Chapter 11: Reproductive Behaviors

1. Chapter 11:Reproductive Behaviors

2. Sex and Hormones • The sex hormones are a special kind of steroids, released mostly by the gonads and to a lesser degree by the adrenal glands. • affect the brain, genital and other organs • Two types of sex hormones include: • Androgens • Estrogens • Both sexes have these categories in varying quantities .

3. Sex and Hormones • Androgens are a groups of sex hormones that include testosterone and others. • Generally referred to as “male hormones” because men have higher levels than women.

4. Sex and Hormones • Estrogens include estradiol and others and are referred to as “female hormones” because women have higher levels. • Progesterone is a type of hormone that prepares the uterus for the implantation of a fertilized ovum and promotes the maintenance of pregnancy.

5. Sex and Hormones • “Sex limited genes” are those activated by androgens or estrogens and control most of the differences between male and female. • Example: estrogens activate the gene for breast growth; androgens activate the gene for the growth of facial hair in men. • Sex hormones increase or decrease the rate of apoptosis in various regions of the brain. • Certain areas are slightly larger in males or females

6. Sex and Hormones • Sex hormones can have the following effects: • Organizing effects- occur mostly at sensitive stages of development. -Determine whether the brain and body will develop male or female characteristics • Activating effects- occur at any time of life and temporarily activate a particular response.

7. Sex and Hormones • The distinction between the activating and organizing effects of hormone is not absolute. • Example: hormones early in life can exert temporary effects; during puberty hormones can also induce long-lasting structural changes

8. Sex and Hormones • Obvious differences can exist between the reproductive organs and the gonads of males and female. • Sexual differentiation begins with the chromosomes. • Female mammal has two X chromosomes and a male has an X and a Y. • During an early stage of prenatal development, both male and female have a set of Mullerian ducts and a set of Wolffian ducts as well as primitive gonads.

9. Sex and Hormones • Wolffian ducts are the precursors to other male reproductive organs. • Develop into the vas deferens and seminal vesicles. • Mullerian ducts are precursors to the female’s oviducts, uterus, and upper vagina.

10. Sex and Hormones • The male Y chromosome includes the SRY gene which causes the primitive gonads to develop into testes, the sperm-producing organ. • The developed testes produce the hormone testosterone. • Testosterone induces the development of the penis and scrotum. • Females are not exposed to high testosterone levels and their gonads develop into ovaries, the egg-producing organs.

11. Sex and Hormones • Sensitive periods are early periods when hormones have long-lasting effects. • Sexual differentiation depends mostly on the level of testosterone during a sensitive period. • The human sensitive period for genital formation is about the third and fourth month of pregnancy.

13. Sex and Hormones • Female rats exposed to testosterone shortly before or after birth are partly masculinized in anatomy and behavior. • Clitoris grows larger than normal • At maturity, pituitary and ovaries produce steady levels of hormones instead of cycles • Parts of the hypothalamus appear more male • Sexual behavior becomes masculinized

15. Sex and Hormones • Extra estradiol does not determine whether the individual looks female or male. • Estradiol and other estrogens do modify various aspects of the development of the brain and the internal sexual organs. • The absence of sex hormones generally leads to female-looking external genitalia • If a male rat lacks androgen receptors or is castrated, it develops female-like anatomy and behavior.

16. Sex and Hormones • Sex hormones early in life bind to receptors in specific areas of the hypothalamus, amygdala, and other brain areas and produce anatomical and physiological differences. • The sexually dimorphic nucleus is an area in the anterior hypothalamus that is larger in the male and contributes to control of male sexual behavior. • Parts of the female hypothalamus generate a cyclical pattern of hormone release; the hypothalamus of a male cannot.

17. Sex and Hormones • During early development in rodents, testosterone is converted within certain brain cells to estradiol, which masculinizes development. • Alpha-fetoprotein is found in the blood during early sensitive periods and binds to estrogen and prevents it from entering developing cells. • Testosterone does not bind to alpha-fetoprotein and freely enters the cell.

18. Sex and Hormones • In adulthood, sex hormones exert activating effects to temporarily modify behavior. • Behavior can also influence hormone secretion. • Hormones do not cause behavior but rather alter the activity in various brain areas to change the way the brain responds to certain stimuli. • Hormones also change sensitivity in the penis, vagina and cervix.

19. Sex and Hormones • Sex hormones facilitate sexual behavior. • Arousal also depends on previous sexual experience. • Sex hormones activate sexual behavior by enhancing sensations. • Estrogens increase the sensitivity of the pudendal nerve, which transmits tactile stimulation from the pubic area to the brain.

