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== Basic Anatomy and Physiology ==

== Basic Anatomy and Physiology ==

=== Introduction ===

Introduction  

The intestines are a portion of the alimentary tract extending from the pylorus to the anus.  In mammals, the intestines are divided into two main segments:  the small intestine and the large intestine.  The small intestine, consisting of the duodenum, jejunum and ileum, acts as the main site of absorption for digestive products in the gastrointestinal tract. The large intestine, consisting of the caecum and colon, functions to extract water, electrolytes and nutrients as well as to concentrate and propulse faecal material to the rectum for defaecation.  

The intestines are a portion of the alimentary tract extending from the pylorus to the anus.  In mammals, the intestines are divided into two main segments:  the small intestine and the large intestine.  The small intestine, consisting of the duodenum, jejunum and ileum, acts as the main site of absorption for digestive products in the gastrointestinal tract. The large intestine, consisting of the caecum and colon, functions to extract water, electrolytes and nutrients as well as to concentrate and propulse faecal material to the rectum for defaecation.  

Functional differences between the small and large intestine are reflected in their anatomic and histologic organisation (Figure 1).  The small intestinal mucosa in many species is highly folded and made up of numerous villi that greatly increase the absorptive surface area.  Enterocytes, the main absorptive cells, are the most numerous and characteristic cells of the small intestinal epithelium. Others include goblet cells, paneth cells, neuroendocrine cells, stem cells, and intraepithelial lymphocytes. Another important feature of the small intestine is the presence of Peyer's patches within the lamina propria.  They contribute to immune function and generation of immune responses within the mucosa.   

Functional differences between the small and large intestine are reflected in their anatomic and histologic organisation (Figure 1).  The small intestinal mucosa in many species is highly folded and made up of numerous villi that greatly increase the absorptive surface area.  Enterocytes, the main absorptive cells, are the most numerous and characteristic cells of the small intestinal epithelium. Others include goblet cells, paneth cells, neuroendocrine cells, stem cells, and intraepithelial lymphocytes. Another important feature of the small intestine is the presence of Peyer's patches within the lamina propria.  They contribute to immune function and generation of immune responses within the mucosa.