Page 231 - Veterinary Histology of Domestic Mammals and Birds, 5th Edition

Digestive system (apparatus digestorius) 213

ventral borders of the ventriculus. Lying between the thick roscopic appearance of these components (for more detail
VetBooks.ir muscles are the weaker m. tenuis craniodorsalis and m. see anatomy textbooks).
tenuis caudoventralis. In grain feeders, the ventriculus is
The function of the small intestinal mucosa, supported
by the activity of the muscular layers, is digestion of nutri-
the site of mechanical breakdown of food. Further diges-
tion of protein also occurs in this portion of the stomach. ents and absorption of the resulting breakdown products.
The cuticle terminates at the ostium pyloricum. The For the most part, the digestive processes that com-
mucosa of the pylorus contains pyloric glands (glandulae mence in the proximal portion of the gastrointestinal tract
pyloricae) and numerous endocrine cells responsible for are completed by reactions occurring in the small intestine.
local hormone production (e.g. gastrin cells, somatostatin Further digestion takes place in the large intestine (within
cells). fermentation chambers in the pig and horse). Ruminants
The histological features of the wall of the avian glan- represent a special case, due to the role played in digestion
dular and muscular stomachs are listed in Table 10.4. by the forestomach.
Breakdown of nutrients is completed by the combined
Small intestine (intestinum tenue) action of gastric juice (pepsin) and secretions of the intestinal
The small intestine comprises three structurally and func- glands (including 1,6-glucosidase, aminopeptidase, dipepti-
tionally distinct segments, the duodenum, the jejunum and dases and phosphodiesterases) and the pancreas (including
the ileum. Considerable species variation exists in the mac- lipase, α-amylase, trypsin, chymotrypsin, carboxypeptidase,

Table 10.5 Comparative structure of the intestinal wall in domestic mammals.
Segment Epithelium Glands Muscle Special features
Small intestine (villi present throughout in domestic mammals)
Duodenum Simple columnar Tubular, branched or Lamina muscularis mucosae Isolated lymphatic
with brush unbranched glands present – sends smooth nodules (GALT),
border, isolated (crypts of Lieberkühn), muscle cells into intestinal submucosal glands
goblet cells extend into the lamina villi, inner circular and (mucous in dog and
propria, tubulo-alveolar outer longitudinal tunica ruminant, may be
glands (Brunner’s glands) muscularis with plexus mixed in the pig and
in submucosa, endocrine nervorum myentericus horse).
cells
Jejunum Similar to Similar to duodenum Similar to duodenum Increasing numbers of
duodenum, but no glands in lymphatic follicles
microvilli longer submucosa
and finer
Ileum Similar to Similar to jejunum Similar to duodenum Well-developed GALT,
jejunum Peyer’s patches (all
domestic mammals,
particularly horse and
calf)
Large intestine (villi absent in all domestic mammals)
Caecum Simple columnar Numerous goblet Lamina muscularis GALT near ileocaecal
with low brush cells, simple tubular mucosae present, inner orifice in the dog, pig
border intestinal glands circular and outer and ruminant, more
longitudinal smooth developed in the colon
muscle layers in the cat and horse;
taeniae (musculoelastic
bands) and haustra in
pig and horse
Colon Simple columnar Marked increase in Similar to caecum Taenia (musculoelastic
with low brush goblet cells, simple bands) and haustra in
border tubular intestinal pig and horse
glands
Rectum Similar to colon Similar to colon Muscle more prominent
than in caecum and colon

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