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Chapter 5

Chapter 5

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Western University
Psychology 2075
William Fisher

Chapter 5: Sex Hormones, Sexual Differentiation, and Menstruation CHAPTER OVERVIEW - Major sex hormones are testosterone (produced in males by the testes) and estrogen and progesterone (produced in females by the ovaries) o Both men and women have both testosterone and estrogen - Levels of sex hormones are regulated by two hormones secreted by the pituitary: FSH (follicle-stimulating hormone) and LH (luteinizing hormone) which are in turn regulated by GnRH (gonadotropin releasing hormone) secreted by the hypothalamus - The gonads, pituitary, and hypothalamus regulate one another’s output through a negative feedback loop - Biologically, the menstrual cycle is divided into four [4] phases: follicular phase, ovulation, luteal phase, menstruation - Corresponding to these phases, there are changes in the levels of pituitary hormones (FSH and LH) and in the levels of ovarian hormones (estrogen and progesterone), as well as changes in the ovaries and the uterus o A fairly common menstrual problem is dysmenorrhea (painful menstruation) - At conception males and females differ only in the sex chromosomes (XX in females and XY in males) - As the fetus grows the SRY gene on the Y chromosome directs the gonads to differentiate into the tests - In the absence of the SRY gene, ovaries develop - The ovaries and the testes then secrete different hormones in females and males, respectively, and these hormones stimulate further differentiation of the internal and external reproductive structures of males and females - A male organ and a female organ that derive from the same embryonic tissue are said to be homologous to each other - Intersex conditions (disorders of sex development) are generally the result of various syndromes (such as CAH) and accidents that occur during the course of prenatal sexual differentiation o Currently there is a debate over the best medical treatment for these individuals - Puberty is characterized by a great increase in the production of sex hormones - Pubertal changes in both males and females include body growth, the development of pubic and anxillary hair, and increased output from the oil-producing glands o Changes in the female include beast development and the beginning of menstruation o Changes in the male include growth of the penis and testes, the beginning of ejaculation, and the deepening of the voice - Research indicates that some, but not all, women experience changes in mood over the phases of the menstrual cycle o For those who experience such changes, their mood is generally positive around the middle of the cycle (around ovulation), whereas depression and irritability are more likely just before and during menstruation o These negative moods and physical discomforts are termed premenstrual syndrome (PMS) o Research indicates that there are no fluctuations in performance over the cycle o There is evidence suggesting that fluctuations in mood are related to changes in hormone levels as well as to cultural factors o Research attempting to document whether men experience monthly cycles is now in progress Sex Hormones - Prenatal period – the time from conception to birth where many structural differences between males and females arise (process called the prenatal sexual differentiation) - Hormones – chemical substances secreted by the endocrine glands into the bloodstream o The effects are felt fairly rapidly and at places in the body quite distant from where they were manufactured - Most important sex hormones are testosterone, estrogens, and progesterone - Testosterone – a hormone secreted by the testes in the male (and also present at lower levels in the female) - Androgens – the group of “male” sex hormones, one of which is testosterone - Estrogens – the group of “female” sex hormones - Progesterone – a “female” sex hormone secreted by the ovaries - The thyroid, the adrenals, and the pituitary are examples of endocrine glands - Pituitary gland– a small endocrine gland located on the lower side of the brain below the hypothalamus; the pituitary is important in regulating levels of sex hormones (“master gland” of the endocrine system) o Divided into three [3] lobes: anterior, intermediary, posterior lobe  Anterior: interacts with gonads - Hypothalamus – a small region of the brain that is important in regulating many body functions, including the functioning of the sex hormones - These three structures (hypothalamus, pituitary, and gonads (testes/ovaries) function together and influence important sexual functions Sex Hormone Systems in Males - Testosterone produced from both the pituitary and the testes which stimulates and maintains secondary sex characteristics (such as beard growth), maintaining the genitals and their sperm-producing capability, and stimulating the growth of bone and muscle - Pituitary produces two [2] important hormones (as well as others that aren’t as important): FSH and LH - Follicle-stimulating hormone (FSH) – a hormone secreted by the pituitary; it stimulates follicle development in females and sperm production in males - Luteinizing hormone (LH) – a hormone secreted by the pituitary; it regulates estrogen secretion and ovum development in the female and testosterone production in the male - Testosterone levels in males relatively constant because hypothalamus, pituitary, and testes operate in a negative feedback loop o The levels of LH are regulated by a substance called gonadotropin-releasing hormone (GnRH) o Gonadotropin-releasing hormone (GnRH) – a hormone secreted by the hypothalamus that regulates the pituitary’s secretion of gonad-stimulating hormones o System is a full circle because hypothalamus