HCG is produced by
**Core Concept**
Human Chorionic Gonadotropin (HCG) is a hormone produced during pregnancy that is essential for maintaining the corpus luteum and supporting embryonic development. HCG is a glycoprotein hormone that shares structural and functional similarities with luteinizing hormone (LH).
**Why the Correct Answer is Right**
HCG is produced by the placental syncytiotrophoblast cells, which are a layer of cells that form the outer layer of the blastocyst during early pregnancy. These cells produce HCG in response to the implantation of the embryo into the uterine wall, and it is secreted into the maternal bloodstream. HCG plays a crucial role in maintaining the corpus luteum, which produces progesterone to support embryonic development until the placenta can take over this function.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because HCG is not produced by the ovaries. While the ovaries do produce LH, which is structurally and functionally similar to HCG, they do not produce HCG itself.
**Option B:** This option is incorrect because HCG is not produced by the testes. The testes produce testosterone and other hormones, but not HCG.
**Option C:** This option is incorrect because HCG is not produced by the pituitary gland. The pituitary gland produces LH, but HCG is a separate hormone produced by the placental syncytiotrophoblast cells.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that HCG is a pregnancy-specific hormone, and its presence or absence can be used as a marker for pregnancy or pregnancy-related complications.
**Correct Answer: D. Placental syncytiotrophoblast cells**