The decidua is the modified mucosal lining of the

uterus The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ...

(that is, modified endometrium) that forms every month, in preparation for

pregnancy Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occurs by sexual intercourse, but ca ...

. It is shed off each month when there is no fertilised egg to support. The decidua is under the influence of progesterone. Endometrial cells become highly characteristic. The decidua forms the maternal part of the

placenta The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mate ...

and remains for the duration of the pregnancy. After birth the decidua is shed together with the placenta.

Structure

The part of the decidua that interacts with the

trophoblast The trophoblast (from Greek : to feed; and : germinator) is the outer layer of cells of the blastocyst. Trophoblasts are present four days after fertilization in humans. They provide nutrients to the embryo and develop into a large part of the p ...

is the ''decidua basalis'' (also called ''decidua placentalis''), while the ''decidua capsularis'' grows over the

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

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 The myometrium is the middle layer of the uterine wall, consisting mainly of uterine smooth muscle cells (also called uterine myocytes) but also of supporting stromal and vascular tissue. Its main function is to induce uterine contractions. Struc ...

(''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. This layer is absent in

placenta accreta Placenta accreta occurs when all or part of the placenta attaches abnormally to the '' myometrium'' (the muscular layer of the uterine wall). Three grades of abnormal placental attachment are defined according to the depth of attachment and invas ...

The decidua has a

histologically Histology, also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures vis ...

-distinct appearance, displaying large polygonal

decidual cells Before the fertilized ovum reaches the uterus, the mucous membrane of the body of the uterus undergoes important changes and is then known as the decidua. The thickness and vascularity of the mucous membrane are greatly increased; its glands are el ...

in the stroma. These are enlarged endometrial stromal cells, which resemble

epithelium Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...

(and are referred to as "epithelioid").

Decidualization Decidualization is a process that results in significant changes to cells of the endometrium in preparation for, and during, pregnancy. This includes morphological and functional changes (the decidual reaction) to endometrial stromal cells (ESCs), ...

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 Fibronectin is a high- molecular weight (~500-~600 kDa) glycoprotein of the extracellular matrix that binds to membrane-spanning receptor proteins called integrins. Fibronectin also binds to other extracellular matrix proteins such as collage ...

and

laminin Laminins are a family of glycoproteins of the extracellular matrix of all animals. They are major components of the basal lamina (one of the layers of the basement membrane), the protein network foundation for most cells and organs. The laminins ...

(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 B cells are scant. The large granular lymphocytes (

CD56 Neural cell adhesion molecule (NCAM), also called CD56, is a homophilic binding glycoprotein expressed on the surface of neurons, glia and skeletal muscle. Although CD56 is often considered a marker of neural lineage commitment due to its discove ...

bright) are called

uterine natural killer cells Uterine natural killer cells make up approximately 70% of maternal lymphocytes during pregnancy, occupying both the decidua basalis of the endometrium at the implantation site and the mesometrial lymphoid aggregate of pregnancy (MLAp) that surrou ...

, (uNK cells).

Development

After

ovulation Ovulation is the release of eggs from the ovaries. In women, this event occurs when the ovarian follicles rupture and release the secondary oocyte ovarian cells. After ovulation, during the luteal phase, the egg will be available to be fertilize ...

, in

placental mammal Placental mammals (infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguishe ...

s, the endometrial lining becomes hypertrophic and vascular under the influence of the

sex hormone Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormones that interact with vertebrate steroid hormone receptors. The sex hormones include the androgens, estrogens, and progestogens. Their effect ...

estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal ac ...

and progesterone. In animals exhibiting

hemochorial placentation Placentation refers to the formation, type and structure, or arrangement of the placenta. The function of placentation is to transfer nutrients, respiratory gases, and water from maternal tissue to a growing embryo, and in some instances to remov ...

, the endometrium undergoes

decidualization Decidualization is a process that results in significant changes to cells of the endometrium in preparation for, and during, pregnancy. This includes morphological and functional changes (the decidual reaction) to endometrial stromal cells (ESCs), ...

following implantation. If implantation does not occur, the secretory lining will be absorbed (

estrous cycle The estrous cycle (, originally ) is the set of recurring physiological changes that are induced by reproductive hormones in most mammalian therian females. Estrous cycles start after sexual maturity in females and are interrupted by anestro ...

) or shed ( menstrual cycle). The decidua is shed with the placenta during

birth Birth is the act or process of bearing or bringing forth offspring, also referred to in technical contexts as parturition. In mammals, the process is initiated by hormones which cause the muscular walls of the uterus to contract, expelling the f ...

