3-01 The Effects Of Sex Hormones (Part 1)

Front 1

Objective

Distinguish between the organizing and activating effects of sex hormones.

Back 1

The organizing effects of sex hormones occur mostly at a sensitive stage of development—shortly before birth in humans—and determine whether the brain and body will develop female or male characteristics. Activating effects can occur at any time in life, when a hormone temporarily activates a particular response. Activating effects on an organ may continue for an extended period of time but they do not last indefinitely. The distinction between the two kinds of effects is not absolute; hormones early in life exert temporary effects even while they are organizing body development, and during puberty, hormones can induce long-lasting structural changes as well as activating effects.

Front 2

Objective

Explain how testosterone and estrogen affect sexual differentiation.

Back 2

Nature’s “default setting” is to make every mammal a female. Add early testosterone and the individual becomes a male; without testosterone, it develops as a female, regardless of the amount of estradiol or other estrogens. This is not to downplay the role of estradiol, however. A genetic female that lacks estradiol during the early sensitive period develops approximately normal female external anatomy but does not develop normal sexual behavior. Even if she is given estradiol injections as an adult, she shows little sexual response toward either male or female partners. So, estradiol contributes to female development, including some aspects of brain differentiation

Front 3

Objective

Compare the male and female hypothalamus.

Back 3

One area in the anterior hypothalamus, known as the sexual dimorphic nucleus, is larger in the male than in the female and contributes to control of male sexual behavior. Part of the female hypothalamus can generate a cyclic pattern of hormone release, as in the human menstrual cycle. The male hypothalamus cannot, and neither can the hypothalamus of a female who was exposed to extra testosterone early in life.

Front 4

Objective

Compare the cerebral cortex and intellectual performance of men and women.

Back 4

Men tend to have more white matter than women, whereas women on average have a greater density of neurons in part of the temporal lobe that is important for language. The language-related areas are larger in the left than right hemisphere for both sexes, but that difference is usually larger in men than women.

In terms of intellectual performance, males and females differ in many small but consistent regards. Girls generally receive higher grades than boys at most school subjects—especially reading. On average, boys do better than girls at mental rotation tasks and line orientation tasks. However, performance on these tasks does not consistently correlate with people’s current levels of male or female sex hormones. Therefore, if performance relates to hormones, it probably depends more on organizational than activating effects.

Males usually do better than females on spatial orientation tasks. However, much of the difference relates to the strategies with which individuals approach spatial problems. If you ask people for directions to some location, more men than women answer in terms of coordinates, such as “go two blocks north and then three blocks east”. More women than men respond in terms of landmarks: “go until you reach the elementary school, then go down the hill toward the coffee shop”.

Front 5

Objective

Explain why men and women use different spatial strategies.

Back 5

The most commonly held hypothesis is that males of many species travel over wider geographical areas than females do, often in search of mating opportunities. That hypothesis fits with the fact that in some species, males perform best on spatial tasks during the breeding season.

Front 6

steroid hormone

Back 6

A class of hormones that contains four carbon rings; they are derived from cholesterol

Front 7

androgen

Back 7

Male hormone; a group that includes testosterone and several others; men have higher levels

Front 8

estrogen

Back 8

Female hormone; a group that includes estradiol and others; women have higher levels

Front 9

estradiol

Back 9

Type of estrogen

Front 10

progesterone

Back 10

Predominantly female hormone; prepares the uterus for the implantation of a fertilized ovum and promotes the maintenance of pregnancy

Front 11

sex-limited gene

Back 11

Genes that androgens or estrogens activate

Front 12

organizing effect

Back 12

Effects of sex hormones that occur mostly at a sensitive stage of development; determine whether the brain and body will develop female or male characteristics

Front 13

activating effect

Back 13

Effects that can occur at any time in life, when a hormone temporarily a particular response

Front 14

SRY (sex-determining region on the Y chromosome) gene

Back 14

Causes the primitive gonads to develop into testes, the sperm-producing organs

Front 15

testes

Back 15

Sperm-producing male organs; developing testes produce the hormone testosterone

Front 16

testosterone

Back 16

An androgen that increases the growth of the testes and maturation of other sex organs; causes Wolfian ducts to develop into seminal vesicles and vas deferens

Front 17

Wolffian ducts

Back 17

Precursors to other male reproductive structures

Front 18

Mullerian ducts

Back 18

Precursors to the female’s oviducts, uterus, and upper vagina

Front 19

ovaries

Back 19

Egg producing female organs

Front 20

sensitive period

Back 20

An early period when hormones have long-lasting effects

Front 21

sexually dimorphic nucleus

Back 21

Area of the anterior hypothalamus that is larger in the male than in the female and contributes to control of male sexual behavior

Front 22

alpha-fetoprotein

Back 22

Protein that binds with estrogen and blocks it from leaving the bloodstream and entering the cells that are developing in this early period