They also play an important part in the normal development of the growing fetus. In the womb or egg, hormones guide the development of sexual characteristics, the immune and nervous systems, the brain, behavioural characteristics and growth. Thyroid hormones, for instance, are essential for brain development. Testosterone, progesterone and estrogen are essential for reproductive organ development and functioning. Insulin regulates blood sugar in the body.
Natural hormones are extremely potent and operate at minute concentrations in the body.
For example, estradiol, the body's key estrogen hormone, operates at concentrations in the parts per trillion range. Hormones Activate Genes Hormones do not alter or damage genes. Rather, they cause the gene to act in a specific way, telling it when to reproduce or activate. It is much like a transmitter sending signals to a cellular phone or radio. If the hormone system works properly, then the right message is sent and is received by genes within the cell.