The endocrine gland which secrets a hormone into the blood. The target tissue containing receptor that binds hormone. Cellular machinery that transducts signal into cellular response. A trophic hormone regulates another endocrine gland. Receptors bind hormones with specificity, affinity and saturation.
Receptors are subject to up and down regulation.
See Table 7-5 in Vander. The process of gylcogen breakdown, which utilizes this second messenger path, is used as illustration of select transduction steps. Epinephrine is produced by the adrenal glands that lie just above the kidney. The receptor undergoes a conformational change causing it to bind all G-proteins moving by within the membrane. Gylcogen synthetase is also inactivated by cAMP-dependent protein kinase thus blocking any glycogen synthesis.