Module 3

Module 3—The Male and Female Reproductive Systems

Lesson 8—Phases of Menstruation

 

Get Focused

 

The beginning of menstruation represents the beginning of a female’s reproductive years. The start of the menstrual cycle is generally considered the pivotal event of puberty for females, and it indicates the time from which a female can conceive. The ability to be fertile means the ability to have offspring and, therefore, the ability to help in the continuation of the species.

 

 

The menstrual cycle is said to begin on the first day of bleeding and is usually a 28 day cycle. Both the ovarian and uterine cycles begin on this day. The ovarian cycle, which takes place in the ovaries, is divided into the follicular stage and the luteal stage. During the follicular stage, levels of FSH are high while stimulating normally one follicle to mature. The maturing follicle releases the ovarian hormones estrogen and progesterone. Estrogen then negatively feeds back to the pituitary to cause a reduction in the release of FSH. Estrogen also causes the hypothalamus to secret GnRH, which then leads to an increase in the pituitary hormone of LH. LH activates ovulation of the primary oocyte from the follicle.

 

The end of ovulation is considered the end of the follicular stage and the start of the luteal stage. With the release of the egg, the follicle develops into the corpus luteum under the influence of LH. Both ovarian hormones are secreted from the corpus luteum and their increased levels feedback negatively to the anterior pituitary to inhibit production of FSH and LH. As the corpus luteum disintegrates, the ovarian hormone levels decrease in the blood. The low blood levels of progesterone and estrogen are detected by the anterior pituitary and cause an increase in FSH and LH; the cycle starts again.

 

On the first day of menstrual flow, the corpus luteum degeneration causes estrogen and progesterone to be at low levels in the blood. Estrogen blood levels begin to rise as a new follicle begins to mature, releasing the ovarian hormone. When estrogen levels are high, it causes the endometrium to thicken. A more rapid thickening of the endometrium lining occurs once the corpus luteum begins to produce progesterone, after ovulation has occurred. If fertilization takes place, the zygote travels through the oviduct and implants in the freshly, blood-engorged endometrial lining of the uterus. If fertilization does not occur, there is a disintegration of the endometrium lining, and it is expelled from the body during menstruation.

 

Without this intricate dance of pituitary and ovarian hormones, the menstrual cycle would not take place, and there would be no possibility of fertilization.

 

As women age, the number of functioning follicular cells decreases, resulting in reduced production of estrogen and progesterone. The menstrual cycle becomes irregular and eventually ceases. This is called menopause, a period when the homeostasis of many hormones is interrupted, often resulting in the symptom of hot flashes.

 

Hormone replacement therapy can be used to treat some of the symptoms of menopause, however, there are several possible side effects, such as the increased possibility of breast cancer, heart attack, stroke, and blood clots.

 

Just because a female begins menstruation does not mean that she is limited to doing only certain activities or that there is a clear and easy path to fertilization. As you have been learning, there are many, many obstacles to fertilization and the birth of a healthy child.

 

In the role of fertility doctor, you have identified that Maria suffers from dysmenorrhea and Jane from amenorrhea. To understand her disorder, each woman needed to learn more about the structure and function of a healthy, properly functioning reproductive system, which includes a regular menstrual cycle. Understanding the “normal” function of the reproductive system helped them to understand the disorders from which they were suffering, as well as the choice of treatment options that were available to them.

 

In addition to menstrual problems, a clear understanding of the menstrual cycle helps you understand when fertility can and cannot happen. This understanding is important for both men and women in family planning and prevention of unplanned or unexpected pregnancies.

 

In this lesson you will study the events of the menstrual cycle, how hormones control the cycle of menstrual events, and where the cycle occurs in the female life cycle. You will consider the following focusing questions:

• What are the physiological events of menstruation?

• What hormone(s) control the specific events of menstruation?

• When does menstruation naturally begin and end?

Module 3: Lesson 8 Assignment

 

Download a copy of the Module 3: Lesson 8 Assignment to your computer now. You will receive further instructions on how to complete this assignment later in the lesson.

 

In addition to the lesson work you complete for your course folder, you answer assignment questions based on how the pituitary and ovarian hormones control and are controlled by the events of the menstrual cycle.

 

You must decide what to do with the questions that are not marked by the teacher.

 

Remember that these questions provide you with the practice and feedback that you need to successfully complete this course. You should respond to all of the questions and place those answers in your course folder.

 

Make any notes about “A Fertility Case Study” from this lesson and place them in your course folder for your teacher’s feedback.

 

Remember that you also have the option of trying additional questions from the textbook for further practice. Consult with your teacher for the answers to these questions. The Key will also provide you with many Diploma Exam-style multiple-choice, numerical-response, and written-response questions that will be an excellent review of the module. Practising your responses to these types of questions is good preparation for the Diploma Exam.

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