1. Chapter 13 Hormones and Sex
What’s Wrong with the Mamawawa
This multimedia product and its contents are protected under copyright law. The following are prohibited by law:
any public performance or display, including transmission of any image over a network;
preparation of any derivative work, including the extraction, in whole or in part, of any images;
any rental, lease, or lending of the program.
Copyright © 2006 by Allyn and Bacon

2. Developmental and Activational Effects of Sex Hormones
Developmental – “organizational” - influencing the development of anatomical, physiological and behavioral characteristics that differentiate the sexes
Activational – activating reproduction-related behavior in mature individuals
Copyright © 2006 by Allyn and Bacon

3. Copyright © 2006 by Allyn and Bacon
Glands
Exocrine – Release chemicals into ducts which carry them to their targets.
Sweat glands, for example.
Endocrine – Ductless. Release hormones directly into the circulatory system.
Only organs whose primary function is hormone release are referred to as endocrine glands.
Copyright © 2006 by Allyn and Bacon

4. Copyright © 2006 by Allyn and Bacon
Hormones
Amino acid derivatives
Epinephrine, for example (adrenal medulla)
Peptides and proteins
Short and long chains of amino acids
Steroids
Synthesized from cholesterol (fat)
Fat-soluble – able to enter cells and bind to receptors in cytoplasm or nucleus
Copyright © 2006 by Allyn and Bacon

5. Copyright © 2006 by Allyn and Bacon
Gonads
Male testes produce sperm cells
Female ovaries produce ova
Sperm and ova each have 23 chromosomes
Fertilization
Sperm cell + ovum = zygote
23 pairs of chromosomes
X and Y – sex chromosomes
XX = female, XY = male
Copyright © 2006 by Allyn and Bacon

6. Sex Steroids – Released by Gonads
Androgens - e.g., testosterone
Estrogens - e.g., estradiol
Adult testes release more androgens and ovaries more estrogens
Progestins – also present in both sexes
progesterone prepares uterus and breasts for pregnancy
Adrenal cortex – also releases sex steroids
Copyright © 2006 by Allyn and Bacon

7. Hormones of the Pituitary
“Master gland”
Tropic hormones influence the release of hormones by other glands
Posterior pituitary – hormones synthesized in the hypothalamus
Anterior pituitary – tropic hormones
Copyright © 2006 by Allyn and Bacon

11. Copyright © 2006 by Allyn and Bacon
Sexual Development
We are dimorphic – exist in 2 forms
Initially there is a primordial gonad
Cortex – potential to be ovary
Medulla – potential to be a testis
If XY, Y triggers the synthesis of H-Y antigen and promotes development of the medulla
No H-Y antigen, cortex develops into ovary
Copyright © 2006 by Allyn and Bacon

12. Copyright © 2006 by Allyn and Bacon

13. Copyright © 2006 by Allyn and Bacon
Sexual Development
6-weeks post-conception:
H-Y antigen > testes
No H-Y antigen > ovaries
Both sexes begin with 2 sets of reproductive ducts
Wolffian system – male – seminal vesicles, vas deferens
Mullerian system – female – uterus, vagina, fallopian tubes
Differentiation occurs in the 3rd prenatal month
Copyright © 2006 by Allyn and Bacon

14. Copyright © 2006 by Allyn and Bacon
Sexual Development
6-weeks: gonads develop
3rd prenatal month: differentiation of ducts
Testes produce testosterone and Mullerian-inhibiting substance
Wolffian system develops, Mullerian degenerates, testes descend
No testes – no testicular hormones
Mullerian system develops, Wolffian degenerates
Copyright © 2006 by Allyn and Bacon

15. Copyright © 2006 by Allyn and Bacon

16. Copyright © 2006 by Allyn and Bacon
A terminology note
Ovariectomy – removal of ovaries
Orchidectomy – removal of testes
Gonadectomy or castration – removal of gonads, either ovaries or testes
Such procedures are often used to study the effects of sex hormones
Copyright © 2006 by Allyn and Bacon

17. Copyright © 2006 by Allyn and Bacon
Sexual Development
External reproductive structures – genitalia – develop from one bipotential precursor
Differentiation occurs in 2nd month
Testosterone > male
No testosterone > female
Copyright © 2006 by Allyn and Bacon

18. Copyright © 2006 by Allyn and Bacon

19. Sexual Dimorphisms in the Brain
Pfeiffer (1936) – gonadectomized and implanted gonads in neonatal rats
Gonadectomy > cyclic hormone release
Transplant of testes or ovaries > steady
Perinatal hormones lead to male pattern
Why do both ovaries and testes lead to male pattern?
What masculinizes the brain?
Copyright © 2006 by Allyn and Bacon

20. Sexual Dimorphisms in the Brain
What masculinizes the brain?
Sex steroids are all derived from cholesterol and are readily converted from one to the other
Aromatize testosterone > estradiol
Evidence suggests that estradiol masculinizes the brain
Copyright © 2006 by Allyn and Bacon

