1036
UNIT 5
Continuity
27
Follicles at different stages of maturation are distinguished by
their structure, which ranges from
primordial follicles
with a sin-
gle layer of follicle cells surrounding the oocyte to more mature
follicles with several layers of granulosa cells. Te fully mature
vesicular follicle
, also called an
antral
, or
tertiary
,
follicle
, is
identified by its central fluid-filled cavity called an
antrum
(Fig-
ure 27.13). When mature, the follicle extends from the deepest
part of the ovarian cortex and bulges from the surface of the
ovary, and its oocyte “sits proudly” on a stalk of granulosa cells
at one side of the antrum.
Each month in women of childbearing age, one of the rip-
ening follicles ejects its oocyte from the ovary, an event called
ovulation
(see Figure 27.20,
5
). A±er ovulation, the ruptured
follicle is transformed into a very different looking glandular
structure called the
corpus luteum
(lu
9
te-um; “yellow body”;
plural: corpora lutea), which eventually degenerates (not shown
in Figure 27.13). As a rule, most of these structures can be seen
within the same ovary. In older women, the surfaces of the ova-
ries are scarred and pitted, revealing that many oocytes have
been released.
Check Your Understanding
19.
Briefly, what are the internal genitalia of a woman?
20.
What two roles do the ovaries assume?
21.
What name is given to the fluid-filled cavity of a mature
follicle?
For answers, see Appendix H.
held in place by several ligaments in the fork of the iliac blood
vessels within the peritoneal cavity. Te
ovarian ligament
an-
chors the ovary medially to the uterus; the
suspensory liga-
ment
anchors it laterally to the pelvic wall; and the
mesovarium
(mez
0
o-va
9
re-um) suspends it in between (see Figures 27.12
and 27.14). Te suspensory ligament and mesovarium are part
of the
broad ligament
, a peritoneal fold that “tents” over the
uterus and supports the uterine tubes, uterus, and vagina. Te
broad ligament encloses the ovarian ligaments.
Te ovaries are served by the
ovarian arteries
, branches of
the abdominal aorta (see Figure 19.24c), and by the
ovarian
branch of the uterine arteries
. Te ovarian blood vessels reach
the ovaries by traveling through the suspensory ligaments and
mesovaria (see Figure 27.14).
Like each testis, each ovary is surrounded externally by a fi-
brous
tunica albuginea
(Figure 27.13)
, which is in turn covered
externally by a layer of cuboidal epithelial cells called the
germinal
epithelium
, actually a continuation of the peritoneum. Te ovary
has an outer
cortex
, which houses the forming gametes, and an
inner
medulla
containing the largest blood vessels and nerves, but
the relative extent of each region is poorly defined.
Embedded in the highly vascular connective tissue of the
ovary cortex are many tiny saclike structures called
ovarian
follicles
. Each follicle consists of an immature egg, called an
oocyte
(o
9
o-sīt;
oo
5
egg), encased by one or more layers of
very different cells. Te surrounding cells are called
follicle cells
if a single layer is present, and
granulosa cells
when more than
one layer is present.
Germinal
epithelium
Tunica
albuginea
Antrum of a vesicular
(antral) follicle
Secondary
follicle
Primary
follicles
Cortex
Medulla
Figure 27.13
Photomicrograph of a mammalian ovary showing follicles in different
developmental phases.
Note that most follicles are in the cortex (3
3
).
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