Follicle Development (Nursing)

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.