Chapter 8 (Answers)

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Alison Fleming

Chapter 8: Answers 1. Cloacal exstrophy is a developmental defect wherein a male is born with normal testes but short split/no penis at all; raises debate over factors that influence gender identity: is it a matter of genetics or environment? 2. The point of this chapter is to describe how biological and social forces combine to produce gender identities—how hormones affect the brain to influence sexual and parental behaviour and how fetus develops into male or female form, not just in terms of body, but also in terms of brain and behaviour. PART I: THE ENDOCRINE SYSTEM Hormones Act in a Great Variety of Ways throughout the Body 1. The body’s cells use chemicals/hormones to communicate which are produced by endocrine glands (glands that release their hormones within the body) 2. Berthold removed the testes of roosters from their normal position and reimplanted them elsewhere in the abdomen (disconnected innervations); when he reimplanted these testes the roosters grew up to look and act like normal males. He concluded that the testes must have secreted a signal, which today we know as hormones (testosterones); if he had waited until the castrated chicks were adults before transplanting the testes, Berthold would have seen little effect; Testosterones must therefore be present EARLY in life to influence brain/behaviour 3. i) Endocrine communication- hormones are released into the bloodstream to selectively affect target distant organs (Chapter 8) ii) Synaptic communication- communication via synapses where chemicals are released by the presynaptic membrane to produce changes in the postsynaptic membrane (Chapter 3 and 4) iii) Pheromone communication- chemicals (i.e. dogs’ urine) that are released outside the body to affect other individuals of the same species (Chapter 6) iv) Allomone communication- chemical signals that are released by members of one species to affect the behaviour of individuals of another species (i.e. flowers exuding scented allomones to attract insect and birds) 4. i) Protein hormones (aka peptide hormones)- composed of strings of amino acids of different combinations ii) Amine hormones- smaller and simpler than protein hormones; modified version of single amino acids iii) Steroid hormones- composed of four interconnected rings of carbon atoms 5. Different types of hormones interact with different types of receptors Hormones Act on a Wide Variety of Cellular Mechanisms 1. They bind to specific receptor proteins located on the surface of the target cell which activate chemical signals inside the cell that are called second messengers; only cells that produce the appropriate receptor proteins for a hormone can respond to that hormone 2. Steroid hormones’ receptors are located inside the target cell and easily pass through the cell membrane; different classes of steroids have their own specific receptors (i.e. estrogens only bind to estrogen receptors); they control specific genes and protein production by binding to specific regions of DNA; slower acting than protein and amine receptors; injecting radioactively tagged molecules and observing which brain regions they accumulate in tells us where steroid hormones are active and which behaviour(s) they are likely to influence i) observe behaviour of an intact animal (copulatory behaviour in male rats), remove endocrine gland (testes) and look for changes in behaviour (loss of copulatory behaviour); if hormones are injected back into the animal or process is reversed, does lost behaviour return (if castrated rats are injected testosterones, copulatory behaviour does come back) ii) *GO BACK TO THIS ONE 3. True—even though hormones bind with specific receptors, i.e. estrogens only bind with estrogen receptors, there are at least 2 different receptors for estrogens; for other hormones there may be 4 or more; meanwhile, the same receptor may sometimes have a different effect with the same hormone because the target cell responds differently *REVIEW THIS Each Endocrine Gland Secretes Specific Hormones 1. The pituitary gland aka the master gland regulates other endocrine glands and is connected to the hypothalamus (above endocrine glands) by the pituitary stalk 2. Neuroendocrines are a blend of neuronal cells and endocrine cells; like neurons they receive synaptic signals from other neurons and produce action potentials; unlike neurons, they do not release neurotransmitters into a synapse but secrete hormones into the bloodstream; thus electrical signals are converted into hormonal signals 3. i) posterior pituitary- neuroendocrine cells produce the hormones: oxytocin (triggers milk letdown reflex in nursing females, gives