The endocrine system is made up of organs and tissues that produce hormones. Hormones are natural chemicals produced in one location, secreted into the bloodstream, then used by certain other target organs and system.

The hormones control the target organs. Some organ systems have their own internal control systems instead of, or in addition to, hormones.

With aging, changes naturally occur in the way that body systems are controlled. Some target tissues become less sensitive to their controlling hormone. The amount of hormones produced may also change.

Blood levels of some hormones increase, some decrease, and some are unchanged. Hormones are also broken down (metabolized) more slowly.

Many of the organs that produce hormones are, in turn, controlled by other hormones. Aging also changes this process. For example, an endocrine tissue may produce less of its hormone than it did at a younger age, or it may produce the same amount at a slower rate.

AGING CHANGES

The hypothalamus is located in the brain. It produces hormones that control the other structures in the endocrine system. The amount of these regulating hormones stays about the same, but the response by the endocrine organs can change with aging.

For example, a hormone called TRH makes the pituitary gland produce thyrotropin, or thyroid stimulating hormone (TSH). In women, the amount of TSH produced does not decrease with time, but it does in men.

The pituitary gland is also located in the brain. This gland reaches its maximum size in middle age and then gradually becomes smaller. It has two parts:

• The back (posterior) portion stores hormones produced in the hypothalamus.
• The front (anterior) portion produces hormones that affect the thyroid gland (TSH), adrenal cortex, ovaries, testes and the breasts.

The thyroid gland is located in the neck and produces hormones that help control metabolism. With aging, the thyroid often becomes lumpy (nodular). Metabolism gradually declines, beginning about age 20.

Less thyroid hormone may be produced, but there is also less body mass (because of loss of muscle and bone tissue), so that thyroid function tests usually show results within the normal range.

The parathyroids are four tiny glands located around the thyroid. Parathyroid hormone affects calcium and phosphate levels. This, in turn, affects the strength of the bones. Changes in the level of parathyroid hormones may contribute to osteoporosis.

Insulin is produced by the pancreas. Insulin hormone fits into a place on the cell wall called an insulin receptor site, and acts like a lock and key to help sugar (glucose) go from the blood to the inside of cells, where it can be used for energy.

The normal or average fasting glucose level rises 6 to 14 mg/dL (milligrams per deciliter) for each 10 years after age 50. This is because the cells become less sensitive to the effects of insulin, probably because of a loss in the number of insulin receptor sites in the cell wall.

Because of these changes, older people periodically should have blood drawn to check glucose levels and make sure they aren't in the early stages of diabetes, or high blood sugar.

The adrenal glands are located just above the kidneys. The adrenal cortex, the surface layer, produces the hormones aldosterone and cortisol.

• Aldosterone regulates fluid and electrolyte balance.
• Cortisol is the "stress response" hormone. It affects the breakdown of glucose, protein, and fat, and has anti-inflammatory and anti-allergy effects.

Aldosterone secretion decreases with age, which can contribute to light-headedness and a drop in blood pressure with sudden position changes (orthostatic hypotension). Cortisol secretion decreases, but the level stays about the same.

The ovaries and testes have two functions. They produce the reproductive cells (ova and sperm). They also produce the sex hormones that control secondary sex characteristics, such as breasts and facial hair.

• With aging, men sometimes experience a slightly decreased level of testosterone.
• Women have decreased levels of estradiol and estrogen after menopause.

EFFECT OF CHANGES

Overall, some hormones are decreased, some unchanged and some increased with age. Hormones that are usually decreased include:

• Aldosterone
• Renin
• Calcitonin
• Growth hormone

In women, estrogen and prolactin levels usually decrease.

Hormones that remain unchanged or only slightly decreased include:

• Thyroid hormones T3 and T4
• Cortisol
• Insulin
• Epinephrine
• Parathyroid hormone
• 25-hydroxyvitamin D

Testosterone levels usually decrease slightly as men age.

Hormones that may increase include:

• Follicle-stimulating hormone (FSH)
• Luteinizing hormone (LH)
• Norepinephrine

RELATED TOPICS

• Aging changes in immunity
• Aging changes in organs, tissues, and cells
• Aging changes in the female reproductive system
• Aging changes in the male reproductive system
• Menopause