00:01 So now let's take a closer look look at the ovarian cycle. 00:06 The ovarian cycle is approximately a monthly or 28-day series of events that are associated with the maturation of an egg or ovum. 00:20 There are two consecutive phases that are going to occur in the ovarian cycle with ovulation being the midpoint between these two phases. 00:32 The first phase of the ovarian cycle is the follicular phase. 00:37 This is a period of vesicular follicle growth and occurs between days 1 through 14 of a 28-day cycle. 00:47 The second phase and the ovarian cycle is the luteal phase. 00:52 This is a period where the corpus luteum is active. 00:56 This occurs in days 14 through 28 of a 28 day cycle. 01:04 Only about 10 to 15 percent of females have a 28 day cycle. 01:11 While the first follicular phase can vary in women. 01:16 The luteal phase is always 14 days from ovulation to the end of a cycle. 01:25 So let's take a closer look at the first phase of the ovarian cycle the follicular phase. 01:32 Starting with the development of the follicle. 01:36 So in this phase, a primordial follicle is going to become the primary follicle. 01:43 Squamous-like cells surrounding the primary oocyte will become cuboidal and the oocyte will begin to become larger. 01:53 This process can take about one year. 01:57 Now this follicle is known as the primary follicle. 02:04 So now that the primordial follicle has become the primary follicle, the follicular cells are going to proliferate forming a stratified epithelium around the oocyte. 02:18 When more than one layer of cells are present, we now refer to these follicular cells as granulosa cells. 02:26 And now the primary follicle is referred to as the secondary follicle. 02:33 At this point the granulosa cells and the oocyte are going to guide one another's development via gap j unction connections between the two. 02:44 In the secondary follicle, connective tissue and granulosa cells are going to condense in order to form the theca folliculi. 02:55 Also, we have the formation of the zona pellucida, which is a thick glycoprotein rich membrane that is secreted by the oocyte encapsulating the oocyte within it. 03:09 Early vesicular follicles are formed when a clear liquid begins to accumulate between the granulosa cells as they secrete follicular fluid. 03:22 This fluid builds up in a large cavity known as the antrum. 03:28 Once you have antrum formation, we are now going to refer to this as the vesicular follicle because it looks like a large vesicle. 03:38 This is going to distinguish it from the previous follicles or the pre antral follicles versus the antral follicles. 03:48 The antrum is going to continue to expand with this follicular fluid further isolating the oocyte. 03:57 At this point, the oocyte is surrounded by the zona pellucida and the granulosa cells. 04:04 These granulosa cells are now referred to as the corona radiata. 04:12 The corona radiata sits on a stalk on one side of the follicle. 04:19 When the follicle is at full-size it begins to bulge from the external ovary surface. 04:27 At this point, the follicle is ready to be ovulated and it is now referred to as the mature or graafian follicle. 04:38 To recap, if we compare the events of meiosis with the development of the follicle, we find that before birth we have our primordial follicles in the ovaries. 04:50 In the follicle, in the primordial follicle, we have our oogonia, which are going to eventually go through mitosis to form primary oocytes. 05:03 Throughout infancy and childhood, our primary oocytes going to be preparing for the divisions that will happen in puberty. 05:13 Also, the primordial follicle will be preparing or just waiting as well. 05:19 Once we hit puberty the primary oocyte is going to complete meiosis 1 forming the secondary oocyte and the first polar body. 05:30 This occurs, in the secondary and eventually the vesicular follicle. 05:36 The secondary oocyte is released during ovulation where it is arrested in metaphase 2.
The lecture Follicle Development (Nursing) by Jasmine Clark, PhD is from the course Female Reproductive System – Physiology (Nursing).
After the primordial follicle becomes the primary follicle, what is the next step in follicle development?
What happens to the primary oocyte before ovulation?
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