What is the difference between primary follicle and secondary follicle? Follicular development in female ovary is one of the important biological process leads to formation of mature haploid ovum from germinal epithelium of ovary commonly known as primordial cell.
Follicular development start during the embryonic or 6 to 8 months of gestation period of female and at birth time it will be arrested and then begin at puberty after attending the sexual maturity of 12 years age in girls child. After this tertiary follicles develop into Graafian follicles and release secondary oocytes for fertilization with sperm. All these follicles have some difference in development and structure, but in this topic we explain some maijor difference between primary follicles and secondary follicles.
Most of the organelles are concentrated in one pole of the oocyte. The graph below shows the changes in human germ cell numbers in the ovary with age, peaking at about 7 million occuring in early fetal development and then decreasing by apopotic cell death. Menstrual Cycle. Human ovary non-growing follicle model [7]. Graph shows species comparison in oocyte size growth diameter at different stages of follicle development.
In females, the total number of eggs ever to be produced are present in the newborn female initially arrested at the diplotene stage of the meiosis I from fetal life through childhood until puberty, when the lutenizing hormone LH surges stimulate the resumption of meiosis. The polar body is a small cytoplasmic exclusion body formed to enclose the excess DNA formed during the oocyte egg meiosis and following sperm fertilization.
There are polar bodies derived from the oocyte present in the zygote, the number is dependent upon whether polar body 1 the first polar body formed during meiosis 1 divides during meiosis 2. This exclusion body contains the excess DNA from the reductive division the second and third polar bodies are formed from meiosis 2 at fertilization.
These polar bodies do not contribute to the future genetic complement of the zygote, embryo or fetus. Recent research in some species suggest that the space formed by the peripheral polar body between the oocyte and the zona pellucia can influence the site of spermatozoa fertilization. The following cartoon model from mouse oocyte study of polar body extrusion, involving cortical cap protrusion and spindle midzone-induced membrane furrowing.
Assisted reproductive techniques involving intracytoplasmic sperm injection ICSI have looked at the "quality" of the polar body and found that the morphology is related to mature oocyte viability and has the potential to predict oocyte fertilization rates and pregnancy achievement. Earlier in oocyte meiosis, between prophase I germinal vesicle stage and MII, this release mechanism is developed within the cell.
The release of cortical granules by exocytosis, the "cortical reaction", occurs following spermatozoa fertilisation and is the main block to polyspermy by modifying the zone pellucida. These granules develop from the golgi apparatus initially forming smaller vesicles that coalesce to form mature membrane bound cortical granules 0. In mammals, cortical granule production in the developing follicular oocyte is an ongoing and continuous process, with newly synthesized granules translocating to the cortex until the time of ovulation.
The oocyte and the surrounding granulosa cells have a complex paracrine interactions during follicle growth and development. Oocyte maturation has been shown to depend on secretory products of both the granulosa and cumulus cells. Table 8 Reference: Hartman CG. How Large is the Mammalian Egg? The Balbiani body Balbiani vitelline body; mitochondrial cloud is a large organelle aggregate found in developing oocytes of many species. In the human fetal ovary oocyte development, the RNA binding protein VASA protein is expressed in primordial follicles has been shown to colocalise to Balbiani's vitelline space.
For more information see Hertig's presentation. Balbiani EG. Comparative study of mammalian ovum at the different periods of ovogenesis, according to the work of the histology and embryology laboratory of the University of Ghent. In the mouse, the secondary follicle stage through to large antral follicle stage the oocyte has a highly oxidative metabolism.
In contrast, the surrounding surrounding granulosa and cumulus cells are highly glycolytic. In this second group, the cumulus cells are found to be more glycolytic than the granulosa cells. In the cat oocyte, in pre-antral oocytes mitochondria have a homogeneous distribution throughout the cytoplasm.
In the antral stage they have relocated to a mainly pericortical distribution. The table above shows the pattern of protein expression as percentages of total in the mouse germinal vesicle and MII oocyte according to 14 molecular function categories. There is a redistribution of the enzyme that regulates telomere length during oocyte development.
The following oocyte images are from a recent study of sheep in vitro follicle development. Primary ovarian insufficiency - depletion or dysfunction of ovarian follicles with cessation of menses before age 40 years.
Oocyte maturation arrest - arrest of human oocytes may occur at different stages of meiosis. Meiotic non-disjunction resulting in aneuploidy, most are embryonic lethal and not seen. The potential for genetic abnormalities increase with maternal age. Hamilton WJ. Phases of maturation and fertilization in human ova. Pincus G. The comparative behavior of mammalian eggs in vivo and in vitro. PMID The road to maturation: somatic cell interaction and self-organization of the mammalian oocyte.
Cell Biol. Molecular control of oogenesis. Acta , , Liu M. The biology and dynamics of mammalian cortical granules. Cite this page: Hill, M. Navigation Main page. Site map. Site updates. Recent changes. New images. The zona pellucida is a thin band of glycoproteins that separates the oocyte and follicular cells. Proteins on the surface of sperm will bind to specific glycoproteins in the zona pellucida.
The late primary follicle stage is reached when the follicular cells proliferate into a stratified epithelium known as the zona granulosa.
The zona pellucida enlarges and can be seen even more clearly in this image. The characteristic feature that distinguishes secondary from primary follicles is the appearance of a follicular antrum within the granulosa layer. The antrum contains fluid which is rich in hyaluronan and proteoglycans. Note the increase in cell layers of the zone granulosa, the thicker zone pellucida, and larger oocyte. At this stage, a layer of cells outside the follicle become evident. These cells compose the theca interna and contribute to the production of estrogens.
Recall that the production of estrogen requires both the cells of the theca interna and granulosa cells. Estrogens, like all steroid hormones, are produced from cholesterol through a multi-step process that requires several different enzymes. Neither the cells of the theca interna nor the granulosa cells contain all of the enzymes necessary to convert cholesterol into estrogens. Theca cells contain enzymes that catalyze the initial conversion of cholesterol into androgens but lack aromatase that carries out the final steps of converting androgens into estrogens.
Consequently, androgens produced by theca cells diffuse into the granulosa cells which contain aromatase but lack the enzymes for the initial steps in estrogen synthesis. The theca cells are in a better position to catalyze the initial steps in estrogen synthesis because they are closer to blood vessels and can take up LDL to obtain cholesterol. I had searched different blogs for follicle topics. From this blog, I got all the necessary points of fertility.
Also, people from the UAE have doubts about the fertility aspects. So, It would be better if you explain more about fertility treatments and diagnosis. Hello Zaynah. First of all, thank you for your comments and your interest in our blog. If you check it, we give many information about fertility, treatmenst and diagnosis.
Thanks again! Your email address will not be published. Request information. By the Editorial Comitee IVI Blog When we talk about the female reproductive system, we tend to say that a woman is born with all the eggs she will ever have.
What is a primordial follicle? The primordial follicle is the starting point. These follicles are so small that they are invisible to the naked eye. These are the stages for those few that reach full maturity: Primary follicles are the next stage. A few of the original primordial follicles progress into the primary follicle stage every day.
The process starts at puberty and continues each day, regardless of other factors, regardless of whether you are pregnant or even ovulating at all, right through until menopause.
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