What type of cells secrete the zona pellucida during oocyte development?

The correct answer is granulosa cells because these cells play a crucial role during oocyte development in the ovarian follicles. Granulosa cells are located surrounding the developing oocyte and are responsible for secreting the zona pellucida, which is a glycoprotein layer that forms around the oocyte. This zona pellucida is essential for protecting the oocyte and plays a pivotal role in fertilization as it contains specific receptors for sperm binding.

Granulosa cells also contribute to the hormonal environment of the follicle by producing estrogen and supporting oocyte maturation. Their function is crucial to create an appropriate microenvironment for oocyte development and maturation which is essential for successful reproduction.

While follicular cells also surround oocytes, the term "follicular cells" is broader and encompasses both granulosa and theca cells. Sertoli cells are specialized cells found in males that support spermatogenesis in the testes but are not involved in oocyte development. Theca cells, on the other hand, primarily contribute to the production of androgens that are converted to estrogens by granulosa cells but do not secrete the zona pellucida.