Ovary Development: Difference between revisions

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==Follicle Classification==
==Follicle Classification==
There are several different nomenclatures for the stages of follicle maturation. It probably does not matter which naming system you use, as long as you are consistent and use the same set of terminology for all stages.
There are several different nomenclatures for the stages of follicle maturation. It probably does not matter which naming system you use, as long as you are consistent and use the same set of terminology for all stages.
Gonadotropin is sometimes abbreviated Gn. The British spelling is gonadotrophin.


[[File:Ovary-_follicle_stages.jpg]]
[[File:Ovary-_follicle_stages.jpg]]

Revision as of 11:39, 3 May 2010

Ova41he.jpg

Introduction

The ovary and uterus

The female gonad is the ovary and is closely associated with female internal genital (reproductive) tract development. In humans, these laterally paired organs lie within the peritoneal cavity. Genes such as Wnt-4 and DAX-1 necessary for initiation of female pathway ovary development, female gonad is not considered a default process.

Initial gonad development in females and males is virtually identical with germ cells migrating into an indifferent gonad. In females with XX, the ovary then begins to develop and the subsequent structure and timecourse of germ cell then differs between males and females. In the ovary oocytes proliferate prior to birth and arrest in meiosis 1.

Genital Links: genital | Lecture - Medicine | Lecture - Science | Lecture Movie | Medicine - Practical | primordial germ cell | meiosis | endocrine gonad‎ | Genital Movies | genital abnormalities | Assisted Reproductive Technology | puberty | Category:Genital
Female | X | X inactivation | ovary | corpus luteum | oocyte | uterus | vagina | reproductive cycles | menstrual cycle | Category:Female
Male | Y | SRY | testis | spermatozoa | ductus deferens | penis | prostate | Category:Male
Historic Embryology - Genital 
General: 1901 Urinogenital Tract | 1902 The Uro-Genital System | 1904 Ovary and Testis | 1912 Urinogenital Organ Development | 1914 External Genitalia | 1921 Urogenital Development | 1921 External Genital | 1942 Sex Cords | 1953 Germ Cells | Historic Embryology Papers | Historic Disclaimer
Female: 1904 Ovary and Testis | 1904 Hymen | 1912 Urinogenital Organ Development | 1914 External Genitalia | 1914 Female | 1921 External Genital | 1927 Female Foetus 15 cm | 1927 Vagina | 1932 Postnatal Ovary
Male: 1887-88 Testis | 1904 Ovary and Testis | 1904 Leydig Cells | 1906 Testis vascular | 1909 Prostate | 1912 Prostate | 1914 External Genitalia | 1915 Cowper’s and Bartholin’s Glands | 1920 Wolffian tubules | 1935 Prepuce | 1935 Wolffian Duct | 1942 Sex Cords | 1943 Testes Descent | Historic Embryology Papers | Historic Disclaimer

| Menstrual Cycle | X Chromosome | Genital System - Female | Oogenesis

Human Timeline

Approximate Timeline of human development listed below.

24 days - intermediate mesoderm, pronephros primordium

28 days - mesonephros and mesonephric duct

35 days - uteric bud, metanephros, urogenital ridge

42 days - cloacal divison, gonadal primordium (indifferent)

49 days - paramesonephric duct, gonadal differentiation

56 days - paramesonephric duct fusion (female)

100 days - primary follicles (ovary)

Oogenesis

Human ovary oocyte number

The 2 human ovaries gradually lose follicles both before and after puberty (the beginning of ovulation); beginning with about 7 million before birth, 2 million at birth, 300-400,000 by puberty and finally by late 40’s have only a few follicles left. The number of antral follicles detected within the ovary also decreases with increasing materal age. In humans, a primodial follicle take about 150 days to develop into a preantral follicle (primary) and another 120 days to form an antral follicle (secondary). A number of antral follicles will then "compete" for 14-15 days to become the dominant follicle, which will undergo ovulation.

  • The graph shows the changes in human germ cell numbers in the ovary with age.
  • Total numbers peak at about 7 million (occuring in early fetal development) and then decreasing by apopotic cell death.
  • At puberty there remain only about 400,000 and only about 10% of these will be released through reproductive life.

Infant Ovary

Histology of the female infant ovary

This image shows a region (see inset) of the infant ovary cortex.

There are a large number of developing oocytes which will eventually form a dense primordial germ layer at the ovary periphery.

Later stages of follicle development are completely absent and will begin to only appear just prior to puberty.

Postnatal Oogenesis

There is a dogma in mammalian development that new oocyte and follicle production does not occur during postnatal life. There is substantial data that shows human ovarian changes postnatally are loss by apoptosis of prenatal oocytes. A research group (Tilly JL, Johnson J. 2004, 2007) has recently published experiments using mice, showing potentially other sources/sites (bone marrow) of oocyte (putative germ cell) generation. They recently stated that the argument should be based upon "experimental approaches than simply an absence of evidence, especially from gene expression analyses". Several other research groups (Eggan K etal. 2004 and Veitia etal. 2007) have argued against these findings.

