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Structure of the musculature of the chicken small intestine
Abstract:
The small intestine of the chicken was studied by light and electron microscopy. The musculature, measuring about 180 microns in thickness in the distended intestine, consists of four layers (outer longitudinal, outer circular, inner circular and inner longitudinal) which are directly apposed to one another. There is no layer of connective tissue equivalent to the submucosa of mammalian intestine, and the intestinal glands lie close to the inner longitudinal muscle. Mucosal folds are not formed during isotonic contraction of the intestine. The muscle cells of the chicken small intestine are characterized by large, numerous and sharply outlined dense bodies, by the presence of an extremely thin basal lamina, by prominent dense bands at the cell surface but relatively few intermediate junctions. There are many areas of direct apposition between cell membranes of adjacent cells and little collagen between the muscle cells. The four muscle layers have each distinctive structural features. Gap junctions between muscle cells occur only in the outer circular layer. The outer circular and outer longitudinal layers are closely apposed and numerous junctions of the adherens type link cells of the two layers. Intramuscular blood capillaries are rare and are found virtually only in the outer circular layer; their endothelial cells are joined by tight junctions. In the outer circular layer (but not in the other layers) there are two further cell types, fibroblasts and interstitial cells, which can be clearly distinguished from one another. The latter cells are intimately related to nerve bundles and are connected by gap junctions to some muscle cells.
Insights
The chicken small intestine lacks a submucosa and features four directly apposed muscle layers. Unique muscle cell structures and specialized junctions were observed in different layers, impacting intestinal function.
Area of Science:
- Comparative anatomy
- Gastrointestinal histology
- Avian biology
Background:
- The structural organization of the avian small intestine differs significantly from mammalian counterparts.
- Understanding the unique histological features of the chicken small intestine is crucial for avian health and nutrition research.
Purpose of the Study:
- To elucidate the detailed ultrastructure of the chicken small intestine's musculature.
- To identify and characterize distinct cellular components and their arrangements within the intestinal wall.
Main Methods:
- Light microscopy was employed to examine overall tissue architecture.
- Electron microscopy provided high-resolution ultrastructural details of muscle cells and associated structures.
Main Results:
- The chicken small intestine possesses four directly apposed muscle layers without a submucosa.
- Muscle cells exhibit large dense bodies, thin basal laminae, and prominent surface dense bands.
- Gap junctions were exclusively found in the outer circular layer; adherens junctions linked outer layers.
- Intramuscular capillaries were rare, primarily in the outer circular layer, with endothelial tight junctions.
- Fibroblasts and interstitial cells, associated with nerve bundles, were identified in the outer circular layer.
Conclusions:
- The chicken small intestine's muscularis externa exhibits a unique structural arrangement compared to mammals.
- Specialized cellular junctions and structures within the muscle layers likely influence intestinal motility and function.
- The presence of interstitial cells associated with nerves suggests a role in neuromuscular regulation within the avian gut.