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Endocrinology at a Glance



Location of different Endocrine glands.
Source: Tortora Gerald, Principles of Anatomy and Physiology 12th edition



Nearly a hundred years ago, Starling coined the term hormone to describe secretin, which is a substance that stimulates secretion of pancreatic juice and bile that is secreted by the small intestine via the blood stream. In his Croonian Lectures, Starling considered the endocrine and nervous systems as the main organ systems that works in coordination with each other in order to regulate and control bodily organ functions. Thus, endocrinology found its earliest domicile in the mammalian physiology discipline.

Over the next several decades, many works by physiologists, biochemists, and clinical investigators led to the categorization of an array of hormones secreted into the blood stream from discrete glands and/or other organs. These investigators were the first to show that diseases such as hypothyroidism and diabetes could be successfully treated by replacing specific hormones. These initial triumphs fashioned the foundation of the clinical specialty of endocrinology. Distinct advances in molecular biology, cell biology, and genetics over the consequent years began to help elucidate the mechanisms of hormone secretion and action and nature of endocrine diseases.

Both circulating and local hormones of the endocrine system contribute to homeostasis by the regulation of the growth and activity of the different target cells in the body. Hormones also participate in the regulation of body metabolism.

As boys and girls come into puberty, they start to develop remarkable differences in their behavior and physical appearances. There may be no other period in life so significantly shows the endocrine system’s impact in regulating body functions and directing development. In girls, estrogen promotes the buildup of adipose tissue in the breasts and hips, molding a feminine shape. Meanwhile, boys begin to build muscle mass and enlarge the vocal cords, producing a lower pitched voice; due to increasing production of testosterone in their body. These bodily changes are just a few examples of the powerful and dynamic influence of endocrine secretions. Perhaps, multitudes of hormones help maintain and regulate homeostasis in the body on a daily basis. They control the activity of cardiac muscle, smooth muscle, and some glands; modify body metabolism; prompt growth and development; manipulate reproductive processes; and take part in the circadian (daily) rhythms recognized by the suprachiasmatic nucleus of the hypothalamus.

Moreover, both the nervous and endocrine systems work hand in hand to bring together functions of all body systems. Bear in mind that the nervous system’s actions are made through nerve impulses (action potentials) that are conducted along axons of neurons. At synapses, nerve impulses elicit the release of substances called neurotransmitters which serves as mediator or messenger molecules. Also, the endocrine system controls the body’s activities by releasing mediators, called hormones. However, the means of control of the two systems are very different.

Responses of the endocrine system often are slower compare with those of the responses of the nervous system; even though some hormones act only within seconds, to be able to cause a response, most get several minutes or more. The effects of the activation of the nervous system are generally briefer than those of the endocrine system. The nervous system actually acts on specific muscles and glands. The endocrine system’s influence is much broader; it helps control almost all types of cells in the body.

Endocrine glands exude their products (hormones) not into ducts of the body, but into the interstitial fluid adjacent to the secretory cells. Then from the interstitial fluid, hormones disseminate into the blood capillaries and blood serves as carrier that will deliver them to target cells throughout the body. Since most hormones are required only in very small amounts, most of the time the circulating levels are typically low.

The endocrine glands include the pituitary, parathyroid, adrenal, pineal glands thyroid. In addition, several organs and tissues are not solely classified as endocrine glands but contain cells that liberate hormones. These include the hypothalamus, thymus, stomach, liver, small intestine, pancreas, ovaries, testes, kidneys, skin, heart, adipose tissue, and placenta. When taken together, all endocrine glands and cells that secrete hormones constitute the endocrine system. The vast body of knowledge that deals with the structure and function of the endocrine glands and the diagnosis and treatment of disorders of the endocrine system is endocrinology.






References:
Larsen, Reed et. al, William’s Textbook of Endocrinology 10th edition, 2003
Tortora Gerald, Principles of Anatomy and Physiology 12th edition, 2009

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