What is the morphology and embryology of the concept that certain endocrine glands are part of the nervous system?

Answer 1

I'll use the pituitary gland as an example. Anatomically, the pituitary gland is located at the base of the brain attached to it by a puny little stalk called the infundibulum. In a gross specimen of the brain, it looks as though the pituitary gland is brain tissue, but brain tissue that's organized and separated from the rest of the brain. It turns out that the pituitary gland is really two separate glands smashed together: the anterior pituitary and the posterior pituitary. Embryologically, the anterior pituitary comes from the early roof of the mouth, called Rathke's pouch. The posterior pituitary is a direct extension of the hypothalamus. It's this latter relationship that makes the pituitary gland a real, bona fide part of the nervous system.

Another example is the medulla of the adrenal gland, which is an endocrine organ that secretes the hormones adrenaline and noradrenaline. The adrenal medulla comes from the same embryonic tissue that much of the sympathetic nervous system comes from (called the neural crest cells). So the adrenal medulla is really just a modified part of the sympathetic nervous system. Specifically, the medulla is made of specialized postganglionic neurons of the sympathetic nervous system.