BGDA Practical 3 - Oogenesis and Ovulation

Introduction

This page covers gametogenesis, formation of the oocyte (egg, ovum) within the ovary. With the help of the tutors and other students you will work your way through identifying features described in the text.

Begin by looking at the ovary and the formation of the follicle containing the egg which matures and is released upon ovulation. The images are arranged in series so that progressive stages of the maturing follicle can be seen. The final image on this current page is a link to a movie showing follicle development and ovulation. Use the series of images of the cat ovary below to identify the key features described in the associated text.

Note: This should be a revision of the Female Histology Practical (support page) you have already completed. If you have trouble with the terms, there is a glossary at the bottom of each page.

Oogenesis

The graph below shows the changes in human germ cell numbers in the ovary with age, peaking at several 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. (More? Menstrual Cycle)

In the developing human ovary, oocytes remain at the diplotene stage of the first meiosis from fetal life through postnatal childhood, until puberty when the lutenizing hormone (LH) surges stimulate the resumption of meiosis.

Meiosis and Oogenesis

Whole Ovary

Ovary (cat, cross-section) showing histology and maturation of follicle.

Image (low magnification) showing cortical primordial follicles with primary (preantral) and secondary (antral) follicles lying deeper. Mesovarium at lower right and blood vessels in medullary region.

At this magnification, the overall organization of the ovary can be observed, cortex/medulla organization and arrangement of the maternal blood vessels, but few specific follicle details can be seen.

The next image is of the ovarian cortical region.

Ovary Cortex (low power)

Ovary cortex showing primordial follicles.

At the top of the image, is the outside of the ovary.

The thick connective tissue outer layer is the tunica albuginea. Over which a single layer of cells called the germinal epithelium (not visible) cover the surface of the ovary.

The next layer contains the earliest primordial follicles, single cells with pale cytoplasm and darkly stained nuclei.

The next layer contains many growing follicles at various stages of maturity and development. There is also evidence of degeneration as atretic follicles.

At the bottom of the image, is the medullary region of the ovary. Note the large number of maternal blood vessels which are the circulatory conduits for the estrogens and progesterones produced by the theca surrounding the ovarian follicles.

Note: germinal epithelium, tunica albuginea, primordial and atretic follicles. Note larger preantral follicle with (from the centre out) nucleus of maturing oocyte, oocyte cytoplasm, zona pellucida (pink ring), follicle cells, stromal cells.

Ovary Cortex Primordial and Primary Follicles

View of cortical ovary region showing primordial follicles and a single preantral follicle, with atretic follicle to its left. Bottom of picture shows outer cells of antral follicle.

High power view of ovary cortical region showing primordial follicles and a single preantral follicle.

Features: germinal epithelium, tunica albuginea, preantral follicle, nucleus of oocyte, oocyte cytoplasm, zona pellucida, Call-Exner body, stratum granulosa, basement membrane, theca, blood vessels surrounding follicle in theca layer.

Ovary Cortex and Medulla

Low power view of ovary cortex and medullary region and high power image within an antral follicle.

In the low power image note 3 stages of follicle development (primordial, preantral and antral).

Features:

• cortical primordial follicles
• oocyte
• follicular cells
• stromal cells
• preantral follicle- zona pellucida, stratum granulosa, theca
• early preovulatory follicle (Graafian) - oocyte, zona pellucida, corona radiata, cumulus oophorus, liquor folliculi, stratum granulosa, theca interna, theca externa, blood vessels surrounding follicle

Follicle Development

Human ovary follicle development

The development of a primordial follicle to a preovulatory follicle takes in excess of 120 days. After it has become a primary follicle of about 0.2 mm diameter it takes about 65 days to develop into a preovulatory follicle. Cohorts of follicles continually develop but only one is most sensitive to hormonal stimulation and is "selected", becoming the dominant follicle. All others in this cohort will undergo atresia.

Fertility Treatments

Superovulation therapy is a fertility drug treatement (oral clomiphene citrate and/or injectable FSH with or without LH) aimed at stimulating development/release of more than one follicle during a single menstrual cycle.