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 The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinte ...

. Further, the decidua has to allow a very controlled invasion of the trophoblast. In invasive placental disorders like

decidualization have been consistently found to be deficient.

Hormone production

The decidua secretes hormones,

growth factor A growth factor is a naturally occurring substance capable of stimulating cell proliferation, wound healing, and occasionally cellular differentiation. Usually it is a secreted protein or a steroid hormone. Growth factors are important for regul ...

s, and

cytokine Cytokines are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are peptides and cannot cross the lipid bilayer of cells to enter the cytoplasm. Cytokines have been shown to be involved in autocrin ...

s. It has receptors for

, progesterone,

growth hormone Growth hormone (GH) or somatotropin, also known as human growth hormone (hGH or HGH) in its human form, is a peptide hormone that stimulates growth, cell reproduction, and cell regeneration in humans and other animals. It is thus important in h ...

, and others. Among its products are hormones commonly associated with other organs such as cortisol, CRF,

GnRH Gonadotropin-releasing hormone (GnRH) is a releasing hormone responsible for the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary. GnRH is a tropic peptide hormone synthesized and releas ...

prolactin Prolactin (PRL), also known as lactotropin, is a protein best known for its role in enabling mammals to produce milk. It is influential in over 300 separate processes in various vertebrates, including humans. Prolactin is secreted from the pit ...

, and

relaxin Relaxin is a protein hormone of about 6000 Da first described in 1926 by Frederick Hisaw. The relaxin family peptide hormones belong to the insulin superfamily and consists of seven peptides of high structural but low sequence similarity; rela ...

. Decidual prolactin is not under dopaminergic control. Insulin-like growth factor-binding protein 1 (IGFBP1) also called placental protein 12, and

PAEP Glycodelin (GD) also known as human placental protein-14 (PP-14) progestogen-associated endometrial protein (PAEP) or pregnancy-associated endometrial alpha-2 globulin is a glycoprotein that inhibits cell immune function and plays an essential ...

(glycodelin) appear to be specific products of the secretory and decidual lining. Other factors released include

interleukin-15 Interleukin-15 (IL-15) is a cytokine with structural similarity to Interleukin-2 (IL-2). Like IL-2, IL-15 binds to and signals through a complex composed of IL-2/IL-15 receptor beta chain (CD122) and the common gamma chain (gamma-C, CD132). IL- ...

and

vascular endothelial growth factor Vascular endothelial growth factor (VEGF, ), originally known as vascular permeability factor (VPF), is a signal protein produced by many cells that stimulates the formation of blood vessels. To be specific, VEGF is a sub-family of growth factors, ...

(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 The peritoneum is the serous membrane forming the lining of the abdominal cavity or coelom in amniotes and some invertebrates, such as annelids. It covers most of the intra-abdominal (or coelomic) organs, and is composed of a layer of meso ...

and ovary during a pregnancy, and represents a response of stromal tissue to progesterone. *Decidua in a lymph node may mimic

metastatic Metastasis is a pathogenic agent's spread from an initial or primary site to a different or secondary site within the host's body; the term is typically used when referring to metastasis by a cancerous tumor. The newly pathological sites, then, ...

carcinoma.

Clinical significance

A long-lasting

infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dis ...

of the decidua,

chronic deciduitis Chronic deciduitis is a type of long-lasting inflammation that arises in pregnancy and affects the endometrial stromal tissue (decidua). It is associated with preterm labour. The diagnosis rests primarily on the presence of plasma cells. Image ...

, is associated with pre-term labour. File:Chronic deciduitis - intermed mag.jpg,

Micrograph A micrograph or photomicrograph is a photograph or digital image taken through a microscope or similar device to show a magnified image of an object. This is opposed to a macrograph or photomacrograph, an image which is also taken on a mic ...

H&E stain Hematoxylin and eosin stain ( or haematoxylin and eosin stain or hematoxylin-eosin stain; often abbreviated as H&E stain or HE stain) is one of the principal tissue stains used in histology. It is the most widely used stain in medical diagnos ...

. File:Histopathology of acute choriodeciduitis.jpg, Acute choriodeciduitis, with

neutrophil Neutrophils (also known as neutrocytes or heterophils) are the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. They form an essential part of the innate immune system, with their functions varying ...

s seen in the chorion and decidua.

History

The word comes .

Additional images

File:Gray39.png, Scheme of placental circulation.

References

External links

* * {{Authority control Mammal female reproductive system Obstetrics Midwifery