The decidua is the modified mucous membrane of the uterus (that is, modified endometrium) that forms every month, in preparation for pregnancy. It is shed off each month when there is no fertilized egg to support.
Structure
The part of the decidua that interacts with the
trophoblast is the
decidua basalis (also called
decidua placentalis), while the
decidua capsularis grows over the
embryo on the luminal side, enclosing it into the endometrium. The remainder of the decidua is termed the
decidua parietalis or
decidua vera, and it will fuse with the decidua capsularis by the fourth month of gestation.
Three morphologically distinct layers of the decidua basalis can then be described:
-
Compact outer layer ( stratum compactum)
-
Intermediate layer ( stratum spongiosum)
-
Boundary layer adjacent to the myometrium ( stratum basalis)
Within the decidua, occasional fibrinoid deposits form where the syncytiotrophoblast is damaged. The region of fibrinoid deposition where trophoblasts meet the compact portion of the decidua basalis is called
Rohr's layer, while the fibrinoid deposits that occur between the compact and spongy layer of the decidua basalis is termed
Nitabuch's layer (for
Raissa Nitabuch). This layer is absent in
placenta accreta.
of decidualized
endometrium due to
exogenous progesterone. H&E stain.]]
The decidua has a
histology-distinct appearance, displaying large polygonal
decidual cells in the stroma. These are enlarged endometrial stromal cells, which resemble
epithelium (and are referred to as "epithelioid").
Decidualization includes the process of differentiation of the spindle-shape stromal fibroblasts into the plump secretory decidual cells, which create a pericellular extracellular matrix rich in fibronectin and laminin (similar to epithelial cells).
Vascularity, as well as vascular permeability, is enhanced in the decidualizing endometrium.
Its leukocyte population is distinct, with the presence of large endometrial granular leukocytes being predominant, while polynuclear leukocytes and are scant.
The large granular lymphocytes (CD56 bright) are called uterine natural killer cells (uNK cells).
Development
After
ovulation, in
, the endometrial lining becomes hypertrophic and vascular under the influence of the
,
estrogen and
progesterone.
In animals exhibiting hemochorial placentation, the endometrium undergoes decidualization following implantation. If implantation does not occur, the secretory lining will be absorbed (estrous cycle) or shed (menstrual cycle).
The decidua is shed with the placenta during birth.
Function
As the maternal interface to the embryo the decidua participates in the exchanges of nutrition, gas, and waste with the gestation. It also protects the pregnancy from the maternal
immune system. Further, the decidua has to allow a very controlled invasion of the trophoblast.
In invasive placental disorders like placenta accreta decidualization have been consistently found to be deficient.
Hormone production
The decidua secretes
hormones,
, and
. It has receptors for
estrogen,
progesterone,
growth hormone, and others.
Among its products are hormones commonly associated with other organs such as cortisol, CRF, GnRH, prolactin, and relaxin. Decidual prolactin is not under control.
Insulin-like growth factor-binding protein 1 (IGFBP1) also called placental protein 12, and PAEP (glycodelin) appear to be specific products of the secretory and decidual lining.
Other factors released include interleukin-15 and vascular endothelial growth factor (VEGF). A reasonable understanding of the role and interplay of these hormones and factors has not been evolved.
Other
-
In case of an ectopic pregnancy, the endometrium nevertheless becomes decidualized. A woman may shed the lining in the form of a decidual cast, which may be mistaken as a miscarriage, when, in fact, the ectopic pregnancy still persists.
-
A decidual reaction can be observed in tissue of the peritoneum and ovary during a pregnancy, and represents a response of stromal tissue to progesterone.
-
Decidua in a lymph node may mimic metastasis carcinoma.
Clinical significance
A long-lasting
infection of the decidua, chronic deciduitis, is associated with
preterm birth.
of chronic deciduitis. H&E stain.]]
seen in the chorion and decidua.]]
Etymology
The word comes .
==Additional images==
External links