Follicle Classification

The above images show the histological changes that occur with follicle development (folliculogenesis). In humans, this entire process occurs over the timecourse of at least 3 menstrual cycles. This means that within the ovary during each cycle (at any point in time) many follicles can be either developing (folliculogenesis), regressing (atresis) and only a single follicle will be selected as ready for release. The selected follicle readied for release, generally one of the largest antral follicle, and can be classifed or described as: an antral preovulatory follicle or Graafian follicle or type 8 follicle (depending upon the classification used).

Classification systems - There are several different nomenclatures for the stages of follicle maturation (shown below) all of which makes the literature very confusing.

The simplest is primordial, preantral, antral, Preovulatory (Graaffian). You can also use the 5 step follicle classification: Primordial, Primary, Secondary, Tertiary, Preovulatory. Note that some classifications refer to the antral follicle as a secondary follicle and do not use the term tertiary follicle.

Note that along with follicle development, the oocyte also grows significantly in size, with the human oocyte (green) significantly larger than in other model species.

Primordial Follicle

Alternative nomenclature: small follicle or type 1, 2, 3 (25 cells) less than 50 micron diameter

Primary Follicle

Alternative nomenclature: preantral follicle or type 4 (26-100 cells), type 5 (101-300 cells) up to 200 micron diameter

Secondary Follicle

Alternative nomenclature: small antral type 6 (301-500 cells), small antral 500 micron diameter.

Tertiary Follicle

Alternative nomenclature: large antral type 7 (501-1000 cells) large antral 1000-6000 micron diameter.

Preovulatory Follicle

Alternative nomenclature: largest antral follicle or Graafian follicle or type 8 (>1000 cells) greater than 6000 micron diameter

Human Ovarian Follicle Classification
Class	Alternate nomenclature	Type	Number of Cells	Size (diameter µm)	Size ultrasound (mm)
primordial follicle	small	1, 2, 3	25	less than 50
primary follicle	preantral	4 5	26 - 100 101 - 300	up to 200
secondary follicle	antral small antral large antral	6 7	3001 - 500 501 - 1000	500 1000 - 6000	less than 18
preovulatory follicle	Graafian	8	greater than 1000	greater than 6000	18 – 28
Links: ovary | oocyte | menstrual cycle

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.

• 

  Atretic follicle

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  Atretic oocytes

Ovulation

Human Ovulation

Simplified Menstrual Cycle (see detailed Box 6.42 The human menstrual cycle)

‎‎Ovulation Page | Play | Audio

‎‎Ovulation Page | Play

Movie showing process of ovulation (release of oocyte and follicular fluid). Click on image or links to start movie.

Note that following ovulation the remnant of the follicle will degenerate if implantation does not occur (non-pregnant) forming a corpus albicans or following implantation (pregnancy) a corpus luteum which provides endocrine support to the uterus.

An endocrine signal (hCG human Chorionic Gonadotropin) from the implanting conceptus syncitiotrophoblasts maintains the corpus luteum, which in turn supports the uterine functional lining, preventing menstruation.

Oogenesis Interactive Component

Attempt the Quiz - Oogenesis and Ovulation

Here are a few simple Quiz questions that relate to Oogenesis and Ovulation from the lecture and practical. See your Quiz Result - Answer all the questions, then click "submit" to complete. The page will reload and you can then reopen this table to see your result and feedback. 1 Oogonia divide by mitosis During the fetal period. After birth. After puberty. During the reproductive period. All of the above. 2 Oocytes in follicles enter prophase 1 of meiosis and are arrested at the diplotene stage. Which of the following block the further stages of mitosis? follicular stimulating hormone (FSH) leutenising hormone (LH) cyclic AMP (cAMP) secreted by follicles androgens Oestrogens 3 Which of the following is the most correct sequence of ovarian follicle development classifications. Preovulatory, Secondary, Primary, Primordial Graafian, Primary, Small antral, large antral Primordial, Primary, Secondary, Preovulatory Primary, Secondary, Preovulatory None of the above 4 Follicle development involves only growth of supporting cells not the oocyte. true false

Terms

Oocyte Development

oocyte

Note there are additional specific term glossaries available listed at bottom of this table.

• antral follicle - (secondary) the stage following preantral in the decription of the sequence ovarian follicle development.

• antrum - (L. a cave), cavity; a nearly-closed cavity or bulge. In the ovary this refers to the follicular fluid-filled space within the follicle.

• atretic follicle - An ovarian follicle that fails to mature and degenerates. Also called "atresia" refering to the process of degeneration of the ovarian follicle. This process can occur at any stage of follicle development (folliculogenesis).

