Theca of follicle

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Theca of follicle
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Identifiers
Latin theca folliculi
Anatomical terminology

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

Contents

The theca are divided into two layers, the theca interna and the theca externa . [1]

Theca cells are a group of endocrine cells in the ovary made up of connective tissue surrounding the follicle. They have many diverse functions, including promoting folliculogenesis and recruitment of a single follicle during ovulation. [2] Theca cells and granulosa cells together form the stroma of the ovary.

Androgen synthesis

The anterior pituitary complex and hypophyseal portal system, where FSH and LH are released. 1808 The Anterior Pituitary Complex.jpg
The anterior pituitary complex and hypophyseal portal system, where FSH and LH are released.

Theca cells are responsible for synthesizing androgens, providing signal transduction between granulosa cells and oocytes during development by the establishment of a vascular system, providing nutrients, and providing structure and support to the follicle as it matures. [2]

Conversion of testosterone to estradiol through the action of aromatase. Testosterone estradiol conversion.png
Conversion of testosterone to estradiol through the action of aromatase.

Theca cells are responsible for the production of androstenedione, and indirectly the production of 17β estradiol, also called E2, by supplying the neighboring granulosa cells with androstenedione that with the help of the enzyme aromatase can be used as a substrate for this type of estradiol. [3] FSH induces the granulosa cells to synthesize aromatase, an enzyme that converts the androgens made by the theca interna into estradiol. [3]

Signaling cascade

Gonadotropin releasing hormone (GnRH) is released by projections of the hypothalamus into the anterior pituitary gland. Gonadotrophs are stimulated to produce follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which are released into the bloodstream to act upon the ovaries. Luteinizing hormone serves to directly stimulate theca cells. Together, these organs comprise the HPG axis.

Within the ovaries, transmembrane G-protein coupled receptors (GPCRs) bind to LH in the bloodstream, and the signal is transduced to the interior of theca cells through the action of the second messenger cAMP and third messenger protein kinase A (PKA). Theca cells are then stimulated to produce testosterone, which is sent in a paracrine fashion to neighboring granulosa cells for conversion to estradiol. [4]

Disorders

Hyperactivity of theca cells causes hyperandrogenism, and hypoactivity leads to a lack of estrogen. [5] Granulosa cell tumors, while rare (less than 5% of ovarian cancers), may both granulosa cells and theca cells. [6] Thecomas are benign proliferations of theca cells that may present with hormonal dysfunction. [7]

Theca cells (along with granulosa cells) form the corpus luteum during oocyte maturation. Theca cells are only correlated with developing ovarian follicles. [5] They are the leading cause of endocrine-based infertility, as either hyperactivity or hypoactivity of the theca cells can lead to fertility problems.

Folliculogenesis

A depiction of the ovarian cycle in animals Anatomy and physiology of animals Ovarian cycle showing from top left clockwise.jpg
A depiction of the ovarian cycle in animals

In human adult females, the primordial follicle is composed of a single oocyte surrounded by a layer of closely associated granulosa cells. In early stages of the ovarian cycle, the developing follicle acquires a layer of connective tissue and associated blood vessels. This covering is called the theca.

As development of the secondary follicle progresses, granulosa cells proliferate to form the multilayered membrana granulosum. Over a period of months, the granulosa cells and thecal cells secrete antral fluid (a mixture of hormones, enzymes, and anticoagulants) to nourish the maturing ovum.

In tertiary follicles, the single-layered theca differentiates into a theca interna and theca externa. The theca interna contains glandular cells and many small blood vessels, while the theca externa is composed of dense connective tissue and larger blood vessels. [8]

See also

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 released, an ovum travels through the fallopian tube/oviduct into the uterus. There is an ovary on the left and the right side of the body. The ovaries are endocrine glands, secreting various hormones that play a role in the menstrual cycle and fertility. The ovary progresses through many stages beginning in the prenatal period through menopause.

<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. Menarche usually occurs around the age of 12 years; menstrual cycles continue for about 30–45 years.

<span class="mw-page-title-main">Luteinizing hormone</span> Gonadotropin secreted by the adenohypophysis

Luteinizing hormone is a hormone produced by gonadotropic cells in the anterior pituitary gland. The production of LH is regulated by gonadotropin-releasing hormone (GnRH) from the hypothalamus. In females, an acute rise of LH known as an LH surge, triggers ovulation and development of the corpus luteum. In males, where LH had also been called interstitial cell–stimulating hormone (ICSH), it stimulates Leydig cell production of testosterone. It acts synergistically with follicle-stimulating hormone (FSH).

<span class="mw-page-title-main">Follicle-stimulating hormone</span> Gonadotropin that regulates the development of reproductive processes

Follicle-stimulating hormone (FSH) is a gonadotropin, a glycoprotein polypeptide hormone. FSH is synthesized and secreted by the gonadotropic cells of the anterior pituitary gland and regulates the development, growth, pubertal maturation, and reproductive processes of the body. FSH and luteinizing hormone (LH) work together in the reproductive system.

