Sex Hormones ❖ The gonads produce steroid hormones, regulating reproduction ➢ Testes ■ Leydig cells produce and secrete testosterone (androgen) ■ Changes in voice, hair growth, genital size. ■ Declines with age ➢ Ovaries ■ Two major classes ● Progestins: help maintain pregnancy ● Estrogen: includes estradiol, sexual receptivity ■ Ovulatory cycle ● FSH stimulates ovarian follicles to grow and secrete estrogens ● Induces the release of LH → triggers the release of an egg from a follicle → develops as a corpus luteum (estrogen is lower) → secretes progesterone to prepare uterus → progesterone goes down ■ Oral contraceptives have small doses of synthetic hormones which exert continuous negative feedback on the hypothalamus and pituitary → inhibits the release of GnRH → prevents the release of LH (surge) that would normally release the egg ➢ Relations among gonadal hormones ■ All based on the chemical structure of cholesterol ■ Males and females differ in the relative amount they produce ❖ Hormonal and neural systems interact to produce integrated responses ➢ Four kinds of signals possible ■ Neural-to-neural: male dove sees an attractive female ■ Neural-to-endocrine: male sees possibility to mate → GnRH ■ Endocrine-to-endocrine: stimulation of pituitary to release gonadotropins ■ Endocrine-to-neural: testosterone alters excitability of neurons (displays courtship behavior) → females responds → another cycle ➢ Interactions between endocrine activity and behavior are cyclical ❖ Reproductive behavior ➢ Four stages ■ Sexual attraction: emit stimuli that attract opposite sex ■ Appetitive behaviors: helps establish or maintain sexual behavior ● Proceptive: females advertises readiness ● Males stay close to female ■ Copulation: coitus, intromissions ● Refractory phase ● Coolidge effect: males that appears sexually satisfied w current partner will resume sexual activity if provided w a new partner ■ Postcopulatory behavior: vary greatly w species ➢ Copulation brings gametes together ■ Activational effect of testerone ➢ Neural circuitry of the brain regulates reproductive behavior
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- Fall '08
- Sexual intercourse, Sexual differentiation