Quick Facts
Granulosa cells are cells surrounding the vesicular ovarian follicle and forming the stratum granulosum and cumulus oophorus; after ovulation they are transformed into lutein cells (Dorland, 2011).
Structure and/or Key Feature(s)
When a primordial follicle develops into a primary follicle, the single layer of squamous follicular cells proliferates and becomes cuboidal. As the follicle develops, the oocyte secretes specific proteins to form an extracellular layer called the zona pellucida. It is located between the oocyte and the follicle cells. The single layer of cuboidal follicle cells undergoes rapid mitotic divisions to form a stratified epithelium called the granulosa that surrounds the oocyte. These follicular cells are now called granulosa cells. A basement membrane remains in position between the outermost layer of the granulosa cells (which are columnar) and the connective tissue stroma which is destined to become the thecal layers around the developing follicle.
Extensive gap junctions form between adjacent granulosa cells but in the basal layer there are no tight junctions (zonulae occludens) most likely because nutrients, chemical messengers, etc. from the blood need to nourish the developing oocyte and granulosa cells (Ross and Pawlina, 2006).
Anatomical Relations
The granulosa is situated between the primary oocyte and the follicular basement membrane.
Function
Under the influence of follicle-stimulating hormone (FSH), the granulosa cells transform androstenedione into estrogen. Estrogen then returns to the vascular theca interna and enters the blood stream to be transported throughout the body.
Estrogen stimulates granulosa cells to proliferate increasing the size of the follicle. A surge in the release of FSH and luteinizing hormone (LH) from the anterior pituitary gland occurs about 24 hours before ovulation, which desensitizes the LH receptors on the granulosa cells and the granulosa cells no longer produce estrogen (Ross and Pawlina, 2006; Mescher, 2013).
References
Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.
Mescher, A. (2013) Junqueira's Basic Histology: Text and Atlas. 13th edn.: McGraw-Hill Education.
Ross, M. H. and Pawlina, W. (2006) Histology: A text and atlas. Lippincott Williams & Wilkins.
