The Evolution Of The Endocrine System

In most creatures, an endocrine system will be present if there is a well development circulatory system and nervous system. However, even then the endocrine system is categorized as being highly evolved or primitive. Typically, in the primitive system, it has been seen that the hormones are released by the nervous system. These hormones, also known as neurohormones, are released directly into the bloodstream or they are stored in neurons known as neurohemal organs. These endings of these neurons are directly connected with blood vessels. Hence, when the need arises, the neurohemal organs can secrete substantial amounts of hormones into the bloodstream.

Researchers believe that glands of the endocrine system evolved at a later stage during evolution. They reckon that nerve cells were responsible for formation of hormone secreting glands, as some cells of glands of the endocrine system have come to being from nerve cells. While the nervous system was evolving, some cells relocated to other parts of the body forming glands of the endocrine system. In all the animals, individual endocrine glands are only seen in vertebrates and arthropods. However, in the latter, neurohormones are still the main way how endocrine messages are sent. The vertebrates have highly developed endocrine system.

As more and more research is being done on the evolution of the endocrine system, researchers have found out that some hormones which were earlier thought to be present just in vertebrates are also produced by invertebrates. A good example of such a hormone is insulin, which is produced by the pancreas. Also, researchers have found that certain hormones seen in invertebrates have been found in vertebrate, including in humans. Even single-celled organisms have chemical messengers that are used just like hormones. This has led researchers to conclude that hormone or chemical messengers that form the endocrine system have been present from the time life evolved on Earth. However, as life form evolved, the way these chemical messengers were used has changed.

In humans, the endocrine system is highly developed. This development has taken millions of years to occur. The fact that humans have evolved from primitive life form, it is not a surprise that several hormones in the human endocrine system are found in other vertebrates and invertebrates. These hormones are considered as primitive hormones. However, researchers are still trying to understand the endocrine systems of invertebrates, but as more and more research is being done in this field, hopefully soon we will know more about evolution of the endocrine system in invertebrates.

More Articles :

• Endocrine Systems Overview
• Function Of Endocrine System
• Organs Of The Endocrine System
• Overview Of Endocrine System
• The Evolution Of The Endocrine System
• What Is Endocrinology ?
• What Is Reproductive Endocrinology ?

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Encyclopaedia Britannica: Evolution of Endocrine Systems
http://www.britannica.com/EBchecked/topic/186879/endocrine-system/45465/Evolution-of-endocrine-systems