Bayliss and Starling state that the swaying pendulum movements are
essentially due to peristaltic waves recurring in the same place and
running rapidly downward. This form of the movements I have seen only
once. At this time about 90 c.c. of soapy water had been injected.
This procedure has the effect of exaggerating in every particular the
movements of the small intestine. In this instance a broad constriction
appeared about the middle of a long string of food and persisted there
while it spread down the gut. As the contraction spread, the gut swayed
slowly to and fro before it. Then there was a relaxation, followed by
a recurrence of the constriction in the same place, a spreading of the
contraction, and a swinging of the loop just as before. This phenomenon
was repeated again and again, till finally the string was divided and
the forward piece pushed through a tortuous course to the colon.
_The course of the food in the small intestine._--Chyme is not forced
from the stomach by every wave that passes over the antrum, but only
at intervals. When the pylorus relaxes, the food, moved towards the
pylorus under considerable pressure, is squirted along the duodenum
for two centimetres or more. Careful watching of this food shows that
usually it lies for some time in the curve of the duodenum until
additions have been made to it from the stomach, and a long, thin
string of food is formed. While it is resting in this place it is
exposed to the outpouring of the bile and pancreatic juices. All at
once the string becomes segmented (see Fig. 5) and the process of
rhythmic segmentation continues several minutes, thoroughly mixing
the intestinal digestive juices with the chyme. In this region the
alternate positions of the segments are sometimes far apart, and the
to-and-fro movements of the particles may be a relatively extensive
and very energetic swinging. Finally the little segments unite into
a single mass, or form in groups, and begin to move forward. The
peristalsis here, as already mentioned, is much more rapid than the
normal peristalsis elsewhere in the small intestine. The masses, once
started, go flying along, turning curves, whisking hither and thither
in the loops, moving swiftly and continuously forward. After passing on
in this rapid manner for some distance the food is collected in thicker
and longer strings, resembling the strings seen characteristically in
the other loops. Towards the end of digestion the small masses shot
out from the stomach, after a few segmentations, may move on in the
rapid course without being accumulated in a larger mass until the swift
movement ceases.
Public-domain text, read in full here on John Shaqi.
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