What causes the lining of the follicle to thicken?

The thickening of the follicular lining is primarily stimulated by hormones, particularly estrogen. During the follicular phase of the menstrual cycle, rising levels of follicle-stimulating hormone (FSH) promote the growth and maturation of ovarian follicles, leading to increased estrogen production. This estrogen, in turn, induces cellular proliferation and thickening of the follicular lining to prepare for ovulation. Additionally, local growth factors and signaling pathways also contribute to this process.