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2 - Developing follicle 3 - Mature follicle 4 - Ovulation 5 - Corpus luteum 6 - Deterioration of corpus luteum. In biology, folliculogenesis is the maturation of the ovarian follicle, a densely packed shell of somatic cells that contains an immature oocyte.
The follicular phase, also known as the preovulatory phase or proliferative phase, [1] is the phase of the estrous cycle (or, in primates [2] for example, the menstrual cycle) during which follicles in the ovary mature from primary follicle to a fully mature Graafian follicle.
A set of follicles starts to develop near the end of proestrus and grows at a nearly constant rate until the beginning of the subsequent estrus when the growth rates accelerate eightfold. Ovulation occurs about 109 hours after the start of follicle growth. Estrogen peaks at about 11 am on the day of proestrus.
Ovarian follicle activation can be defined as primordial follicles in the ovary moving from a quiescent (inactive) to a growing phase. The primordial follicle in the ovary is what makes up the “pool” of follicles that will be induced to enter growth and developmental changes that change them into pre-ovulatory follicles, ready to be released during ovulation.
An ovarian follicle is a roughly spheroid cellular aggregation set found in the ovaries.It secretes hormones that influence stages of the menstrual cycle.In humans, women have approximately 200,000 to 300,000 follicles at the time of puberty, [1] [2] each with the potential to release an egg cell (ovum) at ovulation for fertilization. [3]
This can be done with either a blood test or another ultrasound exam to visually count the number of follicles (i.e., the small fluid-filled sacs that hold one mature egg) on the ovaries.
The immature ova originate from cells from the dorsal endoderm of the yolk sac. Once they have reached the gonadal ridge they are called oogonia. Development proceeds and the oogonia become fully surrounded by a layer of connective tissue cells (pre-granulosa cells). In this way, the rudiments of the ovarian follicles are formed.
Oocytes are then able to mature within the follicle through meiosis. In humans with ovaries, this process occurs continuously, as they are born with a finite number of follicles (between 500,000-1,000,000 follicles), and about 99% of follicles undergo atresia. [4] Only one follicle will be mature enough to release an egg and may be fertilized. [5]