Theca Interna (of Secondary Ovarian Follicle)

Structure and/or Key Feature(s)

The theca interna is the very vascular innermost layer of cuboidal cells adjacent to the basement membrane and outer layer of granulosa cells. When completely differentiated, cells of the theca interna exhibit ultrastructural characteristics typical of a steroid-secreting cell. That is, they contain abundant smooth (agranular) endoplasmic reticulum, mitochondria with tubular cristae, and numerous lipid droplets (Ross and Pawlina, 2006; Mescher, 2013).

Anatomical Relations

The theca interna is adjacent to the follicular basement membrane and outer layer of granulosa cells.

Function

Cells of the theca interna possess large number of luteinizing hormone (LH) receptors. When stimulated by LH secreted by the anterior pituitary gland, they manufacture and then secrete androgens (androstenedione) which are then transported to the granulosa. Under the influence of follicle-stimulating hormone (FSH), the cells of the granulosa transform androstenedione into estrogen. Estrogen then returns to the stroma and enters the blood stream to be transported throughout the body.

Estrogen stimulates granulosa cells to proliferate, thus increasing the size of the follicle. A surge in the release of FSH and 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.