The duodenum is a highly specialized part of the small intestine. Identify and explain how the structure of the different tissue types relates to their functions in the duodenum.  

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The duodenum has four layers. The innermost layer, or mucosa, consists of columnar epithelium with microvilli that increase the surface area for digestion. The submucosa contains Brunner's glands that secrete alkaline mucus. Surrounding the submucosa is a layer made of circular and longitudinal muscle tissue that generates peristalsis. The outermost...

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The duodenum has four layers. The innermost layer, or mucosa, consists of columnar epithelium with microvilli that increase the surface area for digestion. The submucosa contains Brunner's glands that secrete alkaline mucus. Surrounding the submucosa is a layer made of circular and longitudinal muscle tissue that generates peristalsis. The outermost layer or serosa consists of simple squamous epithelial cells. Its function is to prevent friction between the duodenum and the adjacent organs.

The partially digested food or chyme enters the duodenum from the stomach. The mucus neutralizes the acid in the chyme, protects the walls of the duodenum, and helps the chyme to achieve an optimal pH for digestion. The peristaltic movement of the duodenum propels the chyme towards the ampulla of Vater, a cavity in the middle of the duodenum. The ampulla receives the common bile duct (from the liver and gallbladder) and the pancreatic ducts. The secretions contain peptidases (that breakdown peptides into amino acids), and lipase (that breaks down neutral fats into fatty acids and glycerol). There are four enzymes, sucrase, maltase, isomaltase, and lactase that split disaccharides into monosaccharides.

The microvilli in the mucosa help to absorb the nutrients, and the peristaltic movements of the duodenum propel the chyme towards the jejunum.

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