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Although the process is similar in many animals, this article will deal exclusively with human folliculogenesis. Order of changes in ovary. 1 - Menstruation 2 - Developing follicle 3 - Mature follicle 4 - Ovulation 5 - Corpus luteum 6 - Deterioration of corpus luteum
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.
Under regulation by gonadotropic hormones, ovarian follicles mature and estrogen secretions exert their biggest influence. The female then exhibits sexually receptive behavior, [12] a situation that may be signaled by visible physiologic changes. Estrus is commonly seen in the mammalian species, including some primates.
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]
Sexual differentiation is the process of development of the sex differences between males and females from an undifferentiated zygote. [1] [2] Sex determination is often distinct from sex differentiation; sex determination is the designation for the development stage towards either male or female, while sex differentiation is the pathway towards the development of the phenotype.
The inner mass of cells differentiate to become embryoblasts and polarise at one end. They close together and form gap junctions, which facilitate cellular communication. This polarisation leaves a cavity, the blastocoel, creating a structure that is now termed the blastocyst. (In animals other than mammals, this is called the blastula).
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.
In both males and females, the sex organs consist of two structures: the internal genitalia and the external genitalia. In males, the gonads are the testicles and in females, they are the ovaries. These are the organs that produce gametes (egg and sperm), the reproductive cells that will eventually meet to form the fertilized egg .