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The main functions of the uterus are receiving the embryo, sheltering the fetus during pregnancy and delivering the newborn at term. The uterus is a pear-shaped, muscular, hollow organ with a triple-layered wall: an outer tunica serosa, the perimetrium, a thick tunica muscularis, the myometrium, and an inner tunica mucosa, the endometrium. The endometrium is the layer in which the implantation takes place. This layer experiences morphologic and functional changes that are closely associated with the cyclic release of sexual hormones. In absence of periodic hormonal influence, i.e., before puberty or following menopause, this tissue has a constant morphology and thickness. Following the menarche the uterus prepares itself in each menstrual cycle for receiving a fertilized oocyte. This takes place via the proliferation and differentiation of the endometrium. If the implantation does not occur, the functional (outermost) layer of the endometrium is shed and expulsed, leading to menstruation.

Fig. 1 - Schematic drawing of the uterus (frontal section)

Uterine body (Corpus uteri)
Uterine cavity (Cavitas uteri)
Uterine cervix (Cervix uteri)
Cervical canal (Canalis cervicis)
Isthmus of the tube
Interstitial segment
Fallopian tube
Single-layered prismatic epithelium of the uterine body
Single-layered cylindric epithelium of the cervical canal

Fig. 1

The endometrium of the uterine body (A) consists of a single-layered prismatic surface epithelium, penetrating into the underlying connective tissue and thus forming tubular glands (glandulae uterinae). The epithelium has 3 types of cells: secretory (that secrete glycogen), ciliated, and basal cells.

The endometrium of the cervical canal (B) consists of a simple cylindrical surface epithelium with basal cells, cilia-carrying cells and secretory cells (mucous-producing). This epithelium invaginates into the underlying connective tissue forming branched glands (glandulae cervicales).

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The uterus consists of two anatomically different sections: the uterine body (corpus uteri with the uterine cavity), which is coated on the inside by a tunica mucosa, as well as the uterine cervix (with the cervical canal), which is also coated with a tunica mucosa.

The mucosa of the uterine body, the endometrium, has a cell-rich connective tissue that surrounds the uterine glands The uterine epithelium consists of a single-layered prismatic epithelium that has three different types of cells: secretory cells (glycogen), cells with cilia, and basal cells. In each menstruation cycle the superficial functional layer of the endometrium is shed and reconstituted out of the underlying basal layer.

Functional anatomy of the endometrium

The endometrium consists of a single-layered prismatic epithelium with or without cilia (depending on how far along the menstruation cycle is) and its basal lamina, uterine glands, and a specialized, cell-rich connective tissue (stroma) containing a rich supply of blood vessels. One recognizes the spiral arteries (end branches of the uterine arteries as well as a venous outflow system.

Fig. 2 - Schematic drawing of the endometrium

  1. Single-layered prismatic epithelium
  2. Basal lamina
  3. Uterine glands (glandulae uterinae)
  4. Connective tissue
  5. Blood vessels

Fig. 3 - Endometrium
secretory phase

Superficial, functional layer
Basal layer

Fig. 2, 3

Schematic drawing of the superficial functional and basal layer of the endometrium as well as the uterine glands and the myometrium.
In the inset, the cells of the single layered prismatic epithelium, the basal lamina and the blood vessels are shown enlarged. Note that a few glands reach into the myometrium. A regeneration, e.g., after a curettage, is thereby ensured.

Fig. 3

Endometrial functions

  • Cyclic alterations of the uterine glands and blood vessels during the course of the menstruation, as preparation for the implantation
  • Location where the blastocyst is normally implanted
  • Location where the placenta develops