Some signalling chemicals act locally, while hormones can be produced in one body region and affect distant target tissues, linking signal detection to a specific target-cell response.
Coverage 2017–2017 · Updated 15 Jul 2026
A localized signal acts near its source, whereas an endocrine signal travels through circulation to distant target cells.
Paracrine and synaptic signals reach nearby cells with short delays and limited dilution. Endocrine hormones can reach the whole body but only cells with the correct receptor respond.
Locate the signal’s range:
A neurotransmitter acts across a tiny synaptic gap, while thyroxine circulates and affects distant tissues with thyroid-hormone receptors.
Circulation makes a signal widespread, not automatically effective in every tissue.
This objective is assessed through structured response, commonly using State.
State
Build the answer around this relationship: Local signals act near their release site.
Representative question
Leptin is a hormone. Hormones are chemicals produced in one part of the body that have an effect in another part of the body. State the target that leptin normally acts on.
A ligand only affects target cells with the matching receptor. Quorum sensing uses autoinducers and thresholds for group behaviour. Animal signals differ by source, distance, speed, target-cell response, and chemical class. Hydrophilic ligands use transmembrane receptors and relays; steroid and thyroid hormones use intracellular receptors that affect transcription. Named pathways then show the logic: acetylcholine opens sodium channels, GPCRs switch G proteins through GDP-GTP exchange, epinephrine uses cAMP and kinase cascades, insulin RTKs use dimerisation/autophosphorylation to move GLUT4 and promote glycogenesis, steroid hormones change gene expression, and feedback either amplifies or restores stability.
