Lecture 3: The Ovary and Ovarian cycle Flashcards
Insert diagram of female reproductive organs
now
What is oogenesis?
Formation and development of the ovum
What constitutes a follicle?
Oocytes and surrounding support cells, which together constitute a follicle, are located near the surface of the ovaries in the cortex. In a mature ovary different stages of development can be seen
What are the stages of follicle development:
Primordial follicles
Primary follicle
Secondary follicle
Tertiary follicle (or Graafian follicles)
-> Released secondary oocyte + Corona radiata
Corupus luteum
Corpus albicans
What happens to the number of oocytes throughout life?
Peaks in utero and rapidly declines over life. Million present at birth. Only 400 ovulated throughout life.
When are oogonia called oocytes?
Following mitotic divisions (The produce the large number of germ cells (oogonia) in the developing ovary), meiosis begins, but is not completed.
Meiosis halts just prior to metaphase 1 at end of prophase.
Oogonia now called oocytes
Describe the ovarian cycle:
- > From time follicles are formed a small number of them become activated in a process we do not understand until menopause.
- > Until puberty all of these activated follicles die.
-> Following puberty waves of ovarian follicles become responsive to FSH and are recruited to continue maturing.
–> Activated and maturing follicles can be recognised by the changes in the morphology and number of granulosa cells surrounding the oocyte.
–> Initial follicular growth is very slow taking from 3-12 months from the time of activation of a follicle to when it starts to form an antrum (containing follicular fluid) and be capable of ovulation
-> With each menstural cycle groups of developing follicles are stimulated to grow very rapidly
= The follicular waves.
Describe the ovarian cycle follicle selection:
- During the follicular phase of the cycle one follicle will dominate over the others in terms of growth. (1 in 20 survive)
- Usually in women there is only one dominant follicle which goes on to be ovulated.
Describe the timeline of follicles at different stages:
- Primordial follicles
-> 12-50 years arrested state - Primary follicles (30-50)
~ 2-12 months active but slow growth - Secondary follicles (15-20) Upregulation of FSH receptors.
~2 weeks rapid growth (Major loss by atresia) - Tertiary or Graafian follicles (1-2)
Describe the structure of the primordial follicles:
Insert diagram (slide 15)
Describe the granulosa/oocyte crosstalk:
- Cumulus cells communicate to the oocyte
- Gap junctions
- Oocyets communicate back to cumulus cells
Describe the structure of the secondary follicles
Insert diagram (Slide 17)
What is the two cell theory of follicular steroidogenesiis:
Thecal and granulosa cells combine their efforts to produce steroids.
What is the zona pellucida:
Three proteins make up the zona pellucida (ZP-1) present in primordial follicles.
ZP2 and ZP3 added to activated follicles.
Important for filtering normal sperm and in blocking polyspermy.
Describe the structure of the tertiary follicle:
Insert diagram
