59: Male Reproductive Endocrinology

Question 1

Genotypic sex = ____, gonadal sex = ___ which encodes testes determining transcription factor, & phenotypic sex = hormones produced by _____ = masculinization via ______.

Answer 1

Genotypic sex = Y chromosome, gonadal sex = SRY gene which encodes testes determining transcription factor, & phenotypic sex = hormones produced by the gonads = masculinization via testosterone.

Question 2

In rare cases, the SRY gene translocates to the _ chromosome during male meosis. The ovum getting the X chromosome with the SRY gene wil develop into a male with an __ genotype. __ male is infertile. Conversely, if the sperm cell carries a Y chromosome lacking its TDF, the result can be a 46, XY individual that appears to be _____.

Answer 2

In rare cases, the SRY gene translocates to the X chromosome during male meosis. The ovum getting the X chromosome with the SRY gene wil develop into a male with an XX genotype. XX male is infertile. Conversely, if the sperm cell carries a Y chromosome lacking its TDF, the result can be a 46, XY individual that appears to be female.

Question 3

Transformation of the genital ducts.

A) When the gonad is still ______, it is closely associated with the mesonephros, as well as the excretory duct (mesonephric or Wolffian duct) that leads from the mesonephros to the _____ sinus. Parallel to the Wolffian ducts are the paramesonephric or Müllerian ducts, which merge caudally to form the ______.

B) In males, the mesonephros develops into the _____. The ______ duct develops into the vas deferens, seminal vesicles, and ejaculatory duct. The Müllerian ducts degenerate. (In females the Mullerian ducts develop into the fallopian tubes, uterus and cervix.)

Answer 3

Transformation of the genital ducts.

A) When the gonad is still indifferent, it is closely associated with the mesonephros, as well as the excretory duct (mesonephric or Wolffian duct) that leads from the mesonephros to the urogenital sinus. Parallel to the Wolffian ducts are the paramesonephric or Müllerian ducts, which merge caudally to form the uterovaginal primordium.

B) In males, the mesonephros develops into the epididymis. The Wolffian duct develops into the vas deferens, seminal vesicles, and ejaculatory duct. The Müllerian ducts degenerate. (In females the Mullerian ducts develop into the fallopian tubes, uterus and cervix.)

Question 4

______ produced by the Leydig cells promote the development of 1) the ____ ducts and derived structures (epididymis, vas deferens, seminal vesicles, ejaculatory duct. This requires _____ NOT DHT. 2) the prostate develops from a series of endodermal buds located proximal to the urethra; requires _____.

Prostate & external male genitalia dependent on _____. Testosterone is converted to ____, a testosterone derivative. DHT leads to beard _____ & DHT also leads to _____.

Answer 4

Androgens (testosterone) produced by the Leydig cells promote the development of 1) the wolffian (mesonephric) ducts and derived structures (epididymis, vas deferens, seminal vesicles, ejaculatory duct. This requires testosterone NOT DHT. 2) the prostate develops from a series of endodermal buds located proximal to the urethra; requires DHT.

Prostate & external male genitalia dependent on DHT (dihydrotestosterone). Testosterone is converted to DHT, a testosterone derivative. DHT leads to beard growth & DHT also leads to baldness.

Question 5

Differentiation of the External Genitalia: In the absence of testosterone, the undifferentiated external genitalia develop into the ____ structures. Testosterone, after conversion to dihydrotestosterone, stimulates the formation of male external _____ from the undifferentiated structures. Begins at about 10 weeks of gestation.

Answer 5

Differentiation of the External Genitalia: In the absence of testosterone, the undifferentiated external genitalia develop into the female structures (internal genitalia). Testosterone, after conversion to dihydrotestosterone, stimulates the formation of male external genitalia from the undifferentiated structures. Begins at about 10 weeks of gestation.

Question 6

The hypothalamic-pituitary-gonadal axis regulates: spermatogenisis & androgen production. GnRH stimulation is _____, therefore, LH & FSH release is _____. GnRH binds G-protein coupled gonadotroph receptors and activates phospholipase C (PLC) that ultimately causes Ca2+ release, DAG production and protein kinase C activation.

