ABSTRACT
This chapter examines the relevance of basic cellular mechanisms to the patient and the scientist. It aims to distinguish the difference between extra- and intracellular receptors with examples. Knowledge of cellular mechanisms contributes to an understanding of the cellular events underlying hormone action, for example, the study of iodide uptake into the thyroid cell and the mechanisms resulting in thyroglobulin production and release. The binding reaction initiates a cascade of reactions, usually starting with a conformational change in the receptor, resulting in intermediate physical and chemical cellular changes ending in the cellular response to the binding reaction. Receptors may be: extracellular and intracellular. Extracellular receptors are situated on the cell membrane. Intracellular receptors bind to hormones after they have penetrated the cell membrane, for example, the lipophilic steroid hormones such as estradiol, progesterone, testosterone, thyroid hormone and vitamin D.
