  Peristalsis enables transport of the food bolus in the gut. Here, I show by
dynamic ex-vivo intra-cellular calcium imaging on living embryonic gut
transverse sections that the most primitive form of peristalsis that occurs in
the embryo is the result of inter-cellular, gap-junction dependent calcium
waves that propagate in the circular smooth muscle layer. I show that the
embryonic gut is an intrinsically mechanosensitive organ, as the slightest
externally applied mechanical stimulus triggers contractile waves. This dynamic
response is an embryonic precursor of the "law of the intestine (peristaltic
reflex). I show how characteristic features of early peristalsis such as
counter-propagating wave annihilation, mechanosensitivity and nucleation after
wounding all result from known properties of calcium waves. I finally
demonstrate that inter-cellular mechanical tension does not play a role in the
propagation mechanism of gut contractile waves, unlike what has been recently
shown for the embryonic heartbeat. Calcium waves are an ubiquitous dynamic
signaling mechanism in biology: here I show that they are the foundation of
digestive movements in the developing embryo.
