Yolk muscle pair is
**Core Concept**
The yolk sac muscles, also known as the yolk sac muscles or yolk sac pair, are a set of muscles located in the umbilical cord. These muscles are derived from the mesoderm and play a crucial role in the development and functioning of the umbilical cord.
**Why the Correct Answer is Right**
The yolk sac muscles are responsible for contracting and relaxing to facilitate the exchange of nutrients and waste products between the fetus and the mother through the umbilical cord. This process is essential for fetal growth and development. The yolk sac muscles are innervated by the vagus nerve, which regulates their contraction and relaxation.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the yolk sac muscles are not responsible for regulating blood pressure in the umbilical cord.
* **Option B:** This option is incorrect because the yolk sac muscles do not play a role in the production of urine in the fetus.
* **Option C:** This option is incorrect because the yolk sac muscles are not derived from the ectoderm, but rather from the mesoderm.
**Clinical Pearl / High-Yield Fact**
It's essential for obstetricians and neonatologists to understand the anatomy and function of the yolk sac muscles, as abnormalities in these muscles can lead to complications during pregnancy and childbirth. A mnemonic to remember the yolk sac muscles is "UMBILICAL": U - Umbilical cord, M - Mesoderm-derived, B - Blood exchange, I - Innervated by the vagus nerve, L - Location in the umbilical cord, I - Important for fetal growth, C - Contracting and relaxing, A - Associated with the vagus nerve, L - Linked to fetal development.
**Correct Answer:** C. The yolk sac muscles are derived from the mesoderm.