• clomiphene citrate - drug taken orally to promote the process of follicle/egg maturation.

• COCs - (cumulus-oocyte complexes) term used in Assisted Reproductive Technology to describe the ovulated Graafian follicle consisting of the oocyte surrounded by a packed layers of cumulus cells.

• corona radiata - Layer of follicle cells of cumulus oophorus remaining directly attached to zona pellucida of the oocyte. These cells communicate with the oocyte through the zone pellucida, also called granulosa cells.

• corpus albicans - (L. corpus = body, L. albicans = whitish); a degenerating corpus luteum in ovary.

• corpus luteum - (L. corpus = body, L. luteum = yellow) The remains of the ovulating ovarian follicle after ovulation, that acts as the initial endocrine organ supporting pregnancy and preventing menstruation (loss of the endometrial lining). de Graaf first observed it in the ovary of a cow as a yellow structure.

• cortical - (L. corticalis) at the outside (like the bark of a tree), usually combined with medulla meaning the core.

• cumulus oophorus - (L. cumulus = a little mound G. oon = egg + phorus = bearing); part of the wall of an ovarian follicle surrounding and carrying the ovum (oocyte).

• dictyate arrest - (prophase arrest) the oocyte meiosis state before puberty resumed with a surge of pituitary luteinizing hormone.

• first polar body - a small cytoplasmic exclusion body contains the excess DNA from the oocyte meiosis formed during meiosis 1.

• follicle - (L. folliculus = little bag,dim. of L. follis). A structure which develops in the ovary and contains a developing egg (oocyte).

• follicle stimulating hormone - (FSH, gonadotropin) A glycoprotein hormone secreted by anterior pituitary (adenohypophysis gonadotrophs, a subgroup of basophilic cells) and acts on gametogenesis and other systems in both males and females. Females, FSH acts on the ovary to stimulate follicle development. Males, acts on the testis Sertoli cells to increase androgen-binding protein (ABP) that binds androgens and has a role in spermatogenesis. pituitary

• follicular fluid - the fluid found in the antrum of a secondary follicle. Secreted by cells in the wall of the follicle. This fluid is released along with the oocyte at ovulation.

• germinal epithelium - cellular component covering surface of ovary, it is continuous with mesothelium covering mesovarium. Note that it is a historical misnomer, as it is not the actual site of germ cell formation.

• Graafian follicle - named after Regnier de Graaf (1641-1673), an historic Dutch physician embryologist who studied pregnancy using rabbits.

• granulosa cells - the supporting cells that surround the developing egg within the follicle thecal layers.

• homologs - maternal and paternal homologous chromosomes.

• Izumo1 - a protein located on the equatorial segment of acrosome-reacted spermatozoa recognizes its receptor Juno, on the oocyte surface, for plasma membrane binding and fusion. Named for a Japanese shrine dedicated to marriage. OMIM609278

• Juno - (folate receptor-δ; FOLR-δ) a glycophosphatidylinositol (GPI)-anchored, cysteine-rich glycoprotein on the oocyte surface for fertilisation that is the receptor of Izumo1 on the spermatozoa, for plasma membrane binding and fusion. OMIM615737

• luteinizing hormone - (LH, gonadotropin, lutropin, Interstitial Cell Stimulating Hormone, ICSH) glycoprotein hormone releasd from anterior pituitary hormone that acts on the gonad and has a role in male and female reproduction. Female, LH triggers ovulation (release of the oocyte). Male, LH stimulates testis interstital cell (Leydig cell) production of testosterone. Have been used clinically in humans for the treatment of female infertility.

• meiosis - oocyte reductive (diploid to haploid) cell division, with 1 round of DNA replication is followed by 2 rounds of chromosome segregation. The process beginning in the fetus and only completed at fertilization.

• mesovarium - mesentry of the ovary formed from a fold of the broad ligament that attaches the ovary.

• medullary - (L. medius = in the middle) relating to the medulla; pith, marrow, inner portion of an organ. Usually combined with cortex (cortical) meaning the outer layer.

• oocyte - (Greek, oo = egg, ovum) The term used to describe the haploid egg or ovum formed within the ovary (female gonad) and released to enter the uterine tube and be transported to the uterus. The mature oocyte is the cell released from the ovary during ovulation.

