Neurotransmitters vs Hormones
Nervous system and endocrine system are very important systems, which regulate the various activities of the body, and are dependent on the release of special chemicals either as neurotransmitters or hormones. These two specific chemicals are known as the two types of chemical messengers of the body. There are some similarities exist between these two chemicals. For example, both chemicals are released from vessels into the surrounding fluid by similar mechanisms. Also, certain neurotransmitters and hormones have similar origins (for example; amino acid derivatives). Furthermore, some hormones, as well as the neurotransmitters, are produced by the tissues in the Central Nervous System. Some molecules act as both hormones and neurotransmitters. For example, norepinephrine is released into the blood by the adrenal glands as a hormone, but it also released as a neurotransmitter by sympathetic nerve endings. While there are similarities between these two chemical messengers, there are some obvious differences.
Neurotransmitters are the chemical messengers found in the nervous system that specifically do the transmission across the synaptic cleft, where the space exists between two axons. After neurotransmitters are released into the synaptic cleft, they diffuse into postsynaptic cleft, where they bind to receptor proteins and stimulate the postsynaptic membrane. Some common examples for neurotransmitters are acetylcholine, dopamine and noradrenaline.
Hormones are the chemical messengers of the endocrine system and are transported by blood to distal target cells. Organs that produce and secrete hormones are called glands, while the organs they affect are called target organs. (Read the Difference Between Gland and Organ). Hormones are able to stimulate a specific set of cells that are located somewhere else and have no direct connection with their glands. Chemically, there are four types of hormones; (1) hormonal amine, peptide, (2) Peptide, protein, or glycoprotein. (3) Steroids and (4) Eicosanoid. The main endocrine glands that release hormones are pituitary, pineal, thyroid, parathyroid, adrenal, ovaries (in females) and testes (in males). Each gland releases a specific hormone or several hormones, which help to regulate body activities. For example, parathyroid gland releases PTH, which is able to raise the blood calcium level and stimulate calcium absorption.
What is the difference between Neurotransmitters and Hormones?
• Neurotransmitters belong to the nervous system, whereas hormones belong to the endocrine system.
• Transmission of neurotransmitters is across the synaptic cleft, whereas that of hormones is by blood.
• Hormones are produced by endocrine glands while neurotransmitters are produced by neurons.
• Target cells of neurotransmitters can be specific neurons or other cells, whereas that of hormones can be some distance from endocrine gland.
• Action of neurotransmitters is extremely fast, which could be up to few milliseconds. In contrast, effect of hormones could be last for a long period which could be in the range of few seconds to few days.
• Hormones are able to regulate their target organs, whereas neurotransmitters are able to stimulate the postsynaptic membranes.
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