Endocrine System - History Of Endocrinology, Basic Endocrine Principles, The Pituitary, The Pineal, The Thyroid, The Parathyroids
hormones glands body chemical
The endocrine system is the body's network of nine glands and over 100 hormones which maintain and regulate numerous events throughout the body. The glands of the endocrine system include the pituitary, thyroid, parathyroids, thymus, pancreas, pineal, adrenals, and ovaries or testes: in addition, the hypothalamus, in the brain, regulates the release of pituitary hormones. Each of these glands secrete hormones (chemical messengers) into the blood stream. Once hormones enter the blood, they travel throughout the body and are detected by receptors that recognize specific hormones. These receptors exist on target cells and organs. Once a target site is bound by a particular hormone, a cascade of cellular events follows that culminates in the physiological response to a particular hormone.
The endocrine system differs from the exocrine system in that exocrine glands contain ducts which direct their hormones to specific sites; whereas endocrine hormones travel through blood until they reach their destination. The endocrine is also similar to the nervous system, because both systems regulate body events and communicate through chemical messengers with target cells. However, the nervous system transmits neurotransmitters (also chemical messengers) between neighboring neurons via nerve extension, and neurotransmitters do not generally enter the circulation. Yet, some overlap between hormones and neurotransmitters exists which gives rise to chemical signals called neurohormones which function as part of the neuroendocrine system. The endocrine system oversees many critical life processes involving metabolism, growth, reproduction, immunity, and homeostasis. The branch of medicine that studies endocrine glands and the hormones which they secrete is called endocrinology.
Additional Topics
Although some ancient cultures noted biological observations grounded in endocrine function, modern understanding of endocrine glands and how they secrete hormones has evolved only in the last 300 years. Ancient Egyptian and Chinese civilizations castrated (removed the testicles of) a servile class of men called eunuchs. It was noted that eunuchs were less aggressive than other men, but the link o…
Most endocrine hormones are maintained at specific concentrations in the plasma, the non-cellular, liquid portion of the blood. Receptors at set locations monitor plasma hormonal levels and inform the gland responsible for producing that hormone if levels are too high or too low for a particular time of day, month, or other life period. When excess hormone is present, a negative feedback loop is i…
The pituitary gland has long been called "the master gland," because it secretes multiple hormones which, in turn, trigger the release of other hormones from other endocrine sites. The pituitary is roughly situated behind the nose and is anatomically separated into two distinct lobes, the anterior pituitary (AP) and the posterior pituitary (PP). The entire pituitary hangs by a thin p…
The thyroid is a butterfly-shaped gland that wraps around the back of the esophagus. The two lobes of the thyroid are connected by a band of tissue called the isthmus. An external covering of connective tissue separates each lobe into another 20-40 follicles. Between the follicles are numerous blood and lymph vessels in another connective tissue called stroma. The epithelial cells around the edge …
The pancreas is a large endocrine and exocrine gland situated below and behind the stomach in the lower abdomen. The pancreas is horizontally placed such that its larger end falls to the right and its narrower end to the left. Clusters of exocrine pancreatic cells called acini secrete digestive enzymes into the stomach; while endocrine cells secrete hormones responsible for maintaining blood gluco…
One of the two adrenals sit atop each kidney and are divided into two distinct regions, the cortex and the medulla. The outer area makes up about 80% of each adrenal and is called the cortex. And the inner portion is called the medulla. The adrenals provide the body with important buffers against stress while helping it adapt to stressful situations. The cells of the cortex form three distinct lay…
The ovaries are located at the end of each fallopian tube in the female reproductive tract, and they produce the female reproductive hormones: estrogen, progesterone, and relaxin. Although the fluctuation of these hormones is critical to the female menstrual cycle, they are initially triggered by a hormone from the hypothalamus, called a releasing factor, that enables gonadotrophs in the pituitary…
As much as 10% of the population will experience some endocrine disorder in their lifetime. Most endocrine disorders are caused by a heightened or diminished level of particular hormones. For example, excess growth hormone can cause giantism (unusually large stature). Tumors in endocrine glands are one of the major causes of hormone overproduction. Hormone underproduction is often due to a mutatio…
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User Comments
about 11 years ago
Good information but lacks visual aids