Physiology of Male Reproduction Chapter 22

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

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 22-22

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

Mechanism of Penile Erection 22-23

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

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

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

Mechanism of Emission and Ejaculation 22-24

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

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

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

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 22-26

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

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 22-25