Table of Contents
5. A New Theory: Endometriosis is a disease pertaining to the archimetra.
5.2 Functions of the archimetra
5.1 The archimetra
The uterus is composed of several layers. Starting from the inside, it consists of the surface epithelium of the mucous tissue (epithelial endometrium), the connective tissue of the mucous tissue (endometrial stroma), and of three separate muscle layers. The innermost muscle stratum consists of layers of muscle fibres aligned in circular form (stratum subvasculare); the middle stratum, making up the bulk of the muscle, consists of short muscle bundles in three-dimensional alignment (stratum vasculare), the outer stratum (stratum supravasculare) consisting of layers of muscles fibres running the length of the uterus axis (Figure 1; Table 1).
The endometrial-subendometrial unit or archimetra
Figure 1: The human uterus consists of several layers. Starting from the inside: The epithelial endometrium (green); the endometrial stroma (orange); the subvascular layer with the mainly circular muscle fibres (shaded orange). These three layers compose the archimetra. It is developed at a very early stage in the embryo by fusion of "Mueller's ducts". This fusion entails development of a zone where muscle fibres cross, forming the so-called fundo-cornual raphe. The raphe is positioned along the centre line where the circular muscle fibres of the middle section strive apart into the two uterine horns (cornua uteri), continuing into the fibres of the tubes. The archimetra is a functional unit controlled by the ovary and consisting of the endometrium and the subendometrial muscles.
The middle layer of muscles, the vascular stratum (blue), consists of short, three-dimensional muscle bundles, and the outer layer, the supravascular stratum (blue) of mainly longitudinally aligned muscle fibres. The blue layers form the neometra. The red section is the portio vaginalis (the part reaching into the vagina) of the uterus with the external mouth of the uterus.
The different layers of the uterus are best depicted with high-resolution ultrasonography (Figure 2) and with magnet resonance imaging (Figure 3). The subendometrial myometrium or the subvascular stratum, i.e. the muscular part of the archimetra, appears therein as a hypodense zone (the so-called "halo"), surrounding the mucous tissue from the cervix to the back of the uterus.
|Layers of the human uterus|
Table 1: A tabular list depicting the individual layers of the uterine wall. The archimetra consists of the endometrium with its epithelial and stroma sections as well as of the innermost muscle layer with circular fibres, the subvascular stratum. The neometra consists of the vascular stratum with short, three-dimensional muscle bundles, the external layer being constituted by the supravascular stratum with its longitudinal fibres.
Figure 2: A longitudinal section through the uterus, depicted in an ultrasonography. The endometrium in the middle emits intensive signals and is therefore light. The subvascular stratum emits only little echo, surrounding the mucous tissue like a dark halo. The vascular stratum gives off intensive signals, while the outer, supravascular stratum is recognisable as a dark seam giving weaker signals.
Figure 3: Picture of the uterus in the middle sagittal plane (longitudinal section) as shown by magnetic resonance imaging. The endometrium and vascular stratum emit intensive signals, whereas those emitted by the subvascular stratum are weak, forming a halo around the endometrium similar to that shown in the vaginal sonography. The signals from the outer layer of longitudinal muscles (supravascular stratum) are of medium intensity.
The term archimetra is used for that part of the uterus consisting of the epithelial and connective mucous tissue together with the innermost muscle layer, the circular subvascular stratum. The word "archimetra" expresses the fact that these layers of the uterus exist already in very primitive, land-living vertebrates and are formed at a very early stage in the development of the human embryo. This means that they are very old in the philogenetic and ontogenetic sense (in the development of the species and of the individual human being) (Tables 2 and 3).
|Phylogenetic development of the uterus muscles|
|Species||Muscle layer (stratum)||Manner of giving birth|
|Duck-billed platypus||subvascular||¬†||¬†||egg deposit|
Table 2: The subvascular stratum is the phylogenetically oldest muscle layer of the uterus. The external muscle layers were added when animals began to give birth to living young (viviparity). As humans require particular strength to give birth, this gave rise to the development of the middle vascular stratum, which makes up the main mass of the myometrium in humans.
Table 2 shows that all vertebrates are equiped with the subvascular stratum. The external muscle layer appears in animals along with viviparity, and it is only in humans (probably also in other primates) that the connective tissue in the vascular stratum becomes transformed into the middle muscle layer composing the bulk of the muscular wall. As these two outer muscle layers appear so late in the course of our phylogenetic and ontogenetic development, this part of the uterus is called neometra.
This brief dip into our genetic history makes it evident that the human uterus is composed of two different organs, the inner archimetra and the outer neometra (Figure 1). The two have different functions in the reproductive process. 5. A New Theory: Endometriosis is a disease pertaining to the archimetra.
5.2 Functions of the archimetra