CHAPTER 19
Female Reproductive System
375
Figure 19-4A.
Primordial follicles, ovary.
H&E,
3
290;
inset
3
110
Primordial follicles
are the smallest and most numerous
type of follicles in the cortex of the ovary. Each primordial
follicle contains a
germ
cell
(
primary
oocyte
) in a resting
state that may persist for as long as 50 years. The primary
oocyte is surrounded by a layer of
squamous cells
called
follicular cells
. These follicular cells are somatic cells that
support the oocyte. The oocyte has a pale appearance
and a large nucleus with a prominent nucleolus. About
1 million follicles are present in the ovaries at the time
of birth; however, only a few hundred of these follicles
become mature. The follicles begin to grow at puberty,
and there is a constant loss of follicles throughout the
reproductive years. At menopause, only a few follicles
remain.
Squamous
Squamous
follicular cells
follicular cells
Squamous
follicular cells
Primordial
Primordial
follicles
follicles
Primordial
Primordial
follicle
follicle
Primordial
follicles
Primordial
follicle
A
Follicular
Follicular
cells
cells
Follicular
cells
Basal lamina of follicle
Nucleus of primary oocyte
Nucleus of primary oocyte
Nucleus of
Nucleus of
primary oocyte
primary oocyte
Nucleus of
primary oocyte
Mitochondria of primary oocyte
Mitochondria of
Mitochondria of
follicle cells
follicle cells
Mitochondria of
follicle cells
Granules in oocyte
Nucleus of follicular cell
Nucleus of stromal cell
Junction between
Junction between
follicular cells
follicular cells
Junction between
follicular cells
B
Figure 19-4B.
Primordial follicle.
EM,
3
3,900; inset (
color
) H&E,
3
500
The
primary oocyte
at the center of this
primordial follicle
may appear to be in interphase of the cell cycle, but it is arrested in
dictyo-
tene
of prophase I of meiosis. What appear to be patches of heterochromatin in the nucleus are partially decondensed tetrads com-
posed of paired homologous chromosomes. The oocyte has been in prophase of meiosis I before birth of the individual. Follicular
cells form a simple squamous epithelium that surrounds the oocyte. Note that these cells adhere tightly to the surface of the oocyte.
Indeed, there are junctions between the oocyte and the follicle cells, although they are not readily identi±
able here. Neighboring fol-
licular cells are also connected by junctional complexes, and there is a basal lamina between the follicular cells and the surrounding
interstitial tissue of the ovarian cortex.
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