The ovarian follicle is the functional unit of the ovary composed of an oocyte surrounded by companion somatic cells, including granulosa cells and theca cells. The somatic cell component of the follicle produces hormones important for oocyte development and proper endocrine function. Communication between the granulosa cells and the oocyte, which are mediated by transzonal projections, is essential for proper oocyte growth during oogenesis. The fully-grown oocyte is released from the follicle in response to hormonal cues at the time of ovulation.