[Are all animal and human organs and tissues endocrine in nature and are they secreting peptide hormones into blood?].

Endocrinology was born and developed as the science of endocrine glands and the human and animal diseases induced by the gland dysfunctions. The complex of endocrine glands included pituitary, thyroid and parathyroid glands, adrenals, pancreas and gonads. Further, it has been shown that certain brain structures, hypothalamus in particular, are also endocrine organs which secrete in blood a large number of various peptide hormones. Heart secretes in blood the peptide compound natriuretic hormone which regulates the sodium balance. Recent studies have been demonstrated that the adipose tissue cells adipocytes secrete in blood the peptide hormone leptine which stimulates utilization of lipids from the fat deposits in energy metabolism. Leptine is the product obese (ob) gene which is mainly expressed in white adipose tissue. The first natural compound named "hormone" was the peptide "secretin". It is secreted by not a traditional endocrine gland, but by the duodenal cells, and it controls the exosecretory function of the pancreas. The trend allows us to declare that, similarly to adipose tissue, heart and hypothalamus, all other human and animal tissues are probably also endocrine organs and able to secret in blood the peptide hormones still to be identified, which being informative polymers are better adapted to transmit the information than other chemical compounds, and hence, they are most efficient for regulatory functions.