The hormone of pars intermedia is responsible for :

Options

A. Darkening of skin in lower vertebrates
B. Regulates the growth of the mammary glands and formation of milk in them
C. It stimulates milk ejection from the mammary gland
D. Stimulates the synthesis and secretion of steroid hormones called glucocorticoids

Answer

To solve the question regarding the hormone of the pars intermedia, we will analyze each option provided and determine which one is correct based on the functions of hormones secreted by the pars intermedia.

### Step-by-Step Solution:

1. **Identify the Hormone of Pars Intermedia**:
- The pars intermedia of the pituitary gland primarily secretes the Melanocyte-Stimulating Hormone (MSH). This hormone is responsible for stimulating the production and release of melanin by melanocytes in the skin.

2. **Analyze the Options**:
- **Option 1**: Darkening of skin in lower vertebrates.
- This option is correct because MSH is known to cause skin darkening by stimulating melanin production in lower vertebrates.

- **Option 2**: Regulates the growth of the mammary glands and formation of milk in them.
- This option is incorrect. The hormone responsible for this function is Prolactin, which is secreted by the anterior pituitary gland, not the pars intermedia.

- **Option 3**: Stimulates milk ejection from the mammary gland.
- This option is also incorrect. The hormone that stimulates milk ejection is Oxytocin, which is released from the posterior pituitary gland.

- **Option 4**: Stimulates the synthesis and secretion of the steroid hormones called glucocorticoids.
- This option is incorrect as well. Glucocorticoids are produced in the adrenal cortex and their synthesis is regulated by ACTH (Adrenocorticotropic hormone), which is secreted by the anterior pituitary.

3. **Conclusion**:
- Based on the analysis, the correct answer is **Option 1: Darkening of skin in lower vertebrates**.