13.4: Age Changes in the Male System
- Page ID
- 84095
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On the average, the testes decrease in size and weight with age. The degree of shrinkage is highly variable among individuals and is not present in all men. Therefore, it may be caused by factors other than aging, such as poor nutrition and diseases in other parts of the body. Within the testes, the interstitial cells decrease in number but show no significant changes in structure. Changes in their production of gonadal sex hormones and the effects of those changes are described in Chapter 14.
Changes in the seminiferous tubules include thinning of the wall and narrowing of the lumen. At first, the changes occur in small and widely scattered patches. These modified patches increase gradually in size and number. In some places the lumen becomes so narrow that it completely blocks the tubule. Most of the age-related changes in the seminiferous tubules seem to be due to factors other than aging. Factors include declining blood flow caused by blood vessel changes; injury to the tubules by the immune system; and alterations in sex hormone production. Age-related compensatory increases in stimulatory hormones from the pituitary gland [luteinizing hormone (LH) and follicle-stimulating hormone (FSH)] may help minimize tubule alterations caused by other changes.
Because of these changes, there is an average decline in the rate of sperm production and a higher percentage of irregular nonfunctional sperm cells are produced. However, the decrease in sperm production is highly variable among men, and some men show no decline. Furthermore, sperm production never ceases in a healthy man because only some tubules stop production completely. In other tubules production slows only in the modified patches. Therefore, the reserve capacity for sperm production assures that the number of normal sperm cells produced by a healthy man always remains adequate for fertilization.
Ducts
The effects of aging on the structure and sperm-carrying abilities of the ducts have not been well studied. There is no evidence that aging results in significant changes in their contributions to reproduction.
Glands
Seminal Vesicles
Age changes in the seminal vesicles have no known effect on their contributions to reproduction.
Prostate Age changes in the lining and muscle layer of the prostate gland, which become thinner, are apparent by about age 40. At first the changes occur in widespread patches, but by age 60 essentially all of the prostate has changed. The thickening basement membrane and declining blood flow may reduce nutrient supply and waste removal and therefore may account for some of the shrinkage in the lining and muscle layer. None of the changes in the prostate seem to adversely affect its contributions to reproduction. However, increased binding of testosterone may promote the development of an abnormal condition called benign prostatic hypertrophy. In contrast to the prostate, most body structures show an age-related decline in the binding of testosterone.
Penis
Age changes in the penis appear between ages 30 and 40. The accumulation of fibrous material occurs first in the erectile tissue surrounding the urethra. Some years later fibrous buildup in the other two masses of erectile tissue begins. By age 55 to 60 all areas of erectile tissue show gradually increasing fibrosis.
Age changes in the penis seem to contribute to the gradual decline in the speed with which erection occurs. However, in healthy men under ordinary circumstances the penis retains the ability to become erect and enter a vagina and therefore to assist in placing sperm cells into the female reproductive system.