Steroids are substances derived from cholesterol.
Steroid hormones control sexual maturation, sexual cycles, mating
seasons, and insect metamorphosis.
Primary sexual characteristics:
those which are absolutely necessary for reproduction, like a uterus
or egg production.
Secondary sexual characteristics: those which may help attract a
mate but which are not absolutely necessary for reproduction, like
deep voices, beards, antlers, or peacock feathers.
Seasonal variation: In animals that mate seasonally, the seasonal
production of sex hormones controls the maturation and regression of
sexual characteristics and sexual behavior.
Androgens (masculinizing hormones):
- Testosterone (secreted by testes) causes development of
male primary and secondary sexual characteristics.
- Androgens produced by the adrenal cortex produce male secondary
sexual characteristics only.
Estrogens (feminizing hormones), secreted by the ovaries, cause the
development of both primary and secondary female characteristics.
Progesterone: female hormone secreted by the ovaries after ovulation
Adrenal cortex hormones:
- Outermost layer produces glucocorticoids, affecting some
aspects of carbohydrate metabolism.
- Middle layer produces mineralocorticoids such as
aldosterone, controlling metabolism of Na+ and other ions.
- Inner layer produces androgenic hormones.
Insect hormones:
- Ecdysone (molting hormone) controls molting and metamorphosis
- Juvenile hormone controls the outcome of molting: if present
in a larva, the molt produces a bigger larva, but absence of juvenile
hormone causes the molt to result in metamorphosis into a winged adult.
- 9-keto decanoic acid is secreted by queen bees and fed to
workers and larvae to keep them sterile. If queen dies, absence of this
substance causes some new larvae to develop into a queen.
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