Follicular wave

Three to six follicles are initiated to grow together under the influence of increasing level of FSH which is described as follicular wave.

The first wave of follicles that develop during mid luteal phase reach antral stage and then regress followed by growth of second wave of follicles.

If CL regression begins at this time one of these follicles become dominant and this follicle reaches ovulatory stage. Rest of the growing follicles regress and become atretic follicles.

The dominant follicle produces inhibin and oestradiol which inhibit FSH thereby growth of further antral follicles is blocked.

In sheep, cattle and horses two to three follicular waves occur during luteal phase with the last wave ending in ovulation.

In pigs, rats and human ovulatory follicles develop during follicular phase of the cycle. In these animals, progesterone from CL of diestrus blocks ovulatory surge of gonadotropins. Following luteolysis, serum progesterone falls appreciably low and estradiol level increases favouring ovulatory surge of LH

In monotocous animals, at each heat period normally one follicle develops more rapidly than others and releases one ovum. Rest of the growing follicles regress and form atretic follicles. Polytocous animals produce two or more offspring per gestation and have several follicles developing and rupturing at the same time.

Following ovulation, the follicular antrum is filled with blood and lymph and forms corpus hemorrhagicum. This is gradually converted to corpus luteum. After each oestrous cycle the CL decreases in size and finally leaves a scar called corpus albicans.