• oocyte retrieval - (egg retrieval) A clinical in vitro fertilization (IVF) procedure to collect the eggs contained in the ovarian follicles.

• oogenesis - (Greek, oo = egg + genesis = origin, creation, generation) process of diploid oogonia division and differentiation into an haploid oocyte (egg) within the ovary (female gonad). Mammalian meiosis will only be completed within the oocyte if fertilization occurs.

• oogonia - (Greek, oo = egg) diploid germ cells within the ovary (female gonad) which provide the primary oocytes for oocyte (egg) formation. In humans, all oogonia form primary oocytes within the ovary before birth.

• oolemma - (zona pellucida, vitelline membrane).

• oophorus - (Greek, oo = egg + phorus = carrying, egg-bearing) cumulus oophorus, used to describe the granulosa cells within the follicle that tether or link the oocyte to the wall of the follicle.

• ovarian reserve - Clinical term for the number of oocytes (non-growing follicles) available for possible fertilization at the different times during female reproductive life. A blood test for Anti-Mullerian Hormone (AMH) levels is used clinically as a measure of the ovarian reserve. human graph

• ovastacin - an oocyte released enzyme following fertilization that cleaves ZP2 protein to prevent polyspermy.

• ovulation - release of the oocyte from the mature follicle. In humans generally a single oocyte is released from a cohort of several maturing follicles.

• ovum - oocyte, note that historically this same term was also used to describe the early stages following fertilisation.

• polar body - small cytoplasmic exclusion body contains the excess DNA from the oocyte meiosis reductive division. The first polar body formed during meiosis 1, the second and sometimes third polar bodies are formed from meiosis 2 at fertilization.

• polyspermy - abnormal fertilization by more that a single spermatozoa, may generate a hydatidiform mole.

• preantral follicle - (primary) the stage following primordial in the description of the sequence ovarian follicle development.

• primary follicle - (preantral) the stage following primordial in the description of the sequence ovarian follicle development.

• primordial follicle - the first stage in the description of the sequence ovarian follicle development. Present in the ovary from birth, located in the stroma of the ovary cortex beneath the tunica albuginea. The primordial follicle is the oocyte and the surrounding follicular cells.

• primordial germ cell - oocyte present in the primordial follicle ovary from birth, located in the stroma of the ovary cortex beneath the tunica albuginea. The primordial follicle is the oocyte and the surrounding follicular cells.

• second polar body - a small cytoplasmic exclusion body contains the excess DNA from the oocyte formed during meiosis 2 at fertilization.

• secondary follicles - the stage following primary in the description of the sequence ovarian follicle development.

• stromal cells - in the ovary, cells surrounding the developing follicle that form a connective tissue sheath (theca folliculi). This layer then differentiates into 2 layers (theca interna, theca externa). This region is richly vascularized and involved in hormone secretion.

• superovulation therapy - a fertility drug treatement (oral clomiphene citrate and/or injectable FSH with or without LH) aimed at stimulating development/release of more than one follicle during a single menstrual cycle.

• tertiary follicle - (preovulatory, Graffian) the stage following secondary in the description of the sequence ovarian follicle development.

• theca folliculi - stromal cells in the ovary, cells surrounding the developing follicle that form a connective tissue sheath. This layer then differentiates into 2 layers (theca interna, theca externa). This region is vascularized and involved in hormone secretion.

• theca externa - stromal cells forming the outer layer of the theca folliculi surrounding the developing follicle. Consisting of connective tissue cells, smooth muscle and collagen fibers.

• theca interna - stromal cells forming the inner layer of the theca folliculi surrounding the developing follicle. This vascularized layer of cells respond to LH (leutenizing hormone) synthesizing and secreting androgens which are processed into estrogen.

• transzonal projection - (TZP) ovarian follicle term describing the cellular membraneous extension from the granulosa cell through the zona pellucida to the oocyte cell membrane where it forms gap junctions or adherens junctions allowing signalling and adhesion between the two cells.

• tunica albuginea - dense connective tissue layer lying near the ovary surface, a layer of simple squamous to cuboidal epithelial covers this layer. A similar named structure is found in male genital system.

• uterus - site of embryo implantation and development. Uterine wall has 3 major layers: endometrium, myometrium, and perimetrium. Endometrium can be further divided into the functional layer (shed/lost during menstruation) and basal layer (not lost during menstruation).