Constant supply of GnRH _____ receptors and fails to induce LH or FSH secretion – used to treat prostate cancer to lower testosterone production.

Products of the testes, sex hormones & inhibins, have a _____ feedback on the hypothalamus & anterior pituitary. GnRH is secreted into the portal vein to the anterior pituitary.

Answer 6

The hypothalamic-pituitary-gonadal axis regulates: spermatogenisis & androgen production. GnRH stimulation is pulsatile, therefore, LH & FSH release is pulsatile. GnRH binds G-protein coupled gonadotroph receptors and activates phospholipase C (PLC) that ultimately causes Ca2+ release, DAG production and protein kinase C activation.

Constant supply of GnRH downregulates receptors and fails to induce LH or FSH secretion – used to treat prostate cancer to lower testosterone production.

Products of the testes, sex hormones & inhibins, have a negative feedback on the hypothalamus & anterior pituitary. GnRH is secreted into the portal vein to the anterior pituitary.

Question 7

Kallmann Syndrome = hypogonadotropic hypogonadism as patients lack the pituitary hormones ___ and ___ and have congenital _____ (complete inability to ____) due to the agenesis of the olfactory lobes. Patients fail to enter puberty. The genes KAL-1 (X-linked), FGFR1 (autosomal dominant) and PROKR2 have been implicated in the disease. Happens to men & women.

The link to the loss of smell is the developmental origin of the odor receptor cells (primary neuroscensory cell) and the GnRH producing cells. Both develop in the olfactory _____ in the rudimentary nose. The primary neurosensory cells extend axons into the olfactory bulb and the GnRH-secreting cells migrate along these axons into the brain then into the hypothalmus. The mutations mentioned above prevent the neurosensory neurons from extending their axons into the brain and this failure prevents the migration of the GnRN neurons into the _____.
The main danger for patients with this syndrome is osteoporosis. Treatments usually include hormone replacement therapy.

Answer 7

Kallmann Syndrome = hypogonadotropic hypogonadism as patients lack the pituitary hormones LH and FSH and have congenital anosmia (complete inability to smell) due to the agenesis of the olfactory lobes. Patients fail to enter puberty. The genes KAL-1 (X-linked), FGFR1 (autosomal dominant) and PROKR2 have been implicated in the disease. Happens to men & women.

The link to the loss of smell is the developmental origin of the odor receptor cells (primary neuroscensory cell) and the GnRH producing cells. Both develop in the olfactory epithelium in the rudimentary nose. The primary neurosensory cells extend axons into the olfactory bulb and the GnRH-secreting cells migrate along these axons into the brain then into the hypothalmus. The mutations mentioned above prevent the neurosensory neurons from extending their axons into the brain and this failure prevents the migration of the GnRN neurons into the hypothalamus.
The main danger for patients with this syndrome is osteoporosis. Treatments usually include hormone replacement therapy.

Question 8

______ cells, the source of sex-steroid (testosterone) production in the testes, make up more than half the testes by day 60 of gestation. Increase in Leydig cells is dependent on maternal chorionic gonadotropin ____ or _____

Prior to puberty there are few GnRH pulses & low FSH & LH levels, the hypothalamus & pituitaty are very sensitive to _____ feedback inhibition by testosterone, spermatogonia exist in a ____ undifferentiated form in the testes.

hCG & LH are very _____ hormones, 1 AA difference.

Answer 8

Leydig cells, the source of sex-steroid (testosterone) production in the testes, make up more than half the testes by day 60 of gestation. Increase in Leydig cells is dependent on maternal chorionic gonadotropin hCG or embryonic leutinizing hormone LH.

Prior to puberty there are few GnRH pulses & low FSH & LH levels, the hypothalamus & pituitaty are very sensitive to negative feedback inhibition by testosterone, spermatogonia exist in a diploid undifferentiated form in the testes.

hCG & LH are very homologous hormones, 1 AA difference.

