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Chapter 4 (page 17)
Chapter 4
The Submucous Coat
The submucous coat is a layer of strong but loose areolar tissue with some elastic fibres,
lying between the muscularis mucosae and the muscularis externa; it is rich in mast cells,
macrophages, lymphocytes, eosinophilic leucocytes and plasma cells. It forms a bed in
which the vessels and nerves break up before entering the mucous membrane;
consequently it contains arteries, veins, lymphatics and Meissner's nerve plexuses. The
plexuses form part of the autonomic nervous system and contain postganglionic
sympathetic fibres as well as pre- and postglanglionic parasympathetic fibres. The nerve
cells are all parasympathetic.
In the stomach the submucous layer does not contain any glands. It is wider than that of
the duodenum and extends into the rugae of the stomach, forming the core of each
"mucosal" fold. A gastric mucosal fold, in other words, consists of a central core of
submucous tissue (constituting the major part of the fold), with a layer of mucosa on each
surface.
During injection of the submucous lymphatic plexus of the pyloric region, Jamieson and
Dobson (1907) found that fluid ran most readily in an orad direction; however, it also
filled a plexus on the orad side of the pyloric ring, and spread into the duodenal plexus.
This was ascribed to well-marked continuity of the gastric and duodenal submucous
lymphatic plexuses. The findings differ from those of Horton (l928, l931) who
investigated the spread of India ink injected into the submucous layer of the pyloric part
of the stomach. While it spread out in all directions from the needle point, it was halted
at the pyloric ring, none passing into the submucosa of the duodenum. To Horton (l928,
l931) this indicated a complete block between the submucous coat of the stomach and
that of the duodenum.
Williams (l962) examined aspects of the mucosa and submucosa of the pyloro-duodenal
junction in 48 fresh post-operative partial gastrectomy specimens. The gastric
submucosa contained loosely knit connective tissue and was found to be considerably
wider than that of the duodenum. The muscularis mucosae on the gastric side was clearly
visible as a thin, continuous band closely applied to the mucosa, thickening as it
approached the pylorus. At the pyloric ring it split up, sending fibres into the mucosa,
and finally petering out in a washer-like band of fibrous tissue applied to the muscular
ring; in this way the mucosa was firmly bound to the muscle. Injection of India ink into
the submucosal layer of the stomach showed that its flow was halted abruptly at the
pylorus, none passing into the submucosa of the duodenum; the band of fibrous tissue
was the point at which the flow stopped. This point was situated either at the apex of the
pyloric muscular ring, or on the duodenal or gastric aspect of the ring. According to
Williams (l962) these findings as well as those of Horton (l928, l931) confirmed the fact
that the gastric mucosa was firmly bound to the muscle at the "sphincter", and that there
was no direct communication between the submucosal compartments of the stomach and
the duodenum. (Comment: the sphincter was equated with the pyloric ring).
The submucous coat of the duodenum is appreciably narrower than that of the stomach;
it also differs from the gastric submucosa in that it contains glands, viz. the duodenal
glands of Brunner. (Comment: As a possible link between Brunner's glands and
transpyloric extension of gastric carcinoma cannot be excluded, as described in Chapter
33, they will be discussed in some detail). Vasoactive intestinal peptide (VIP), substance
P and met-enkephalin immunoreactive neuronal elements are present in the duodenal
submucosa (vide infra).
Brunner's glands are small acino-tubular glands in the submucosa of the duodenum.
Their deep, secretory portions consist of branched and coiled tubules which extend to the
circular muscularis externa. Their ducts pierce the muscularis mucosae to open on the
luminal surface of the mucosa, in the depths of the crypts between the intestinal glands.
Brunner's glands are composed of tall cuboidal cells with dark basal nuclei and a clear
cytoplasm, their glandular portions extending into the ducts.
In the majority of subjects they commence at the pyloro-duodenal junction and are most
numerous in the first part of the duodenum, gradually decreasing in number toward the
third and fourth parts. Occasionally they extend into the upper part of the jejunum; in
exceptional cases some Brunner's glands may be present in the pyloric sphincteric
cylinder. Horton (l928) examined 84 anatomical specimens and found that they
commenced abruptly at the distal portion of the pyloric "sphincter" in all subjects except
one; in this single instance they extended for a distance of 8.0 mm across the "sphincter"
into the stomach.
Landboe-Christensen (l944) examined the proximal delimitation of the Brunner gland
area in 53 anatomical specimens of various age groups. It was found that the border
might lie: (1) on the duodenal steep, i.e. the almost perpendicular duodenal side of the
pyloric ring, (2) at the top of the ring itself and (3) on the sloping gastric side of the ring.
The border between Brunner's glands and pyloric mucosa might run in a regular circle,
might be wavy or dentate, or might present one or more tongues or linear extensions.
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