• zinc sparks following fertilization the oocyte releases a burst of zinc atoms in brief bursts (zinc sparks) has a role in zonal pellucida induced structural changes (hardening) along with ovastacin cleavage of ZP2 protein.

• zona hardening - following fertilization the structural changes that occur to the zona pellucida to prevents further spermatozoa binding acting as a block to polyspermy.

• zona pellucida - extracellular layer lying directly around the oocyte underneath follicular cells. Has an important role in egg development, fertilization and blastocyst development. This thick extracellular matrix consists of glcosaminoglycans and 3 glycoproteins (ZP1, ZP2, ZP3). (More? Zona pellucida)

Cell Division Terms (expand to view)
meiosis | mitosis anaphase - (Greek, ana = up, again) Mitosis term referring to the fourth stage, where the paired chromatids now separate and migrate to spindle poles. This is followed by telophase. anaphase A - Mitosis term referring to the part of anaphase during which the chromosomes move. anaphase B - Mitosis term referring to the part of anaphase during which the poles of the mitotic spindle move apart. aneuploidy - (aneuploid) term used to describe an abnormal number of chromosomes mainly (90%) due to chromosome malsegregation mechanisms in maternal meiosis I. aster - (Latin, aster = star) star-like object visible in most dividing eukaryotic cells contains the microtubule organizing center. astral microtubule - spindle apparatus microtubule (MT) originating from the centrosome which does not connect to a kinetochore. These microtubules only exist during mitosis, the other spindle types are polar and kinetochore microtubules. autosomal inheritance - term used in hereditary diseases which means that the disease is due to a DNA error in one of the 22 chromosome pairs that are not sex chromosomes. Both boys and girls can then inherit this error. If the error is in a sex chromosome, the inheritance is said to be sex-linked. bivalent - (tetrad) a pair of homologous chromosomes physically held together by at least one DNA crossover. bouquet stage - meiosis term for when in prophase transition to the zygotene stage, the chromosome telomeres attachment to the inner nuclear envelope and form a cluster. This occurs before the onset of homologous pairing and synapsis. The name comes from the chromosomes resembling a "bouquet of flowers". diploid - (Greek, di = double + ploion = vessel) having two sets of chromosomes (2n), this is the normal euploidy state for all human cells, other than gametes that are haploid (n, a single set of chromosomes). diplotene stage- (diplotene phase, diplonema; Greek, diplonema = "two threads") meiotic stage seen during prophase I, the chromosomes separate from one another a small amount giving this appearance. In the developing human ovary, oocytes remain at the diplotene stage from fetal life through postnatal childhood, until puberty when the lutenizing hormone (LH) surges stimulate the resumption of meiosis. Prophase I, is divided into 5 stages (leptotene, zygotene, pachytene, diplotene, diakinesis) based upon changes associated with the synaptonemal complex structure that forms between two pairs of homologous chromosomes. euploidy - the normal genome chromosomal set (n, 2n, 3n) or complement for a species, in humans this is diploid (2n). The other classes of numerical chromosomal abnormalities include aneuploidy, polyploidy and mixoploidy. FUCCI - Acronym for Fluorescence Ubiquitination Cell Cycle Indicator a molecular tool for identifying the stage in the cell cycle. In G0/G1 cells express a red fluorescent protein and S/G2/M cells express a green fluorescent protein. (More? Tooth Development Movie) haploid - (Greek, haploos = single) Having a single set of chromosomes (n) as in mature germ/sex cells (oocyte, spermatozoa) following reductive cell division by meiosis. Normally cells are diploid, containing 2 sets of chromosomes. Ploidy refers to the number of sets of chromosomes in the nucleus of a cell. heteroplasmy - presence of more than one type of organellar genome. In humans this can refer to variations in the mitochondrial DNA (mtDNA). (More? PMID 26281784) homologous chromosomes - meiosis term for the two matching (maternal and one paternal) chromosomes that align during meiosis I. homologous recombination - meiosis term when DNA of homologous chromosomes is covalently exchanged to produce chromosomes with new allele combinations, and also links homologous chromosomes with each other to form a bivalent human genome - DNA within the 23 nucleus chromosome pairs and the cytoplasmic mitochondrial DNA. kinetochore - the protein structure formed on chromatids where the spindle kinetochore microtubules attach during cell division. kinetochore microtubule - spindle apparatus microtubule (MT) that attaches to the chromosome kinetochore by its plus end, the other spindle types are astral and polar microtubules. kinesin - a microtubule (MT) motor protein that exists in many isoforms and most move towards the MT positive end. Different isoforms have different functions within the spindle apparatus. PMID 20109570 meiosis - reductive cell division required to produce germ cells (oocyte, spermatozoa) and for sexual reproduction. Note that only spermatozoa complete meiosis before fertilisation. Chromosome number is reduced from diploid to haploid, during this process maternal and paternal genetic material are exchanged. All other non-germ cells in the body divide by mitosis. (More? Meiosis | Spermatozoa Development | Oocyte Development | Week 1) meiosis I - (MI) the first part of meiosis resulting in separation of homologous chromosomes, in humans producing two haploid cells (N chromosomes, 23), a reductional division. meiosis II - (MII) the second part of meiosis. In male human spermatogenesis, producing of four haploid cells (23 chromosomes, 1N) from the two haploid cells (23 chromosomes, 1N), each of the chromosomes consisting of two sister chromatids produced in meiosis I. In female human oogenesis, only a single haploid cell (23 chromosomes, 1N) is produced. Meiosis II: Prophase II - Metaphase II - Anaphase II - Telophase II. meiotic silencing of unsynapsed chromatin - (MSUC) an aneuploidy protective mechanism for subsequent generations, during meiosis where chromosomes are silenced that fail to pair with their homologous partners. merotelic kinetochore - cell division abnormality in chromosomal attachment that occurs when a single kinetochore