Question 9

In Puberty:

• Frequency and amplitude of GnRH pulses ____
• Sensitivity of H-P axis to negative feedback of testosterone _____
• Gonadotroph sensitivity to GnRH ______
• LH and FSH production _____
• Testosterone _____ and spermatogenesis _____
• Androgen-driven changes characteristic of puberty occur

Answer 9

In Puberty:

• Frequency and amplitude of GnRH pulses increase
• Sensitivity of H-P axis to negative feedback of testosterone decreases
• Gonadotroph sensitivity to GnRH increases
• LH and FSH production increases
• Testosterone increases and spermatogenesis begins
• Androgen-driven changes characteristic of puberty occur

Question 10

The hypothalamic-pituitary-testicular axis. Small-bodied neurons in the arcuate nucleus and preoptic area of the hypothalamus secrete GnRH, a decapeptide that reaches the gonadotrophs in the anterior pituitary through the long portal veins. Stimulation by GnRH causes the gonadotrophs to synthesize and release FSH and LH. The LH binds to receptors on the _____ cells, thus stimulating the transcription of several proteins involved in the biosynthesis of testosterone. FSH binds to receptors on the basolateral membrane of the _____ cells, thereby stimulating gene transcription and protein synthesis. These proteins include ABP, aromatase, growth factors, and inhibin.

Negative feedback on the hypothalamic- pituitary-testicular axis occurs by two routes. First, ______ inhibits the pulsatile release of GnRH by the hypothalamic neurons and the release of LH by the gonadotrophs in the anterior pituitary. Second, ____ inhibits the release of FSH by the gonadotrophs in the anterior pituitary.

Answer 10

The hypothalamic-pituitary-testicular axis. Small-bodied neurons in the arcuate nucleus and preoptic area of the hypothalamus secrete GnRH, a decapeptide that reaches the gonadotrophs in the anterior pituitary through the long portal veins. Stimulation by GnRH causes the gonadotrophs to synthesize and release FSH and LH. The LH binds to receptors on the Leydig cells, thus stimulating the transcription of several proteins involved in the biosynthesis of testosterone. FSH binds to receptors on the basolateral membrane of the Sertoli cells, thereby stimulating gene transcription and protein synthesis. These proteins include ABP, aromatase, growth factors, and inhibin.

Negative feedback on the hypothalamic- pituitary-testicular axis occurs by two routes. First, testosterone inhibits the pulsatile release of GnRH by the hypothalamic neurons and the release of LH by the gonadotrophs in the anterior pituitary. Second, inhibin inhibits the release of FSH by the gonadotrophs in the anterior pituitary.

Question 11

Useful mnemonics: “L” for LH and ____, “S” for FSH and ____

LH stimulates G-protein coupled receptor to produce cAMP and activate PKA. This increases the transcription of: 1) enzymes involved in _____ synthesis, 2) stimulates the rate-limiting step ______ to _____, 3) _____ protein, sterol activating protein (also involved in T synthesis).

FSH-primary action on Sertoli cells, activates a similar signaling pathway to LH and increases transcription of: 1) __________ protein- keeps local testosterone levels high, 2) ______ produces estrogen (estradiol), 3) ____ factors that support production of sperm 4) ______ that suppress Leydig cell proliferation, suppress FSH secretion 5) factors that act on Leydig cells.

Secondary effects on Leydig cells and on sperm (increases _____).

The Leydig cells make _____, which acts on the Sertoli cells. Conversely, the Sertoli cells convert some of this testosterone into ______ (product of aromatase), which acts on the Leydig cells. The Sertoli cells also generate growth factors that act on the Leydig cells.

Answer 11

Useful mnemonics: “L” for LH and Leydig, “S” for FSH and Sertoli–both S in fSh & Sertoli

LH stimulates G-protein coupled receptor to produce cAMP and activate PKA. This increases the transcription of: 1) enzymes involved in testoterone synthesis, 2) stimulates the rate-limiting step (cholesterol to pregnenolone), 3) sterol carrier protein, sterol activating protein (also involved in T synthesis).

FSH-primary action on Sertoli cells, activates a similar signaling pathway to LH and increases transcription of: 1) androgen binding protein- keeps local testosterone levels high, 2) P450 aromatase produces estrogen (estradiol), 3) growth factors that support production of sperm 4) inhibins that suppress Leydig cell proliferation, suppress FSH secretion 5) factors that act on Leydig cells.

Secondary effects on Leydig cells and on sperm (increases motility).

