GENERAL HISTOLOGY

Detailed explanation-1: -All hormones act only on their target tissues. The ability of a tissue to react to a hormone is due to the presence of a receptor in or at the cell. There are two classes of hormone receptors: those bound to the membrane and those present in the cytosol. Peptide hormones generally act through membrane receptors.

Detailed explanation-2: -When a hormone binds to the receptor, the G-protein is activated by binding guanosine triphosphate, or GTP, in place of GDP. After binding, GTP is hydrolysed by the G-protein into GDP and becomes inactive. The activated G-protein in turn activates a membrane-bound enzyme called adenylyl cyclase.

Detailed explanation-3: -The binding of the hormone triggers an enzyme inside the cell membrane. The enzyme activates another molecule, called the second messenger, which influences processes inside the cell. Most endocrine hormones are non-steroid hormones, including insulin and thyroid hormones.

Detailed explanation-4: -When steroid and thyroid hormones bind with hormone receptors inside the cell, they trigger the gene expression that ultimately leads to protein production.

Detailed explanation-5: -All the cells that have receptor sites for a given hormone make up the target tissue for that hormone. In some cases, the target tissue is localized in a single gland or organ. In other cases, the target tissue is diffuse and scattered throughout the body so that many areas are affected.