20. Sex and Hormones • Sex hormones also increase responses of certain areas of the hypothalamus. • the ventromedial nucleus, the medial preoptic area (MPOA), and the anterior hypothalamus. • Stimulation of an area known as the sexually dimorphic nucleus (SDN) found in the anterior hypothalamus is larger in males and increases sexual behavior in males of many species.

21. Sex and Hormones • Testosterone and estradiol trigger the release of dopamine by the MPOA and other areas. • Dopamine stimulation of D1 and D5 receptors is associated with sexual arousal. • Facilitates erection of the penis and sexually receptive postures in females • Higher concentrations of dopamine stimulate D2 receptors and lead to orgasm. • Serotonin activity decreases sexual activity by blocking dopamine release.

22. Sex and Hormones • Humans are less dependent on current sex hormones than other species but changes can increase or decrease sexual arousal. • For males, levels of testosterone correlate positively with sexual arousal and the drive to seek out partners.

23. Sex and Hormones • Decreases in testosterone levels generally decrease male sexual activity and interest. • Example: castration • Impotence is the inability to maintain an erection. • usually caused by impaired blood circulation, not low testosterone. • Erection partially depends on testosterone increasing the release of nitric oxide. • facilitates the hypothalamic neurons and increases blood flow to the penis.

24. Sex and Hormones • Most sex offenders have normal testosterone levels. • Hormone levels do not completely explain the behaviors. • Testosterone reduction has been tried as a means of controlling sex offenders as it reduces sexual activities. • Results favorable for those who continue taking medication, but dropout rate is high.

25. Sex and Hormones • In women, the hypothalamus and pituitary interact with the ovaries to produce the menstrual cycle. • The menstrual cycle is the periodic variation in hormones and fertility over the course of about 28 days.

26. Sex and Hormones • After the end of a menstrual period: • the anterior pituitary releases follicle-stimulating hormone (FSH) • FSH promotes the growth of a follicle in the ovary. • The follicle nurtures the ovum and produces estrogen. • Towards the middle of the menstrual cycle, the follicle builds up receptors to FSH. • As a result, the follicle produces increasing amounts of estradiol, a type of estrogen.

27. Sex and Hormones • Increased estradiol causes the anterior pituitary to increase release of FSH and luetinizing hormone (LH). • FSH an LH cause the follicle to release an ovum. • The remnants of the follicle release the hormone progesterone. • prepares the uterus for implantation of a fertilized ovum • inhibits the further release of LH

29. Sex and Hormones • If the ovum is not fertilized, the lining of the uterus is cast off and menstruation occurs. • If the ovum is fertilized, the levels of estradiol and progesterone increase gradually throughout pregnancy.

30. Sex and Hormones • Birth control pills prevent pregnancy by interfering with the usual feedback cycle between the ovaries and pituitary. • The “combination-pill” contains both estrogen and progesterone and prevents the surge of FSH and LH that would release an ovum. • also thickens the mucus of the cervix making it harder for the sperm to reach the egg.

31. Sex and Hormones • The periovulatory period is the time of maximum fertility and high estrogen levels when ovulation occurs. • Studies suggest that women become more sexually responsive during this time when estrogen levels are high. • Show increased attention to sex-related stimuli. • show increased mate preference towards men who act and look more masculine.

32. Sex and Hormones • Oxytocin is a pituitary hormone also important for reproductive behavior. • Stimulates contraction of the uterus during delivery of a baby • Stimulates the mammary gland to release milk. • Released during orgasm and triggers a state of complete relaxation. • Facilitates formation of pair bonds between mating partners and mother and infant

33. Sex and Hormones • Hormones released around the time of giving birth facilitate maternal behavior in females. • Late in pregnancy, the female secretes large amounts of estradiol, prolactin, and oxytocin. • Prolactin is necessary for milk production. • Oxytocin is associated with maternal behavior and social attachment.

34. Sex and Hormones • Females also change patterns of hormone receptors. • Late in pregnancy, the brain increases its sensitivity to estradiol in areas responsible for maternal behavior, but not for sexual behavior. • The hormonal changes increase the attention of the mother to the young after birth. • Hormones also increase activity in the medial preoptic area and the anterior hypothalamus.

36. Sex and Hormones • Vasopressin is a hormone synthesized by the hypothalamus and secreted by the posterior pituitary gland. • associated with establishing long-term bonds in some species. • Mothers are also stimulated by the odors of their babies. • Infant rats release chemicals that stimulate the mother’s vomeronasal organ.

37. Variations in Sexual Behavior • A wide degree of variation exists between people in terms of frequency of sexual behavior, preferred types of sexual activity, and sexual orientation. • Evolutionary explanations are controversial in explaining mating behavior.