The Leydig cells make testosterone, which acts on the Sertoli cells. Conversely, the Sertoli cells convert some of this testosterone into estradiol (product of aromatase), which acts on the Leydig cells. The Sertoli cells also generate growth factors that act on the Leydig cells.

Question 12

First step of androgen synthesis occurs in the mitochondria: _____ removes the side chain of cholesterol. _____ produces pregnenolone–this is the rate limiting step and it is up-regulated by LH. Testes produce approximately 95% of testosterone, but only minor fraction of the body’s DHT. Other sites of androgen production include adipose tissue, skin, adrenals.

Androstenedione = andro = _____ anabolic steroid = is converted to testosterone in the next step.

______ converts testosterone to DHT.

Answer 12

First step of androgen synthesis occurs in the mitochondria: P450 side chain cleavage enzyme (P450 scc, Desmolase) removes the side chain of cholesterol. Desmolase produces pregnenolone–this is the rate limiting step and it is up-regulated by LH. Testes produce approximately 95% of testosterone, but only minor fraction of the body’s DHT. Other sites of androgen production include adipose tissue, skin, adrenals.

Androstenedione = andro = indirect anabolic steroid = is converted to testosterone in the next step.

5a-reductase converts testosterone to DHT.

Question 13

Male pseudohermaphroditism is a deficit in the mechanism by which androgens act in genetic males.

Potential causes include:

1) ______ deficiency, which causes reduced DHT levels with normal testosterone levels. There is faliure of DHT-dependent development of the urogenital sinus & external genitalia

2) Androgen insensitivity syndrome:
• normal levels of testosterone and DHT
• androgen receptors ________
• urogenital sinus and external genitalia develop according to female pattern, Wolffian ducts degenerate
• Normal levels of AMH suppress Müllerian development

Answer 13

Male pseudohermaphroditism is a deficit in the mechanism by which androgens act in genetic males.

Potential causes include:

1) 5a reductase deficiency, which causes reduced DHT levels with normal testosterone levels. There is faliure of DHT-dependent development of the urogenital sinus & external genitalia

2) Androgen insensitivity syndrome:
• normal levels of testosterone and DHT
• androgen receptors are absent or defective
• urogenital sinus and external genitalia develop according to female pattern, Wolffian ducts degenerate
• Normal levels of AMH suppress Müllerian development

Question 14

Androgens affect nearly every tissue in the body & have anabolic or androgenic effects.

____ effects = maturation of the penis, development of secondary sex charictaristics, deepening of voice, and growth of hair.

_____ EFFECTS:
• Promote protein synthesis and growth of tissues expressing androgen receptors
• Growth of muscle and increase in strength
• Increase in bone density and strength, ______ growth and maturation
• Males have larger hearts, lungs, liver, erythrocytes, etc.
• Bone maturation occurs indirectly through ______ metabolites and is more gradual in men than women.
• Men have a larger brain but women have more ______.

Answer 14

Androgens affect nearly every tissue in the body & have anabolic or androgenic effects.

Androgenic effects = maturation of the penis, development of secondary sex charictaristics, deepening of voice, and growth of hair.

ANABOLIC EFFECTS:
• Promote protein synthesis and growth of tissues expressing androgen receptors
• Growth of muscle and increase in strength
• Increase in bone density and strength, linear growth and maturation
• Males have larger hearts, lungs, liver, erythrocytes, etc.
• Bone maturation occurs indirectly through estradiol metabolites and is more gradual in men than women.
• Men have a larger brain but women have more dendritic connections.

Question 15

Androgens increase the expression of erythropoietin from the kidneys which leads to a higher _______ in men (42-52% vs 36- 46%).

Paradoxically _____ regulate male sexual behavior.

Men have 20-40% _____ muscle mass than females.

The penis, seminal vesicles and prostrate increase in size during ______.

Androgen Receptors:
• Free form of testosterone enters cells by diffusion
• Binds _______ receptor (AR/AR)
• Directs transcriptional activity of target genes
• DHT binds the ______ receptor (has greater activity)

Testosterone is bound by sex hormone-binding globulin and albumin. Only 2% of testosterone is _____ and this is the biologically active fraction.

