Pinel basics ch11
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    Pinel basics ch11 Pinel basics ch11 Presentation Transcript

    • Chapter 11 Hormones and Sex What’s Wrong with the Mamawawa
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    • 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
    • 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
        • Primary function is hormone release
    • 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
    • Sex Hormones – Released by Gonads
      • Androgens - e.g., testosterone
      • Estrogens - e.g., estradiol
      • Adult testes tend to release more androgens and ovaries tend to release more estrogens
      • Progestins – also present in both sexes
        • progesterone prepares uterus and breasts for pregnancy
      • Adrenal cortex – also releases sex hormones
    • Hormones
      • Steroids
        • Synthesized from cholesterol (fat)
        • Fat-soluble – able to enter cells and bind to receptors in cytoplasm or nucleus
      • Amino acid derivatives
        • Epinephrine, for example (adrenal medulla)
      • Peptides and proteins
        • Short and long chains of amino acids
    • 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
    • Cyclic Vs Steady Gonadal Hormone Levels
      • Female hormones go through a 28-day cycle, the menstrual cycle
      • Male hormone levels constant
      • Anterior pituitary activity is controlled by the hypothalamus
      • The hypothalamus determines whether or not hormone levels cycle
    • Control of the Pituitary by the Hypothalamus
      • Posterior – neural input from hypothalamus
        • Vasopressin – antidiuretic hormone
        • Oxytocin – labor and lactation
        • Synthesized in hypothalamic paraventricular and supraoptic nuclei
        • These nuclei have terminals in the posterior pituitary
      • Anterior pituitary – hypothalamopituitary portal system carries hormones from the hypothalamus to the anterior pituitary
    • Hypothalamic Releasing Hormones
      • Releasing and inhibiting hormones control production and release of the anterior pituitary
      • All releasing and tropic hormones are peptides
      Gonadotropins (FSH and LH) – stimulate gonads Gonadotropin-releasing hormone Thyrotopin – stimulates thyroid Thyrotropin-releasing hormone Anterior pituitary Hypothalamus
    • Regulation of Hormone Levels
      • Neural
        • All endocrine glands (except the anterior pituitary) receive neural signals
        • From cerebral or autonomic neurons
      • Hormonal
        • Tropic hormones, negative feedback
    • 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
    • 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 3 rd prenatal month
    • Sexual Development
      • 6-weeks: gonads develop
      • 3 rd 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
    • 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
    • Sexual Development
      • External reproductive structures – genitalia – develop from one bipotential precursor
      • Differentiation occurs in 2 nd month
      • Testosterone > male
      • No testosterone > female
    • Sex Differences in the Mammalian 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?
    • Aromatization and Sex Differences 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
    • 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?
    • 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, testosterone enters the brain and then is converted to E
    • Sex Differences in the Brain: What Do They Mean?
      • Many differences, but their significance is not known
      • Links between structural differences and functional differences have not been established
    • 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
    • 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
    • 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
    • Anne S.
      • Knowing how normal development occurs, you should be able to understand what could cause abnormal sexual development
      • Why might a woman not cycle and have no pubic or axillary hair?
        • What determines whether male or female hormone patterns develop?
        • What causes the growth of pubic and axillary hair?
    • Anne S.
      • Anne is chromosomally male, XY
      • Internalized testes, but no ovaries
      • Hormone levels are those of a man
      • What happened?
      • Androgenic insensitivity syndrome
        • Normal male androgen levels, but no response to them
        • She does respond to estrogens, so she effectively has more estrogens than androgens – leading to the development of female secondary sex characteristics
    • Adrenogenital 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
    • John/Joan
      • A surgeon’s error led one of a pair of male twins to be raised as a girl
        • Artificial vagina created
        • Estrogen administered at puberty
      • John/Joan never felt or acted like a girl – indicates that the key to one’s gender is in the brain
      • John/Joan chose to become John later in life, but never recovered from the ordeal
      • John took his life in May of 2004
    • 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
    • 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
    • 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
    • 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)
    • 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
    • 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
    • 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
    • Sexual Orientation
      • Heterosexual – sexually attracted to members of the other sex
      • Homosexual – sexually attracted to members of the same sex
      • Bisexual – sexually attracted to members of both sexes
    • Sexual Orientation
      • Genetic basis established
      • No differences in hormone levels
      • Animal research suggests altered hormone levels during development may play a role, but there is no direct human evidence of this
    • Sexual Body Type, Orientation, and Identity
      • All 3 are independent entities
      • Consider Anne S. – chromosomally a man, but a woman in every other way
      • Consider John/Joan – a man’s brain in a woman’s body
      • How would you define male and female?