Folliculogenesis Flashcards
What are the 4 things required for reproduction?
β Differentiation into male or female
β Sexual maturation
β Production, storage and release sufficient supply of eggs and sperm
β correct number of chromosomes in eggs and sperm
β egg and sperm have to meet
What are cells that will become egg or sperm called?
β Primordial germ cells
When are PGCs first identifiable?
β in the yolk sac 3 weeks after conception
What happens to the PGCs?
β the cells undergo many cycles of mitosis
β They migrate to the genital ridge
What does the genital ridge become?
β The gonad
What does further differentiation of the PGCs depend on?
β The development of the gonad
What do germ cells become when in the ovary?
β oogonia
What are oogonia?
β Egg precursors
When oogonia enter meiosis what are they known as?
β Primary oocytes
What phase do primary oocytes remain in and until when?
β They remain in the first phase of meiosis until it ovulates or dies
Describe mitosis briefly?
β Spindle is formed
β The chromatids are lined up one behind the other
β They then separate to opposite poles of the cell
β The cytoplasm divides and there are two identical cells
Describe meiosis
β Duplication of the chromatids
β They line up adjacent to each other
β Chromosome 1 lines up with chromosome 1 from the other parent
β allows crossing over and biological variation
β homologous chromosomes separate into two haploid cells
β separate again to form gametes
βoocytes are arrested in meiosis 1 until LH surge
where are primary oocytes packed?
β Outer layer of the ovary : cortex
What do the cells around the oocyte become in the fetal ovary?
β Condense around the oocyte and differentiate into granulosa cells
What do granulosa cells secrete?
β Acellullar layer called the basal lamina
What does a primordial follicle consist of?
β Oocyte with granulosa cells and a basal lamina
What do germ cells become in the ovary?
β oogonia
What type of cell are oogonia and how do they multiply?
β Diploid
β Multiply by mitosis
What happens to the follicles at puberty and at menopause?
β Follicles start growing at puberty
β arrests at menopause
What is folliculogenesis defined as?
β Growth and development of follicles from the earliest resting stages as laid down in the fetus through to ovulation
What happens as the follicles start to grow?
β Granulosa cells multiply
β Granulosa cells secrete basal lamina around it
β oocyte secretes another protective acellular layer called the zona pellucida
β Theca cells differentiate around the basal lamina
What are theca cells and what is their purpose?
β Steroid producing
β they sustain the growth of the follicle and the oocyte
What drives most of folliculogenesis?
β FSH
What happens to follicles when FSH is suppressed?
β The follicles will continue early growth but they die
What happens in the second stage of follicle growth?
β Increases rapidly in diameter
β Granulosa cell divisions increase but gaps form in the cell layers
β gaps form an antrum filled with follicular fluid
What are the two main phases of follicular growth?
β Absence or presence of the antrum
What are follicles with an antrum known as?
β antral or secondary follicles
What kind of cells do primordial follicles have and how do they look and grow?
β flattened granulosa cells
β grow in a slow and controlled manner
β become cuboidal in shape
Describe how primordial follicles physically change to become Graffian follicles
β Granulosa cells
β FSH causes granulosa cells to proliferate and the zona pellucida forms around the oocyte
β theca cells are produced around the granulosa cells
βgranulosa cell divisions increase and gaps form which are filled with follicular fluid
βthese join and form the antrum
β the egg is then within follicular fluid
What are the cells directly surrounding the oocyte called?
β Corona radiata
Where are primordial cells arrested in?
β Meiosis I
What is follicle initiation?
β When a cohort of follicles leave the resting pool and grow continuously
What is follicle recruitment?
β When the follicles are big enough to respond to changes FSH they start growing
What do follicles need to continue growing?
β FSH
How long does the follicular phase last?
β 14-15 days
What is atresia?
β When follicles die
What steroids do the granulosa and theca cells produce?
β Theca produces androgens which is stimulated by LH
β androgens go to granulosa and get converted to estrogen which is stimulated by FSH
