Hormones are molecules that carry messages from one group of cells to another through the blood, stimulating (“waking up”) some body processes and inhibiting (“shutting down”) others. Reproduction, growth, sleep, libido (sex drive), and hunger are a few of the things that are affected by various hormones. Hormones are produced by many organs and body tissues but mainly by the endocrine (hormone) glands, which are the pituitary, the thyroid, the adrenal glands, and the gonads (testes and ovaries). Estrogens and testosterone are two types of sex hormones.