the endocrine system is a source of hormones
endocrine_gland is gland. endocrine_signal is hormone. endocrine_system is body_part. thyroid_gland is endocrine_gland. pituitary is endocrine_gland. thyroid is endocrine_gland. endocrine_gland_tissue is tissue. endocrine_system is system. endocrine_system is organ_system.