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Chapter 8 (page 32)
It is of interest to note that, when first describing the pyloric sphincteric cylinder in l906,
Cunningham surmized that its powerful musculature was probably under control of a
special innervation.
The sympathetic nerve supply to the stomach is almost entirely derived from the coeliac
plexus. The gastric branches of the coeliac plexus accompany the vessels supplying the
stomach, and the maximum number are found alongside the left gastric, hepatic and
phrenic arteries, while others accompany the splenic, right gastric and gastro-epiploic
vessels.
According to McCrea (l924) these nerves can be grouped as follows:
- Fibres from the coeliac plexus accompany the left inferior phrenic artery, wind
across the anterior aspect of the lower oesophagus, communicate with branches of the
anterior vagus, and are distributed to the cardia and fornix.
- Fibres from the coeliac plexus pass with the left gastric artery and divide into
three groups: (a) Fibres passing with the oesophageal and superior branches of this artery
to the cardia and proximal part of the body of the stomach; these twigs communicate
with branches of the anterior and posterior vagal trunks. (b) Fibres passing with the main
stem of the artery along the lesser curvature to supply the anterior and posterior surfaces
of the body of the stomach and pyloric "antrum". (c) Fibres passing between the layers
of the lesser omentum towards the porta hepatis, communicating with hepatic branches of
the anterior vagal trunk in most instances.
- Fibres passing from the coeliac plexus along the hepatic artery and distributed
with its branches. They reach the pyloric region of the stomach with the right gastric and
right gastroepiploic arteries.
In all major respects Mitchell's (l940) description agrees with that of McCrea, although
he adds some exceptions. According to Mitchell the terminal twigs accompanying the
main branch of the left gastric artery, i.e. group 2b of McCrea, did not reach the pylorus
in any of the 15 specimens examined by him, but united with the nerve filaments lying
alongside the right gastric artery. The right gastric branches, (group 3 of McCrea) supply
the upper parts of the pyloric region.
Preganglionic sympathetic fibres end in the coeliac ganglia; efferent fibres emerging
from the coeliac ganglia to accompany the arteries are postganglionic. Even though they
traverse the enteric ganglia they probably have no functional relationship to the enteric
plexuses; they are distributed with the postganglionic vagal fibres emerging from the
plexuses.
Afferent visceral fibres from the stomach travel the same course in reverse, to ganglion
cells in the posterior spinal nerve roots. They do not synapse in, or arise from,
sympathetic ganglia. Although the sympathetic nerves are motor, they also carry fibres
from sense organs in the viscera.
It seems that the main sympathetic supply to the pyloric region occurs via fibres
accompanying the hepatic artery and its branches.
The peptidergic system refers to a widespread group of cells, derived from
neuroectoderm embryologically and having certain biochemical features in common.
They are also referred to as neuroendocrine cells and belong to the APUD cell line, based
on their capacity to synthesize monoamines through a process of amine precursor
uptake and decarboxylation. During recent years a large number of biologically active
peptides, produced by APUD cells, have been demonstrated in central and peripheral
neurogenic tissues as well as in the walls of the gastrointestinal tract (Chap. 9). Some of
the peptides, notably gastrin and vasoactive intestinal peptide (VIP), were first detected in
the gut and subsequently in the brain; others, such as somatostatin, enkephalin and
neurotensin were first identified in brain tissue and subsequently in the walls of the
alimentary tract. Substance P has long been known to be present in both locations.
Most of the monoamines have several molecular forms or sizes. Some types are released
into the circulation, producing their biological effects in distant target organs; these can
be looked upon as true hormones acting in an endocrine way. Others act locally in the
vicinity of their site of origin in a paracrine way. A third group functions as
neurotransmitters, acting in a neurocrine way. A clearcut separation of endocrine,
paracrine and neurocrine functions is not always feasible. Burnstock (l986) pointed out
that thinking mainly in terms of antagonistic parasympathetic cholinergic and
sympathetic adrenergic control of functions, is no longer tenable. The involvement of a
multiplicity of neurotransmitters and of sophisticated peripheral control mechanisms such
as neuromodulation and co-transmission, has to be recognized. This is accomplished
through non-cholinergic, non-adrenergic nerves of the purigenic system.
APUD cells and regulatory peptides in the pyloric region of the stomach will be
discussed in somewhat greater detail in the next chapter.
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