Luteal Phase

FOLLICLE-STIMULATING HORMONE (GONADOTROPHINS)

They are released by luteinizing hormone releasing hormone (LHRH) via the hypothalamus. Gonadotrophin cells make up 10-15 % of the anterior pituitary. FSH and LH regulate gonadal steroid hormone biosynthesis and germ cell production. FSH, LH, TSH and HCG are all glycoproteins. The purpose of follicle-stimulating hormone is to stimulate the growth of the follicle on the ovary. FSH, LH, TSH AND HCG all have identical α subunit chains. These are polypeptides containing 92 amino acids, whereas the β subunit chains contain 117, 121 and 145 amino acids. LHRH synthesizes these α and β gonadotrophin subunits forming and secreting FSH, LH, CRH (corticotrophin releasing hormone) and progesterone. 
Follicle stimulating hormone increases estrogen levels. As estrogen levels rise in the bloodstream, they enter the hypothalamic artery and decrease the output of LHRH from the hypothalamus. A group of peptide hormones produced by the gonads called inhibins, which are produced by the follicular luteal and sertoli cells of the gonads that inhibit FSH secretion, without affecting LH secretion. Activins also produced by the above cells stimulate GnRH, which induces FSH production. Activins and inhibins regulate granulose cell growth, differentiation, steroid hormone production, oocyte maturation and follicular development. 
You will notice that most hormones either increase or decrease the output of other hormones through this kind of a feedback mechanism. If a hormone increases the output of another hormone, then it is said to be a positive feedback mechanism. On the other hand, if a hormone decreases the output of another hormone, then it is said to be a negative feedback mechanism.

FSH Levels in the Luteal Phase