21. Evidence that Estradiol (E) Masculinizes the Neonatal Brain
Neonatal injections of E masculinize
Dihydrotestosterone can’t be converted to E – doesn’t masculinize
Block aromatization or E receptors – interferes with masculinizing effects of testosterone
Why doesn’t E masculinize female brains?
Copyright © 2006 by Allyn and Bacon

22. Copyright © 2006 by Allyn and Bacon
Alpha fetoprotein
In blood during perinatal period - protects the female brain from E
Binds to circulating E, so none gets to the brain
How does E get into male brain?
In males, testoterone enters the brain and then is converted to E
Copyright © 2006 by Allyn and Bacon

23. Copyright © 2006 by Allyn and Bacon
Sexual Dimorphisms
Not just a consequence of absence or presence of testosterone (T)
XX and XY cells differ prior to hormone exposure
Female brain development may not automatically occur in absence of T
Various dimorphisms emerge at different stages under different influences
Copyright © 2006 by Allyn and Bacon

24. Perinatal Hormones and Behavioral Development
Masculinize – promoting male behavior, mounting, etc.
Defeminize – preventing female behavior, lordosis
Perinatal T masculinizes and defeminizes
Neonatal castration of male rats – feminizes and demasculinizes
Copyright © 2006 by Allyn and Bacon

25. Copyright © 2006 by Allyn and Bacon
Puberty
Fertility achieved, secondary sex characteristics develop
Features that distinguish sexually mature men and women
Increase in release of anterior pituitary hormones
Growth hormone – acts on bone and muscle
Gonadoptrophic hormone
Adrenocorticotrophic hormone
Copyright © 2006 by Allyn and Bacon

27. Copyright © 2006 by Allyn and Bacon

28. Copyright © 2006 by Allyn and Bacon
Puberty
Relative levels of androgens and estrogens determine whether male or female features develop
Androstenedione – androgen necessary for the growth of axillary and pubic hair in both sexes
Copyright © 2006 by Allyn and Bacon

29. Andrenogenital Syndrome
Androgenic insensitivity leads an XY individual to look female (Anne S.)
Andrenogenital Syndrome is caused by congenital adrenal hyperplasia
Too little cortisol leads to compensatory excessive release of adrenal androgens
No problem for males
May masculinize female genitalia and behavior – surgical and hormonal treatments needed at puberty
Copyright © 2006 by Allyn and Bacon

30. Male Reproduction-Related Behavior and Testosterone (T)
Effects of orchidectomy Bremer (1959)
Reduced sexual interest and behavior
Rate and degree of loss varies
Still have adrenal T
Level of male sexuality is NOT correlated with T levels
Increasing male T levels does NOT increase sex drive
Copyright © 2006 by Allyn and Bacon

31. Female Reproduction-Related Behavior and Gonadal Hormones
Rats and guinea pigs – surges of estrogen and progesterone initiate estrus, a period of fertility and receptivity
Women – sexual motivation and behavior not tied to cycle
Sex drive may be under androgenic control
Copyright © 2006 by Allyn and Bacon

32. Human Female Sexuality and Androgens
T increases the proceptivity of ovariectomized and adrenalectomized female rhesus monkeys
Correlations seen between sexual motivation and T
T found to rekindle sexual motivation in ovariectomized and adrenalectomized women
Copyright © 2006 by Allyn and Bacon

33. Copyright © 2006 by Allyn and Bacon
Anabolic Steroids
Anabolic – growth-promoting
No firm scientific evidence that muscularity and strength are increased
Sex-related side effects
High circulating hormones cause a reduction of natural release
Men - testicular atrophy, sterility, gynecomastia (breast growth in men)
Women – amenorrhea (cessation of menstruation), sterility, hirsutism (excessive growth of body hair)
Copyright © 2006 by Allyn and Bacon

34. Neural Mechanisms of Sexual Behavior
Sexually dimorphic nucleus (SDN)
medial preoptic area of rat hypothalamus
larger in males, due to estradiol shortly after birth
size of male SDN correlated with T levels and aspects of sexual activity
Nuclei in preoptic, suprachiasmatic, and anterior regions of the hypothalamus are larger in men than in women
Copyright © 2006 by Allyn and Bacon

35. Medial Preoptic Area of the Hypothalamus
Contains the SDN
Destruction abolishes sexual behavior of all mammalian males studied, but does not affect female sexual behaviors females
Stimulation elicits copulatory behaviors
Copyright © 2006 by Allyn and Bacon

36. Ventromedial Nucleus of the Hypothalamus
Contains circuits critical for female rat sexual behavior
Lesion eliminates lordosis
Microinjections of E and progesterone induce estrus
Lesions of periaqueductal gray (PAG) or the tracts to it eliminate lordosis
Copyright © 2006 by Allyn and Bacon