Folliculogenesis Flashcards
Where do egg/sperm cells originate from?
primordial germ cells
What is the Function of genital ridge?
this bipotential cluster of cells becomes either the ovary or testis, which are responsible for the differentiation of PGCs into male/female gametes
What happens if primordial germ cells enter the ovary?
If PGCs enter ovary:
- they become oogonia which multiply by mitosis
- oogonia stop mitosis and enters meiosis I, becoming primary oocytes
- primary oocytes surrounded by granulosa cells+basal lamina membrane, forming primordial follicle
- ovarian reserve established- females born with entire stock of primordial follicles
How does the primary oocyte become the primordial follicle?
primary oocyte arrested in meiosis I for years:
- becomes surrounded by granulosa cells
- granulosa cells secrete basal lamina layer (acellular)
What does the primordial follicle consist of?
primary oocyte + granulosa cells + basal lamina
What is the most immature stage of an ovarian follicle’s development?
primordial follicle
Describe the Effect of puberty on primordial follicle.
primordial follicles recruited from ovarian reserve and start growing
- some will enter menstrual cycle and ovulate
- majority of follicles will die through atresia
Describe the Effect of puberty on primordial follicle development.
Primordial follicles will grow to primary follicles and then:
- granulosa cells multiply
- primary oocyte secretes zona pellucida (acellular)
- theca cells differentiate around basal lamina (internal+external), with a rich blood supply therefore forming fluid-filled granulosa spaces
- fluid-filled spaces form an antrum filled with follicular fluid, creating secondary (antral) follicle
- STILL IN MEIOTIC ARRSET
Describe the structure of a Secondary Follicle.
- Primary oocyte
- Coated by zona pellucida
- Surrounded by several layers of granulosa cells
- Follicle becomes encased by a new layer of cells called the theca
- Follicular antrum filled with follicular fluid, displacing oocyte to one side
Granulosa cells in the antral follicle surrounding the primary occyte are known as…
cumulus granulosa cells
Granulosa cells on the outer structure of the antral follicle are known as…
mural granulosa cells
What drives folliculogenesis?
FSH drives antral follicle growth
BUT
EARLY follicular growth is independent of FSH
Describe the Stages of Follicular Development After Puberty.
INITIATION (gonadotrophin independent)
- primordial follicles leave ovarian reserve and continuously grow, forming pre-antral follicles
- pre-antral follicles grow until they form early antrum
RECRUITMENT (gonadotrophin dependent)
-follicles will only continue to grow when they reach size at which they respond to changes in FSH that occur in menstrual cycle
SELECTION
- follicles respond to FSH and are recruited into menstrual cycle to continue growing
- only one follicle from the group will be selected for ovulation
What is the Function of ovarian follicle?
Steroid production via 2-cell, 2-gonadotrophin theory :
- LH stimulates thecal cells to produce androgens and progesterone
- FSH stimulates granulosa cells to produce oestrogens from androgens via aromatase
What receptors will granulosa cells acquire? And why?
Granulosa cells of the dominant follicle will acquire LH receptors to respond to the LH surge midcycle and undergo ovulation