Adult Follicle Structure

Secondary (Antral) Follicle Structure

A follicle usually contains a single oocyte (egg, ovum, female gamete) and a series of supporting cells and a single fluid-filled space in layers surrounding this cell. The 3 layers below are arranged in layers outward from the oocyte.

Granulosa Cells

  • A specific cell type that proliferates in association with the oocyte within the developing follicles of the ovary. These cells form the follicle stratum granulosa and are also given specific names based upon their position within the follicle.
  • The membrana granulosa cells sit on the follicular basal lamina and line the antrum as a stratified epitelium. Following ovulation, these granulosa cells contribute to corpus luteum.
  • The cumulus oophorus is a column of granulosa cells that attaches the oocyte to the follicle wall. At ovulation, this column of cells is broken or separates to release the oocyte from its follicle attachment.
  • The corona radiata are the granulosa cells that directly surround the oocyte, and are released along with it at ovulation. Following ovulation, the corona radiata provide physical protection to the oocyte and are the initial structural barrier that spermatazoa must penetrate during fertilization.

Follicular Fluid

  • The antrum is a fluid-filled space in the secondary (antral) follicle
  • At ovulation, fluid is released along with the oocyte
  • Thought to "carry" the oocyte out of the follicle (like a boat on a wave)
  • Aids entry into the uterine tube

Theca Interna

(Greek, thek = box) The ovarian follicle endocrine cells forming the inner layer of the theca folliculi surrounding the developing follicle within the ovary. This vascularized layer of cells respond to leutenizing hormone (LH) synthesizing and secreting androgens (androstendione) transported to glomerulosa cells which process initially into testosterone and then by aromatase into estrogen (estradiol). Theca cells do not begin hormonal functions until puberty.

Theca Externa

(Greek, thek = box) The ovarian follicle stromal cells forming the outer layer of the theca folliculi surrounding the developing follicle within the ovary. Consisting of connective tissue cells, smooth muscle and collagen fibers.

Follicle Classification

There are several different nomenclatures for the stages of follicle maturation. It probably does not matter which naming system you use, as long as you are consistent and use the same set of terminology for all stages.

Gonadotropin is sometimes abbreviated Gn. The British spelling is gonadotrophin.

Ovary- follicle stages.jpg

Primordial Follicle

Alternate nomenclature: small follicle or type 1, 2, 3 (25cells)

Primary Follicle

Alternate nomenclature: preantral follicle or type 4 (26-100 cells), type 5 (101-300 cells)

Secondary Follicle

Alternate nomenclature: small and large antral follicle or type 6 (3001-500 cells), type 7 (501-1000 cells)

Preovulatory Follicle

Alternate nomenclature: Graafian follicle or type 8 (>1000 cells)

Atresia

At any one time the majority of follicles are destined not to complete maturation and at any stage (from type 4-7) degeneration of the follicle can occur. This process is called ATRESIA.

Follicle Factors

There are both external endocrine factors and internal follicle factors that can influence the development and atresia of ovarian follicles.

External Factors

Leutenizing Hormone (LH)

  • from the anterior pituitary
  • stimulate the theca interna to synthesize and secrete androgens (androstendione) transported to granulosa cells
  • granulosa cells process initially into testosterone and then by aromatase into estrogen (estradiol)

Follicle-stimulating hormone (FSH)

  • from the anterior pituitary
  • initiates follicle growth through the granulosa cells
  • involved in selecting the most advanced (sensitive) follicle to proceed to ovulation

Internal Factors

Oocyte Factors

  • Growth Differentiation Factor-9 (GDF-9) - involved in the differentiation of theca cells during this early stage of follicular development OMIM 601918

Granulosal Factor(s)

  • stimulates the recruitment of theca cells from cortical stromal cells

Thecal Factor(s)

  • appear to be several inhibitors of apoptotic cell death
  • Epidermal growth factor (EGF)
  • Transforming growth factor alpha (TGF-α)
  • keratinocyte growth factor (KGF)
  • hepatocyte growth factor (HGF)
  • Bone morphogenetic protein 7 (BMP-7) also known as osteogenic protein-1 or OP-1

References

Reviews

Articles

  • Oocyte-granulosa-theca cell interactions during preantral follicular development. Orisaka M, Tajima K, Tsang BK, Kotsuji F. J Ovarian Res. 2009 Jul 9;2(1):9. PMID: 19589134 | J Ovarian Res.
  • The forkhead transcription factor FOXL2 is expressed in somatic cells of the human ovary prior to follicle formation. Duffin K, Bayne RA, Childs AJ, Collins C, Anderson RA. Mol Hum Reprod. 2009 Dec;15(12):771-7. Epub 2009 Aug 25. PMID: 19706741 | Mol Hum Reprod.

Search Pubmed

Search Pubmed: Ovary Development | Follicle Development | Follicle Atresia

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