Comparative endocrinologists investigate the evolution of endocrine systems and the role of these sy.... hormon system

In addition, the isolation and purification of many mammalian hormones was made possible in large part by using other vertebrates as bioassay systems; that is, primitive animals have served as relatively simple, sensitive indicators of the amount of hormone activity in extracts prepared from mammalian endocrine glands. Finally, some vertebrate and invertebrate animals have provided model systems for research that have yielded valuable information on the nature of hormone receptors and the mechanisms of hormone action. ne of the most intensively studied systems for understanding hormone actions on target tissues has been the receptors for progesterone and estrogens (hormones secreted by the gonads) from the oviducts of chickens. The most primitive endocrine systems seem to be those of the type, in which the nervous system either secretes (hormones that act on, or are secreted by, nervous tissue) directly into the circulation or stores them in neurohemal organs (neurons whose ! endings directly contact blood vessels, allowing neurohormones to be secreted into the circulation), from which they are released in large amounts as needed. hormon system