Reproductive System, Male Health Article

Male sexual act

The male sexual act can be divided into three main steps: erection, emission, and ejaculation. Erection is the result of increased blood flow to the erectile tissues of the penis; stimulation of the nervous system during arousal causes a release of acetylcholine (a neurotransmitter) that in turn causes vasodilation (increase in the diameter of blood vessels). Emission is the passage of sperm and secretions into the urethra mediated by release of the hormone adrenaline. Ejaculation occurs when the sperm are forced from the urethra by contraction of the bulbocavernous muscles. A release of noradrenaline causes the blood vessels in the penis to contract, decreasing blood flow and resulting in detumescence (loss of erection).

Fertilization

In order to fertilize the ovum, ejactulated sperm must move into the vaginal tract, pass through the cervix, survive in the uterus, and enter the fallopian tubes. Usually only healthy, motile sperm will reach the ovum and have the opportunity to fertilize it. Numerous protective layers (including the oolemma, the zona pellucida, and the zona radiata) surround the ovum, and sperm cells must penetrate each of these layers for fertilization to occur. Binding of a sperm cell to the zona pellucida induces the acrosome reaction, which permits the sperm to penetrate the zona pellucida and reach the egg membrane. The sperm and egg membranes fuse to form a zygote, and subsequent reactions prevent the binding of additional sperm cells to the egg membrane.

Common diseases and disorders

Diseases of the male reproductive system are classified based on the localization (e.g. testis, pituitary gland, etc.) and cause (e.g. congential malformation, cancerous tumor, etc.) of the disorder. Some common examples of andrological disorders include:

• Infertility: Male infertility may be the symptom of multiple disorders. A blockage in both of the vasa deferentia or a testicular disorder may result in the complete absence of sperm (azoospermia). Low sperm counts might result from a prolonged increase in scrotal temperature—as in the case of a varicocele, a disturbance in testicular blood circulation. Retrograde ejaculation is another cause of male infertility; semen travels in the wrong direction, up the urethra to the bladder instead of down toward the penis.
• Hypogonadism: This describes a condition in which there is decreased sexual development and growth of the testes. Hypogonadism may result from tumors, hormone imbalances, or chromosomal abnormalities. Its symptoms (after puberty) include voice alteration, decreased size of testes, gynecomastia (enlargement of mammary glands), an infantile penis, or osteoporosis.
• Erectile dysfunction: It is estimated that the incidence of erectile dysfunction (ED) is twice as high as that of coronary heart disease. ED may result from reduced penile blood flow, low serum levels of testosterone, use of psychotropic drugs, alcohol abuse, such metabolic disorders as diabetes mellitus, or muscle cell impairment.
• Prostate cancer: The prostate surrounds the urethra and secretes seminal fluids. Prostate cancer is the second most common cause of cancer death of men in the United States, and the second most commonly diagnosed form of cancer (after skin cancer).