monitors levels of testosterone present, amus monitors levels of testosterone present, and this way testosterone influences the output of GnRH o Feedback loop sometimes called HPG axis – hypothalamus-pituitary-gonad axis, the negative feedback loop that regulates sex hormone production o Cycle called negative feedback loop because increases in temp turn off the furnace and decreases in temp turn on the furnace  i.e., when testosterone levels are high  hypothalamus reduces production of GnRH which makes the pituitary’s production of LH reduce  lower levels of testosterone (vice-versa) - Inhibin – a substance secreted by the testes and ovaries that regulates FSH levels o Similar to the negative feedback loop (HPG axis) but for FSH/sperm production Sex Hormone Systems in Females - Two important hormones are estrogen and progesterone - Estrogen: brings many changes of puberty (stimulating growth of uterus and vagina, enlarging pelvis, stimulating breast growth) o Responsible for maintaining mucous membranes of the vagina and stopping the growth of bone and muscle, which accounts for why women generally are smaller than men - FSH and LH regulate the levels of estrogen and progesterone (negative feedback loop of hypothalamus, pituitary, and ovaries) o i.e., increase in level of GnRH = increase in level of LH = increase output of estrogen - Inhibin produced by ovaries (just as it is in the testes) and inhibits FSH production - Pituitary produces two [2] other hormones: prolactin and oxytocin o Prolactin stimulates production of milk by the mammary glands after a woman has given birth to a child o Oxytocin stimulates ejection of milk from the nipple as well as contractions of the uterus during childbirth  Known as the ‘snuggle chemical’ to promote affectionate bonding (with ones new born baby) The Menstrual Cycle - Only few other species of apes and monkeys also have menstrual cycles (all other mammals have estrous cycles) o In estrous cycles there is no bleeding or only a slight spotting of blood (not real menstruation) o Also the timing of ovulation in relation to bleeding is different in the two cycles  i.e., ovulation occurs in heat/estrus while occurring midway between periods of menstruation o Female animals with estrous cycles engage in sexual behaviour only when they are in heat The Phases of the Menstrual Cycle - Four [4] phases: follicular phase, ovulation, luteal phase, menstruation - Follicular phase (proliferative phase) – first phase of menstrual cycle, beginning just after menstruation, during which an egg matures in preparation for ovulation o Pituitary secretes high levels of FSH (follicle development) - Ovulation – release of an egg form the ovaries; the second phase of the menstrual cycle o Follicle ruptures releasing the mature egg, with high levels of estrogen to stimulate the hypothalamus to produce GnRH which causes the pituitary to begin production of LH to trigger ovulation - Luteal phase (secretory phase) – third phase of menstrual cycle, following ovulation o Egg and follicle turn into a glandular mass of cells called the corpus luteum under stimulation of LH o Corpus luteum – mass of cells of the follicle remaining after ovulation; it secretes progesterone o Falling levels of estrogen stimulate pituitary to begin production of FSH and restart the whole cycle - Menstruation – fourth phase of menstrual cycle, which endometrium of the uterus is sloughed off in the menstrual discharge o Shedding of the inner lining of the uterus (endometrium) which then pass out though the cervix and the vagina o Discharge normally 2 ounces (4 tablespoons) Length and Timing of the Cycle - Generally anywhere from 20-36 days (average is around 28 days) - Menstruation (day 1-4/5); Follicular phase (day 5-13); Ovulation (day 14); Luteal phase (day 15-28/end) - Ovulation to menstruation is always 14 days (i.e., 44-day cycle = ovulation on day 30; 22-day cycle = ovulation on day 8) - When women feel themselves ovulate it is called Mittelschmerz (middle pain) a.k.a. cramps - Ovulation does not occur in every menstruation cycle (anovulatory cycle) Other Cyclic Changes - Cervical mucus cycle (protects entrance to the cervix keeping bacteria out) becomes more watery with LH - Basal body temperature cycle fluctuates (low temp during follicular phase, then rises by 0.3 degrees Celsius+ throughout rest of cycle) Menstrual Problems - Most common menstrual problem is dysmenorrhea – painful menstruation - Dysmenorrhea caused by prostaglandins – chemicals secreted by the uterus that cause the uterine muscles to contract; they area likely cause of painful menstruation - Best treatment for menstrual cramps is non-steroidal anti-inflammatory drugs such as aspirin or sometimes sex/masturbation - Menstrual problem often mistaken for dysmenorrhea is endometriosis – condition in which the endometrium grows abnormally outside the uterus; the symptom is usually painful periods with excessive bleeding - Another menstrual problem is amenorrhea – absence of menstruation (primary = not yet menstruated by 18; secondary = had one period) Prenatal Sexual Differentiation Sex Chromosomes - Only difference in sex chromosomes carried in that fertilized egg (XX = female; XY = male) - Single cell develops into a 2-celled organism  4-cell  8-cell  etc Gonads - Seventh week after conception is when sex chromosomes direct the gonads o Testes in males (7 weeks); Ovaries in females (10-11 weeks) - Important gene directs the differentiation of the gonads in the Y chromosome, sex-determining region, Y chromosome (SRY) - Sex-determining region, Y chromosome (SRY) – gene on the Y chromosome that causes testes to differentiate prenatally o If SRY present, causes manufacture of substance called testes-determining factor (TDF)
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