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69 Cards in this Set
- Front
- Back
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When is genetic sex determined?
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At conception
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What determines the male genotype?
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-SRY gene on the Y chromosome
-The presence of testosterone and MIF |
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What do the presence of testosterone and MIF ensure?
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That normal internal AND external genitalia develop.
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What does MIF do?
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Causes the mullerian ducts (fallopian tubes) to regress.
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What are the 2 types of testosterone that control male reproductive development?
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-Testosterone (prohormone)
-DHT (more potent form) |
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What does Testosterone itself regulate?
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Male reproductive tract development (wolfians)
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What does DHT itself regulate?
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Male genitalia development
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What is SRY?
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The sex-determining gene on the Y chromosome that induces the gonads to differentiate into the testes.
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Where does testosterone and MIF come from?
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The testes, after the SRY gene tells the gonads to become testes.
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So in utero, before the baby is even born, what 3 hormones do you see rise during the first 8 weeks?
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-MIF (to inhibit the fallopian tubes)
-LH -FSH |
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Why do LH and FSH rise early in utero?
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For the same reason that they do in female babies; SOMATIC SEX DIFFERENTIATION.
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What does the presence of LH and FSH in the male fetus cause?
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Steroidogenesis - the production of androgens
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What would this do in females?
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Cause virilization
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What hormones rise after birth between 3-7 months in the male baby?
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Another surge of LH/FSH
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Why does this LH/FSH surge occur in male babies?
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For the same reason as in females - we don't know, but maybe brain sex differentiation
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What are testosterone levels like in childhood?
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Low, but measurable.
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What is the function of testosterone during childhood?
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It's necessary for normal growth and just being normal.
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Is putting on body fat the switch for puberty in males like it is in females?
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No
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What does trigger the hypothalamic pulses of GnRH to begin in males at puberty?
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We don't know
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What is the result of the increase in GnRH pulses?
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-Increased FSH/LH
-Wakes up Testosterone -Spermatogenesis |
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How long does the reproductive age extend in males?
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It goes on ad infinitum
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What is usually the thing that prevents reproduction in males?
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Plumbing problems
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What are the 2 important androgens?
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1. Testosterone
2. DHT - dihydrotestosterone |
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What is DHT?
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A much more potent form of testosterone that is formed by enymatic conversion.
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What enzyme makes DHT from testosterone?
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5-alpha reductase
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Why is 5-alpha reductase important to know?
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Because there are specific drugs that act to inhibit it to reduce the effects of androgens.
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What are some 5-alpha reductase inhibitors?
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-Propecia (hair follicles are very sensitive to testosterone)
-Proscar (prostate cancer that is induced by testosterone) |
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What are the 2 main sites of androgen production?
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-Testicular
-Adrenal |
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What is the primary androgen secretion from the adrenals?
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DHEA sulfate
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What is the primary androgen secretion from the testes?
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Tesosterone
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Where is most DHT produced?
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By PERIPHERAL conversion from testosterone
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What other androgens are made in males?
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Estradiol and Estrone
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Where are the Estradiol and Estrone made?
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Mostly from peripheral conversion of precursors.
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What enzyme converts testosterone to estrogens?
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Aromatase
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Where is Aromatase in men?
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-Some in testes
-Most in fat |
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What causes men to be feminized?
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Obesity
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How does Testosterone exert its effect on cells?
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By binding to a nuclear receptor and inducing protein synthesis
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What does a target tissue do if it wants more action for the same amount of testosterone?
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Converts it to DHT with 5 alpha reductase
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In the male, when puberty begins, what does LH do?
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Stimulates the Leydig cell to produce TESTOSTERONE
(LTL - leydig and theca both produce androgen via LH stim) |
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What does Testosterone stimulate at puberty?
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1. Linear growth
2. Spermatogenesis 3. Secondary sex characteristics |
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What is the primary stimulator of spermatogenesis?
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FSH
(LTL FGS - FSH stimulates granulosa and sertoli) |
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What hormones rise in addition to LH/FSH during puberty?
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GH and ACTH
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Why does GH increase?
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Because the TESTOSTERONE stimulates it!
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What do high prolactin levels do during puberty?
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Induce hypogonadism
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How does Prolactin cause hypogonadism?
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By inhibiting the gonadotrophs from releasing LH/FSH, so there is no development and spermatogenesis.
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So what do high levels of prolactin cause in
-Females at puberty -Males at puberty |
Females = amenorrhea
Males = hypogonadism |
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So what is the main change that occurs at puberty?
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Pulsatile release of GnRH increases from the hypothalamus
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What does the pulsatile GnRH stimulate?
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Pulsatile release of FSH and LH from the pituitary
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What are the 2 main effects of the LH and FSH?
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-LH stimulates the leydig cell to produce testosterone and have virilizing effects
-FSH stimulates the Sertoli cell to support spermatogenesis |
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What is necessary for the adequete production of sperm?
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BOTH the testosterone from the leydig cells, AND the FSH stimulation.
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Does all of the testosterone from the leydig cells only cause virilizing effects and stimulate sertoli spermatogenesis?
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No, a little bit is converted to estradiol in the sertoli cells via aromatase like in girls.. but only a little bit.
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What is the Sertoli cell's other function other than spermatogenesis?
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Production of INHIBIN
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What is inhibin?
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A hormone that inhibits FSH and GnRH release.
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So what type of feedback is exerted by FSH and LH?
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A PARALLEL FEEDBACK LOOP
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Does inhibin work as a male contraceptive?
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no
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In addition to stimulating spermatogenesis, what does FSH binding its receptor on Sertoli cells stimulate?
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The production of ABP
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What is ABP?
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Androgen binding protein
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How does ABP function?
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As an ANDROGEN SINK that sucks up testosterone and holds onto it, to increase the local concentration.
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What is the effect of an increased local concentration of testosterone?
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The sertoli cell and spermatogonia are BATHED in testosterone
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What are the 3 visible results of puberty in males?
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1. Penile growth
2. Pubic hair 3. Growth spurt |
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What is the termination of the growth spurt caused by?
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The gonadotropins
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Why is taking androgens for increasing muscle mass bad?
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Because it actually causes feminization.
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How does taking androgens cause feminization?
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By conversion via aromatase in adipose tissue.
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What genetic disease can cause hypopituitarism?
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Hereditary hemochromatosus
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What does hereditary hemochromatosus do?
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Causes iron deposits in the pituitary that suppress the output of especially Gonadotrophs (LH/FSH)
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If a man has no testes but has measurable testosterone, where is it coming from?
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The adrenals.
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What results from hypopituitarism?
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Lack of development of the testes.
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What is a bad side effect of the increased iron?
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It gets taken up by the thyroid and causes primary hypothyroidism.
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Does hereditary hemochromatosus affect the adrenals?
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No - they put out everything fine.
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