<span class="mw-page-title-main">Corpus luteum</span> Temporary endocrine structure in ovaries

The corpus luteum is a temporary endocrine structure in female ovaries involved in the production of relatively high levels of progesterone, and moderate levels of estradiol, and inhibin A. It is the remains of the ovarian follicle that has released a mature ovum during a previous ovulation.

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

Oogenesis or ovogenesis 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.

Gonadotropins are glycoprotein hormones secreted by gonadotropic cells of the anterior pituitary of vertebrates. This family includes the mammalian hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH), the placental/chorionic gonadotropins, human chorionic gonadotropin (hCG) and equine chorionic gonadotropin (eCG), as well as at least two forms of fish gonadotropins. These hormones are central to the complex endocrine system that regulates normal growth, sexual development, and reproductive function. LH and FSH are secreted by the anterior pituitary gland, while hCG and eCG are secreted by the placenta in pregnant women and mares, respectively. The gonadotropins act on the gonads, controlling gamete and sex hormone production.

<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">Corpus albicans</span> Structure derived from the corpus luteum

The corpus albicans is the regressed form of the corpus luteum. As the corpus luteum is being broken down by macrophages, fibroblasts lay down type I collagen, forming the corpus albicans. This process is called "luteolysis". The remains of the corpus albicans may persist as a scar on the surface of the ovary.

<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">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">Follicular phase</span> Phase of the estrous or menstrual cycle

The follicular phase, also known as the preovulatory phase or proliferative phase, is the phase of the estrous cycle during which follicles in the ovary mature from primary follicle to a fully mature graafian follicle. It ends with ovulation. The main hormones controlling this stage are secretion of gonadotropin-releasing hormones, which are follicle-stimulating hormones and luteinising hormones. They are released by pulsatile secretion. The duration of the follicular phase can differ depending on the length of the menstrual cycle, while the luteal phase is usually stable, does not really change and lasts 14 days.

<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.

Theca interna cells express receptors for luteinizing hormone (LH) to produce androstenedione, which via a few steps, gives the granulosa the precursor for estrogen manufacturing.

<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.

The theca externa is the outer layer of the theca folliculi. It is derived from connective tissue, the cells resembling fibroblasts, and contains abundant collagen. During ovulation, the surge in luteinizing hormone increases cAMP which increases progesterone and PGF2α production. The PGF2α induces the contraction of the smooth muscle cells of the theca externa, increasing intrafollicular pressure. This aids in rupture of the mature oocyte, or immature oocyte at the germinal vesicle stage in the canine, along with plasmin and collagenase degradation of the follicle wall.

<span class="mw-page-title-main">Antral follicle</span> Part of an ovary

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

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.

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. ↑ Melmed, Shlomo; Koenig, Ronald; Rosen, Clifford; Auchus, Richard; Goldfine, Allison (2020). "17:Physiology and Pathology of the female reproductive axis". Williams Textbook of Endocrinology. Vol. 1: Section V:Sexual Development and Function (14th. ed.). Elsevier Health Sciences. pp. 586–587. ISBN   978-8131262160.
  2. 1 2 Young, J. M.; McNeilly, A. S. (2010). "Theca: the forgotten cell of the ovarian follicle". Reproduction. 140 (4): 489–504. doi: 10.1530/REP-10-0094 . PMID   20628033.
  3. 1 2 Hall, John E. (2016). Guyton and Hall Textbook of Medical Physiology (13th ed.). Philadelphia, Pennsylvania: Elsevier. pp. 1042, 1044. ISBN   9781455770052. OCLC   900869748.
  4. ↑ Boron, Walter F.; Boulpaep, Emile L., eds. (2017). Medical Physiology (Third ed.). Philadelphia, Pennsylvania: Elsevier. ISBN   978-1-4557-3328-6. OCLC   951680737.
  5. 1 2 Magoffin, Denis A. (2005). "Ovarian theca cell". The International Journal of Biochemistry & Cell Biology. 37 (7): 1344–9. doi:10.1016/j.biocel.2005.01.016. PMID   15833266.
  6. ↑ Kottarathil, Vijaykumar Dehannathparambil; Antony, Michelle Aline; Nair, Indu R.; Pavithran, Keechilat (2013). "Recent Advances in Granulosa Cell Tumor Ovary: A Review". Indian Journal of Surgical Oncology. 4 (1): 37–47. doi:10.1007/s13193-012-0201-z. PMC   3578540 . PMID   24426698.
  7. ↑ Burandt, Eike; Young, Robert H. (August 2014). "Thecoma of the ovary: a report of 70 cases emphasizing aspects of its histopathology different from those often portrayed and its differential diagnosis". The American Journal of Surgical Pathology. 38 (8): 1023–1032. doi:10.1097/PAS.0000000000000252. ISSN   1532-0979. PMID   25025365. S2CID   10739300.
  8. ↑ Jones, Richard E.; Lopez, Kristin H. (2006). Human Reproductive Biology (3rd ed.). Amsterdam: Elsevier Academic Press. ISBN   978-0-12-088465-0. OCLC   61351645.
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