616
Chapter 17
containing 46 chromosomes, each with two sister chromatids.
The cells are said to be in a state of
meiotic arrest.
This state continues until puberty and the onset of
renewed activity in the ovaries. Indeed, only those primary
oocytes destined for ovulation will ever complete the fi rst mei-
otic division, for it occurs just before the egg is ovulated. This
division is analogous to the division of the primary spermato-
cyte, and each daughter cell receives 23 chromosomes, each
with two chromatids. In this division, however, one of the
two daughter cells, the
secondary oocyte,
retains virtually all
the cytoplasm. The other, called the fi rst polar body, is very
small and nonfunctional. Thus, the primary oocyte, which is
already as large as the egg will be, passes on to the secondary
oocyte just half of its chromosomes but almost all of its nutri-
ent-rich cytoplasm.
The second meiotic division occurs in a fallopian tube
after ovulation,
but only if the secondary oocyte is fertilized—
that is, penetrated by a sperm. As a result of this second mei-
(a)
(b)
Fallopian
tube
Fallopian
tube
Ovary
Ovary
Uterus
Ovary
Uterus
Cervix
Pubic
bone
Urinary
bladder
Urethra
Vagina
Vagina
Anus
Fimbriae
Cervix
Opening of
fallopian tube
Figure 17–13
Female reproductive system. (a) Section through a female pelvis. (b) Diagram cut away on the right to show the continuity between the organs
of the reproductive duct system—fallopian tubes, uterus, and vagina.
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