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Anatomy and Cell Biology
Anatomy and Cell Biology 3319
Peter Merrifield

Anatomy NotesMar 1512 The lower digestive system consists of the small intestine large intestine rectum and anus Small intestine It is involved in digestion and absorption During digestion the small intestine undergoes segmentation movements which shuffle the chime back and forth and increase its contact with the nutrientabsorbing mucosa Peristalsis propels the chime through the small intestine The small intestine runs from the pyloric sphincter to the first part of the large intestine It has three distinct regions and is about 6m long in total The duodenum is about 25cm long is Cshaped and is secondarily retroperitoneal The jejunum makes up 25 of the total length and the ileum makes up 35 of the total length The jejunum and ileum are attached to the posterior abdominal wall via the fanshaped mesentery of the small intestine They are intraperitoneal structures The jejunum makes up the superior left part and the ileum the inferior right part of the intestinal mass Structural features of the small intestine The small intestine has three structural features that increase its absorptive surface Most absorption occurs in the proximal region of the small intestine so these features decrease towards the distal end Plicae circulares are ridgescircular folds composed of mucosa and submucosa They increase the surface area and slow the movement of chyme allowing for complete absorption of nutrients Villi are fingerlike projections of the mucosa located on top of the circular folds that are covered by a simple columnar epithelium made up of absorptive cells specialized for absorbing digested nutrients Microvilli are found on the surface of the absorptive cells of the villi and they secrete enzymes that are important in the final processes of digestion The lining epithelium of the villi contain absorptive cells goblet cells secrete mucus and enteroendocrine cells release hormones that signal the gallbladder and pancreas to secrete Differences between jejunum and ileum The jejunum is located in the upper left peritoneal cavity and its diameter is 5cm Its wall thickn
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