AP BIOLOGY

Detailed explanation-1: -Depending on the ligand’s origin (from the same cell, from the neighbour cell or from far distance), recptor-ligand interaction and signaling pathway activation is classified into four different types: autocrine, endocrine, paracrine and juxtacrine.

Detailed explanation-2: -Exocrine signaling occurs when cells secrete signaling molecules into the blood. For example, the ovaries in females and the testes in males are stimulated by hormones produced by the brain.

Detailed explanation-3: -The highly conserved receptors and pathways can be organized into four major families based on similar structures: fibroblast growth factor (FGF) family, Hedgehog family, Wnt family, and TGF- superfamily.