CHAPTER 19
Female Reproductive System
377
Figure 19-6A.
Secondary follicles, ovary.
H&E,
3
108; inset
3
211
The
secondary follicle
develops from the
continued
growth of the
multilaminar primary follicle
.
Spaces F lled with
follicular fl uid (liquor folliculi)
appear among the granulosa cells within the sec-
ondary follicle. These spaces gradually merge to
form a single large space called the
antrum
. The
zona pellucida
is distinct, and the theca folliculi
(surrounding the follicle) develops into the
theca
interna
and
theca externa
. The
theca interna
is the inner vascular layer containing cuboidal
(steroid-producing) secretory cells. These cells
secrete
androgens
, which diffuse into the granu-
losa cells where they are converted into
estrogens
in response to ±SH. The
theca externa
is an outer
connective tissue layer containing mainly colla-
gen and some small squamous cells mixed with a
few smooth muscle cells.
Primary
Primary
oocyte
oocyte
Primary
oocyte
Secondary
Secondary
follicle
follicle
Secondary
follicle
Antrum
Antrum
Antrum
Granulosa
Granulosa
cells
cells
Granulosa
cells
Zona
Zona
pellucida
pellucida
Zona
pellucida
Theca
Theca
interna
interna
Theca
interna
Theca
Theca
externa
externa
Theca
externa
A
Granulosa cells
Theca interna
Theca externa
Cumulus
oophorus
Corona radiata
Nucleus of oocyte
Zona pellucida
Blood
Blood
vessel
vessel
Blood
vessel
Cumulus oophorus
Antrum
Antrum
Antrum
Primary
Primary
follicle
follicle
Primary
follicle
Membrana granulosa
Membrana granulosa
(g
(g
ranulosa cells)
ranulosa cells)
Membrana granulosa
(granulosa cells)
Corona
Corona
radiata
radiata
Corona
radiata
Oocyte
Oocyte
Oocyte
Cumulus
Cumulus
oophorus
oophorus
Cumulus
oophorus
Theca interna
Theca interna
Theca interna
Theca externa
Theca externa
Theca externa
B
Figure 19-6B.
Graa± an follicles, ovary.
H&E,
3
54; inset (
upper
)
3
429; inset (
lower
)
3
178
The
Graa± an follicle
is a mature follicle; it is also called a
preovulatory follicle
. At this stage, the follicle has grown to a large size
(about 25 mm) and bulges from the surface of the ovary. The decreased number of granulosa cells and increased volume of fl
uid in
the
antrum
result in the oocyte being located at the periphery of the follicle. The
membrana granulosa
is formed by multiple cellular
layers of granulosa cells lining the inner wall of the antrum. Some granulosa cells form a hillock called the
cumulus oophorus
, which
supports and houses the oocyte. The inner granulosa cells of the
cumulus oophorus
form a single layer called the
corona radiata
,
which immediately surrounds the oocyte. As the follicle grows, most of the granulosa cells gradually loosen from the cumulus
oophorus, but the corona radiata remains in contact with the oocyte. Eventually, the oocyte, with the corona radiata, fl
oats freely in
the antrum before ovulation. The oocyte remains as a primary oocyte in the graaF an follicle until pituitary secretion of LH increases
sharply (
LH surge
); this stimulates the primary oocyte to complete the
± rst
meiotic division
and become a
secondary oocyte
. The
secondary oocyte with the corona radiata and
polar body
(from the F
rst oocyte division) are released from the graaF
an follicle of the
ovary. After the secondary oocyte reaches the
ampulla
of the
oviduct
, the
second meiotic division
occurs, if fertilization takes place.
A spermatozoan must penetrate the corona radiata and zona pellucida to complete the fertilization process. The
upper inset
shows
the
theca folliculi (theca interna
and
theca externa
). The
lower inset
shows the oocyte surrounded by granulosa cells.
The
ovarian cycle
is under the control of the hormones
FSH
and
LH
produced by the
gonadotrophs
of the
anterior pituitary
gland
.
FSH
stimulates
estrogen
production and follicular growth;
LH
stimulates meiotic division of the
primary oocyte, ovulation
,
and development of the
corpus luteum
. The
estrogens
play an important role in the stimulation of follicle growth by promoting
proliferation of the
granulosa cells
, and they also stimulate the mammary glands to prepare for
lactation
.
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