ENDOCRINE GLANDS ::
Protein kinase in the nucleus or cytoplasm producing metabolic and physiological responses These include the degradation of protein fat and glycogen the relaxation of smooth muscles in various organs and contraction of cardiac muscles Some hormones bind to receptors which cause an increase in cGMP (cyclic guanine monophosphate ) to produce opposite effects
The term hormone is often confused with various other related substances like local hormones neurohormones pheromones neurotransmitters etc
Neurohormones are the chemical agents that are synthesized by special neurons and function like gland cells Such neurons are often called neurosecretory cells Examples of neurohormones are oxytocin vasopressin (or antidiuretic hormone ) and various hormone releasing factors produced by neurosecretory cells of hypothalamus in the brain
Neurotransmitters are chemical agents that are synthesized by neurons and stored in their terminals Here the neurons do not work like neurosecretory cells and the substances released may act locally or at distant organs Examples are noradrenaline (at adrenergic or sympathetic nerve terminals ) acetylcholine (at parasympathetic or cholinergic nerve terminals ) dopamine and GABA (y-aminobutyric acid ) Adrenaline is synthesized in adrenal medulla which is not a nerve ending so it is not a neurotransmitter but it is a hormone
Pheromones are chemical agents that affect the physiology of animals in a population For example female dogs in heat are known to release a pheromone that attracts male dogs
Besides the above mentioned substances there are substances produced locally in response to a stimulus and produce various physiological actions in very minute quantities These are popularly termed as local hormones or autacoids Histamine 5-hydroxytryptamine or serotonin prostaglandins prostacyclins leucotrienes angiotensin renin bradykinin kalidin etc are the common examples of local hormones Besides these some gastrointestinal secretions like gastrin secretin enterogastrin cholecystokinin and enterokinin are also considered as local hormones
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