1. Sherwood’s Human Physiology 20-13 5th Ed. & 20-14 6th Ed. Follicular Phase During the first few days of each ovarian cycle the concentrations of LH and FSH increase and this results in the rapid growth of 6-12 primary follicles. Rapid proliferation of the granulosa cells giving rise to many more layers.

2. Sherwood’s Human Physiology 20-13 5th Ed. & 20-14 6th Ed. Follicular Phase Ovary interstitial cells outside the granulosa cells divide and differentiate into theca cells. –Theca interna cells appear epithelioid and secrete _estrogen_ and progesterone precursors. –Theca externa cells form a highly vascularized capsule. –After a couple of days, an antrum is formed from follicular fluid (containing estrogen) secreted by granulosa cells.

3. Sherwood’s Human Physiology 20-16 5th Ed. & 20-17 6th Ed. Follicular Phase

4. Sherwood’s Human Physiology 20-13 5th Ed. & 20-14 6th Ed. Follicular Phase This rapid growth is followed by an even faster accelerated growth of the follicles into vesicular (secondary) follicles.

5. Estrogen (from theca cells & granulosa cells) is secreted into the follicle inducing granulosa cells to produce more FSH receptors and thus become more sensitive to FSH. FSH and estrogen promote LH receptor expression on the original granulosa cells causing greater LH stimulation of these cells resulting in increased follicular secretion. Estrogen and LH induce proliferation of and secretion by the theca cells. Guyton’s Textbook of Medical Physiology 81-3

7. Sherwood’s Human Physiology 20-13 5th Ed. & 20-14 6th Ed. Follicular Phase After a week or more of growth but before ovulation: –One follicle out grows the others. –The others involute and become _atretic_. –This is believed to be due to a negative feedback of estrogen on FSH production by the anterior pituitary gland.

8. Sherwood’s Human Physiology 20-17 5th Ed. & 20-18 6th Ed. Follicular Phase

9. Guyton’s Textbook of Medical Physiology 81-3 Negative Feedback of Estrogen As a result, FSH production decreases. The largest follicle has the most FSH receptors thus it is least effected and survives while the rest involute.

10. Sherwood’s Human Physiology 20-13 5th Ed. & 20-14 6th Ed. Follicular Phase The single vesicular follicle survives and is called a mature follicle. It continues to grow until ovulation.