Answer 15

Androgens increase the expression of erythropoietin from the kidneys which leads to a higher hematocrit in men (42-52% vs 36- 46%).

Paradoxically estrogens regulate male sexual behavior.

Men have 20-40% more muscle mass than females.

The penis, seminal vesicles and prostrate increase in size during puberty.

Androgen Receptors:
• Free form of testosterone enters cells by diffusion
• Binds homodimeric receptor (AR/AR)
• Directs transcriptional activity of target genes
• DHT binds the same receptor (has greater activity)

Testosterone is bound by sex hormone-binding globulin and albumin. Only 2% of testosterone is free and this is the biologically active fraction.

Question 16

There is a shot of testosterone to male babies 4 months after fertilization. With the exception of a short-lived increase in testosterone after birth, levels remain ____ until puberty.

Senescence (Andropause):
• unlike menopause ____ abrupt loss of fertility
• testosterone decreases with age especially ___ yrs. years
• quantity and quality of ____ also decreases
• FSH & LH levels ____

Reduced testosterone causes some of the problems of aging: decreased bone formation, muscle mass, appetite, libido, blood hematocrit.

Testosterone levels fall by 10% per year beginning in the 30’s. By mid fifties 30% of men experience andropause.

Answer 16

There is a shot of testosterone to male babies 4 months after fertilization. With the exception of a short-lived increase in testosterone after birth, levels remain low until puberty.

Senescence (Andropause):
• unlike menopause no abrupt loss of fertility
• testosterone decreases with age especially >40 yrs. years
• quantity and quality of sperm also decreases
• FSH & LH levels increase

Reduced testosterone causes some of the problems of aging: decreased bone formation, muscle mass, appetite, libido, blood hematocrit.

Testosterone levels fall by 10% per year beginning in the 30’s. By mid fifties 30% of men experience andropause.

Question 17

Low testosterone symptoms =

Testosterone supplementation may worsen:

Side effects of testosterone treatment can include _____ in hematocrit, significant hair ____.

Hair loss can be treated with Propecia (Finasteride), which blocks production of _____. Women may benefit from testosterone treatments to reduce bone loss.

Answer 17

Low testosterone symptoms = low sex drive, erectile dysfunction, loss of muscle mass, mood problems, fatigue, sleep disturbances, loss of body & facial hair. These symptoms can be alleviated with testosterone supplemenation. Men with breast or prostate cancer should not be treated with testosterone.

Testosterone supplementation may worsen sleep apnea, severe benign prostatic hypertrophy, severe congestive heart failure or high red blood cell counts (erythrocytosis). Too much testosterone can increase the chance of developing prostate cancer.

Side effects of testosterone treatment can include increase in hematocrit, significant hair loss.

Hair loss can be treated with Propecia (Finasteride), which blocks production of DHT. Women may benefit from testosterone treatments to reduce bone loss.

Question 18

Anabolic steroids are _____ steroids.

Effects of anabolic steroid abuse:

Answer 18

Anabolic steroids are synthetic steroids.

• Anabolic steroids abused by individuals attempting to increase muscle mass or gain a competitive advantage can lead to the following:
• Reduced sperm count, shrinkage of the testicles
• Permanent damage to heart, liver, and kidneys, psychiatric problems
• Irreversible breast enlargement in men
• Women and girls can develop excessive body hair and deepening of the voice

Anabolic steroid use can cause premature heart failure, high blood pressure, liver tumors, stroke and kidney failure. Also causes increase in LDL and decrease in HDL. Since it is often injected, there is the potential to transmit diseases such as HIV and hepatitis if needles are reused.

Question 19

Kennedy’s Disease = spinobulbar muscular atrophy. It is a ___ disease caused by mutation in the _____ receptor. Expansion of a CAG repeat in the gene causes a ____ expansion in the androgen receptor. The mutation in the receptor causes a toxic gain of function to neurons. Patients display progressive weakness due to degeneration of motor neurons in the brain stem and spinal cord.

