The Hormone Foundation

Endo 101: Factors That Affect Endocrine Function

Everyone's body undergoes changes, some natural and some not, that can affect the way the endocrine system works. Some of the factors that affect endocrine organs include aging, illness, stress, the environment, and genetics.

Aging

Despite age-related changes, the endocrine system functions well in most older people. However, some changes do occur because of normal damage to cells during the aging process and genetically programmed cellular changes. These changes may alter the following:

• hormone production and secretion
  
• hormone metabolism (how quickly excess hormones are broken down and leave the body, for example, through urination)
  
• hormone levels circulating in blood
  
• biological activities
  
• target cell or target tissue response to hormones
  
• rhythms in the body, such as the menstrual cycle

For example, increasing age is thought to be related to the development of Type II diabetes. With aging, the target cell response time becomes slower, especially in people who might be at risk for this disorder.

The signs and symptoms of endocrine system diseases affect many body systems. In elderly persons, they are frequently subtle and may be harder to detect than in younger persons. At times, these signs are incorrectly linked with other causes, such as the changes of normal aging, other medical disorders or conditions, or drug therapy.

The aging process affects nearly every gland. For example, the hypothalamus is responsible for releasing hormones that stimulate the pituitary gland. During aging, there is either impaired secretion of some hypothalamic hormones or impaired pituitary response. These changes appear to influence the endocrine system's ability to respond to the body's internal environment. As a result, the body cannot not respond as well either to internal or external stresses.

With increasing age, the pituitary gland can become smaller and more fibrous and may not work as well. For example, production of growth hormone may decrease. This may lead to a hormone imbalance that causes problems such as decreased lean muscle, decreased heart function, and osteoporosis.

Aging can affect a woman's ovaries. These organs eventually exhibit the most common endocrine change related to aging: menopause. In menopause, the ovaries stop responding to follicle-stimulating hormone and luteinizing hormone from the anterior pituitary. Ovarian hormone production of estrogen and progesterone slows down and then stops. Eventually a woman stops having her periods altogether.

Illness

Illness may affect endocrine system function in several ways. Acute or chronic conditions may change endocrine functions.

Chronic/Acute Conditions

Hormones are cleared from blood during their circulation to the target tissues. The liver and kidneys are primarily responsible for clearing hormones. Several clearance processes become altered or slowed in individuals who have chronic heart, liver, or kidney disorders.

Acute physical or mental stressors can trigger a preprogrammed stress response. The stress response is complex and can influence heart, kidney, liver, and endocrine system function.

Endocrine Pathologies

Endocrine pathologies can result from the following:

• congenital (birth) or genetic defects (see section on Genetics below)
  
• surgery
  
• traumatic injuries
  
• cancerous and non-cancerous tumors
  
• infection
  
• autoimmune destruction (the immune system turns against the body's own organs and causes damage)

In general, endocrine pathologies create a hormone imbalance typified by either hyposecretion (underproduction) or hypersecretion (overproduction) of hormones. The underlying problem may be the endocrine gland itself or a source outside the gland.

Stress

Many factors can start the stress response, but physical stressors are most important. In order for the body to respond to, and cope with, physical stress, the adrenal glands make more cortisol. If the adrenal glands do not respond, this can be a life-threatening problem. Some medically important factors causing a stress response are as follows:

• trauma (severe injury) of any type
  
• severe illness or infection
  
• intense heat or cold
  
• surgical procedures
  
• serious diseases
  
• allergic reactions

Other types of stress include emotional, social, or economic, but these do not require the body to produce high levels of cortisol in order to survive the stress.

External Factors

An environmental endocrine disruptor (EED) is a substance outside of the body that may cause adverse effects to normal function of the endocrine system. Some EEDs mimic natural hormone binding at the target cell receptor. These substances start the same processes between body cells that the natural hormone would start. EEDs of this type are referred to as hormone agonists.

Other EEDs block cellular events associated with hormone binding. These EEDs are called hormone antagonists. Still other EEDs can directly interfere with the production, storage, release, transport, clearance, binding, or elimination of endogenous hormones in the body. This can greatly affect the function of certain body systems.

There are currently over 84,000 commercial synthetic chemical substances in use around the world. At least 30,000 have been introduced into the U.S. environment since 1979. We do not know the extent to which they can interfere with the endocrine system and cause endocrine system diseases. Based on our knowledge of the effects of certain synthetic chemicals, such as DDT, diethylstilbestrol and PCBs, and the increasing evidence that reproductive function in wildlife and humans is changing, scientists are now examining a broad range of chemical effects.

EEDs can affect people and animals in many ways:

• disrupted sexual development
  
• decreased fertility
  
• birth defects
  
• decreased hatching in animals
  
• reduced immune response
  
• neurological and behavioral changes, including reduced stress tolerance

Genetics

Portions of your endocrine system can be affected by genes. Genes are units of hereditary information passed from parent to child. Genes contain the instructions for the production of proteins, which are some of the essential components of the body. Genes are contained in chromosomes. The normal number of chromosomes is 46 (23 pairs).

Sometimes extra, missing, altered, or damaged chromosomes can result in diseases or conditions that affect hormone production or function. The 23rd pair, for example, is the sex chromosome pair. A mother and father each contributes a sex chromosome to the child. Girls have two X chromosomes (one from the mother and one from the father), while boys have one X (from mother) and one Y (from father) chromosome. Sometimes, however, a chromosome or piece of a chromosome may be missing. In Turner syndrome, only one normal X chromosome is present and this can cause poor growth. In another example, a child with Prader-Willi syndrome (PWS) may be missing all or part of chromosome 15, which also affects growth, metabolism, and puberty.

Your genes also may place you at increased risk for certain diseases, such as breast cancer. Taking estrogen can cause breast tissue to grow faster. Cancer usually appears in fast-growing tissue. This is one of the ways that scientists believe that taking estrogen for symptoms of menopause may be related to developing breast cancer. Another idea is that breast tissue breaks down estrogen into chemicals that can bind to DNA (genetic material) and damage it. Damage to DNA is a common cause of cancer. At this time, it is not known exactly why estrogen might cause breast cancer or what role it does play in breast cancer growth.

Cycles of Hormone Release

Time appears to affect the release of certain types of hormones. Some hormones have a typical cycling pattern of release. This pattern often fits with daily body rhythms or the sleep-wake cycle.

• Cortisol builds up early in the day, decreases toward evening, rises again toward the end of sleep, and peaks during the morning hours.
  
• Thyroid-stimulating hormone (TSH) peaks during sleep and reaches its low point three hours after an individual awakens.
  
• Levels of growth hormone (GH) are high 90 minutes after sleep begins. GH typically increases during the first 2 hours of deep sleep. It also increases if a person is hypoglycemic (low blood sugar), starving, exercising, excited or is a victim of severe injury.
  
• There is a very definite rise-and-fall pattern to both estrogen and progesterone activity during a woman's menstrual cycle, which lasts an average of 28 days.