Oogenesis- Lecture 5 Flashcards
Mitosis
Diploid cell —> Diploid cell Two identical daughter cells are produced.
1st meiotic “reductional” division
Separates homologous chromosomes —> each daughter cell has only 1 copy of each homolog (recombination). Prophase 1, Metaphase 1, Anaphase 1, Telophase 1 (polar body), Prophase 2, Metaphase 2, Anaphase 2, Telpphase 2 (polar body).
Primary follicle
Activation of primordial follicle. Oocyte surrounded by a single layer of cuboidal granulosa cells. Formation of zona pellucida starts
Oogenesis
Formation of female gamete. The differentiation of a highly specialized gamete, the oocyte, starting from an undifferentiated stem cell. The progress of oogenesis starts in early embryonic life.
Follicle
Oocyte surrounded by stomatic cells (granulosa). There are different developmental stages.
Prophase 1
Leptotene- thin threads. Zygotene- paired threads. Pachytene- thick threads. Diplotene- two threads Diakinesis- moving through.
Secondary follicle
The granulosa cells proliferate so the oocyte is now surrounded by several layers of granulosa cells. Stromal cells by the basement membrane align and become theca cells. Follicle has an independent blood supply and sensitive to hormonal regulation.
Tertiary/antral follicle
Fluid filled cavities form between the granulosa cells that come together to form the antrum. The theca differentiates into theca externa and interna. Theca externa: fibroblast like required from for ovulations. Theca interna: LH responsive steroidogenic.
LH
Luteinizing hormone. Receptors on thecal cells and then also of granulosa cells. Responsible for maturation of oocyte and triggers ovulation.
Prenatal oogenesis
Primordial follicle number is set by birth.
Steroid production
Theca interna: LH responsive, produce androgen. Granulosa cells: FSH responsive, aromatase androgen to estradiol. Estradiol increases as follicles grow.
2nd meiotic division
separates the two sister chromatids from each other.
Primordial follicle
Formation occurs during foetal life. A pool of primordial follicles become progressively depleted during a females lifetime. The primordial follicle is surrounded by a single layer of pregranulosa cells.
Graffian/preovulatory follicle
The fluid filled cavity has reached maximum size. Oocyte is located inside antrum.
Oogonia
Once the PGC reach genital ridge they lose motility and become oogonia. They are interconnected by cytoplasmic bridges and multiple by mitosis.
Gonadotropins
Follicles become sensitive to the gonadotropins FSH and LH. Receptors expressed on follicle cells.
Folliculogenesis
Formation of a antral follicle starting from a primordial follicle.
Primordial germ cells
The stem cells of oogenesis. They migrate from yolk sac to genital bridge and multiply by mitosis
Spermatogenesis
Formation of male gamete
FSH
Follicle stimulating hormone. FSH receptors on granulosa cells. Stimulates follicular growth.
Meiosis
A specialized form of cellular division which only occurs in gametes i.e. oocytes and spermatozoa. The number of chromosomes is reduced so that the resulting cells only have copy of each homolog. Diploid cell —> Haploid cell
1st meiotic block of meiosis
The oocyte grows, increasing in volumne 200 times. The zona pellucida forms and cytoplasm matures.
