Endometrium (from ancient Greek ἔνδο (ν) éndo (n) , German 'inside' and ancient Greek μήτρα mḗtrā , German 'uterus' ) or German uterine lining is a thin, pink-colored mucous membrane that forms the inner wall of the uterus (uterus). The endometrium is the place of implantation of the fertilized egg cell ( nidation or implantation). If no nest egg follows in primates which menstruation is repelled and excreted in which, inter alia, the upper layer of the endometrium. The uterine lining consists of an epithelium , glands ( glandulae uterinae ) and a supporting tissue ( stroma ) between the glands, which is equipped with numerous blood vessels .
The endometrium is subject to cyclical changes from sexual maturity. They are controlled by the hormonal regulation of ovulation ( ovulation ). This takes place on three levels: hypothalamus - pituitary gland - ovary . This is quite complex and takes place via longer and shorter feedback mechanisms. There are two main hormones that affect the endometrium: estrogen and progesterone (the most important representative of the progestins , which are also called luteal hormones). The endometrium builds up through increased estrogen production after menstruation and is converted under the additional influence of progesterone after ovulation, which is triggered by the luteinizing hormone (LH), so that a fertilized egg can implant. The time before ovulation is called the proliferation phase , the 14 following days are called the secretion phase .
In women of fertile age, the endometrium undergoes morphological and functional changes that are controlled by the release of sex hormones . This prepares the mucous membrane for implantation. Before puberty or after menopause , the cyclical hormonal influence is absent and the tissue does not undergo any changes. With menarche , the uterus prepares for each cycle to receive a fertilized egg. It does this through the growth and specialization (differentiation) of the endometrium during a menstrual cycle . In primates, the endometrium consists of an upper ( functionalis ) and a lower layer of cells ( basalis ).
The epithelium of the so-called functionalis increases in height before menstruation, the glands produce more secretions, the blood flow increases and so-called pseudo- or predecidual cells appear. Remains an implant, which functionalis of the endometrium is secreted in primates and eliminated: it comes to menstruation ( menstruation ). Decisive for the destruction of the cell layer is the withdrawal of progesterone, which in the case of implantation (also called nidation or nidation ) is continuously formed by the corpus luteum, which in turn is stimulated by the signal hormone human chorionic gonadotropin (HCG) from the embryo. This is why the functionalis in preparation for menstruation is also called decidua (Latin decidere , to fall off), more precisely decidua menstrualis .
If, on the other hand, a fertilized egg cell implants and a pregnancy occurs, extensive hormonally controlled modifications of the endometrium, which is now called decidua graviditatis , take place. In the form of the decidua capsularis , this encloses the embryo, more precisely its outer pericarp, the chorion . The decidua capsularis and chorion together arch further and further into the uterine lumen as the embryo grows , until finally the decidua capsularis fuses with the decidua of the opposite uterine walls. The decidua in the area where the egg cell originally attached to the uterine wall is called the decidua basalis . Together with the chorion, it forms the placenta .
Endometrium in non-primates
In other mammals, the endometrium is not shed cyclically, and menstruation does not occur. But there are also morphological and functional changes (proliferation phase and secretion phase) during the sexual cycle .
In ruminants , the endometrium has raised gland-free areas, the caruncles ( carunculae ). Only in the area of these caruncles does the placenta attach itself . The corresponding counterpart of the caruncle of the fetal part of the placenta is called the cotyledon. Caruncula and cotyledon are combined as a placentome.
- Johannes W. Rohen, Elke Lütjen-Drecoll: Functional Embryology - The Development of the Functional Systems of the Human Organism. 3rd, revised and expanded edition. Schattauer, Stuttgart / New York 2006, ISBN 978-3-7945-2451-8