Lesson 6 — Effects of Reproductive Hormones


Effects of Reproductive Hormones

Without proper hormonal control of the reproductive system, events such as ovulation and sperm production cannot occur; this results in the lack of fertilization. Normal hormone control may be altered knowingly by taking hormones to enhance or prevent pregnancy and to treat disorders. Hormone control may be altered unknowingly through the effects of endocrine disruptors.

Hormone Replacement Therapy

Although men can produce viable sperms throughout their lives, women are born with a limited number of follicles. While women age, their fertility declines gradually until their ovarian follicles deplete and the hormones that they produce decline as well. Menopause is the end of the menstrual cycle in women, occurring normally about age 50.

Several symptoms of menopause are the result of declining hormone levels. The decrease of progesterone can result in abnormal growth of the endometrium. Decreasing estrogen levels can result in hot flashes and mood swings. After menopause, low levels of estrogen can lead to high cholesterol levels, osteoporosis, uterine cancer, breast cancer, and heart disease.

Therefore, many women consider hormone replacement therapy (HRT) to replace the estrogen and progesterone levels in the body. Hormone replacement therapy can also be used to treat andropause, impotence, low sperm count, arthritis, and osteoporosis in men.

Although HRT can alleviate some of the menopausal symptoms, many health risks are associated with HRT. Studies have shown that HRT increases risks of breast cancer and strokes, and does not reduce the risk of heart disease. The debate on the risks and benefits of HRT is ongoing.


Oral Contraceptive Pill
Progestin, a synthetic progesterone, was the first chemical used as a female oral contraceptive known as 'the pill'. Varying quantities of estrogen and progesterone are used in today's contraception pills to prevent the release of FSH and LH. Without FSH, the follicles do not mature, and without LH, ovulation does not occur.

The estrogen levels in the pill are low so do not stimulate the uterus to build up a thick lining.   This reduced endometrial thickening leads to a lighter menstrual flow.  Normally, the pill is taken for the first 21 days and placebos (sugar pills) are taken for the remaining 7 days of the menstrual cycle to trigger menstruation. 

Endocrine Disruptors

Endocrine disruptors are synthetic or naturally occurring substances that interfere with the functioning of the body's normal production of hormones. The endocrine disruptors can be absorbed into the body through contaminated water, food, or air. Their effects can halt or stimulate normal hormone levels, or they may change how hormones travel in the body, affecting what the hormone controls.

Some known human endocrine disruptors are dioxin, PCBs, DDT, and diethylstilbestrol (DES). Many pregnant women were prescribed diethylstilbestrol (DES) to prevent miscarriages and premature labours. However, it was discovered that DES was ineffective in preventing miscarriages, but it also increased the likelihood of cervical and vaginal cancer among people who were exposed to DES during prenatal development.

Exposure to endocrine disruptors during development can have permanent effects on an organism. Further evidence suggests that endocrine disruptors may have consequences for many generations, not just for the immediate person or organism.

Understanding how normal reproductive hormones control and affect the body can help you understand how these reproductive hormones are used to promote or reduce conception potential and to treat diseases as well as how they are influenced by endocrine disruptors.



Reflect and Connect

From previous lessons in this unit, you should have a good grasp of how the function of normal human sexual reproductive hormone pathways. Reproductive hormones are used to help or prevent reproductive potential. They are also used to treat various diseases.

A constant bombardment of chemicals infiltrates our environment. How these chemicals influence normal hormone control is beginning to be understood. Endocrine disruptors are an issue of growing importance in the concern and desire to maintain healthy lifestyles for many organisms. Observation of other organisms sheds light on how these chemicals may affect our own human endocrine pathways.

As scientists and researchers gain further understanding of how endocrine disruptors affect wildlife, more information is gained of how these chemicals can affect human populations. Could these chemicals be causing some of the infertility problems seen in North America today?


 Biology 30 © 2008  Alberta Education & its Collaborative Partners ~ Updated by ADLC 2019