during a vaginal examination by a physician. Endometrial carcinoma is a cancer of the endometrium. It occurs mainly in women after the menopause. The only symptom is usually bleeding or other discharge. Traditionally dismissed as a “woman’s disease,” particularly severe menstrual cramps can be a sign of endometriosis. In this disease, endometrial lesions proliferate outside the uterus and cause symptoms there. Endometriosis also often means limited fertility. Endometriosis lesions can settle unfavorably and clog fallopian tubes. Endometriosis is present in about 30% of women with an unfulfilled desire to have children. Other symptoms may include severe pain that also radiates to the legs or back, as well as pain during sexual intercourse and when going to the toilet. Ovarian cysts are often formed and can be seen on ultrasound. However, since there are other causes of cysts, a definite diagnosis can only be made through diagnostic surgery, for example in the form of a minimally invasive laparoscopy. Neither causes of endometriosis nor definitive cures are known. The growths can be surgically removed, which is usually followed by about six months of hormone treatment. In some patients the treatment is successful, in others the growths recur. Patients without a desire to have children may achieve freedom from symptoms by continuing to take hormones, but may have to contend with side effects.
