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Mayazoey
Joined 31 July 2007
→Basic Anatomy and Physiology
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. (Dyce et. al, 2002; Young & Heath, 2000).
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. (Dyce et. al, 2002; Young & Heath, 2000).
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. Other cells 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 are important in 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.
In contrast to the small intestine, the large intestinal mucosa has no villi and consists of 2 main cell types: absorptive cells and mucus secreting goblet cells. A distinguishing histologic and anatomic characteristic is the thick muscularis mucosa layer that aids in propulsion of faeces to the rectum. Another important feature of the large intestine is the presence of commensal bacteria which plays different digestive roles depending upon the type of animal.
In contrast to the small intestine, the large intestinal mucosa has no villi and consists of 2 main cell types: absorptive cells and mucus secreting goblet cells. A distinguishing histologic and anatomic characteristic is the thick muscularis mucosa layer that aids in propulsion of faeces to the rectum. Another important feature is the presence of commensal bacteria which plays different roles depending upon the type of animal.
=== Defense Mechanisms ===
=== Defense Mechanisms ===
*Epithelial cells have a very high turnover rate thus preventing pathogens with a longer life cycle from successfully colonising.
*Epithelial cells have a very high turnover rate thus preventing pathogens with a longer life cycle from successfully colonising.
==== Commensal flora ====
==== Commensal flora ====
*Commensal flora competitively inhibit attachment of pathogens to enterocytes in addition to competing for nutrition and substrates. Many also produce inhibitory growth substances that are toxic to other bacteria (McGavin and Zachary, 2007.
*Commensal flora competitively inhibit attachment of pathogens to enterocytes in addition to competing for nutrition and substrates. Many also produce inhibitory growth substances that are toxic to other bacteria (McGavin and Zachary, 2007).
==== Movement ====
==== Movement ====
*Continuous peristalsis discourages persistence of toxins and aids in their elimination from the gut.
*Continuous peristalsis discourages persistence of toxins and aids in their elimination from the gut.
*The lamina propria contains macrophages, B and T lymphocytes, plasma cells, and mast cells.
*The lamina propria contains macrophages, B and T lymphocytes, plasma cells, and mast cells.
*Lymphoid aggregates known as Peyer's patches within the small intestine aid in immunity.
*Lymphoid aggregates known as Peyer's patches within the small intestine aid in immunity.
*Secretory IgA and IgM are important and help prevent attachment of pathogens to the intestinal epithelium.
*Secretory IgA and IgM provide humoural immunity and help prevent attachment of pathogens to the intestinal epithelium.
*Lysozyme from Paneth cells inhibits bacterial growth (McGavin & Zachary, 2007).
=== Comparative ===
=== Comparative ===
carnivores, ruminants,horse, swine, rabbits [pictures]
carnivores, ruminants,horse, swine, rabbits [pictures]