How The Hormone Systems Work


Your pet's body has a magnificent ability to respond to the opportunities, threats and challenges of life. While the brain and nervous system initiates instantaneous changes in body function, hormones are responsible for the longer term balance of body activities. Like thermostats, they control themselves by a method called biofeedback. When a hormone has done what it needs to do, it stimulates a chemical response that travels back to the hormone-producing gland with instructions to turn off. The pituitary gland at the base of the brain, the 'master gland', produces hormones that stimulate other endocrine glands, the thyroids, parathyroids, adrenals, ovaries or testes, in their own hormone production. The pituitary produces additional hormones that instruct the kidneys how to concentrate urine (anti-diuretic hormone or ADH), and control body growth and cellular health (growth hormone or GH). If hormone production, is insufficient or does not turn on or off properly a variety of medical conditions develop, some of which are subtle and difficult to diagnose; others devastating and life threatening. Treatment of endocrine disorders is one of the great success stories of twentieth century medicine.

Every single cell in your pet's body has receptor sites for one or more endocrine hormones. Thyroid hormone influences growth, energy production and energy consumption. The parathyroid glands are responsible for calcium metabolism. Adrenal glands produce cortisol, the body's natural corticosteroid, and adrenalin, both central to 'fight or flight'. In clusters on the surface of the pancreas, cells produce insulin, vital for sugar metabolism. The activity of most hormones is controlled by "biofeedback" activity. This involves the hypothalamus region of the brain, the pituitary, circulation and regional hormone-producing glands this way.

  1. The brain is stimulated, sending signals to the hypothalamus.
  2. The hypothalamus sends releasing signals to the pituitary
  3. The pituitary sends releasing hormone via the blood stream to a hormone-producing gland
  4. The targeted gland releases its hormone into the blood stream
  5. That gland hormone circulates in the blood stream back to the pituitary, inducing it to stop sending out releasing hormone.

What A Hormone Is

Hormones are molecular messengers that influence the activity of cells. During early medical research, scientists concentrated on discovering the molecular messengers produced by the body's visible glands and called these products "hormones". It was only much later that other messenger biochemicals such as dopamine and serotonin, the neurotransmitter substances in the brain, were discovered. These too are hormones but present in infinitesimally smaller amounts. Later still, other trace messenger chemicals called cytokines were discovered. New cytokines are being discovered almost monthly. All of these substances trigger cellular activity and technically are hormones.

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