Final answer:
The smooth endoplasmic reticulum (SER) is responsible for the synthesis of steroid hormones in endocrine cells.
Step-by-step explanation:
The site of steroid hormone synthesis in endocrine cells is the smooth endoplasmic reticulum (SER). This organelle is responsible for synthesizing lipids, including phospholipids and steroid hormones. The SER is also involved in other functions such as the regulation of cellular calcium levels, metabolism of carbohydrates, and detoxification processes. Endocrine cells that produce steroid hormones, such as those found in the adrenal glands or gonads, typically have a high concentration of SER to accommodate this function.