Endocrine System

The endocrine system is a control system of ductless glands that secrete chemical "instant messengers" called hormones that circulate within the body via the bloodstream to affect distant cells within specific organs. Endocrine glands secrete their products immediately into the blood or interstitial fluid, without storage of the chemical. Hormones act as "messengers," and are carried by the bloodstream to different cells in the body, which interpret these messages and act on them. Typical endocrine glands are pituitary, thyroid, and adrenal glands, but not exocrine glands such as salivary glands, sweat glands and glands within the gastrointestinal tract.

The field of medicine that deals with disorders of endocrine glands is endocrinology, a branch of the wider field of internal medicine.

1. The hypothalamus and pituitary gland

The pituitary gland is called the “master gland” but it is under the control of the hypothalamus. Together, they control many other endocrine functions. These include follicle-stimulating hormone (FSH), which stimulates development and maturation of a follicle in one of a woman’s ovaries, and leutinizing hormone (LH), which causes the bursting of that follicle (= ovulation) and the formation of a corpus luteum from the remains of the follicle.

There are a number of other hypothalamus and pituitary hormones which affect various target organs.

One non-sex hormone secreted by the posterior pituitary is antidiuretic hormone or ADH. This hormone helps prevent excess water excretion by the kidneys. Ethanol inhibits the release of ADH and can, thus, cause excessive water loss. That’s also part of the reason why a group of college students who go out for pizza and a pitcher of beer need to make frequent trips to the restrooms. Diuretics are chemicals which interfere with the production of or action of ADH so the kidneys secrete more water. Thus diuretics are often prescribed for people with high blood pressure, in an attempt to decrease blood volume.

Another group of non-sex hormones that many people have heard of is the endorphins, which belong to the category of chemicals known as opiates and serve to deaden our pain receptors. Endorphins, which are chemically related to morphine, are produced in response to pain. The natural response to rub an injured area, such as a pinched finger, helps to release endorphins in that area. People who exercise a lot and push their bodies “until it hurts” thereby stimulate the production of endorphins. It is thought that some people who constantly over-exercise and push themselves too much may actually be addicted to their own endorphins which that severe exercise regime releases.

2. the thyroid gland

Thyroid hormones regulate metabolism, therefore body temperature and weight. The thyroid hormones contain iodine, which the thyroid needs in order to manufacture these hormones. If a person lacks iodine in his/her diet, the thyroid cannot make the hormones, causing a deficiency. In response to the body’s feedback loops calling for more thyroid hormones, the thyroid gland then enlarges to attempt to compensate (The body’s plan here is if it’s bigger it can make more, but that doesn’t help if there isn’t enough iodine.). This disorder is called goiter. Dietary sources of iodine include any “ocean foods” because ocean-dwelling organisms tend to accumulate iodine from the seawater, and would include foods like ocean fish (tuna) and seaweeds like kelp. Because of this, people who live near the ocean do not have as much of a problem with goiter as people who live inland and don’t have access to these foods. To help alleviate this problem in our country, our government began a program encouraging salt refiners to add iodine to salt, and encouraging people to choose to consume this iodized salt.

3. the pancreas

This organ has two functions. It serves as a ducted gland, secreting digestive enzymes into the small intestine. The pancreas also serves as a ductless gland in that the islets of Langerhans secrete insulin and glucagon to regulate the blood sugar level. The -islet cells secrete glucagon, which tells the liver to take carbohydrate out of storage to raise a low blood sugar level. The -islet cells secrete insulin to tell the liver to take excess glucose out of circulation to lower a blood sugar level that’s too high. If a person’s body does not make enough insulin (and/or there is a reduced response of the target cells in the liver), the blood sugar rises, perhaps out of control, and we say that the person has diabetes mellitus.

4. the adrenal glands

These sit on top of the kidneys. They consist of two parts, the outer cortex and the inner medulla. The medulla secretes epinephrine (= adrenaline) and other similar hormones in response to stressors such as fright, anger, caffeine, or low blood sugar. The cortex secretes corticosteroids such as cortisone. Corticosteroids are well-known as being anti-inflammatory, thus are prescribed for a number of conditions. However, these are powerful regulators that should be used with caution. Medicinal doses are typically higher than what your body would produce naturally, thus the person’s normal feedback loops suppress natural secretion, and it is necessary to gradually taper off the dosage to trigger the adrenal glands to begin producing on their own again. Because the corticosteroids suppress the immune system, their use can lead to increased susceptibility to infections, yet physicians typically prescribe them for people whose immune systems are hard at work trying to fight off some pathogen. For example, back when I was in grad school, I was diagnosed with mono, and the campus doctor prescribed penicillin and cortisone. Since mono is a virus and penicillin only is effective against