1. OOCYTE LIPIKA PATTANAIK FEMELIFE FERTILITY www.femelife.com
EMBRYOLOGIST
FEMELIFE FERTILITY

2. An oocyte is a female gametocyte or germ cell involved in reproduction
It is an immature ovum or an egg
An oocyte is produced in the ovary during female gametogenesis
The female germ cells produce a primordial germ cell which undergoes mitosis to form an oogonium
During oogenesis the oogonium becomes a primary oocyte

3. It is the creation of an ovum
It is the female form of gametogenesis and involves the development of various stages of the immature ovum
In mammals the first part of oogensis starts in germinal epithelium, which gives rise to the development of ovarian follicles, the functional unit of the ovary
Oogenesis consists of several sub processes – oocytogenesis, ootidogenesis and the maturation to form an ovum
Folliculogenesis is a separate sub process and supports all three oogenetic sub process

5. Oogenesis starts with the process of developing oogonia,which occurs via the transformation of primordial follicles into primary oocytes, a process called oocytogenesis
Oocytogenesis is complete either before or shortly after birth

6. NUMBER OF PRIMARY OOCYTES
Oocytogenesis is complete
Primary oocytes reach their max. development at 20 weeks of gestational age,when approx 7 million primary oocytes have been created,this no. will be approx. reduced to 1-2 million

7. OOTIDOGENESIS
The succeeding phase of ootidogenesis occurs when the primary oocyte develops into an ootid.
This is achieved by the process of meiosis
Although this process begins at pre natal age, it stops at prophase I.
All oocytes ,still primary oocytes, have halted at this stage of development,called dictyate
After menarche these cells then continue to develop

8. MEIOSIS I
Meiosis I of ootidogenesis begins during embryonic development ,but halts in the diplotene stage of prophase I until puberty
For those primary oocytes that continue to develop in each menstrual cycle synapsis occurs and tetrads form enabling chromosomal cross over to occur
As a result of meiosis I the primary oocyte develops into the secondary oocyte and the first polar body

9. MEIOSIS II
Immediately after meiosis I ,the haploid secondary oocyte initiates meiosisII.
This process is also halted at the mataphase II stage until fertilization
When meiosisII has completed ,an ootid and another polar body have now been created

10. MATURATION INTO OVUM
Both polar bodies disintegrate at the end of meiosis II,leaving only the ootid,which then undergoes maturation into mature ovum
The function of forming polar bodies is to discard the extra haploid sets of chromosomes

11. FOLLICULOGENESIS
It is the maturation of ovarian follicle,a densely packed shell of somatic cells that contains an immature oocyte
This describes the progression of number of small primordial follicles into large pre ovulatory follicles that enter the menstrual cycle
Folliculogenesis ends when the remaining follicles in the ovaries are incapable of responding to the hormones that had recruited some of the follicles to mature
This depletion of follicle supply signals the beginning of menopause

12. Female Gametogenesis

13. HUMAN OOGENESIS
At the start of the menstrual cycle some primary follicles begin to develop under the influence of elevated FSH to form secondary follicles.
By around day 9 of the cycle only one healthy secondary follicle remains with the rest having undergone ovarian follicle atrasia
The remaining follicle is called the dominant follicle and is responsible for producing large amount of estradiol during the late follicular phase.

14. Estradiol production depends upon the co operation between theca and granulosa cells
On day 14 of the cycle an LH surge occurs which is triggered by the estradiol
This causes the secondary follicle to develop into tertiary follicle which then ovulates hours later
When the development of the tertiary follicle occurs the primary oocyte completes the first meiotic division resulting in the formation of a polar body and a secondary oocyte
The empty follicle then forms a corpus luteum which releases progestrone hormone

15. CHARACTERISTICS CYTOPLASM
Oocytes are rich in cytoplasm which contains yolk granules to nourish the cell in early development

16. NUCLEUS
During the primary oocyte stage of oogenesis the nucleus is called a germinal vesicle
The human type secondary oocyte has 23rd sex chromosomes as 23,x female determining chromosome

17. NEST
The space where an ovum or immature ovum is located is the cell nest

18. MITOCHONDRIA
The oocyte receives mitochondria from maternal cells,which will go on to control embryonic metabolism
The partitioning of mitochondria is carried out by a system of microtubules which will localize mitochondria throughout the oocyte

