Pars intermedia of hypophysis cerebri from?
**Core Concept**
The pars intermedia is a part of the hypophysis cerebri (pituitary gland) that plays a crucial role in the regulation of hormone secretion. It is a thin layer of tissue located between the anterior and posterior lobes of the pituitary gland.
**Why the Correct Answer is Right**
The pars intermedia is derived from the intermediate lobe of the pituitary gland, which is a remnant of the embryonic Rathke's pouch. During fetal development, the Rathke's pouch differentiates into the anterior lobe (adenohypophysis) and the posterior lobe (neurohypophysis). The intermediate lobe, which gives rise to the pars intermedia, is responsible for the production of melanocyte-stimulating hormone (MSH).
**Why Each Wrong Option is Incorrect**
* **Option A:** The pars intermedia is not derived from the anterior lobe of the pituitary gland, which is responsible for the production of adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), and growth hormone (GH).
* **Option B:** The pars intermedia is not derived from the posterior lobe of the pituitary gland, which is responsible for the storage and release of oxytocin and vasopressin.
* **Option C:** The pars intermedia is not a distinct embryonic structure, but rather a derivative of the intermediate lobe of the pituitary gland.
**Clinical Pearl / High-Yield Fact**
The pars intermedia is a thin layer of tissue that can be difficult to distinguish from the surrounding tissue, and its dysfunction can lead to a range of hormonal imbalances.
**Correct Answer:** D.