1. Physiology of Male Reproduction Chapter 22

2. Male Reproduction
The functions of the male system are the generation and release of sperm for fertilization of the female
The functions are accomplished by the neural and hormonal mechanisms

3. Neural Mechanisms Erection parasympathetic nerve impulses
blood accumulates in erectile tissues
Orgasm
culmination of sexual stimulation
accompanied by emission and ejaculation
Ejaculation
emission is the movement of semen into urethra
ejaculation is the movement of semen out of the urethra
largely dependent on sympathetic nerve impulses
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4. Neural Mechanisms
Mainly involved in the process of erection, orgasm and ejaculation
Involves the production of autonomic impulses—originate from the hypothalamus or as a reflex from the spinal cord in response to sensory stimuli
When stimuli are not present the spaces within the erectile tissue of the penis are empty
When stimuli begin parasympathetic nerve impulses pass to the walls of the arteries in the penis and cause them to dilate—arterial blood enters the erectile tissue spaces
As the tissue fills with blood, it swells, compressing the veins that carry blood away from the penis—causing more blood to enter the erectile tissue than is leaving causing an erection—first step in sexual arousal

5. Mechanism of Penile Erection
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6. Neural Mechanisms
c. Sympathetic impulses are conducted to the walls of the ducts—stimulate peristaltic contractions of the testicular ducts—causes movement of sperm cells called emission

7. Neural Mechanisms
d. As the urethra fills with semen, impulses are sent to the spinal cord, then routed to the skeletal muscles at the base of the penis causing them to rhythmically contract
Increases the pressure within the erectile tissue and forces semen through the urethra—ejaculation
As semen flows through the urethra, secretions from the bulbourethral gland flow in first, followed by secretions form the seminal vesicles and prostate gland that mix with sperm cells and a small amount of testicular fluid

8. Neural Mechanisms
e. Combination of sensory impulses, erection, emission and ejaculation invokes a pleasurable experience—physical and mental tension followed by complete relaxation—orgasm
f. In some individuals ejaculation is a requirement for orgasm
1. Once ejaculation is completed, sympathetic impulses travel to the artery walls causing constriction, releasing pressure from the veins and blood exits the erectile tissue
g. Penis will then return to its original flaccid state

9. Mechanism of Emission and Ejaculation
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10. Hormonal Mechanisms
Play a profound role in the development of reproductive structures and the regulation of reproductive functions, the development of secondary sex characteristics and sexual behavior
Arise from the hypothalamus, the anterior pituitary gland, and the testes
Hypothalamus and pituitary gland regulate the activity of the testes, which secrete the primary male sex hormone testosterone

11. Hormonal Mechanisms Hypothalamic and Pituitary Influences
As male approaches puberty the hypothalamus begins to secrete gonadotropin-releasing hormone (GnRH)
GnRH enters blood vessels to target the anterior pituitary gland—presence of the hormone stimulates the secretion of two hormones that are called gonadotropins—luteinizing hormone (LH) and follicle-stimulating hormone (FSH)
LH promotes the development of interstitial cells in the testes—which will secrete testosterone at maturity
FSH prepares the germinal epithelium of the testes to become responsive to the effects of testosterone—once responsive, the cells stimulate the process of spermatogenesis when in the presence of FSH and testosterone

12. Hormonal Mechanisms Testosterone
Male sex hormones are collectively called androgens—the most abundant is testosterone
Secreted by the interstitial cells in the testes once they have matured
After puberty its secretion continues for life
Early presence of testosterone in the body of a young male causes many changes—occur during puberty (begins between 10 & 12 and completes by 18)
Changes include functional development and enlargement of the testes and other reproductive structures and the development of secondary sexual characteristics

13. Actions of Testosterone
enlargement of larynx and thickening of vocal cords
increased growth of body hair
sometimes decreased growth of scalp hair (balding)
increased muscular growth and strengthening of the bones
thickening of skin
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14. Hormonal Mechanisms
Amounts of testosterone released by the testes determines the extent of the secondary sexual characteristics
Important that testosterone blood levels stay relatively constant—done by hypothalamus in a negative feedback system
Increase in testosterone inhibits the production of GnRH by the hypothalamus reduces the production of LH and testosterone
As testosterone levels in the blood decreasehypothalamus increases the rate of GnRH production which produces more LH by the pituitary glandstimulates the production of more testosterone

15. Hormonal Control of Male Reproductive Functions
hypothalamus controls maturation of sperm cells and development of male secondary sex characteristics
negative feedback controls concentration of testosterone
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