Your sense of well-being -- your body's ability to respond and function normally -- depends on the coordinated responses of various organ systems. The organ systems most affected by aging are:

• cardiovascular system: heart and blood vessels

• genitourinary system: kidneys, bladder, genitals, and sexual organs (penis, testicles, and prostate)

• musculoskeletal system: bones, muscles, and joints

• skin and connective tissues beneath the skin.

To function properly, these organ systems depend on:

• a good blood supply to carry oxygen, nutrients, and hormones to the tissues of the body

• a healthy nervous system, which ensures an alert mind, good sight and hearing, and efficient response to other bodily needs such as respiration (breathing) and digestion.

The health and well-being of men over 45 years old depend largely on whether they have in the past gotten adequate sleep and exercise, eaten nutritious foods, and avoided excessive dependency on nonprescribed drugs, alcohol, and tobacco.

The Role of Sex Hormones

Human sexuality is a coordinated response of both the nervous system and circulatory system (supplies blood to the organs). Sexual response also depends on a balance of hormones, controlled by the pituitary gland, which is located at the base of the brain.

The follicle-stimulating hormone (FSH) and the luteinizing hormone (LH), which are produced by the pituitary gland, stimulate the testes to produce the male hormone testosterone. The balance of these hormones is responsible for initiating and maintaining the production of sperm from early adolescence throughout adulthood. During childhood and adolescence these hormones are responsible for:

• growth of the genitals

• secondary sexual characteristics such as deepened pitch of the voice, increased muscle mass and tone, and the appearance of body and facial hair.

Decrease in Male Hormone

Testosterone levels decrease normally with age. This may cause men to experience erectile problems or loss of sexual interest. Men of all ages receiving supplemental testosterone usually experience a sense of well-being that they attribute to the hormone. Testosterone is an anabolic agent, which means that it enhances physical strength and stamina.

Middle-aged and older men should take testosterone only at the advice of their physician because it may enlarge the prostate. Men taking testosterone should ask to be examined for signs of prostatic tenderness or enlargement. Men who have to urinate frequently during the day or who are getting up at night to do so should see their doctor. Men with family histories of prostatic cancer may want to have a PSA (prostate specific antigen) test.

Aging and Sexual Response

As men grow older, many continue to have active, enjoyable sexual lives. However, some men find the quickness and intensity of their sexual responses decrease:

• Erections during sleep and at the time of waking are less frequent.

• The erection takes longer to achieve and is usually less rigid.

• Penetration can be difficult without a lubricant.

• An erection is more easily lost.

• Ejaculation is less forceful in older men and may become seepage.