Antral follicle

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Antral follicle

An antral or secondary follicle, also known as Graafian follicle and tertiary follicle, is an ovarian follicle during a certain latter stage of folliculogenesis.

Contents

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, [1] and others stating that it occurs when entering the tertiary stage. [2]

Appearance

The antral follicle is marked by the formation of a fluid-filled cavity adjacent to the oocyte called the antrum. 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. The Graaf follicle reaches its maximum diameter (20–22 mm) during ovulation. Antral follicles can attain a tremendous size that is hampered only by the availability of follicle stimulating hormone (FSH), on which it is dependent 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 is interior to the basal lamina, periantral that is adjacent to the antrum, and cumulus oophorus 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 hormone (LH). LH kicks off the production of androgens by the theca cells, most notably androstenedione, which are aromatized by granulosa cells to produce estrogens, primarily estradiol. 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 specified otherwise. 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. [3] However, it does not appear to add any predictive information about success rates of an already established pregnancy after IVF. [4]

It is also a major determinant of the success of ovarian hyperstimulation.

There are three categories when performing an ultrasound to cheek the antral follicle count:

It has been suggested that counting the antral follicles measuring 2–5 or 4–6 mm in diameter is preferable. On the other hand, the number of smaller antral follicles (2–5 mm) is highly correlated with the total number of antral follicles (2–10 mm), and therefore it is suggested that counting all identifiable antral follicles of 2–10 mm in diameter would provide the most practical method for assessment of AFC in clinical practice. [5]

Three-dimensional (3D) automated follicular tracking is a developing technique that can substantially decrease both intra- and inter-observer variability in estimating the AFC. [5]

Related Research Articles

<span class="mw-page-title-main">Ovary</span> Female reproductive organ that produces egg cells

The ovary is a gonad in the female reproductive system that produces ova. When an ovum is released, this travels through the fallopian tube/oviduct into the uterus. There is an ovary found on the left and the right side of the body. The ovaries also secrete hormones that play a role in the menstrual cycle and fertility. The ovary progresses through many stages beginning in the prenatal period through menopause. It is also an endocrine gland because of the various hormones that it secretes.

<span class="mw-page-title-main">Menstrual cycle</span> Natural changes in the human female reproductive system

The menstrual cycle is a series of natural changes in hormone production and the structures of the uterus and ovaries of the female reproductive system that makes pregnancy possible. The ovarian cycle controls the production and release of eggs and the cyclic release of estrogen and progesterone. The uterine cycle governs the preparation and maintenance of the lining of the uterus (womb) to receive an embryo. These cycles are concurrent and coordinated, normally last between 21 and 35 days, with a median length of 28 days, and continue for about 30–45 years.

<span class="mw-page-title-main">Oogenesis</span> Egg cell production process

Oogenesis, ovogenesis, or oögenesis is the differentiation of the ovum into a cell competent to further develop when fertilized. It is developed from the primary oocyte by maturation. Oogenesis is initiated in the embryonic stage.

<span class="mw-page-title-main">Ovarian follicle</span> Structure containing a single egg cell

An ovarian follicle is a roughly spheroid cellular aggregation set found in the ovaries. It secretes hormones that influence stages of the menstrual cycle. At the time of puberty, women have approximately 200,000 to 300,000 follicles, each with the potential to release an egg cell (ovum) at ovulation for fertilization. These eggs are developed once every menstrual cycle with around 450–500 being ovulated during a woman's reproductive lifetime.

<span class="mw-page-title-main">Granulosa cell</span> Mammal reproductive system cell

A granulosa cell or follicular cell is a somatic cell of the sex cord that is closely associated with the developing female gamete in the ovary of mammals.

<span class="mw-page-title-main">Anti-Müllerian hormone</span> Mammalian protein found in humans

Anti-Müllerian hormone (AMH), also known as Müllerian-inhibiting hormone (MIH), is a glycoprotein hormone structurally related to inhibin and activin from the transforming growth factor beta superfamily, whose key roles are in growth differentiation and folliculogenesis. In humans, it is encoded by the AMH gene, on chromosome 19p13.3, while its receptor is encoded by the AMHR2 gene on chromosome 12.

<span class="mw-page-title-main">Folliculogenesis</span> Process of maturation of primordial follicles

In biology, folliculogenesis is the maturation of the ovarian follicle, a densely packed shell of somatic cells that contains an immature oocyte. Folliculogenesis describes the progression of a number of small primordial follicles into large preovulatory follicles that occurs in part during the menstrual cycle.

<span class="mw-page-title-main">Ovarian reserve</span>

Ovarian reserve is a term that is used to determine the capacity of the ovary to provide egg cells that are capable of fertilization resulting in a healthy and successful pregnancy. With advanced maternal age, the number of egg cell that can be successfully recruited for a possible pregnancy declines, constituting a major factor in the inverse correlation between age and female fertility.

<span class="mw-page-title-main">Follicular atresia</span>

Follicular atresia refers to the process in which a follicle fails to develop, thus preventing it from ovulating and releasing an egg. It is a normal, naturally occurring progression that occurs as mammalian ovaries age. Approximately 1% of mammalian follicles in ovaries undergo ovulation and the remaining 99% of follicles go through follicular atresia as they cycle through the growth phases. In summary, follicular atresia is a process that leads to the follicular loss and loss of oocytes, and any disturbance or loss of functionality of this process can lead to many other conditions.

