Secreted by different endocrine glands, hormones are various in their chemical structure. Whereas, all hormones can be grouped into 3 basic chemical categories:
- Catecholamines contain epinephrine and norepinephrine;
- Polypeptides and glycoproteins contain shorter chain polypeptides, just like antidiuretic hormone and insulin; and thyroid-stimulating hormone is the large glycoprotein.
- Lipophilic hormones (those that are lipid) contain steroids, for example, cortisol and estrogens, and the peptide hormone thyroxine.
Derived from cholesterol, steroid hormones are lipids and thus are not water soluble. Sex steroids are secreted by the gonads, which contain testes and ovaries; corticosteroids which contain cortisol and aldosterone among others are secreted by the adrenal cortex.
Two derivatives of the amino acid tyrosine bonded together form the major thyroid hormones, which are the only hormones that contain iodine. The hormone is named tetraiodothyronine (T4), or thyroxine when it includes 4 iodine atoms. It is named triiodothyronine (T3) when it includes 3 atoms of iodine. These hormones are similar to steroids in that they are relatively small and nonpolar molecules even though they are peptides and not steroids. When taken orally as a pill, steroid and thyroid hormones are active for their chemical similarities. Sex steroids are administered as contraceptive pills. People who are hypothyroid take thyroid hormone pills. Before being absorbed into the blood, for the reason that other types of hormones wound be digested into inactive fragments, so they cannot be taken orally.
- March 24, 2011 @ 07:56:48 [Current Revision] by Ji Guanghua
- March 24, 2011 @ 07:56:45 by Ji Guanghua