renal cortex) and lipid droplets. The signal may act over a long distance, e.g. endocrine signalling
through the release of hormones into the blood stream, or neuronal
lipid droplets synaptic signalling via electrical impulse transmission along axons
Lipid droplets are spherical bodies of various sizes found within many and subsequent release of chemical transmitters of the signal at syn-
cells, but are especially prominent in the adipocytes (fat cells) of apses or neuromuscular junctions. A specialized variation of endocrine
adipose connective tissue. They do not belong to the Golgi-related vacu- signalling (neurocrine or neuroendocrine signalling) occurs when neu-
olar system of the cell. They are not membrane-bound, but are droplets rones or paraneurones (e.g. chromaffin cells of the suprarenal medulla)
of lipid suspended in the cytosol and surrounded by perilipin proteins, secrete a hormone into interstitial fluid and the blood stream.
which regulate lipid storage and lipolysis. See Smith and Ordovás Alternatively, signalling may occur at short range through a paracrine