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EGENTS BIOLOGY NAME ______________________ MENSTRUAL CYCLE LAB DATE _______________________ Background: When a human female is born, her ovaries already contain all the cells that will eventually mature and form eggs. These cells do not begin to mature until the girl reaches puberty. At that time, hormonal changes occur that stimulate the maturation of eggs, approximately every 28 days. Most commonly, only 1 egg is stimulated to mature each month, and usually from alternating ovaries. The regular steps involved in egg maturation and release are called the menstrual cycle. The menstrual cycle has 2 distinct phases – the follicular phase and the luteal phase. In the follicular phase, an egg receives stimulation from a hormone called FSH (follicle stimulating hormone) triggering development of the egg inside an egg sac (the follicle). When the egg is fully mature, the follicle ruptures, releasing the egg. This is called ovulation, and it signals the end of the follicular phase. It’s important to notice that another really important event occurs during the follicular phase. As the follicle is growing and developing, it releases estrogen, which causes the lining of the uterus to thicken. This would allow implantation of a fertilized egg, leading to pregnancy. The second phase is called the luteal phase. In the luteal phase, the ruptured follicle is stimulated by LH (luteinizing hormone), causing it to grow and become a structure called a corpus luteum. The corpus luteum releases its own hormone – progesterone – which maintains the thickened lining of the uterus for a few extra days. The end of the menstrual cycle occurs after the luteal phase. If the egg is NOT fertilized and does NOT implant in the wall of the uterus, levels of both estrogen and progesterone crash. This causes the lining of the uterus to deteriorate and pass out of the body, a process known as menstruation. Then the cycle starts over again with the stimulation of another egg. 1. There are 4 different hormones discussed in the background section. a)Which one stimulates development of the follicle? b)Which one stimulates development of the corpus luteum? c)Which one is made by the follicle, & thickens the uterine lining? ___________ d)Which one is made by the corpus luteum, and maintains the uterine lining? 2. What is ovulation? 3. Does ovulation happen at the beginning or the end of the follicular phase? 4. What structure is formed during the luteal phase? 5. Why is it necessary for the lining of the uterus to thicken? 6. If a fertilized egg does NOT implant in the uterus, what happens?
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