Concept Practice
Hormones and Sexual Desire

Chapter 98. Hormones and Sexual Desire

androgens
sex hormones found in high concentrations in males
estradiol
the primary estrogen; influences sexual development in females, as well as the menstrual cycle
estrogens
sex hormones found in high concentrations in females
hormones
chemical messengers of the endocrine system; travel to their target through the bloodstream
menopause
the period of years (usually in the 40s and 50s) surrounding the end of a female’s menstrual cycle
puberty
period of hormone-based physical changes which help a child's body mature into an adult body capable of reproduction
testosterone
the primary androgen; triggers sexual development in males during infancy and puberty, as well as influencing sexual desire in both men and women
adrenal gland
part of the endocrine system; located just above each kidney; releases stress hormones and a small amount of the sex hormone <i>testosterone</i>
Hormones and Sexual Desire
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illustration: Show male-female couple in silhouette, with body posture, suggesting romantic attraction
Learning Objectives:

Describe the main hormones that influence sexual motivation.

Contrast the hormonal effects on sexual behavior in rats and humans.

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Illustration: Show two heads in profile, facing each other; on left, head is blue and contains male symbol; to left of head is large text “Androgens” and small text “Estrogens”, both in blue; on right, head is pink and contains female symbol; to right of head is large text “Estrogens” and small text “Androgens”, both in pink (composite illustration by T. Ludwig)

1. Hormones are chemical messengers carried in the blood. Sexual development and adult sexual behavior are influenced by a family of closely related hormones called androgens (primarily testosterone) and estrogens (primarily estradiol). Females have higher concentrations of estrogens, and males have higher concentrations of androgens.

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Illustration: Show either simple cartoon-type illustration of two rats in close proximity, with one sniffing the other

2. In rats and many other animals, hormones tightly control sexual behavior. Female rats are sexually receptive only when their level of estrogens is high. Male rats seek females only when their level of androgens is high.

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Photo: male-female couple in bed, facing opposite directions, suggesting failed intimacy
IuriiSokolov/Getty Images

3. Human sexual desire is more complicated (and more difficult to measure). Surprisingly, short-term fluctuations (across hours or days) in estrogens have very little impact on female sexual interest or sexual behavior, and the same is true for fluctuations in androgens for males.

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The image includes two diagrams of the human body, each with body parts labeled related to puberty. The first diagram is a female with the following parts labeled: pituitary gland in the brain, growth of underarm hair, development of breasts, adrenal glands in the upper abdomen, ovaries in the lower abdomen, growth of uterus and vagina, and growth of pubic hair. The second diagram is a male with the following parts labeled: pituitary gland in the brain, growth of facial and underarm hair, growth of larynx in the throat, adrenal glands in the upper abdomen, growth of pubic hair, growth of testes and penis, testes, and ejaculation occurs.

4. In contrast, long-term changes (over months or years) in sex hormones have dramatic effects on humans. During puberty, the surge in androgens and estrogens produces the familiar characteristics of adult male and female bodies.

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The image describes how the reduction in hormones during menopause are related to sexual motivation. A decrease in estradiol results in no reduction in sexual motivation. However, a decrease in testosterone results in a reduction in sexual motivation.

5. During middle age (the 40s and 50s), females experience a sharp drop in estradiol associated with menopause, but little change in sexual interest. However, women who have an abnormally low level of testosterone typically report reduced sexual interest.

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The image describes how a decrease in testosterone results in a reduction in sexual motivation.

6. There is no “male menopause” or other sudden drop in hormone production. Instead, males experience a gradual decline in testosterone levels across the decades of adulthood, and a corresponding gradual decline in sexual interest.

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Practice 1: Sex Hormones Across the Lifespan

Try to predict the lifespan changes in the hormones testosterone and estradiol for males and females. Then, select each button to see a graph of the typical pattern.

The image is an empty line graph. The X axis is labeled Age in years and ranges from 0 to 90 in increments of 10. The Y axis is labeled Hormone production and ranges from low to high. Data is populated in the graph when one of the two buttons below the graph are selected, which include Typical Male Pattern and Typical Female Pattern.Typical Male Pattern Estradiol levels remain low across a males life span, with only a slight increase over time. Testosterone levels are low until around 10 years of age, where they increase sharply to high. These levels gradually decrease over the rest of the lifespan, ending between low and medium at 90 years. Typical Female Pattern Testosterone levels remain low across a females life span, with only a slight increase around 10 years of age to just above low. This hormone decreases over the rest of the lifespan to low. Estradiol levels are low until around 10 years of age, where they start to increase sharply to high at 15 years of age. This level remains high until around 40 years, where it sharply decreases to medium at 50 years of age. It decrease over the rest of the lifespan, ending between just below medium at 90 years.
Testosterone begins at Low for age 0, holds steady until 10, then then rises sharply between 10 and 20, reaching its peak at High around 20, then declines gradually and steadily between 25 and 90 Estradiol line begins at Low for age 0, holds steady until age 10, then rises slightly between 10 and 50, then rises slowly and steadily between 50 and 90.
Estradiol line begins at Low for age 0, holds steady until age 10, then rises sharply between 10 and 20, reaching its peak at High in late teens, then declining slightly during 20s and 30s, then dropping sharply between 40 and 50, reaching the middle (“50%”) of the vertical axis by age 50, then declining just a bit between 50 and 90. Testosterone begins at Low for age 0, holds steady until 10, then bumps up to about the “20%” level by mid-teens, then declines gradually and steadily between 30 and 90.
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Practice 2: Predicting Changes in Sexual Desire

How do changes in androgens and estrogens influence sexual motivation? Try to predict what would happen with each of the changes indicated here. Then, select each button to see the typical outcome.