19. NUCLEOLUS
The nucleolus of the oocyte is derived solely from the maternal ceels
It is a structure found within the nucleus, is the location where the rRNA is transcribed and assembled into ribosomes
Nucleolus is dense and inactive in mature oocyte, it is reuired for proper development of the embryo

20. RIBOSOMES
Maternal cells also synthesise and contribute a store of ribosomes that are reuired for the translation of proteins before the zygotic genomes is activated
Maternally derived ribosomes and some mRNAs are stored in a structure called cytoplasmic lattices
They are the network of fibrils, protein and RNA s

21. PATERNAL CONTRIBUTIONS
The spermatozoon which fertilizes an oocyte will contribute its pronucleus ,the other half of the zygotic genome
The sperm provides three essential parts
. An activating factor which causes the dormant oocyte to activate
The haploid paternal genome
The centrosome which is responsible for maintaining the microtubule system

22. ABNORMALITIES Nondisjunction
A failure of proper homolog separation in meiosisI or sister chromatid separation in meiosis II can lead to aneuploidy in which the oocyte has the wrong number of chromosomes -22x,or 24x
Downs syndrome and edwards syndrome
Advanced maternal age
Some oocytes have multiple nuclei ,although it is thought they never mature

23. Different Patterns of Cumulus cells

24. Oocytes under the Stereo-microscope

25. Grading of Oocyte Zona Pellucida Perivetiline Space Polar Body
Cytoplasmic Texture
Inclusions

26. Zona Pellucida
The zona pellucida (ZP) may vary in thickness and rigidity.
Some patients have clearly thiner ZP than others.
It is usually a characteristics associated with the patient more than with the oocyte.
Although thickness may vary slightly around the oocyte, the following categories can be defined.

27. Parameters Parameters Morphological aspects Thin
the ZP is less than 15 µm
Thick
the ZP is greater or equal to 25 µm
Normal
the ZP is around 20 µm (15-25)
Abnormal
the ZP is quite irregular both in thickness and in shape

28. Periviteline Space
The periviteline space surrounds the ooplasm. It is generally clearly visible, at least in the vicinity of the polar bodies. It may contain fragments.
Parameter
Parameter
Morphological aspect
Small
the ooplasma is adherent to the ZP and the periviteline space is almsot inexistent
Large
the ooplasma is clearly retraced away from the ZP leaving a clearly identifiable space all around the cytoplasm
With fragments
presence of clearly identifiable fragments
Normal
the ooplasm is slightly retracted away from the ZP at least in the vicinity of the polar body

29. Polar Body
The polar body appear when the first meiotic division has been completed. It appears as an small cell close to the oocyte and may undergo a second division.
It usually rapidly degenerates and appears as a fragmented structure
Parameter
Morphological Aspects
Unclear or absent
the polar body may not always be clearly identifiable, depending on how the oocyte is oriented. It is absent in a metaphase I oocyte (before the first meiotic division)
Intact
clearly identifiable smooth round/oval cell lying close to the oocytes
Fragmented
the polar body material is irregular in shape and show clear signs of disorganization
Giant
usually intact, giant polar bodies a clearly recognizable, they may achive size of about half of that of an oocyte

30. Cytoplasmic Texture
The cytoplasm of the oocyte exhibits usually a granular texture.
Depending on the oocyte, this texture may appear homogeneous or exhibit a gradient in the granulated texture.
In some cases, it may contain a dark cluster and exhibit sign of fragmentation.

31. Parameters Parameter Morphological Aspect Fragmented
the cytoplasm shows signs of fragmentation or appear as an undefined mass with absent or degraded oolema
Homogeneous
the cytoplasmic material appears homogeneously distributed with little signs of granulation
Polarised
zones more or less granulated are visible as two opposing hemispheres
Dark cluster
a dark zone is clearly identifiable inside the cytoplasm

32. Inclusions The cytoplasm may contain several remarkable structures.
Parameter
Morphological aspect
Vacuole
one large or several small vacuoles bounded with a clearly identifiable membrane
SER cluster
smooth endoplasmic reticulum appearing as clear spherical zones inside the cytoplasm. The boundaries of these structures may not be easily identified as in the case of vacuoles
Refractile body
Refractile bodies constitute one of the main morphological abnormalities in human oocytes and are made of auto fluorescing lipofucsin (appear yellowish)
None
absence of the above mentioned structures

33. Abnormal Polar Body
Immature Oocyte

34. Abnormal Oocytes Granulated Refractile Bodies SER Perivitiline Space
Vacuolated
MUGS

35. THANK YOU