It’s the primary sex organ in females which is connected with the uterus with the help of ovarian ligaments. The ovary has three protective layers which include outer germinal epithelium, inner tunica albuginea, and innermost ovarian cortex, where ovarian follicles are located and the development of follicles takes place.
The process by which the female gamete (egg) is produced is known as oogenesis. It starts during fetal development when primordial cells / primitive cells (The initial cells) migrate from the yolk sac to ovaries where they differentiate to form oogonia which divides through a biological process of mitosis to produce millions of oogonia or primary oocyte. Now primary oocytes get arrested in the prophase of cell division until puberty is attained.
Each month after puberty until menopause, gonadotropin’s i.e. FSH (Follicular Stimulating Hormones) and LH (Luteinising Hormone) are secreted by the anterior pituitary gland. FSH induces the development of ovaries, which in turn produce the hormone estrogen (Female sex hormone). This hormone is responsible for the development of secondary female sexual characters.
The formation of an ovum is called oogenesis which occurs in the ovary. Oogenesis occurs in 3 steps: Multiplication, Growth, and Maturation.
Multiplication phase: In fetal development, certain cells in the germinal epithelium of the ovary of the fetus are larger than others. These cells divide mitotically producing millions of oogonia. Oogonia multiply mitotically forming primary oocyte then get surrounded by the primary follicle.
Growth phase: This phase occurs for a very long time in which the primary follicle grows by taking food for surrounding follicles.
Maturation phase: Each primary oocyte undergoes two meiotic divisions. In the first meiotic division, one big haploid secondary oocyte and a very small first polar body are produced. In the second meiotic division, the secondary oocyte divides into a big ootid, which later matures into the ovum, and the first polar body divides into two smaller polar bodies. Polar bodies do not take part in reproduction.
The cycle completes itself in 28 days. Menstruation is bleeding from the uterus of adult females. It begins at the age of 13 years generally and continues until about 45 to 50 years.
This phase usually lasts for 10 to 12 days. The follicular stimulating hormone (FSH) secreted by the anterior lobe of the pituitary gland stimulates the ovarian follicles to secrete estrogen. In this phase, the production of FSH and estrogen increases. Oestrogen stimulates the proliferation of the endometrium of the uterus wall by making it thick and increases in uterine glands and vessels.
Both FSH and LH ( luteinizing hormone) attain their peak level in the middle of the cycle and on the 14th day, the rapid secretion of LH induces the release of secondary oocyte which is arrested at its metaphase of meiosis II, from the ovary.
This phase lasts for 10 to 12 days after ovulation. When the secondary oocyte leaves the ovary the remaining part of the ovarian follicle secretes LH to develop the corpus luteum, which starts secreting progesterone. Progesterone is very essential for maintaining a thick uterus lining for implantation of the embryo if fertilization occurs.
If fertilization does not occur, production of LH is reduced which results in the degeneration of corpus luteum. No corpus luteum means the production of progesterone is reduced. This results in the disintegration of the endometrium and blood vessels. Thus menstruation begins with all the endometrium secretions, blood vessels, and unfertilized egg coming out of the vagina as menstrual flow. Blood clotting here does not occur due to the presence of fibrinolysis. Those last for 3 to 5 days.
Gonadotropin-releasing hormone (GnRH) is secreted by the hypothalamus which stimulates the pituitary gland to release LH and FSH.
: Stimulates the growth of follicles inside the ovary and also the development of oocytes within the Graafian follicle to complete the meiosis I to the secondary oocyte. FSH also stimulates the production of estrogen.
: Induces ovulation and formation of corpus luteum which in turn release progesterone The rising level of progesterone inhibits the formation of GnRH, which in turn, inhibits the production of FSH and LH and progesterone.
The entire reproductive cycle is mainly governed by the complex interplay of hormones. Any imbalance in the hormonal level impacts the entire cycle altering the reproduction leading to infertility and conditions like irregular periods. These are some of the basic symptoms of PCOS conditions that occur mainly due to the hormonal imbalance, a result of poor lifestyle, unhealthy diet, exposure to environmental factors like xeno-estrogens, and more. So, if you are suffering from any of the above symptoms mentioned please do check with your doctor and follow a healthy lifestyle to bring back the balance because remember PCOS condition can be healed with the right guidance. If you have any queries about the condition, feel free to connect with our experts.
Drafted By : Swati Shri Pal Sing
Edited By : Dr. Amol Raut
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