Orgasm in Males
As sexual stimulation intensifies, sperm enter the urethra from each vas deferens, and the glands add their fluids. Once seminal fluid is in the urethra, rhythmic muscle contractions expel it in spurts from the penis. During ejaculation, a sphincter closes off the bladder so that no urine enters the urethra.
The contractions that expel semen from the penis are a part of male orgasm, the physiological and psychological sensations that occur at the climax of sexual stimulation. The psychological sensation of pleasure is centered in the brain, but the physiological reactions involve the genital (reproductive) organs and associated muscles, as well as the entire body. Marked muscular tension is followed by contraction and relaxation.
Following ejaculation and/or loss of sexual arousaL the penis returns to its normal flaccid state. After ejaculation, a male typically experiences a refractory period, during which stimulation does not bring about an erection. The length of the refractory period increases with age.
In excess of 400 million sperm may be present in the 3.5 milliliters of semen expelled during ejaculation. The sperm count can be much lower than this, however, and fertilization still can take place.
Regulation of Male Hormone levels
The hypothalamus has ultimate control of the testes' sexual functions because it secretes gonadotropic-releasing hormone (GnRH), which stimulates the anterior pituitary to produce the gonadotropic hormones. Two gonadotropic hormones, FSH (follicle-stimulating hormone) and LH (luteinizing hormone), are named for their function in females but exist in both sexes, stimulating the appropriate gonads in each. FSH promotes spermatogenesis in the seminiferous tubules, and LH promotes testosterone production in the interstitial cells. LH in males is also called interstitial cell-stimulating hormone (ICSH).
The hormones mentioned are regulated by negative feedback, a mechanism that maintains testosterone production at a fairly constant level. For example, when the amount of testosterone in the blood rises to a certain level, it causes the anterior pituitary to decrease its secretion of LH. As the level of testosterone begins to fall, the anterior pituitary increases its secretion of LH, and stimulation of the interstitial cells recurs. Only minor fluctuations of the testosterone level occur in the male, and the feedback mechanism in this case acts to maintain testosterone at a normal level. The sustentacular cells in the wall of the seminiferous tubules produce a hormone called inhibin that blocks FSH secretion.
Testosterone
The male sex hormone, testosterone, has many functions. It is essential for normal development and function of the primary sex organs, those structures we have just discussed. It is also necessary for the sperm production. FSH causes spermatogenic cells to take up testosterone, which promotes spermatogenesis.
Greatly increased testosterone secretion at the time of puberty stimulates maturation of the penis and the testes. Testosterone also brings about and maintains the male secondary sexual characteristics, which develop at the time of puberty. Testosterone causes growth of a beard, axillary (underarm) hair, and pubic hair. It prompts the larynx and the vocal cords to enlarge, causing the voice to change. It is responsible for the greater muscular strength of males, which is why some athletes take a supplemental anabolic steroid, which is either testosterone or a related chemical. The disadvantages of anabolic steroid use are discussed in a Medical Focus reading in chapter 10. Testosterone also causes oil and sweat glands in the skin to secrete, thereby contributing to acne and body odor. A side effect of testosterone activity is baldness. Genes for baldness are probably inherited by both sexes, but baldness is seen more often in males because of the presence of testosterone. This makes baldness a sex-influenced trait.
Testosterone is believed to be largely responsible for the sex drive. It may even contribute to the supposed c: gressiveness of males.
In males, FSH promotes spermatogenesis in the seminiferous tubules, and LH promotes testosterone production by the interstitial cells. Testosterone stimula growth of the male genitals during puberty and is necessary for sperm maturation and development of the male secondary sexual characteristics.
