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Ovarian follicle

 

 
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Ovarian follicle is the basic unit of female reproductive biology and is composed of roughly spherical aggregations of cell
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
s found in the ovary
Ovary

The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in females are homology to testicle in males, in that they are both gonads and endocrine glands....
. They contain a single oocyte
Oocyte

An oocyte, ovocyte, or rarely ocyte, is a female gametocyte or germ cell involved in biological reproduction. In other words, it is an immature ovum, or ovum cell....
 (aka ovum
Ovum

An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization....
 or egg). These structures are periodically initiated to grow and develop, culminating in ovulation
Ovulation

Ovulation is the process in the menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum that participates in reproduction....
 of usually a single competent oocyte. These eggs/ovum are only developed once every menstrual cycle (i.e, once a month).

cells of the ovarian follicle are the oocyte, granulosa cells and the cells of the internal and external theca layers.

oocyte in a follicle is in the stage of a primary oocyte.






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Encyclopedia


Ovarian follicle is the basic unit of female reproductive biology and is composed of roughly spherical aggregations of cell
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
s found in the ovary
Ovary

The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in females are homology to testicle in males, in that they are both gonads and endocrine glands....
. They contain a single oocyte
Oocyte

An oocyte, ovocyte, or rarely ocyte, is a female gametocyte or germ cell involved in biological reproduction. In other words, it is an immature ovum, or ovum cell....
 (aka ovum
Ovum

An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization....
 or egg). These structures are periodically initiated to grow and develop, culminating in ovulation
Ovulation

Ovulation is the process in the menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum that participates in reproduction....
 of usually a single competent oocyte. These eggs/ovum are only developed once every menstrual cycle (i.e, once a month).

Structure

Gray1164
The cells of the ovarian follicle are the oocyte, granulosa cells and the cells of the internal and external theca layers.

Oocyte

The oocyte in a follicle is in the stage of a primary oocyte. The nucleus of such an oocyte is called a germinal vesicle (see picture).

Granulosa

Granulosa cells within the follicle surround the oocyte; their numbers increase directly in response to heightened levels of circulating gonadotropins or decrease in response to testosterone
Testosterone

Testosterone is a steroid hormone from the androgen group. In mammals, testosterone is primarily secreted in the testis of males and the ovaries of females, although small amounts are also secreted by the adrenal glands....
. They also produce peptides involved in ovarian hormone synthesis regulation. Follicle-stimulating hormone
Follicle-stimulating hormone

Follicle-stimulating hormone is a hormone synthesized and secreted by gonadotropes in the anterior pituitary gland. FSH regulates the development, growth, pubertal maturation, and reproductive processes of the human body....
 (FSH) induces granulosa cells to express leutenizing hormone (LH) receptors on their surfaces; when circulating LH binds to these receptors, proliferation stops.

Theca

The granulosa cells, in turn, are enclosed in a thin layer of extracellular matrix
Extracellular matrix

In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal Cell in addition to performing various other important functions....
 – the follicular basement membrane or basal lamina (fibro-vascular coat in picture). Outside the basal lamina, the layers theca interna and theca externa are found.

Development

Folliclesinovary
Primordial follicles are indiscernible to the naked eye. However, they develop to primary, secondary and finally mature vesicular follicles. Mature vesicular follicles are sometimes called Graafian follicles (after Regnier de Graaf
Regnier de Graaf

Regnier de Graaf was a The Netherlands physician and anatomy who made key discoveries in reproductive biology. His first name is often spelled Reinier or Reynier....
).

In humans, oocytes are established in the ovary before birth, and may lay dormant awaiting initiation for up to 50 years .

After rupturing, the follicle is turned into a corpus luteum
Corpus luteum

The corpus luteum is a temporary endocrine structure in mammals, involved in production of progestogen, which is needed to maintain pregnancy....
.

Development of oocytes in ovarian follicles

In a larger perspective, the whole folliculogenesis from primordial to preovulatory follicle is located in the stage of meiosis I of ootidogenesis in oogenesis.

The embryonic development doesn't differ from the male one, but follows the common path before gametogenesis
Gametogenesis

Gametogenesis is a process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes....
. Once gametogonia enter the gonadal ridge
Gonadal ridge

In embryology, the gonadal ridge is the precursor to the gonads. The gonadal ridge initially consists mainly of mesenchyme and cells of underlying mesonephric origin....
, however, they attempt to associate with these somatic cells. Development proceeds and the gametogonia turns into oogonia, which become fully surrounded by a layer of cells (pre-granulosa cells).

Oogonia multiply by dividing mitotically; this proliferation ends when the oogonia enter meiosis. The amount of time that oogonia multiply by mitosis is not species specific. In the human fetus, cells undergoing mitosis are seen until the second and third trimester
Trimester

Trimester means a period of three months. It is most commonly used in physiology related to pregnancy and at some universities to describe an academic term....
 of pregnancy ; . After beginning the meiotic process, the oogonia (now called primary oocytes) can no longer replicate. Therefore the total number of gametes is established at this time. Once the primary oocytes stop dividing the cells enter a prolonged ‘resting phase’. This ‘resting phase’ or dictyate
Dictyate

The dictyate or dictyotene is a prolonged resting phase in oogenesis. It occurs in the stage of meiotic prophase I in ootidogenesis. It starts late in fetal life and is terminated shortly before ovulation by the LH surge....
 stage can last anywhere up to fifty years in the human.

For each primary oocyte that undergoes meiosis, only one functional oocyte is produced. The other two or three cells produced are called polar bodies. Polar bodies have no function and eventually deteriorate.

The primary oocyte turns into a secondary oocyte in mature ovarian follicles. Unlike the sperm, the egg is arrested in the secondary stage of meiosis until fertilization.

Upon fertilization by sperm, the secondary oocyte continues the second part of meiosis and becomes a zygote
Zygote

A zygote is a cell that is the result of fertilization. That is, two ploidy cells—usually an ovum from a female and a sperm cell from a male—merge into a single ploidy cell called the zygote ....
.

Pathology

Any ovarian follicle that is larger than about two centimeters is termed an ovarian cyst
Ovarian cyst

An ovarian cyst is any collection of fluid, surrounded by a very thin wall, within an ovary. Any ovarian follicle that is larger than about two centimeters is termed an ovarian cyst....
.

Additional images


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