Fig. 2: Illustration of the small intestine with organization of circular and longitudinal muscles, and the enteric nervous system, and schematic representation of the intestine showing fluid filling and muscle contractions for droplet discharge.
From: Advancing peristalsis deciphering in mouse small intestine by multi-parameter tracking
a The illustration shows the entry of artery, veins and nerves from the mesentery through the serosa and the distribution of the myenteric plexus between the longitudinal and circular layers of smooth muscle. The orientation of the myenteric plexus is such that the ganglia (collection of nerve cell bodies) are stretched circumferentially and inter-ganglionic fibers run longitudinally, parallel to the longitudinal muscle fibers to allow transmission of signals and coordination of muscle contractions without exerting excessive traction or tension on the nerve fibers. Meissner’s plexus or submucosal plexus is a network of nerve fibers and ganglia located in the loose connective tissue of the submucosal layer of the GI tract. Receptive nerve endings from Meissner’s plexus projects into the mucosa as intrinsic primary afferent neurons and transmit the signals to submucosal neurons or Myenteric plexus. b Figure showing longitudinal muscle contraction with gathering of circular muscle rings (muscle fibers) toward the distal end that results in contraction with narrowing of the lumen at the aboral end, favouring fluid-filling. Fluid filling leads to ballooning proximal to the contracted region (bold arrows). Intestinal flow is reduced during the filling stage (thin arrow). Arrows within the lumen depicts more retrograde movement. c Figure showing longitudinal muscle contraction (parallel lines) with gathering of circular muscle rings (muscle fibers) and narrowing of the lumen at the proximal end that favors droplet discharge (bold arrows). Arrows within the lumen suggest more anterograde movement. a was created using Sketchbook® App in iPad (7th generation) and imported to Adobe Illustrator version 27.1 (2023) for final adjustments and labeling, while (b, c) were drawn using Adobe Illustrator version 27.1 (2023).
