These notes include developmental and activational effects of sex hormones, classes of hormones, sex steroids, hormones of the pituitary, regulation of hormone levels, sex differences in the brain, perinatal hormones and behavioral development, and neural mechanisms of sexual behavior.
DEVELOPMENTAL AND ACTIVATIONAL SEX STEROIDS
EFFECTS OF SEX HORMONES
➔ Released by gonads Androgens - e.g.,
➔ Developmental (or “organizational”) - testosterone
influencing the development of anatomical, ➔ Estrogens - e.g., estradiol
physiological, and behavioral characteristics ➔ Adult testes release more androgens and
that differentiate the sexes ovaries more estrogens
➔ Activational - triggering reproduction-related ➔ Progestins – also present in both sexes
behavior in mature individuals ◆ Progesterone prepares uterus and
➔ Adolescent surges have both developmental breasts for pregnancy
and activational effects ➔ Adrenal cortex – also releases sex steroids
NEUROENDOCRINE SYSTEM: GLANDS HORMONES OF THE PITUITARY
➔ Exocrine – release chemicals into ducts ➔ “Master gland”
which carry them to their targets ➔ Tropic hormones influence the release of
◆ Sweat glands, for example hormones by other glands
➔ Endocrine – ductless; release hormones ➔ Posterior pituitary – hormones synthesized in
directly into the circulatory system the hypothalamus
◆ Only organs whose primary function ➔ Anterior pituitary – tropic hormones
is hormone release are referred to
as endocrine glands Cyclic vs. Steady Gonadal Hormone Levels
➔ Male testes produce sperm cells
➔ Female ovaries produce ova ➔ Female hormones go through a 28-day
◆ Sperm and ova each have 23 cycle, the menstrual cycle
chromosomes ➔ Male hormone levels are constant
➔ Fertilization ➔ Anterior pituitary activity is controlled by the
◆ Sperm cell + ovum = zygote hypothalamus
◆ 23 pairs of chromosomes ➔ The hypothalamus determines whether
➔ X and Y – sex chromosomes hormone levels cycle
◆ XX = female, XY = male
NEURAL CONTROL OF THE PITUITARY
CLASSES OF HORMONES
➔ Bird research was first to implicate the
➔ Amino acid derivatives control over pituitary function by the nervous
◆ Epinephrine, for example (adrenal system
medulla) ➔ Light/dark cycling and breeding changed
➔ Peptides and proteins hormone release
◆ Short and long chains of amino ➔ Lesion and stimulation experiments
acids established the hypothalamus as the
➔ Steroids regulator of the anterior pituitary
◆ Synthesized from cholesterol (fat) ➔ Did not explain how the signal was mediated
◆ Fat-soluble – able to enter cells and as the anterior pituitary is not “connected” to
bind to receptors in cytoplasm or the hypothalamus by neurons
nucleus
, HORMONES AND SEXUAL DEVELOPMENT OF
Control of the Pituitary by the Hypothalamus
THE BODY
➔ Posterior – neural input from hypothalamus
◆ Vasopressin – antidiuretic hormone ➔ Humans are dimorphic – exist in two forms
◆ Oxytocin – labor and lactation ➔ Genetic information on the sex
◆ Synthesized in hypothalamic chromosomes normally determines male or
paraventricular and supraoptic female development
nuclei
◆ These nuclei have terminals in the FETAL HORMONES AND DEVELOPMENT OF
posterior pituitary REPRODUCTIVE ORGANS: GONADS
➔ Anterior pituitary – hypothalamopituitary
portal system carries hormones from the
hypothalamus to the anterior pituitary ➔ Initially there is a primordial gonad
◆ Cortex – potential to be an ovary
◆ Medulla – potential to be a testis
DISCOVERY OF HYPOTHALAMIC RELEASING ➔ If XY, The Sry gene on the Y chromosome
HORMONES triggers the synthesis of Sry protein
➔ If no Sry protein present, cortex develops
➔ Thyrotropin-releasing hormone first isolated into ovary
from the hypothalamus of sheep and then
pigs FETAL HORMONES AND DEVELOPMENT OF
➔ Triggers the release of thyrotropin from the REPRODUCTIVE ORGANS: INTERNAL
anterior pituitary REPRODUCTIVE DUCTS
➔ Thyrotropin then stimulates release of
hormones from the thyroid gland
➔ Both sexes begin with two sets of
reproductive ducts
REGULATION OF HORMONE LEVELS ◆ Wolffian system – male – seminal
vesicles, vas deferens
➔ Neural ◆ Müllerian system – female – uterus,
◆ All endocrine glands (except the vagina, fallopian tubes
anterior pituitary) receive neural ➔ Third prenatal month: differentiation of ducts
signals ◆ Testes produce testosterone and
◆ From cerebral or autonomic Müllerian-inhibiting substance
neurons ● Wolffian system develops,
➔ Hormonal Müllerian degenerates,
◆ Tropic hormones, negative testes descend
feedback ➔ No testes – no testicular hormones
➔ Nonhormonal chemicals ◆ Müllerian system develops, Wolffian
◆ Glucose, Ca2+, Na+ degenerates
➔ Hormones tend to be released in pulses ➔ External reproductive structures – genitalia –
➔ Leads to often large minute-to-minute develop from one bipotential precursor
fluctuations in levels of hormones ➔ Differentiation occurs in second month
◆ Testosterone produces male
structures
◆ Without testosterone, female
structures develop
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