Menstrual Cycle in Women
Menstrual Cycle is the cyclic reproductive cycle that occurs in women periodically at regular interval of 28 to 29 days. In the middle of each menstrual cycle one ovum is released after rupturing of Graafian follicle. Menstrual cycle begins in female after attaining puberty and is called menarche. It ceases around 50 years of age and is known as menopause. Menstrual cycle is common in the females of all placental primates. During menstruation significant changes occur in the uterus or womb. Uterus in women is composed of three layers of tissue that are mainly outer perimetrium, middle myometrium and inner glandular endometrium. It is endometrium that undergoes cyclic changes during the menstrual cycle while myometrium exhibits vigorous contraction during the delivery of the baby.
Menstrual cycle has been broadly classified into 3 phases that are mainly Menstrual phase, Follicular phase and Luteal Phase. During Menstrual phase menstrual flow occurs. It lasts for 3 to 5 days. Menstrual flow is due to the breakdown of endometrial lining and its blood vessels that comes out through vagina in the form of liquid. Always remember that menstrual cycle occurs only when the released ovum is not fertilised. Lack of menstrual cycle is an indicator of pregnancy. But sometimes lack of menstrual cycle can also occur due to poor health and diseases.
Menstrual phase is followed by Follicular phase during which primary follicle matures into Graafian follicle due to increase in the secretion of pituitary and ovarian hormones. In this phase endometrium regenerates through proliferation. During the middle of menstrual cycle i.e., around 14th day the secretion of LH hormone increase by manifold called LH Surge and induces the rupturing of Graafian follicle to release ovum. This process is known as ovulation.
After ovulation the remnants of Graafian follicle transforms into Corpus Luteum during the Luteal Phase which secretes pregnancy hormone “Progesterone”. Progesterone maintains endometrium for the implantation of the fertilised ovum. When ovum is not fertilised, corpus luteum disintegrates causing breakdown of endometrium initiating new menstrual cycle. This cyclic reproductive process is called Menstruation.
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Reference: All facts in this article have been inspired from Class 12 NCERT Biology Book