Discovering Human Sexuality 4e Chapter 3 Summary

The male external genitalia comprise the penis and the scrotum. A man’s penis contains three erectile structures and encloses the urethra. Its erotic sensitivity is highest on the glans and frenulum. The foreskin, which covers the glans, is removed in circumcision. Circumcision offers some health advantages, but the prevalence of this operation in the United States is decreasing.
Health problems affecting the penis include inflammation of the glans (balanitis), inability to retract the foreskin (phimosis), entrapment of the foreskin behind the glans (paraphimosis), pathological curvature of the penis (Peyronie’s disease), and penile cancer.
Penile erection, like clitoral erection, involves vasocongestion. The vascular spaces (sinusoids) fill with blood, under the control of the autonomic nervous system. The neurotransmitter nitric oxide plays a key role in this process.
The scrotum contains the testicles and has muscular and vascular mechanisms for maintaining them below the regular body temperature.
A man’s internal reproductive structures include six paired structures—the left and right testicle, epididymis, vas deferens, seminal vesicle, ejaculatory duct, and bulbourethral gland—as well as two unpaired midline structures, the prostate gland and urethra.
The testicles contain seminiferous tubules, in which sperm are produced. Between the seminiferous tubules lie interstitial cells, which secrete sex steroids, including testosterone. The most important health problem affecting the testicles is testicular cancer. This can affect young men, but it is one of the most curable cancers.
The epididymis is the location where sperm mature and become more concentrated. The vas deferens stores sperm and trans-ports them to the urethra. Sperm constitute only about 1% of the volume of the ejaculate.
The prostate gland and seminal vesicles add the noncellular portion of semen, which consists of proteins, enzymes, antioxidants, water, salts, fructose, and buffers. The bulbourethral glands produce a slippery secretion (“pre-cum”) that may be discharged from the urethra in small amounts before ejaculation.
The prostate gland can be affected by inflammation (prostatitis), age-related enlargement (benign prostatic hyperplasia), and prostate cancer. It is possible to screen for prostate cancer by regular digital rectal examination and by a blood test (PSA test). The treatments for prostate cancer often have a serious impact on a man’s sex life, and the question of whether and how to treat early-stage prostate cancer is controversial.
Sexual functions are regulated by the nervous and endocrine systems. Erection of the penis and the clitoris involves a spinal reflex that begins with stimulation of nerve endings in the genital skin. Inputs from the brain powerfully modulate these reflexes. Erection involves the filling with blood of spongy tissue—the corpora cavernosa and corpus spongiosum. The neurotransmitter nitric oxide promotes erection.
Seminal emission is the loading of the various glandular components of semen into the urethra. It is followed quickly by ejaculation, in which muscular contractions squeeze the urethra and eject the semen in a sequence of pulses from the urethra. Orgasm is the subjective pleasurable experience that usually accompanies ejaculation, along with the physiological events that underlie it.
In men, testosterone levels and sperm production are regulated by a negative feedback hormonal loop. This involves GnRH secreted by the hypothalamus, the gonadotropins LH and FSH secreted by the pituitary, and testosterone secreted by the testes.
Testosterone supports the normal structure and function of male genital tissues, has a broad anabolic (tissue-building) effect, guides development in a male direction, and stimulates sexual feelings and behavior.
Most societies prohibit public exposure of the genitals, apparently to regulate sexual arousal and minimize sexual conflicts. Contemporary American attitudes toward nudity vary greatly.