This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General physiology, Subject name: Physiology
All of the following are involved in the transmission of regulatory signals through the ECF, except 
Select and explain. 
A. Synaptic signals through neurotransmitters, B. Endocrine signals through hormones, C. Direct contact through gap junctions, D. G protein coupled receptors
C: Direct contact through gap junctions
Answer: C: Direct contact through gap junctions 
Explanation: When transmitted through gap junctions there is no involvement of ECF. Gap junctions are a specialized intercellular connection between a multitude of animal cell-types. They directly connect the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to directly pass through a regulated gate between cells. Hence there is a direct transpo without the involvement of ECF Ref guyton and hall textbook of medical physiology 12/e p45-46