After the fertilized ovum has implanted itself, the endometrium is known as:
A. Perimetrium
B. Decidua
C. Myometrium
D. All above
Correct Answer: B. Decidua
Explanation: After the fertilized ovum (blastocyst) implants into the uterine lining, the endometrium undergoes transformation and is then called the Decidua .
Specifically:
• The portion of the endometrium directly beneath the implanted embryo becomes the decidua basalis (forms the maternal part of the placenta).
• The portion that covers the embryo becomes the decidua capsularis .
• The remaining endometrium lining the rest of the uterus is the decidua parietalis (or decidual vera).
So the correct anatomical/physiological term for the post-implantation endometrium is decidua.
This term is used in medical and embryology textbooks (e.g., Langman’s Medical Embryology, Moore’s The Developing Human) from the time of implantation until the placenta is fully formed and the decidua is shed at parturition.
Other Options Details:
Here are the descriptions of all the options in the context of the uterus (these are the three main histological layers of the uterine wall):
A. Perimetrium
• The outermost layer of the uterus.
• It is a thin serous (serosal) layer composed of simple squamous epithelium (mesothelium) and a thin layer of loose connective tissue.
• It is continuous with the peritoneal covering of the pelvic cavity (also called the serosa of the uterus).
• Function: Provides external covering and support; helps anchor the uterus via ligaments.
B. Decidua
• Not a permanent layer of the uterine wall.
• It is the specialized, functional transformation of the endometrium (the innermost layer) during pregnancy.
• After implantation of the embryo, the endometrial stroma undergoes decidualization and is then called the decidua.
• It has three parts during pregnancy:
• Decidua basalis (under the implanted embryo, forms part of the placenta)
• Decidua capsularis (covers the embryo)
• Decidua parietalis (the rest of the endometrium)
• After delivery, the decidua is shed as part of the lochia.
• Important: The decidua is temporary and pregnancy-specific; it is not present in the non-pregnant uterus.
C. Myometrium
• The middle and thickest layer of the uterine wall.
• Composed of bundles of smooth muscle cells arranged in three layers (inner circular, middle oblique/spiral, outer longitudinal).
• Richly supplied with blood vessels.
• Function: Responsible for uterine contractions during labor and menstruation; provides structural strength to the uterus; dramatically hypertrophies during pregnancy.
D. All above
• This would be correct only if the question is asking for layers/components associated with the uterus in general or during pregnancy.
• However, strictly speaking, in a non-pregnant uterus, the three permanent layers are:
1. Endometrium (inner mucosal layer)
2. Myometrium (middle muscular layer)
3. Perimetrium (outer serosal layer)
– The decidua replaces the endometrium functionally only during pregnancy.
Summary table for quick reference:
Layer Permanent? Location Tissue type Main function
Perimetrium Yes Outermost Serosa (mesothelium + connective tissue) External covering, support Myometrium Yes Middle Smooth muscle Contractions, structural support
Decidua No (only in pregnancy) Functional transformation of endometrium Decidualized endometrial stroma Nourishes embryo, forms maternal placenta, shed after birth
So if the question is about the non-pregnant uterus, the correct permanent layers are Perimetrium and Myometrium (plus Endometrium, which is not listed). Decidua is specific to pregnancy.