ENDOCRINE GLANDS Hormone formation may occur either in localized collections of specific cells, in the endocrine glands or in cells that have additional roles Many protein hormones: growth hormone? parathyroid hormone? prolactin? insulin? glucagon 1? Leptin? Formation of small hormone molecules initiates with commonly found Precursors: Such as: adrenals, gonads, or thyroid In the case of the steroid hormones, the precursor is cholesterol which is modified by various hydroxylations, methylations, and demethylation to form the glucocorticoids, androgens, and estrogens In contrast, the precursor of vitamin D, 7-dehydrocholesterol Is produced in ski in keratinocytes, again from cholesterol y a photochemical reaction5 Hormone formation may occur either in localized collections of specific cells, in the endocrine glands, or in cells that have additional roles. Many protein hormones: growth hormone? parathyroid hormone? prolactin? insulin? glucagon? Leptin? Formation of small hormone molecules initiates with commonly found Precursors: Such as: adrenals, gonads, or thyroid. In the case of the steroid hormones, the precursor is cholesterol, which is modified by various hydroxylations, methylations, and demethylations to form the glucocorticoids, androgens, and estrogens. In contrast, the precursor of vitamin D, 7-dehydrocholesterol, is produced in skin keratinocytes, again from cholesterol, by a photochemical reaction. ENDOCRINE GLANDS