The graph is a line graph with one line. The X axis is labeled hours from midnight and ranges from 0 to 24 hours in increments of 6. The Y axis is labeled Hormone production and ranges from 0 to 1000 in increments of 250. The line representing level of testosterone starts at around 300 at midnight (0 hours), decreases slightly at 1 hour, then rises gradually to peak at 650 at around 6 AM. The line drops gradually from this point to return to around 300 at midnight.
The graph is a line graph with one line. The X axis is labeled Days from ovulation and ranges from -12 to +12 in increments of 3. The Y axis is labeled Hormone production and ranges from 0 to 500 in increments of 100. The line representing level of estradiol starts at around 100 at -12 days, remains steady until -6 days, where it starts to rise drastically to peak at 475 at -2 days. The line then drops sharply to about 50 on day 0. Then the line starts to increase again around day 3 to 300, and then decreases again by day 9 to around 100. The line has two humps, with one taller, skinnier peak at -2 days and a shorter, wider peak at 6 days.
The graph is a line graph with one line. The X axis is labeled Age in years and ranges from 6 to 18 in increments of 2. The Y axis is labeled Hormone production and ranges from 300 to 700 in increments of 100. Testosterone levels are low, around 300, until around 10 years of age, where they start to increase gradually to 350 at 12 years. Then the line drastically increases to 650 by 16 years, where it remains until 18 years.
The graph is a line graph with one line. The X axis is labeled Age in years and ranges from 6 to 18 in increments of 2. The Y axis is labeled Hormone production and ranges from 100 to 500 in increments of 100. Estradiol levels are low, around 100, until around 8 years of age, where they start to increase gradually to 200 at 12 years. Then the line drastically increases to 450 by 16 years, where it remains until 18 years.
The graph is a line graph with one line. The X axis is labeled Age in years and ranges from 20 to 80 in increments of 10. The Y axis is labeled Hormone production and ranges from 300 to 700 in increments of 100. Testosterone levels are high around 700 at 20 years of age, and end low at around 325 at 80 years of age. The line is diagonal and gradual from upper left to lower right in the graph.
The graph is a line graph with one line. The X axis is labeled Age in years and ranges from 20 to 80 in increments of 10. The Y axis is labeled Hormone production and ranges from 100 to 500 in increments of 100. Estradiol levels are high around 500 at 20 years of age, and only decrease slightly until a drastic decrease at age 40, where levels drop until they reach 100 at age 60. The line then remains steady at this level until 80 years.

Hourly fluctuations in level of testosterone across a day (blue): In males, testosterone production follows a predictable 24-hour cycle, reaching a peak between 6 am and 8 am, then gradually falling throughout the day to stabilize at about half that level from 7 pm to 2 am. This cycle is not correlated with sexual interest or sexual behavior.

Daily fluctuations in level of estradiol across a month (pink): In females, estradiol production follows a predictable 28-day cycle, reaching a peak a few days before ovulation, then falling sharply to a low at ovulation, and then rising to a second peak a few days after ovulation, along with another important hormone called progesterone, which prepares the uterus for pregnancy. This cycle is weakly correlated with sexual interest, with some studies showing a slight increase in desire as estradiol falls at ovulation.

Long-term increase in level of testosterone at puberty (blue): In males, testosterone rises dramatically at the time of the growth spurt between ages 12 and 14, enabling the development of the male genitals and sperm production. Sexual interest rises along with testosterone level.

Long-term increase in level of estradiol at puberty (pink): In females, estradiol rises gradually at the beginning of puberty, then increases more sharply between ages 12 and 14, reaching adult levels around age 16. This increase, along with the production of other female hormones, allows the maturation of the reproductive tract and the beginning of the menstrual cycle. Sexual interest rises at the same time, but this may have little to do with estradiol level. Instead, the increase in sexual interest may be driven by a smaller rise in testosterone produced by the adrenal glands.

Age-related decrease in level of testosterone (blue): In males, testosterone production typically falls gradually across the decades of adult life. Sexual interest decreases steadily as testosterone level declines.

Age-related decrease in level of estradiol (pink): In females, estradiol declines gradually between ages 20 and 40, and then dramatically between ages 40 and 50 before leveling out for the rest of adulthood. Menopause typically occurs around age 50. Although the drop in estradiol causes thinning of the vaginal walls and a reduction in lubrication, it is not correlated with a decrease in sexual interest, unless the woman has an abnormally low level of testosterone.

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Try to respond to the statements again.

Quiz 1

For each statement, select one of the buttons to indicate whether the statement is True or False. When responses have been chosen for all the statements, select the CHECK ANSWER button.

TrueFalse

In male rats, sexual interest is tightly correlated with the level of testosterone.

Human females experience a sudden decrease in sexual interest as their estradiol level falls at menopause.

In humans, both males and females experience an increase in sexual interest along with the rise of sex hormones at puberty.

Female rats are sexually receptive only when their testosterone level is high.
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Quiz 2

Match the terms to their descriptions by dragging each colored circle to the appropriate gray circle. When all the circles have been placed, select the CHECK ANSWER button.

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Perhaps you should go back to review the main hormones that influence sexual desire.
hormones
androgens
estrogens
testosterone
estradiol
the general term for sex hormones found in higher concentrations in males
the specific hormone that is considered the primary female hormone
the general term for sex hormones found in higher concentrations in females
the general term for chemical messengers of the endocrine system
the specific hormone that is considered the primary male hormone
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