Answer 19

Kennedy’s Disease = spinobulbar muscular atrophy. It is a LMN disease caused by mutation in the androgen receptor. Expansion of a CAG repeat in the gene causes a polyglutamine expansion in the androgen receptor. The mutation in the receptor causes a toxic gain of function to neurons. Patients display progressive weakness due to degeneration of motor neurons in the brain stem and spinal cord.

It is an X-linked disease. Early signs include weakness of the tongue and mouth muscles, fasciculations and progressive weakness of the limbs. Muscle wasting is observed by middle age. The onset is related to the size of the polyglutamine expansion. Generally this disease does not affect longevity. Some signs of reduced androgen receptor function may be present: gynecomastia (male breast development), impotence, erectile dysfunction etc.

Question 20

Interaction of the Sertoli cells and sperm: A single Sertoli cell in a ______ tubule spans from the basal lamina to the lumen of the seminiferous tubule. The adjacent Sertoli cells are connected by ____ junctions and surround developing germ cells. From the basal lamina to the lumen of the tubule, gradual maturation of the _____ cells occurs.

Spermatogenesis is initiated at puberty by _____ via Sertoli cells and further supported by LH- driven increases in testosterone and Sertoli cell growth factors. Rate, approx. 120 million/day.

Answer 20

Interaction of the Sertoli cells and sperm: A single Sertoli cell in a seminiferous tubule spans from the basal lamina to the lumen of the seminiferous tubule. The adjacent Sertoli cells are connected by tight junctions and surround developing germ cells. From the basal lamina to the lumen of the tubule, gradual maturation of the germ cells occurs.

Spermatogenesis is initiated at puberty by FSH via Sertoli cells and further supported by LH- driven increases in testosterone and Sertoli cell growth factors. Rate, approx. 120 million/day.

Question 21

Describe the order of spermatozoa development:

____ spermatocyte (diploid-4n)

Meoisis _

_____ spermatocyte (haploid-2n)

Meosis _

_____ (haploid-1n)

Spermatogenisis

_____ (haploid-1n)

Answer 21

Primary spermatocyte (diploid-4n)

Meoisis 1

Secondary spermatocyte (haploid-2n)

Meosis 2

Spermatids (haploid-1n)

Spermatogenisis

Spermatozoa (haploid-1n)

Question 22

Sperm Maturation:
• After spermiation, spermatids move _____ into rete testis and epididymis
•______-dependent maturation required for fully mobile/fertile sperm
•Total process takes approximately 70 days.

After the sperm are ejaculated they undergo several physiological changes in the female genital tract, which activates them for fertilization. During capacitation the sperm becomes hyperactive. The acrosome provides _____ and carries ______ necessary for the acrosomal reaction that dissolves the jelly coat of the egg during fertilization. The _____ provide the energy required for swimming.

Answer 22

Sperm Maturation:
• After spermiation, spermatids move passively into rete testis and epididymis
•Testosterone-dependent maturation required for fully mobile/fertile sperm
•Total process takes approximately 70 days.

After the sperm are ejaculated they undergo several physiological changes in the female genital tract, which activates them for fertilization. During capacitation the sperm becomes hyperactive. The acrosome provides protection and carries enzymes necessary for the acrosomal reaction that dissolves the jelly coat of the egg during fertilization. The mitochondria provide the energy required for swimming.

Question 23

Accessory Male Sex Glands Produce the Seminal Plasmid:

• Semen is only __% sperm
• Seminal fluid contains a plethora of ___ and ____
• Semen is made in ____, ____, _____ glands
• _____ provide 70% of volume and fructose
• normal concentration > 20 million sperm/mL

Answer 23

• Semen is only 10% sperm
• Seminal fluid contains a plethora of sugars and ions
• Semen is made in seminal vesicles, prostate gland, bulbourethral glands
• Seminal vesicles provide 70% of volume and fructose
• normal concentration > 20 million sperm/mL

Question 24

Sympathetic: Fibers arise from T11-L2 segments of the spinal cord and reaches the genitals via the _____, _____ and ____ plexuses, and the ____ and _____ nerves. It is responsible for emission, and ejaculation. Sympathetic tone maintains detumescence.

Parasympathetic: Fibers arise from S2-S4 segments of spinal cord and travel via ____ nerve to ____ plexus. Post-ganglionic fibers reach penile corpora and vasculature via cavernous nerves. It is responsible for corporeal ____ and corporeal smooth muscle relaxation leading to tumescence (erection).

