## **Core Concept**
Sertoli cells, also known as nurse cells, play a crucial role in the seminiferous tubules of the testes. They provide structural and nutritional support to developing sperm cells. Sertoli cells secrete various factors and proteins essential for spermatogenesis.

## **Why the Correct Answer is Right**
Sertoli cells are known to secrete several important substances, including:
- **Inhibin**: A protein that inhibits the production of follicle-stimulating hormone (FSH) from the anterior pituitary gland.
- **Activin**: A protein that stimulates the production of FSH.
- **Müllerian-inhibiting substance (MIS) or Anti-Müllerian hormone (AMH)**: Involved in the regression of Müllerian ducts in male fetuses.
- **Androgen-binding protein (ABP)**: Helps maintain high levels of androgens near the developing sperm.

## **Why Each Wrong Option is Incorrect**
- **Option A: Inhibin** - This is secreted by Sertoli cells and plays a role in the feedback inhibition of FSH secretion.
- **Option B: Activin** - Also secreted by Sertoli cells, it stimulates FSH production.
- **Option D: Müllerian-inhibiting substance (MIS) or Anti-Müllerian hormone (AMH)** - Secreted by Sertoli cells, crucial for the regression of Müllerian ducts.

## **Why Option C is Correct but Not Detailed Above**
- **Option C: Testosterone** - This is not secreted by Sertoli cells. Testosterone is primarily produced by Leydig cells (also known as interstitial cells of Leydig) in the testes. It is crucial for spermatogenesis and the development of male secondary sexual characteristics.

## **Clinical Pearl / High-Yield Fact**
A key clinical correlation is that **Sertoli cell dysfunction** can lead to abnormalities in spermatogenesis. For instance, in conditions like Sertoli cell-only syndrome, there is a failure of Sertoli cells to support spermatogenesis, leading to azoospermia.

## **Correct Answer: C. Testosterone**