is attached to microtubules arising from both spindle poles. Normal chromosomal attachment in early mitosis, is by only one of the two sister kinetochores attached to spindle microtubules (monotelic attachment) later sister kinetochores attach to microtubules arising from opposite spindle poles (amphitelic attachment). metaphase - mitosis term referring to the third stage where mitotic spindle kinetochore microtubules align chromosomes in one midpoint plane. Metaphase ends when sister kinetochores separate. Originally based on light microscopy of living cells and electron microscopy of fixed and stained cells. A light microscope analysis called a "metaphase spread" was originally used to detect chromosomal abnormalities in cells. Mitosis Phases: prophase - prometaphase - metaphase - anaphase - telophase metaphase spread - In mitosis using light microscope analysis originally used to detect chromosomal abnormalities in cells, as chromosomes are only visible during cell division. microfilament - (MF) cytoskeleton filament normally required for cytoplasmic intracellular transport, motility and cell shape. Named by the actin monomers assembling into the smallest in cross-section of the three filament systems (microtubules and intermediate filaments). This system is disassembled and reassembled as the contractile ring for cytokinesis (cytoplasm division) following cell division mitosis and meiosis. microtubule - (MT) cytoskeleton filament normally required for cytoplasmic intracellular transport and motility. Named by the tubulin monomers assembling into "tubes", and are the largest in cross-section of the three filament systems (microfilaments and intermediate filaments). This system is disassembled and reassembled as the spindle apparatus during cell division. mitochondrial DNA - (mtDNA) multiple copies of a small circular DNA molecule located within the mitochondria matrix. In humans 16,568 bp in length containing 37 genes, originally inherited only from the oocyte (maternal inheritance). mitosis - (M phase) The normal division of all cells, except germ cells, where chromosome number is maintained (diploid). In germ cell division (oocyte, spermatozoa) meiosis is a modified form of this division resulting in reduction in genetic content (haploid). Mitosis, division of the nucleus, is followed by cytokinesis the division of the cell cytoplasm and the cytoplasmic contents. cytokinesis overlaps with telophase. p - chromosome short arm (possibly French, petit) and used along with chromosome and band number to indicate genes located on this arm of the chromosome. The chromosome long arm is identified as q (possibly French, tall) chosen as next letter in alphabet after p. These chromosomal arms are only seen when the chromosome is folded for cell division. polar body - a small cytoplasmic exclusion body containing the excess DNA formed during the oocyte meiosis cycle and following spermatozoa fertilization. polar microtubule - spindle apparatus microtubule (MT) that can arise from either pole and overlap at the spindle midzone. This interdigitating structure consisting of antiparallel microtubules is responsible for pushing the poles of the spindle apart. The other spindle types are astral and kinetochore microtubules. prometaphase - (Greek, pro = before) mitosis term referring to the second stage, when the nuclear envelope breaks down into vesicles. Microtubules then extend from the centrosomes at the spindle poles (ends) and reach the chromosomes. This is followed by metaphase. pronuclear fusion - (Greek, pro = before) the process of the fusion of the two haploid nuclear structures (pronuclei) contributed from the spermatazoa and oocyte to form the first diploid nucleus cell. Can also be called "fusion of pronuclei". pronucleus - (Greek, pro = before; plural, pronuclei) the two haploid nuclei or nuclear structures containing the genetic material from the spermatozoa and the oocyte. These two haploid nuclei will fuse together to form the first diploid nucleus cell, the zygote. Therefore the nuclear structures that exist "before the nucleus", the plural term is pronuclei. prophase - (Greek, pro = before) - mitosis term referring to the first stage, when the diffusely stained chromatin resolves into discrete chromosomes, each consisting of two chromatids joined together at the centromere. prophase I - meiosis term refers to the first phase of meiosis I, which together with meiosis II results in the reductive cell division only occurring gametes. Prophase can be further divided into a number of stages: leptotene zygotene, pachytene, diplotene, diakinesis. q - chromosome long arm (possibly French, tall), the next letter in alphabet after p, and used along with chromosome and band number to indicate genes located on this arm of the chromosome. The chromosome short arm is identified as p (possibly French, petit). These chromosomal arms are only seen when the chromosome is folded for cell division. S phase - during interphase of cell cycle where DNA is duplicated prior to second growth period (G2 phase) that is followed by mitosis (M phase). synapsis - (syndesis) meiosis term for the pairing of two homologous chromosomes that occurs during prophase I. synaptonemal complex - meiosis term for a protein structure essential for synapsis of homologous chromosomes. (proteins SCP3 and SCP1). telomere - region found at each end of the chromosome and involved in cellular ageing and the capacity for division. The regions consist of repeated sequences protecting the ends of chromosomes and harbour DNA repair proteins. In the absence of the enzyme telomerase, these regions shorten during each cell division and becoming critically short, cell senescence occurs. telophase - mitosis term referring to the fifth stage, where the vesicles of the nuclear envelope reform around the daughter cells, the nucleoli reappear and the chromosomes unfold to allow gene expression to begin. This phase overlaps with cytokinesis, the division of the cell cytoplasm. telomerase - the enzyme that maintains the chromosome end length, the telomeres, involved in cellular ageing and the capacity for division. Absence of telomerase activity leads to the chromosome ends shorten during each cell division, becoming critically short and cell senescence then occurs. tetrad - (bivalent) a pair of homologous chromosomes physically held together by at least one DNA crossover.
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Additional Information