The penis also receives both somatic and sensory innervation:

Somatic: Fibers travel via _____ nerve to striated muscles of penis.

Sensory: Afferent fibers are carried mainly in the _____ nerve of the penis which reaches the spinal cord vial the _____ nerve, compression of which (e.g. bicycling) can lead to temporary sexual dysfunction.

Blood supply to penis is primarily from ____ artery.

Answer 24

Sympathetic: Fibers arise from T11-L2 segments of the spinal cord and reaches the genitals via the inferior mesenteric, hypogasteric and pelvic plexuses, and the hypogastric and cavernous nerves. It is responsible for emission, and ejaculation. Sympathetic tone maintains detumescence.

Parasympathetic: Fibers arise from S2-S4 segments of spinal cord and travel via pelvic nerve to pelvic plexus. Post-ganglionic fibers reach penile corpora and vasculature via cavernous nerves. It is responsible for corporeal vasodilation and corporeal smooth muscle relaxation leading to tumescence (erection).

The penis also receives both somatic and sensory innervation.

Somatic: Fibers travel via pudendal nerve to striated muscles of penis.

Sensory: Afferent fibers are carried mainly in the dorsal nerve of the penis which reaches the spinal cord vial the pudendal nerve, compression of which (e.g. bicycling) can lead to temporary sexual dysfunction.

Blood supply to penis is primarily from pudendal artery.

Question 25

Erection: primarily under ______ control. Nerve terminals release _____ and _____. ____ relaxes smooth muscles leading to vasodilation of arteries. NO _____ intracellular cGMP levels. _____ in sympathetic tone allows relaxation of the corpora.

Viagra treats erectile dysfunction by inhibiting ______, keeping cGMP levels high–this leads to vasodilation.

• it stimulates erection ____ during sexual arousal.
• side effects include ____ vision (pilots are not allowed to fly 12 h after dosing).
• Viagra taken with other vasodilators can lead to sudden death–patients should not take with nitrates because both are vasodilatorsand cause unsafe _____ in blood pressure.

In an erection, ____ arterial inflow & ____ venous outflow = stiffening & enlargening of the penis.

Erection
•parasympathetic fibers in cavernous nerve cause ____ of arteriolar smooth muscle
•____ in sympathetic tone to vascular smooth muscle
•____ blood flow to corpora
•____ somatic fiber stimulation results in striated muscle contraction causing _____ venous outflow
•sinusoids of corpora ____- causing erection

Mechanics of erection.

A) In the flaccid state, arterial vessels are ____ and venous vessels are noncompressed.

B) On erection, smooth muscle relaxation in the trabeculae and arterial vasculature results in increased blood flow, which rapidly fills and dilates the cavernosal spaces. Venous outflow _____ as the expanding cavernosal spaces compress the _____ plexus and the larger veins passing through the tunica ______.
Patients with diabetes mellitus have high rates of ______ dysfunction as a result of vascular disease and autonomic dysfunction.

Answer 25

Erection: primarily under parasympathetic control. Nerve terminals release acetylcholine and Nitric Oxide (NO). NO relaxes smooth muscles leading to vasodilation of arteries. NO increases intracellular cGMP levels. Decrease in sympathetic tone allows relaxation of the corpora.

Viagra treats erectile dysfunction by inhibiting cGMP-specific phosphodiesterase type 5, keeping cGMP levels high–this leads to vasodilation.

• it stimulates erection only during sexual arousal.
• side effects include blue vision (pilots are not allowed to fly 12 h after dosing).
• Viagra taken with other vasodilators can lead to sudden death–patients should not take with nitrates because both are vasodilatorsand cause unsafe drop in blood pressure.

In an erection, increased arterial inflow & decreased venous outflow = stiffening & enlargening of the penis.

Erection
•parasympathetic fibers in cavernous nerve cause dilation of arteriolar smooth muscle
•decrease in sympathetic tone to vascular smooth muscle
•increased blood flow to corpora
•increased somatic fiber stimulation results in striated muscle contraction causing decreased venous outflow
•sinusoids of corpora expand causing erection

Mechanics of erection.

