Mechanism of Hormones Secretion and Action

Endocrine system has vital roles and is influenced by complex factors and signaling to achieve accurate rhythm and patterns of hormone secretion and effects. The endocrine system effect is slow to start but it can take long-term actions. Endocrine system is an integrated communicative tool for the human body, performing various functions through its hormones as chemical messengers. The pituitary gland is the master regulator of the endocrine system, which coordinates and controls the function of other glands in the body through secretion and signals of stimulating/inhibiting hormones. The signal transduction mechanism of the hormones is mediated by binding with cell surface receptors and stimulating multifactorial downstream targets including second messengers involving cyclic adenine monophosphate (cAMP), calcium ions, and 3-cyclic guanosine monophosphate (cGMP), to induce cellular response and physiological functions. Hormones govern receptor regulation and number, regulate ion transport and membrane permeability, regulate substances and minerals in the blood and cells. Due to their highly restricted functions, the elasticity and plasticity of human endocrine system suggest a powerful history of adaptation to changing environments. The main axis such as hypothalamus-pituitary-adrenal under stress, hypothalamus-pituitary-gonadal and -pineal axis play key roles over important periods. The circadian clock acts carefully to regulate each level of the pituitary-hypothalamus axis ensuring proper compatibility of physiological functions during daylight, either under normal or abnormal conditions. Additionally, the endocrine system plays a key role in maintenance, regeneration, and remodeling the tissues by governing stem/progenitor cells, sexual and mental maturation. It is also overcoming some limitation of stem cell’s treatment. This chapter details the hormone secretion mediated cellular events and wide spectrum of its functions.