ANATOMICAL AND HISTOCHEMICAL STUDIES OF THE DIGESTIVE SYSTEM OF THE AFRICAN GIANT RAT
ANATOMICAL AND HISTOCHEMICAL STUDIES OF THE DIGESTIVE SYSTEM OF THE AFRICAN GIANT RAT
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Date
2010-12
Authors
OLIVER, NZALAK JAMES
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Abstract
ABSTRACT.
Forty African giant rats (AGRs), (Cricetomys gambianus) were used for morphometric,
morphologic, histologic and histochemical studies. The various segments of the gastrointestinal
tract (GIT) were weighted, measured and photographs taken. Transverse sections of different
segments of the GIT were stained with Haematoxylin and Eosin for normal histological studies.
For histochemical studies, transverse sections were stained with Alcian Blue, Periodic Acid
Schiff and Alcian Blue-Periodic Acid Schiff to determine their nature of secretions. The large
intestine was found to have the highest mean weight (19.98 ± 0.39 g) followed by the stomach
(19.47 ± 0.26 g) and then the small intestine (17.19 ± 0.30 g), respectively. Of all the digestive
glands, the liver was found to have the highest weight (21.29 ± 0.43 g). The small intestine was
observed to be the longest (109.17 ± 28.68 cm) followed by the large intestine (75.57 ± 1.78
cm).Out of all the intestinal segments (small and large), the jejunum was observed to be the
longest (72.26 ± 2.39 cm) followed by the colon (57.30 ± 1.58 cm).Grossly, the AGR had two
upper and two lower incisor teeth and three upper and three lower molar teeth. The parotid and
mandibular salivary glands were found to be non-lobulated and lobulated, respectively. The
esophagus was found to lie dorsal to the trachea throughout its length. The stomach was made
up of glandular and non-glandular parts with a constriction separating the two parts. Esophageal
epithelium was non-keratinized and devoid of lamina muscularis and glands. The stomach was
observed to be divided into two parts (non-glandular and glandular) with an isthmus separating
them. The non-glandular part had papillae which were covered with stratified squamous
epithelium and resembled the rumen of ruminants. The isthmus was made up of keratinized
stratified squamous epithelium with no glands. The glandular stomach had mucous secreting
epithelium with gastric pits and glands at the mucosa. The small intestine was made up of the
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duodenum, jejunum and ileum. The duodenum had villi that were covered by simple columnar
epithelial cells. The duodenal (Brunner’s) glands were seen on the upper part of the submucosa.
The jejunum had intestinal glands (crypts of Lieberkuhn), while the ileum had villi, aggregate
of lymphatic nodules (Payer’s patches) and intestinal glands (crypts of Lieberkuhn).The large
intestine was observed to be made up of the caecum, colon and rectum. They all had similar
basic structures and none had villi. The mucosal surfaces were smooth with goblet cells.
Histochemical studies of the GIT showed a positive response to AB, PAS, and AB-PAS with
the exception of the esophagus that was negative to all the reactions. The jejunum and ileum
were AB positive and PAS negative. The parotid salivary glands consisted entirely of serous
acini as they were PAS positive while the mandibular salivary glands consisted of both serous
and mucous acini as they were AB and PAS positive. The gall bladder had the shape of a
balloon and was found on the visceral surface of the liver. The liver was observed to be divided
into four lobes. The gross and histological features of the stomach of the AGR which resembled
the abomasum and rumen of ruminants may be responsible for its feeding habit
(omnivorous).The thickening of the tunica muscularis of the colon and rectum has been
correlated with the temporary storage and expulsion of fecal materials. Although the esophagus
had no mucous secreting glands, the mucous produced by the salivary glands and the enzymes
of surface origin may protect the mucosal surface and also provides digestive functions for the
esophagus. The production of acidic and neutral mucins in the stomach and duodenum is to
maintain the p.H of the chyme. The presence of large number of mucous secreting cells
provides a mucous layer around the fecal pellets facilitating its release and protecting the
epithelium.
Description
DEPARTMENT OF VETERINARY ANATOMY
FACULTY OF VETERINARY MEDICINE,
AHMADU BELLO UNIVERSITY,ZARIA.
Keywords
ANATOMICAL,, HISTOCHEMICAL,, STUDIES,, DIGESTIVE,, SYSTEM,, AFRICAN., GIANT RAT,, Cricetomys,, gambianus,, Waterhouse.