A) In the flaccid state, arterial vessels are constricted and venous vessels are noncompressed.

B) On erection, smooth muscle relaxation in the trabeculae and arterial vasculature results in increased blood flow, which rapidly fills and dilates the cavernosal spaces. Venous outflow drops as the expanding cavernosal spaces compress the venous plexus and the larger veins passing through the tunica albuginea.
Patients with diabetes mellitus have high rates of erectile dysfunction as a result of vascular disease and autonomic dysfunction.

Question 26

Emission = ?

Sympathetic stimulation of _____ n. causes contraction of smooth muscle of distal epididymis, vas deferense, & accessory glands

Semen is propelled into _____ urethra

Internal sphincter of the _____ prevents retrograde flow of sperm.

Ejaculation:
•a ____ reflex
•often accompanied by ____ (CNS involvement)

Anejaculation:
The pathological \_\_\_\_\_ to ejaculate due to: •sexual inhibition
•pharmacological inhibition
•ANS malfunction
•prostatectomy
•ejaculatory duct obstruction

Ejaculation: Expulsion of semen from the urethra. A rapid spinal reflex stimulated by the entry of semen into the _____ urethra. Response mediated by spinal region _____ and somatic motor fibers in the ____ nerve. Initiates rhythmic contractions of the striated muscles of the perineal area (ischiocavernosus, bulbospongiosus muscles). Ejaculation of semen (3-5 mL, 150-600 million sperm). Followed by a _____ period.

Answer 26

Emission = movement of ejaculate into urethra

Sympathetic stimulation of hypogastric n. causes contraction of smooth muscle of distal epididymis, vas deferense, & accessory glands

Semen is propelled into prostatic urethra

Internal sphincter of the bladder prevents retrograde flow of sperm.

Ejaculation:
•a spinal reflex
•often accompanied by orgasm (CNS involvement)

Anejaculation
The pathological inability to ejaculate due to: •sexual inhibition
•pharmacological inhibition
•ANS malfunction
•prostatectomy
•ejaculatory duct obstruction

Ejaculation: Expulsion of semen from the urethra. A rapid spinal reflex stimulated by the entry of semen into the bulbous urethra. Response mediated by spinal region S2-S4 and somatic motor fibers in the pudenedal nerve. Initiates rhythmic contractions of the striated muscles of the perineal area (ischiocavernosus, bulbospongiosus muscles). Ejaculation of semen (3-5 mL, 150-600 million sperm). Followed by a refractory period.

Question 27

Leydig cells are found adjacent to the seminiferous tubules in the testicle. They produce _____ in the presence of _____ hormone.

Answer 27

Leydig cells are found adjacent to the seminiferous tubules in the testicle. They produce testosterone in the presence of luteinizing hormone (LH).

Question 28

The linear growth spurt that occurs during puberty is mainly attributed to _____ in both boys and girls. _____ hormones increase linear growth of long bones and also promotes the eventual closure of the epiphyseal plates.

Answer 28

The linear growth spurt that occurs during puberty is mainly attributed to estradiol in both boys and girls. Estrogenic hormones increase linear growth of long bones and also promotes the eventual closure of the epiphyseal plates.

Question 29

The hormone inhibin has direct negative feedback effects on the release of?

Answer 29

FSH

Question 30

Human chorionic gonadotropin also binds to _____ hormone receptors on the interstitial cells of the testes of the male fetus, resulting in the production of _____ in male fetuses up to the time of birth. This small secretion or testosterone is what causes the fetus to develop _____ sex organs instead of female sex organs.

Answer 30

Human chorionic gonadotropin also binds to luteinizing hormone receptors on the interstitial cells of the testes of the male fetus, resulting in the production of testosterone in male fetuses up to the time of birth. This small secretion or testosterone is what causes the fetus to develop male sex organs instead of female sex organs.

Question 31

Emission (ejaculation) is elicited by reflexes mediated by the _____ nervous system. Beta adrenergic antagonists interfere with the reflex.

Answer 31

Emission (ejaculation) is elicited by reflexes mediated by the sympathetic nervous system. Beta adrenergic antagonists interfere with the reflex.