<span class="mw-page-title-main">Bone morphogenetic protein 15</span> Protein-coding gene in humans

Bone morphogenetic protein 15 (BMP-15) is a protein that in humans is encoded by the BMP15 gene. It is involved in folliculogenesis, the process in which primordial follicles develop into pre-ovulatory follicles.

<span class="mw-page-title-main">Cumulus oophorus</span> Cluster of cells surrounding an oocyte

The cumulus oophorus is a cluster of cells that surround the oocyte both in the ovarian follicle and after ovulation. In the antral follicle, it may be regarded as an extension of the membrana granulosa. The innermost layer of these cells is the corona radiata.

The theca folliculi comprise a layer of the ovarian follicles. They appear as the follicles become secondary follicles.

Controlled ovarian hyperstimulation is a technique used in assisted reproduction involving the use of fertility medications to induce ovulation by multiple ovarian follicles. These multiple follicles can be taken out by oocyte retrieval for use in in vitro fertilisation (IVF), or be given time to ovulate, resulting in superovulation which is the ovulation of a larger-than-normal number of eggs, generally in the sense of at least two. When ovulated follicles are fertilised in vivo, whether by natural or artificial insemination, there is a very high risk of a multiple pregnancy.

<span class="mw-page-title-main">In vitro maturation</span> Artificial maturation of harvested immature egg cells

In vitro maturation (IVM) is the technique of letting the contents of ovarian follicles and the oocytes inside mature in vitro. It can be offered to women with infertility problems, combined with In Vitro Fertilization (IVF), offering women pregnancy without ovarian stimulation.

Poor ovarian reserve is a condition of low fertility characterized by 1): low numbers of remaining oocytes in the ovaries or 2) possibly impaired preantral oocyte development or recruitment. Recent research suggests that premature ovarian aging and premature ovarian failure may represent a continuum of premature ovarian senescence. It is usually accompanied by high FSH levels.

<span class="mw-page-title-main">Fertility testing</span>

Fertility testing is the process by which fertility is assessed, both generally and also to find the "fertile window" in the menstrual cycle. General health affects fertility, and STI testing is an important related field.

Follicle-stimulating hormone (FSH) insensitivity, or ovarian insensitivity to FSH in females, also referable to as ovarian follicle hypoplasia or granulosa cell hypoplasia in females, is a rare autosomal recessive genetic and endocrine syndrome affecting both females and males, with the former presenting with much greater severity of symptomatology. It is characterized by a resistance or complete insensitivity to the effects of follicle-stimulating hormone (FSH), a gonadotropin which is normally responsible for the stimulation of estrogen production by the ovaries in females and maintenance of fertility in both sexes. The condition manifests itself as hypergonadotropic hypogonadism, reduced or absent puberty, amenorrhea, and infertility in females, whereas males present merely with varying degrees of infertility and associated symptoms.

Ovarian follicle activation can be defined as primordial follicles in the ovary moving from a quiescent (inactive) to a growing phase. The primordial follicle in the ovary is what makes up the “pool” of follicles that will be induced to enter growth and developmental changes that change them into pre-ovulatory follicles, ready to be released during ovulation. The process of development from a primordial follicle to a pre-ovulatory follicle is called folliculogenesis.

Gonadotropin surge-attenuating factor (GnSAF) is a nonsteroidal ovarian hormone produced by the granulosa cells of small antral ovarian follicles in females. GnSAF is involved in regulating the secretion of luteinizing hormone (LH) from the anterior pituitary and the ovarian cycle. During the early to mid-follicular phase of the ovarian cycle, GnSAF acts on the anterior pituitary to attenuate LH release, limiting the secretion of LH to only basal levels. At the transition between follicular and luteal phase, GnSAF bioactivity declines sufficiently to permit LH secretion above basal levels, resulting in the mid-cycle LH surge that initiates ovulation. In normally ovulating women, the LH surge only occurs when the oocyte is mature and ready for extrusion. GnSAF bioactivity is responsible for the synchronised, biphasic nature of LH secretion.

Ovarian follicle dominance is the process where one or more follicles are selected per cycle to ovulate.

References

  1. Sherwood L (2010). "formation of the antrum". Human physiology: from cells to system. Australia ; United States: Brooks/Cole. p. 769. ISBN   978-0-495-39184-5.
  2. Vandenhurk R, Bevers M, Beckers J (1997). "In-vivo and in-vitro development of preantral follicles". Theriogenology. 47: 73–82 (76). doi:10.1016/S0093-691X(96)00341-X.
  3. Klinkert ER, Broekmans FJ, Looman CW, Habbema JD, te Velde ER (March 2005). "The antral follicle count is a better marker than basal follicle-stimulating hormone for the selection of older patients with acceptable pregnancy prospects after in vitro fertilization". Fertility and Sterility. 83 (3): 811–814. doi:10.1016/j.fertnstert.2004.11.005. PMID   15749527.
  4. Broer SL, van Disseldorp J, Broeze KA, Dolleman M, Opmeer BC, Bossuyt P, et al. (2012). "Added value of ovarian reserve testing on patient characteristics in the prediction of ovarian response and ongoing pregnancy: an individual patient data approach". Human Reproduction Update. 19 (1): 26–36. doi: 10.1093/humupd/dms041 . PMID   23188168.
  5. 1 2 La Marca A, Sunkara SK (2013). "Individualization of controlled ovarian stimulation in IVF using ovarian reserve markers: from theory to practice". Human Reproduction Update. 20 (1): 124–140. doi: 10.1093/humupd/dmt037 . PMID   24077980.