MEDICAL PHYSIOLOGY

Detailed explanation-1: -These intracellular receptors respond to small hydrophobic signaling molecules that are able to diffuse across the plasma membrane. The steroid hormones are the classic examples of this group of signaling molecules, which also includes thyroid hormone, vitamin D3, and retinoic acid (Figure 13.2).

Detailed explanation-2: -Second messengers are small, non-protein molecules that are used to transmit a signal within a cell. Some examples of second messengers are calcium ions (Ca2+), cyclic AMP (cAMP), diacylglycerol (DAG), and inositol triphosphate (IP3).

Detailed explanation-3: -Intracellular signaling from receptor tyrosine kinases (RTK) on extracellular stimulation is fundamental to all cellular processes. The protein–protein interactions which form the basis of this signaling are mediated through a limited number of polypeptide domains.

Detailed explanation-4: -Signaling molecules are often called ligands, a general term for molecules that bind specifically to other molecules (such as receptors). The message carried by a ligand is often relayed through a chain of chemical messengers inside the cell.