Antral follicle
Encyclopedia
An antral follicle is an ovarian follicle
during a certain latter stage of folliculogenesis
.
Definitions differ in where the shift into an antral follicle occurs in the staging of folliculogenesis, with some stating that it occurs when entering the secondary stage, and others stating that it occurs when entering the tertiary stage.
. The basic structure of the mature follicle has formed and no novel cells are detectable. Granulosa and theca cells continue to undergo mitosis concomitant with an increase in antrum volume. Antral follicles can attain a tremendous size that is hampered only by the availability of follicle stimulating hormone (FSH), which it is dependent on in this stage of folliculogenesis.
By command of an oocyte-secreted morphogenic gradient, the antral follicle's granulosa cells begin to differentiate themselves into four distinct subtypes: corona radiata
that surrounds the zona pellucida
, membrana that's interior to the basal lamina, periantral that's adjacent to the antrum, and cumulus oophorous that connects the membrana and corona radiata granulosa cells together. Each type of cell behaves differently in response to FSH.
(LH). LH kicks off the production of androgen
s by the theca cells, most notably androstendione, which are aromatized by granulosa cells to produce estrogens, primarily estradiol
. Consequently, estrogen levels begin to rise.
The antral follicle count (AFC) is the number of antral follicles, generally in both ovaries taken together if not else specified. It can be determined by transvaginal ultrasonography.
A low AFC is a major factor in the diagnosis of poor ovarian reserve, that is, low fertility characterized by low numbers of remaining oocytes in the ovaries, usually accompanied by high follicle stimulating hormone (FSH) levels. Several studies show that an AFC test is more accurate than basal FSH testing for older women (< 44 years of age) in predicting IVF outcome. This method of determining ovarian reserve is recommended by Dr. Sherman J. Silber, author and medical director of the Infertility Center of St. Louis.
It is also a major determinant of the success of ovarian hyperstimulation.
Ovarian follicle
Ovarian follicles are the basic units of female reproductive biology, each of which is composed of roughly spherical aggregations of cells found in the ovary. They contain a single oocyte . These structures are periodically initiated to grow and develop, culminating in ovulation of usually a single...
during a certain latter stage of folliculogenesis
Folliculogenesis
In biology, folliculogenesis is the maturation of the ovarian follicle, a densely-packed shell of somatic cells that contains an immature oocyte...
.
Definitions differ in where the shift into an antral follicle occurs in the staging of folliculogenesis, with some stating that it occurs when entering the secondary stage, and others stating that it occurs when entering the tertiary stage.
Appearance
It is marked by the formation of a fluid-filled cavity adjacent to the oocyte called the antrumFollicular antrum
The follicular antrum is the portion of an ovarian follicle filled with liquor folliculi.-External links: "Graafian Follicle" - "Mammal, canine ovary "*...
. The basic structure of the mature follicle has formed and no novel cells are detectable. Granulosa and theca cells continue to undergo mitosis concomitant with an increase in antrum volume. Antral follicles can attain a tremendous size that is hampered only by the availability of follicle stimulating hormone (FSH), which it is dependent on in this stage of folliculogenesis.
By command of an oocyte-secreted morphogenic gradient, the antral follicle's granulosa cells begin to differentiate themselves into four distinct subtypes: corona radiata
Corona radiata
In neuroanatomy, the corona radiata is a white matter sheet that continues caudally as the internal capsule and rostrally as the centrum semiovale. This sheet of axons contains both descending and ascending axons that carry nearly all of the neural traffic from and to the cerebral cortex...
that surrounds the zona pellucida
Zona pellucida
The zona pellucida is a glycoprotein membrane surrounding the plasma membrane of an oocyte. It is a vital constitutive part of the latter, external but of essential importance to it...
, membrana that's interior to the basal lamina, periantral that's adjacent to the antrum, and cumulus oophorous that connects the membrana and corona radiata granulosa cells together. Each type of cell behaves differently in response to FSH.
Endocrine properties
Theca cells express receptors for luteinizing hormoneLuteinizing hormone
Luteinizing hormone is a hormone produced by the anterior pituitary gland. In females, an acute rise of LH called the LH surge triggers ovulation and development of the corpus luteum. In males, where LH had also been called interstitial cell-stimulating hormone , it stimulates Leydig cell...
(LH). LH kicks off the production of androgen
Androgen
Androgen, also called androgenic hormone or testoid, is the generic term for any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of male characteristics in vertebrates by binding to androgen receptors...
s by the theca cells, most notably androstendione, which are aromatized by granulosa cells to produce estrogens, primarily estradiol
Estradiol
Estradiol is a sex hormone. Estradiol is abbreviated E2 as it has 2 hydroxyl groups in its molecular structure. Estrone has 1 and estriol has 3 . Estradiol is about 10 times as potent as estrone and about 80 times as potent as estriol in its estrogenic effect...
. Consequently, estrogen levels begin to rise.
Antral follicle count
The antral follicle count (AFC) is the number of antral follicles, generally in both ovaries taken together if not else specified. It can be determined by transvaginal ultrasonography.
A low AFC is a major factor in the diagnosis of poor ovarian reserve, that is, low fertility characterized by low numbers of remaining oocytes in the ovaries, usually accompanied by high follicle stimulating hormone (FSH) levels. Several studies show that an AFC test is more accurate than basal FSH testing for older women (< 44 years of age) in predicting IVF outcome. This method of determining ovarian reserve is recommended by Dr. Sherman J. Silber, author and medical director of the Infertility Center of St. Louis.
It is also a major determinant of the success of ovarian hyperstimulation.