Additional Information - Content shown under this heading is not part of the material covered in this class. It is provided for those students who would like to know about some concepts or current research in topics related to the current class page.

• oocyte development detailed information about oocyte formation.
• ovary development detailed information about ovary development (more suitable for BGDB Sexual Development).
• History of the Pap Smear
• Female Histology - covered in another Histology practical class.
• Premature Ovarian Failure
• Menopause
• Gynaecological cancer information, as they are an important clinical topic specific to these reproductive organs.

Follicle Classification

Here are the alternate follicle classifications compared.

Human Ovarian Follicle Classification

Class	Alternate nomenclature	Type	Number of Cells	Size (diameter µm)	Size ultrasound (mm)
primordial follicle	small	1, 2, 3	25	less than 50
primary follicle	preantral	4 5	26 - 100 101 - 300	up to 200
secondary follicle	antral small antral large antral	6 7	3001 - 500 501 - 1000	500 1000 - 6000	less than 18
preovulatory follicle	Graafian	8	greater than 1000	greater than 6000	18 – 28
Links: ovary | oocyte | menstrual cycle

Premature Ovarian Failure

Premature Ovarian Failure (POF) a clinical term describes the absence of normal ovarian function due to the depletion of the primordial follicle pool before 40 years of age a range of factors (autoimmune, iatrogenic, infections, genetic defects). This occurs in approximately 1% of women below 40 years of age.

Premature Ovarian Failure (POF) can be primary or secondary based on puberty.

