▸ Follicular Phase As shown in Figure 34–14, on day 1 of a menstrual cycle, blood estrogen levels are low. The hypothalamus reacts to low estrogen levels by producing a releasing hormone that stimulates the anterior pituitary to secrete FSH and LH. These two hormones travel to the ovaries, where they cause a follicle to mature. Usually, just a single follicle develops, but sometimes two or even three mature during the same cycle.
As the follicle develops, the cells surrounding the egg enlarge and begin to produce increased amounts of estrogens. This causes the estrogen level in the blood to rise dramatically. High blood estrogen levels cause the hypothalamus to produce less releasing hormone, and the pituitary releases less LH and FSH. Estrogens also cause the lining of the uterus to thicken in preparation for receiving a fertilized egg. The development of an egg during this phase takes about 12 days.
VISUAL SUMMARY
THE MENSTRUAL CYCLE
FIGURE 34–14 The menstrual cycle includes several phases. Notice the changes in hormone levels in the blood, the development of the follicle, and the changes in the uterine lining during the menstrual cycle. Interpret Diagrams During which phase of the menstrual cycle are estrogen levels the highest?
dTable of Contents
- Formulas and Equations
- Applying Formulas and Equations
- Mean, Median, and Mode
- Estimation
- Using Measurements in Calculations
- Effects of Measurement Errors
- Accuracy
- Precision
- Comparing Accuracy and Precision
- Significant Figures
- Calculating With Significant Figures
- Scientific Notation
- Calculating With Scientific Notation
- Dimensional Analysis
- Applying Dimensional Analysis