pleasurable feelings in sexual encounters, helps prairie vole couples form stable pair-bonds) and vasopressin or AVP (promotes water conservation and increases blood pressure; more vasoperssion receptors in the ventral pallidum results in monogamy in male prairie voles); axons of neurons pass through pituitary stalk and terminate on the capillaries of the posterior pituitary; the hormones are then released from the terminal into the bloodstream ii) anterior pituitary- unlike the posterior pituitary, it synthesizes its own hormones; a.p. hormones are called tropic hormones; tropic hormones travel throughout the bloodstream, reaching all glands, but only target glands have the receptors to respond to it (i.e. thyroid and ovaries); once the tropic hormone reaches the target gland, it drives the gland to produce its own hormone 4. When an infant sucks on his/her mother’s nipple it produces brain activity in the mother; increased brain activity provides input to the hypothalamus and cells in this region produce oxytocin to release to the posterior pituitary (remember because it’s connected to the p.p. by the pituitary stalk) and into the bloodstream; the oxytocin reaches the mammary glands which causes m.g. cells to contract and make milk available 5. The brain is in charge of hormone secretion; it monitors internal and external cues to decided how much hormone should be released; when action potentials are fired, or when neuroendocrine cells are excited (i.e. a baby sucking mother’s nipple stimulates neuroendocrine cells), hormones are released (oxytocin) 6. Negative feedback is when the brain senses biological response so it stops further hormone release (i.e. once the baby stops sucking milk, the brain stops exciting the neuroendocrine cells and oxytocin release ceases). 7. *GO BACK TO THIS ONE 8. The hypothalamus uses another set of hormones, called releasing hormones, to regulate secretions of tropic hormones from the anterior pituitary (releasing hormones travel via bloodstream until they reach the a.p.; from there they cause the a.p. to release tropic hormones; tropic hormones in turn regulate hormone secretion of endocrine glands) 9. Neuroendocrine cells produce gonadotropin-releasing hormones secreted into capillaries of median eminence travels via hypothalamic-pituitary portal system anterior pituitary a.p. releases tropic hormones (follicle-stimulating hormones and luteinizing hormones) FSH and LH act on gonads/ gonadsotropins (hormones that act on gonads to produce sex steroids and gametes) production of sex steroids and gametes 10. i) Follicle-stimulating hormone- stimulates growth and maturation of egg-containing follicles which in turn secrete estrogen; governs sperm production ii) Luteinizing hormone- stimulates ovulation (egg release) and formation of a corpus luteum (corpus luteum secretes progesterone); stimulates testes to produce testosterone 11. Testes and ovaries have 2 different subcompartments—one to produce hormones (sex steroids) and one to produce gametes (eggs or sperm); the sex steroids produced by testes are testosterone and androgens (development and maintenance of reproductive organs and secondary sex characteristics); the sex steroids produced by the ovaries are progestins (i.e. progesterone which help with pregnancy and milk secretion) and estrogen (development and maintenance of reproductive organs and secondary sex characteristics) 12. Ovarian hormones are produced in cycles (for humans about 4 weeks) 13. FSH stimulates ovarian follicles follicles release estrogen estrogens trigger release of LH from the hypothalamus and pituitary LH triggers ovulation (egg release) follicles develop as corpora lutea corpora lutea secrete progesterone to maintain uterus for pregnancy (if not pregnant, the cycle starts all over again) 14. Birth control pills; steroid hormones that prevent ovulation when they exert a negative feedback on the hypothalamus inhibit the release of GnRH; lack of GnRH halts the release of FSH and LH from the pituitary ovary does not release egg 15. False; no steroid is found exclusive in either males or females because they all have the same chemical base (cholesterol); glands manufacture steroid hormones by using enzymes to modify cholesterol into different steroids. 16. i) Neural-to-neural- visual processing (male dove sees female dove) ii) neural-to-endocrine (neuroendocrine cells in male’s hypothalamus secrete GnRH) iii) endocrine-to-endocrine- GnRH stimulates the pituitary to release gonadotropins and testes release more testosterone iv) endocrine-to-neural- testosterone alters excitability of neurons in male’s brain male displays courtship behaviour v) the female reacts by pro
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