As a follicle matures, its primary oocyte undergoes meiosis
I, giving rise to a secondary oocyte and a F rst polar body. A
shun) releases these cells
from the follicle.
Release of LH from the anterior pituitary gland triggers
ovulation, which rapidly swells the mature follicle and weak-
ens its wall. Eventually the wall ruptures, and the follicular
ﬂ uid, accompanied by the secondary oocyte, oozes outward
from the surface of the ovary.
of a mammalian oocyte.
Although as many as twenty primary follicles may begin
maturing at any one time, one dominant follicle usually out-
grows the others. Typically, only the dominant follicle fully
develops, and the other follicles degenerate
Certain drugs used to treat female infertility, such as Clomid (clomi-
phene), may cause a woman to “superovulate.” More than one follicle
grows, more than one secondary oocyte is released, and if all of these
secondary oocytes are fertilized and complete prenatal development,
multiple births may result.
Light micrograph of the surface of a mammalian ovary (200×).
Ovarian follicle. (
) Structure of a mature (GraaF
an) follicle. (
) Light micrograph of a mature follicle (250×).