Final answer:
Hydrophobic hormones like estrogen and testosterone are protected from degradation by circulating enzymes due to their binding to carrier proteins, which makes them soluble and extends their action compared to freely circulating hormones.
Step-by-step explanation:
Hormones secreted into the bloodstream are inactivated and removed by being degraded or altered enzymatically. Water-soluble hormones, such as peptide hormones and catecholamines, generally circulate in free form and can be rapidly degraded by enzymes in the liver and kidney.
In contrast, hydrophobic hormones like estrogen and testosterone often have longer-lasting effects because they are bound to carrier proteins, which protect them from immediate degradation. This binding not only makes the hormones soluble in blood but also shields them from circulating enzymes, thus extending their half-life within the bloodstream. Termination of hormone signals is essential to prevent continued response by the target cells and to maintain hormonal balance within the body.
In addition to enzymatic degradation, hormones are also removed from the bloodstream through excretion once they have been broken down or altered to a form that can be eliminated. The regulation of hormone secretion often involves negative feedback mechanisms that help maintain homeostasis by reducing overproduction of hormones. Oral contraceptives leverage this mechanism by providing doses of estrogen and/or progesterone to inhibit the natural hormonal signals for ovulation.