Notes problem 5
endocrine and exocrine
Steroids
three ways to exert their effects
1. Bind to membrane receptors like neurotransmitters, to exert rapid effects.
2. Enter cells and activate certain proteins in the cytoplasm.
3. Bind to receptors that bind to chromosomes where they activate or inactivate genes.
Sex hormones: oestrogen, progesterone and androgen
they are a special type of steroids, released by the testes and ovaries and to a lesser extend by the
adrenal glands. Androgens is often referred to as male hormones, this includes testosterone, because
men have higher levels of these steroids. The estrogens, which include estradiol, are female
hormones because women have higher levels of these steroids. Androgen and estrogen are
categories of chemicals and neither is a specific chemical itself.
originally it was believed that the differences between men and women come only from specific sex-
limited genes, those genes are activated by androgens or estrogens.
Effects of sex hormones
organizing effects:
- occur mostly at a sensitive stage of development, well before birth in humans.
- determine whether the brain and body will develop male or female characteristics.
Activating effects:
- can occur at any time in life, when a hormone temporarily activates a particular response.
- activating effects on an organ last longer than the hormones are actually in an organ but they do
not last indefinitely.
The distinction between the two kinds of effects is not absolute though. Hormones early in life exert
temporary effects while they are organizing body development, and during puberty they induce long-
lasting structural changes as well as activating effects.
Sex differences in the gonads (genitalia)
- begins with chromosomes at conception – female XX and male XY.
- men have the SRY gene, which causes them to develop male gonads which produce testosterone.
- wolffian ducts: precursors for other male reproductive structures.
- Mullerian ducts: precursors for the females oviducts, uterus and upper vagina.
- differentiation of the external genitals and some aspects of the brain development depend mainly
on the level of testosterone during a sensitive period (3 rd and 4th month of pregnancy) when
hormones have long-lasting effects. A high level of testosterone develops the male genitalia and a
low level develops female genitalia.
- estrogens produce important effects on the internal organs but they have little effect on the
external genitals.
- early testosterone promotes the male pattern and inhibits the female pattern.
Sex differences in the hypothalamus
in addition to controlling differences in the external genitals, sex hormones early in life bind to
receptors in specific areas of the hypothalamus, amygdala and other brain areas. This creates
anatomical and physiological differences between sexes.
in humans testosterone produces its organizing effects on the hypothalamus by itself.
endocrine and exocrine
Steroids
three ways to exert their effects
1. Bind to membrane receptors like neurotransmitters, to exert rapid effects.
2. Enter cells and activate certain proteins in the cytoplasm.
3. Bind to receptors that bind to chromosomes where they activate or inactivate genes.
Sex hormones: oestrogen, progesterone and androgen
they are a special type of steroids, released by the testes and ovaries and to a lesser extend by the
adrenal glands. Androgens is often referred to as male hormones, this includes testosterone, because
men have higher levels of these steroids. The estrogens, which include estradiol, are female
hormones because women have higher levels of these steroids. Androgen and estrogen are
categories of chemicals and neither is a specific chemical itself.
originally it was believed that the differences between men and women come only from specific sex-
limited genes, those genes are activated by androgens or estrogens.
Effects of sex hormones
organizing effects:
- occur mostly at a sensitive stage of development, well before birth in humans.
- determine whether the brain and body will develop male or female characteristics.
Activating effects:
- can occur at any time in life, when a hormone temporarily activates a particular response.
- activating effects on an organ last longer than the hormones are actually in an organ but they do
not last indefinitely.
The distinction between the two kinds of effects is not absolute though. Hormones early in life exert
temporary effects while they are organizing body development, and during puberty they induce long-
lasting structural changes as well as activating effects.
Sex differences in the gonads (genitalia)
- begins with chromosomes at conception – female XX and male XY.
- men have the SRY gene, which causes them to develop male gonads which produce testosterone.
- wolffian ducts: precursors for other male reproductive structures.
- Mullerian ducts: precursors for the females oviducts, uterus and upper vagina.
- differentiation of the external genitals and some aspects of the brain development depend mainly
on the level of testosterone during a sensitive period (3 rd and 4th month of pregnancy) when
hormones have long-lasting effects. A high level of testosterone develops the male genitalia and a
low level develops female genitalia.
- estrogens produce important effects on the internal organs but they have little effect on the
external genitals.
- early testosterone promotes the male pattern and inhibits the female pattern.
Sex differences in the hypothalamus
in addition to controlling differences in the external genitals, sex hormones early in life bind to
receptors in specific areas of the hypothalamus, amygdala and other brain areas. This creates
anatomical and physiological differences between sexes.
in humans testosterone produces its organizing effects on the hypothalamus by itself.
