What is Decidua?
The term
decidua refers to the modified mucosal lining of the uterus (endometrium) during pregnancy. This transformation occurs post-implantation of the blastocyst, facilitating the establishment and maintenance of pregnancy. The decidua is an essential component in maternal-fetal interactions and plays a crucial role in the nourishment and protection of the developing embryo.
Types of Decidua
The decidua can be classified into three main regions based on their location relative to the implanted embryo:-
Decidua Basalis: This is the part of the endometrium directly beneath the implanted embryo. It contributes to the formation of the maternal part of the placenta, playing a key role in nutrient exchange.
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Decidua Capsularis: This portion of the decidua surrounds the embryo and encapsulates it. As the embryo grows, the decidua capsularis eventually fuses with the decidua parietalis.
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Decidua Parietalis: The remaining part of the decidua lining the rest of the uterine cavity. It provides structural support to the uterus during pregnancy.
Histological Structure of Decidua
Under microscopic examination, the decidua exhibits distinct histological features:- Decidual Cells: These are enlarged, polygonal cells derived from the endometrial stromal cells. They are rich in glycogen and lipids, providing nutritional support to the embryo.
- Vascularization: The decidua is highly vascularized, with numerous spiral arteries supplying blood to the developing placenta. This ensures adequate oxygen and nutrient supply to the embryo.
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Leukocytes: Decidua contains various immune cells, including
decidual natural killer cells and macrophages, which play roles in immune tolerance and protection against pathogens.
Functions of the Decidua
The decidua performs several vital functions during pregnancy:- Nutrient Supply: Decidual cells store glycogen and lipids, which are utilized by the embryo for growth and development.
- Immune Tolerance: The decidua creates an immunologically privileged site by regulating maternal immune responses to tolerate the semi-allogeneic fetus.
- Structural Support: It provides mechanical support to the uterus, accommodating the growing embryo and ensuring proper implantation and placental development.
Decidualization Process
Decidualization is the transformation of endometrial stromal cells into decidual cells. This process is triggered by hormonal signals, primarily progesterone, following ovulation and is further stimulated by the presence of the implanting embryo. Decidualization involves:- Cellular Changes: Stromal cells enlarge, accumulate glycogen, and transform into polygonal decidual cells.
- Angiogenesis: Increased vascularization occurs to support the growing needs of the embryo.
- Immune Modulation: There is an influx of immune cells, which are crucial for maintaining a balanced immune environment.
Clinical Relevance
Understanding the histology of the decidua has significant clinical implications:- Implantation Failure: Abnormalities in decidualization can lead to implantation failure, resulting in infertility or early pregnancy loss.
- Preeclampsia: This pregnancy complication is associated with poor decidualization and inadequate spiral artery remodeling, leading to insufficient blood flow to the placenta.
- Placenta Accreta: In this condition, the decidua basalis is deficient, causing the placenta to abnormally adhere to the myometrium, leading to complications during delivery.
Conclusion
The decidua is a critical component of the uterine lining during pregnancy, with specialized histological features and functions that support embryo implantation and development. Understanding its structure and function is essential for comprehending various aspects of reproductive health and managing pregnancy-related complications.
