Chapter 16, Problem 20Q

Summary Introduction

To explain: The reason why a cell sufficient with nutrients commits cell suicide when it does not receive any signal from other cells.

Concept introduction: Cell signaling is of three types. Endocrine signaling is where the cell secretes ligands called hormones that is sent through the blood stream to a target cell that is located far away from the origin cell. In paracrine signaling, the effector molecules do not enter the blood stream like the endocrine signaling, rather these molecules disseminate through the extracellular matrix and remain locally in the neighborhood of cells which secreted them and hence they are also known as local mediators. Autocrine signaling is a form of paracrine signaling where the cell secretes a ligand for itself to initiate a signaling cascade where the ligand is regulated to stay in the local vicinity.