Page 577 - Textbook of Pathology, 6th Edition

2. The muscularis propria is composed of 2 layers of smooth The blood supply of the whole of small intestine, except 561
muscle tissue—outer thinner longitudinal and inner thicker the first part of the duodenum, is by the superior mesenteric
circular layer. These muscles are functionally important for artery which supplies blood by mesenteric arterial arcades
peristalsis. Between the two layers of muscle lie ganglionated and the straight arteries.
plexus, myenteric plexus of Auerbach. The main functions of the small intestine are digestion
and absorption so that ultimately nutrients passing into the
3. The submucosa is composed of loose fibrous tissue with
blood vessels and lacteals in it. It contains a gangliated bloodstream are utilised by the cells in metabolism. The
plexus, Meissner’s plexus, having fewer and smaller cells mucosal layer of the small intestine has remarkable capacity
than the Auerbach’s plexus. for regeneration and new lining is laid every 3-4 days.
4. The mucosa consists of glandular epithelium overlying CONGENITAL ANOMALIES
the lamina propria composed of loose connective tissue and
contains phagocytic cells and abundance of lymphoid cells Intestinal Atresia and Stenosis
(Peyer’s patches in the ileum) and plasma cells. It is Intestinal atresia is congenital absence of lumen, most
supported externally by thin layer of smooth muscle fibres, commonly affecting the ileum or duodenum. The proximal
muscularis mucosae. The mucous membrane is thrown into segment has a blind end which is separated from distal
folds or plicae which are more in the jejunum and less in the segment freely, or the two segments are joined by a fibrous
ileum, thus increasing the absorptive surface enormously. cord. The condition must be recognised early and treated
The absorptive surface is further increased by the intestinal surgically, as otherwise it is incompatible with life.
villi. Villi are finger-like or leaf-like projections which contain
3 types of cells: Intestinal stenosis is congenital narrowing of the lumen
i) Simple columnar cells. They perform absorptive function affecting a segment of the small intestine. Intestinal segment
due to the presence of brush border consisting of large above the level of obstruction is dilated and that below it is
number of microvilli. collapsed.
ii) Goblet cells. These are mucus-secreting cells and are
interspersed between the columnar cells. Meckel’s Diverticulum CHAPTER 20
iii) Endocrine cells. These are scattered in the villi as well as Meckel’s diverticulum is the most common congenital
are widely distributed throughout the gastrointestinal tract. anomaly of the gastrointestinal tract, occurring in 2% of
These cells have various synonyms as under: population. It is more common in males. The anomaly is
Kulchitsky cells, after the name of its discoverer. commonly situated on the antimesenteric border of the ileum,
Enterochromaffin cells, due to their resemblance to about 1 meter above the ileocaecal valve. Like other true
chromaffin cells of the adrenal medulla. diverticula, Meckel’s diverticulum is an outpouching
Argentaffin cells, as the intracytoplasmic granules stain containing all the layers of the intestinal wall in their normal
positively with silver salts by reduction reaction (argyrophil orientation (Fig. 20.20). It is almost always lined by small
cells, on the other hand, require the addition of exogenous intestinal type of epithelium; rarely it may contain islands of
reducing substance for staining). gastric mucosa and ectopic pancreatic tissue. Embryologic
Endocrine cells, as these specialised cells are considered origin of Meckel’s diverticulum is from incomplete The Gastrointestinal Tract
to be part of APUD cell system (having common properties obliteration of vitellointestinal duct. (Other anomalies
as Amine content, amine Precursor Uptake and Decarboxy- resulting from the remnants of vitellointestinal duct are
lation). APUD cells are considered to be endodermal in origin, vitelline sinus and vitelline cyst).
while previously they were thought to be neural crest The common complications of Meckel’s diverticulum are
derivative. Other endocrine cells belonging to the APUD cell perforation, haemorrhage and diverticulitis.
system are C-cells of the thyroid, chromaffin cells of the In addition to congenital Meckel’s diverticulum, acquired
adrenal medulla, certain cells of the carotid body, bronchi, diverticula also occur in the small intestine. These are
hypothalamus, pituitary and sympathetic ganglia. commonly multiple (diverticulosis), frequently located on the
Endocrine cells are heavily populated in the proximal mesenteric border, and are sometimes associated with
small bowel as this is the most active site for absorption and malabsorption.
secretory activities. They are sparse in the colon which is
less active site for such functions. Intestinal Malrotation
The duodenum contains distinctively branched Brunner’s Malrotation is a developmental abnormality of the midgut
glands present in the submucosa and going up to muscularis (i.e. the portion of intestine between the duodenojejunal
mucosae. The deeper layer of the mucosa of the small flexure and the middle of transverse colon). Due to failure of
intestine elsewhere contains intestinal glands or crypts of normal rotation of midgut, the following consequences can
Lieberkuhn. They are lined by columnar cells, goblet cells, occur:
endocrine cells and Paneth cells. Paneth cells are normally i) Exomphalos i.e. intestinal eventration at the umbilicus.
exclusively found in the small intestine and occasionally in ii) Misplacement of the caecum, appendix and ascending
the caecum. These cells are characterised by the presence of colon.
supranuclear granules rich in lysozyme. iii) Mobile caecum.