Week 3: Ovarian Cycle

Question 1

What is the ovarian cycle?

Answer 1

The ovaries are two structures in a female’s reproductive system that produce her eggs. Each month her eggs go through a maturation process called the ovarian cycle, and that cycle creates a secondary oocyte that can be fertilized by a sperm to result in a pregnancy.

The ovarian cycle is also responsible for the menstrual cycle

Basically the primary oocytes that are destined to be ovulated will develop in the ovaries, complete meiosis one just before ovulation, and then they’ll be ejected out of the ovary as a secondary oocyte to be picked up by the fimbriae and swept into the uterine tube to hope for fertilization

Question 2

Ovarian cycle

Answer 2

Eggs develop inside follicles starting off as primordial follicles

(Follicle is one primary oocyte surrounded by granulosa cells)

Primary follicles begins to separate layers by the zona pellucida between the layers of oocyte and granulosa cells

granulosa cells can send nutrients through gap junctions through the zona pellucida to the oocyte and also keeping the primary oocytes stuck at meiosis I in meitotic arrest

Granulosa cells increase in number and wall of cells on the exterior of the follicle begins to form called the Theca. Theca cells have luteinizing hormone receptors and when it binds to Theca cells they produce Androstenedione and then Theca cells transport Androstenedione to the granulosa cells of the follicle who convert it to Estrogen and release it into the blood and raise Estrogen circulatory levels

Antrum is formed (which is fluid produced by the granulosa cells) the antrum and the fluid in the antrum causes the follicle to expand. A lot of the follilces go through this process however, only one follicle gets to be ovulated, the others die off from atresia (both the follicle and eggs that didn’t make it die off)

This explains how women loses 15 to 25 eggs per menstrual cycle where only 1 gets ovulated

The expanded follicle forms a mound of granulosa cells called the Cumulus Oophorus

The cumulus oophorus and the egg separate from the wall of the follicle and float around in the antrum

The folllcile continues to increase in size from the granulosa cell fluid production

At this point the dominant follicle is called the mature follicle, the mature follicle begins to balloon out the side of the ovary, enzymes within the follicle break down the ovary wall and the egg pops out onto the surface of the ovary which occurs on day 14

Sometimes by chance, 2 or more follicles pop out at the same time which is how twins or triplets are born

The follicle that the egg was in collapses and forms a structure called the corpus luteum

the granulosa cells within the corpus luteum start get a lot bigger and produce more estrogen, progesterone and inhibin

If the egg doesn’t get fertilized then the corpus luteum gets to be a maximum size in about 10 days (day ~25) then it degenerates by apoptosis

If the egg is fertilized then the corpus luteum persists and keeps living producing estrogen and progesterone which prepare the endometrium for implantation

Question 3

Hormones secreted by granulosa cells

Answer 3

• Estrogen
• Progesterone
• Inhibin

Question 4

Duration of ovarian cycle

Answer 4

Lasts 28 days