 The menstrual cycle is approximately a 28-day cycle which is completed in preparation for a human female to reproduce.

 The cycle involves four hormones of chemical messages that tell specific cells to do a job.  The hormones are released from the pituitary gland, which is located at the base of the brain, and the ovaries

 The hormones secreted only react on specific cells because those cells have receptor molecules on the cell membrane, and they allow certain hormones or chemicals into the cell.

 The hormones of the menstrual cycle only react to the cells of the: ◦ Pituitary gland ◦ Ovaries ◦ Uterus of a female because they have the appropriate receptor molecules

 The four main hormones used during the menstrual cycle and the order in which they are secreted are ◦ FSH – secreted by the pituitary ◦ Estrogen – secreted by the ovaries ◦ LH – secreted by the pituitary gland ◦ Progesterone – secreted by the ovaries

 These four hormones cause four major events to occur during the menstrual cycle: ◦ 1 st FSH is secreted and reacts with receptors on the cells of the ovaries. These cells start to develop an egg for eventual ovulation.

◦ Next the cells of the ovaries start to secrete Estrogen, which reacts with the receptors on the cells of the uterus. ◦ Estrogen causes the uterus to thicken with blood vessels and glands preparing it for the development of an embryo of the egg is fertilized.

◦ When levels of estrogen are at high concentration in the blood the hormone will also react with the receptors of the pituitary gland causing them to secrete LH. The LH secreted reacts with the cells of the ovaries causing ovulation to occur or the release of mature egg into fallopian tube

After the final step, the cycle would start all over again with the secretion of FSH ◦ Finally the same cells in the ovaries that developed the egg that was ovulated start to secrete Progesterone which will maintain the thickness of the uterine wall. ◦ If the egg is not fertilized the cells secreting progesterone and the uterine wall breakdown and he excess blood vessels are released through the female’s vagina in a process called menstrual flow or a period.

 The series of hormone secretion that occurs during the menstrual cycle is known as FEEDBACK MECHANSM.  Production and the stop production of the various hormones are kept in balance by this feedback mechanism. If is a way of maintaining HOMEOSTASIS.

Menstrual Cycle