What are 3 ways in which endocrine glands are stimulated to secrete their hormones?

Answer 1

Other hormones - hormones that stimulate the secretion of other hormones from endocrine glands are called tropic hormones. An example of this would be the secretion of human gonadotropin releasing hormone (GnRH) by the hypothalamus. This hormone stimulates the anterior pituitary to secrete follicle stimulating hormone (F SH) and luteurizing hormone (LH), two hormones particularly important in menstruation.

Nerve impulse conduction - when a nerve impulse reaches the end of the nerve axon, neurotransmitters are released. In many cases, these neurotransmitters can act as endocrine hormones. For example, in order to stimulate muscle contraction, a nerve impulse that reaches the axon of a nerve that directly contacts a muscle (i.e. a motor neuron), will stimulate the release of acetylcholine. The acetylcholine binds receptors on the muscle and it contracts.

Changes in concentration of extracellular ions or nutrients - many cells have molecules that can act as sensors of the extracellular environment, and changes in this environment can stimulate them to secrete hormones. A common example of this is the secretion of insulin or glucagon. If glucose concentration in the blood is high, insulin is secretes. If blood glucose is low, glucagon is secreted.

In addition, many hormones can be secreted in response to environmental stimuli like a change in heat or light. Often times this secretion is indirect and utilizes one of the previous mentioned mechanisms. However one example of a direct affect of the environment is the hormone melatonin. Melatonin helps regulate sleep/wake cycles and is produced by the pineal gland when directly stimulated by darkness (i.e. night)
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