Anatomy and function
Granulosa cells form a single flattened layer around the mammalian oocyte in the primary ovarian follicle and later in follicle development (folliculogenesis) they advance to form a multilayered cumulus oophorus surrounding the oocyte in the preovulatory or Graafian follicle.
Also FSH stimulates granulosa cells to convert androgens (coming from the thecal cells) to estradiol by aromatase. However, after ovulation the granulosa cells produce progesterone that may maintain a potential pregnancy and produce a thick cervical mucus which inhibits sperm entry into the uterus
Embryology of ovarian granulosa cells
In the development of the urinary and reproductive organs, the oogonia become invaginated in the gonadal ridge.
In the 1970’s, evidence emerged that the first cells to make contact with the oogonia were of mesonephric origin. It was suggested that mesonephric cells already closely associated with the oogonia proliferated throughout development to form the granulosa cell layer.
Recently this hypothesis has been challenged with some thorough histology. Sawyer et al. hypothesised that in sheep most of the granulosa cells develop from cells of the mesothelium (i.e., epithelial cells from the presumptive surface epithelium of the ovary). 
The embryological origin of granulosa cells remains controversial.
- Satoh M. "Histogenesis and organogenesis of the gonad in human embryos". J Anat. 177: 85–107. PMID 1769902.
- Upadhyay S, Zamboni L (1982). "Preliminary observations on the role of the mesonephros in the development of the adrenal cortex". Anat Rec. 202 (1): 105–111. PMID 7059014.
- Zamboni, L., Bezard, J., and Mauleon, P. (1979). The role of the mesonephros in the development of the sheep fetal ovary. Annales de Biologie Animal Biochimie et Biophysique 19, 1153-78.
- Sawyer H, Smith P, Heath D, Juengel J, Wakefield S, McNatty K (2002). "Formation of ovarian follicles during fetal development in sheep". Biol Reprod. 66 (4): 1134–50. PMID 11906935.
- Histology image: 18404loa – Histology Learning System at Boston University - "Female Reproductive System: ovary, cumulus oophorus"
- Histology image: 14808loa – Histology Learning System at Boston University - "Female Reproductive System: ovary, membrana granulosa"
- Granulosa+Cells at the US National Library of Medicine Medical Subject Headings (MeSH)