1- to 3-mm thick, and the glands are straight, with the spiral arteries only
slightly coiled. This diagram of the early secretory phase shows an edema-
tous endometrium that is 4-mm thick, with glands that are large, beginning
to sacculate in the deeper mucosa, and coiled for their entire length. In the
late secretory phase, the endometrium becomes 6- to 7-mm thick.
252.The answer is c.(Young, pp 342–346, 352. Kierszenbaum, pp 565–568,
- Junqueira, pp 436–439.)The cells labeled AandCin the photomicro-
graph of the Graafian follicle are granulosa cells that produce plasminogen
activator and collagenase. Those molecules, along with plasmin and
prostaglandins, facilitate the rupture of the ovarian follicle, leading to ovu-
lation. The increase in LH in midcycle induces production of collagenase
and plasminogen activator. Those proteases facilitate ovulation by initiating
connective tissue remodeling, including the breakdown of the basement
membrane between thecal and granulosa layers. Connective tissue remod-
eling is involved in the process of follicular atresia. This process occurs
throughout life and involves the death of follicular cells as well as oocytes,
but there is no basement membrane between the theca interna and externa.
In fact, there is an absence of a clear delineation between the theca interna
and externa. Development of ovarian follicles begins with a primordial fol-
licle that consists of flattened follicular cells surrounding a primary oocyte.
During the follicular phase, those cells undergo mitosis to form multiple
granulosa layers (primary follicle) in response to elevated levels of FSH and
LH from the anterior pituitary. A glycoproteinaceous coat surrounds the
oocyte and is called the zona pellucida. The connective tissue around the
follicle differentiates into two layers: theca externa (D)and theca interna
(E).The theca externa is closest to the ovarian stroma and consists of a
highly vascular connective tissue. The theca interna synthesizes androgens
(e.g., androstenedione) in response to LH. Androgens are converted to
estradiol by the action of an aromatase enzyme synthesized by the granu-
losa cells under the influence of FSH. Increased levels of estrogen from the
ovary feed back to decrease FSH secretion from gonadotrophs in the ante-
rior pituitary. Liquor folliculiis produced by the granulosa cells and is
secreted between the cells. When cavities are first formed by the develop-
ment of follicular fluid between the cells, the follicle is called secondary.
When the antrum is completely formed, the follicle is called a mature
(Graafian) follicle, and the antrum is completely filled with liquor folliculi.
The granulosa cells form two structures. The corona radiata (C)represents
382 Anatomy, Histology, and Cell Biology