• primary - absence of puberty, development and primary amenorrhea, generally caused by ovarian dysgenesis (45XO, Turner syndrome, Monosomy X).
• secondary - normal puberty, usually present with the later disappearance of menstrual cycles.

PubMed: Premature Ovarian Failure

Menopause

Term describes the physiological changes that accompany the age related loss of fertility. There is a decrease in ovarian follicle numbers, gradually elevated FSH levels, onset of cycle irregularity leading to the final cessation of menses. A recent review has looked at genetic factors that could affect the age at natural menopause and identified from linkage analyses (9q21.3 and chromosome 8 at 26 cM) and association studies genomic regions (19q13.42 and 20p12.3), containing two promising candidate genes (Bruck syndrome 1, BRKS1) and Menopause quantitative trait locus 3 (MENOQ3)..

Links: BRKS1 | MCM

PubMed: Menopause

Cervical Screening Program

In Australia, the "Pap Smear" test was replaced in 2017 (1 December) by a new "National Cervical Screening Program". This new program will use new technologies to detect HPV DNA rather than pathological screening for abnormal cells from a "Pap Smear". For more information see the external link below.

DOH Information Video
<html5media width="480" height="360">https://www.youtube.com/embed/a22VIXp3cxc</html5media> Department of Health (Published on Nov 1, 2017)

"The two yearly Pap test for women aged 18 to 69 will change to a five yearly human papillomavirus (HPV) test for women aged 25 to 74. Women will be due for the first Cervical Screening Test two years after their last Pap test."

"The Cervical Screening Test detects infection with human papillomavirus (HPV). Partial genotyping is used to determine the type of HPV into one of two groups: oncogenic HPV 16/18 or oncogenic HPV types other than 16/18 as a pooled result." (NCSP Factsheet)

Links: National Cervical Screening Program | Factsheet | Compass Trial |

ABC radio program Monday 27 March 2017 - Death of the pap smear? | ABC Audio - Death of the pap smear?

History of the Pap Smear

The information below relates to the original "Pap Smear" (Papanicolaou smear, pap test, cervical smear) The text below is from the ABC - Great Moments In Science.

"Luckily, we have the famous Pap Smear - an excellent way to find cancer of the cervix before it digs in locally and/or spreads throughout the body. The Pap Smear is named after a certain Dr. Papanicolaou - who did a Pap Smear on his wife virtually every day for 20 years.

George Nikolas Papanicolaou was born in 1883 in Kymi, a small town overlooking the Aegean Sea on the Island of Euboea in Greece. His father, Nikolas Papanicolaou was both the Major of Kymi and a medical doctor. His older brother, Naso, had studied law, so his father convinced George to continue in the family medical tradition. So George studied medicine, and did well, graduating with a degree in honours in 1904............"

Links: Menstrual Cycle - Histology | Dilatation and curettage (D&C) | ABC - Great Moments In Science

Gynaecological Cancers

Main Types: Ovarian cancer (ICD-10 code C56) | Cervical cancer (ICD-10 code C53) | Uterine cancer (ICD-10 codes C54 and C55) | Other gynaecological cancers (ICD-10 codes C51, C52, C57 and C58)

Ovarian cancer in Australia: an overview, 2010

"Ovarian cancer was the most common cause of gynaecological cancer death and the sixth most common cause of cancer-related death among Australian women in 2006."

Cervical screening in Australia 2006-2007

"Incidence and mortality of cervical cancer in Australia remain low, consistent with the Program’s aim to reduce incidence and mortality. There were 9.2 new cases per 100,000 women in 2005, and 1.9 deaths per 100,000 women in 2006 (aged 20-69 years). Incidence for Aboriginal and Torres Strait Islander women has been estimated to be more than double (ABS & AIHW 2008), and mortality found to be five times that of other Australian women."

Links: Ovarian cancer in Australia: an overview, 2010 | Australian Gynaecological cancer projections 2010-2015

References

BGDA: Lecture 1 | Lecture 2 | Practical 3 | Practical 6 | Practical 12 | Lecture Neural | Practical 14 | Histology Support - Female | Male | Tutorial

Glossary Links

Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link

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Cite this page: Hill, M.A. (2024, April 16) Embryology BGDA Practical 3 - Oogenesis and Ovulation. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/BGDA_Practical_3_-_Oogenesis_and_Ovulation

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G