ANATOMY

Detailed explanation-1: -Target cell: this cell has a receptor that can bind the ligand. The ligand binds to the receptor and triggers a signaling cascade inside the cell, leading to a response. Nontarget cell: this cell does not have a receptor for the ligand (though it may have other kinds of receptors).

Detailed explanation-2: -A target cell responds to a hormone because it bears receptors for the hormone. In other words, a particular cell is a target cell for a hormone if it contains functional receptors for that hormone, and cells which do not have such a receptor cannot be influenced directly by that hormone.

Detailed explanation-3: -Signaling molecules interact with a target cell as a ligand to cell surface receptors, and/or by entering into the cell through its membrane or endocytosis for intracrine signaling. This generally results in the activation of second messengers, leading to various physiological effects.

Detailed explanation-4: -In many cases, these receptors are expressed on the target cell surface, but some receptors are intracellular proteins located in the cytosol or the nucleus. These intracellular receptors respond to small hydrophobic signaling molecules that are able to diffuse across the plasma membrane.

Detailed explanation-5: -What determines how a cell responds to such a hormone? A cell is able to respond to a hormone only if it has a receptor protein on the cell surface or inside the cell that can bind to the hormone.