The endocrine system consists of various glands that release substances called hormones, directly into the blood.
The various endocrine glands in the body are:
- Hypothalamus (master endocrine gland in the brain)
- Pituitary (controller of most endocrine hormones located at the base of the brain)
- Pineal gland (controller of the circadian rhythm or the day and night cycle)
- Thyroid (in the neck)
- Parathyroid (embedded in the thyroid tissue)
- Pancreas (in the abdomen)
- Adrenals (on the kidneys)
- Ovaries (female gonads)
- Testes (male gonads)
The activity of all the endocrine glands is very variable in the lifetime of an individual.
Some glands release hormones intermittently, some release constantly and some release in response to stress.
Changes in the endocrine system that occur with healthy aging include:
- Somatopause (decline of growth hormone and insulin like growth factor)
- Menopause (decline of estrogen)
- Andropause (decline of testosterone)
- Adrenopause (decline of adrenal steroids)
- Decline of the hypothalamus-pituitary and thyroid hormones
Growth Hormone (GH) and Insulin like Growth Factor – 1 (IGF-1) are essential hormones during phases of growth like childhood, adolescence, puberty and early adulthood. The levels of GH during these years are high, and they start to fall in mid adulthood.
In old age, the levels of both GH and IGF-1 begin to decrease substantially and in elderly there is almost no secretion of GH. This phase is called the somatopause, and is associated with decreased lean body mass, decreased bone mass, and a diminution of immune function.
From the age of 40, the ovulation frequency decreases and in most women, the reproductive function comes to an end within the next 10-15 years, resulting in menopause. Ovarian follicles function less effectively during this period. The levels of hormones like estrogen, progesterone, FSH, LH, which play a vital role in the ovarian follicular development and regular menstruation reduce as a female approaches menopausal age. Which means, by the time, a woman attains menopause, the levels of all these hormones come to cease.
Estrogen withdrawal is the mainly implicated cause of post menopausal symptoms, which are as under:
- Decreased bone mineral density
- Hot flushes
- Cognitive disturbances
- Thinning of vaginal mucosa
- Decreased sex drive
- Painful intercourse
- Increased risk of coronary artery disease
- Increased urinary frequency and incontinence
Most of these symptoms respond well to hormone replacement therapy (HRT), mainly estrogen replacement, except the cognitive changes. However, unopposed estrogen therapy has been implicated in the rise of breast and uterine cancers and increased risk of thrombo-embolism (formation and dislodging of clots in the blood vessels). Therefore, it is advisable to start estrogen-progesterone combination based HRT under your physician’s guidance.
Age related decline in the blood levels of testosterone in healthy elderly males is called andropause. This decline was earlier thought to be due to confounding effects of concurrent illnesses and long term medications. However, the age related decline in the testosterone levels is proven as an independent event though the mechanism is not very clearly understood.
The changes in the hypothalamus-pituitary-gonadal axis cause the following effects in the body of an elderly male:
- Increased fat mass
- Reduced bone and muscle mass
- Insulin resistance
- Loss of libido and erectile dysfunction
- Higher cardiovascular risk
- Deranged lipid profile
The benefits of testosterone replacement therapy are still under evaluation in the treatment of elderly males with reduced sex steroids.
The adrenal gland secretes an important hormone called cortisol that is essential for all the major metabolic pathways to function properly and also for the maintenance of the day-to-day cycle.
The neuro-endocrine mechanisms of maintenance of the day-to-day cycle are disrupted as a consequence of normal aging. The age related changes in the hypothalamus-pituitary-adrenal (HPA) axis is gender specific and is more profound in females than in males.
Reduced activity of the HPA axis causes brain degeneration leading to higher incidences of dementia in females.
The decline of the HPA axis is linked to:
- Increased body fat content
- Decreased bone mineral density
- Increased tendency of fractures
With age the production of thyroid hormone also goes down. There is increased risk of thyroid disease in old age and therefore interpretation of thyroid function tests in the elderly may prove to be a difficult task. Even a normal elderly with no symptoms may have raised level of thyroid stimulating hormone (TSH).
Aging is associated with various thyroid diseases, mainly the toxic nodular goitre and the multi-nodular goitre. These conditions may lead to hyperthyroidism (very high levels of thyroid hormones) and the patients may show the following symptoms:
- Tremors and
The above conditions require treatment with anti-thyroid drugs or sometimes even a surgical removal of the thyroid gland.
Aging is also associated with development of thyroid auto-antibodies that cause reduced thyroid function leading to hypothyroidism (decreased levels of thyroid hormones) and the patients may show the following symptoms:
- Reduced metabolism
- Coldness of the body
- Slowing of activity
- Weight gain
- Generalised edema
This condition is treated with exogenous thyroid hormone in the form of Thyroxine tablets and a suitable treatment that blocks the production of auto-antibodies.
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