Title: The Small and Large Intestines · Anatomy and Physiology
Headings: 
The Small and Large Intestines
The Small Intestine
Structure
Histology
Circular folds
Villi
Microvilli
Intestinal Glands
Intestinal MALT
Mechanical Digestion in the Small Intestine
Chemical Digestion in the Small Intestine
The Large Intestine
Structure
Subdivisions
Cecum
Colon
Rectum
Anal Canal
Histology
Anatomy
Bacterial Flora
Digestive Functions of the Large Intestine
Mechanical Digestion
Chemical Digestion
Absorption, Feces Formation, and Defecation
Chapter Review
Interactive Link Questions
Review Questions
Critical Thinking Questions
References
Glossary

Content: Small Intestine
The three regions of the small intestine are the duodenum, jejunum, and ileum. The jejunum is about 0.9 meters (3 feet) long (in life) and runs from the duodenum to the ileum. Jejunum means “empty” in Latin and supposedly was so named by the ancient Greeks who noticed it was always empty at death. No clear demarcation exists between the jejunum and the final segment of the small intestine, the ileum. The ileum is the longest part of the small intestine, measuring about 1.8 meters (6 feet) in length. It is thicker, more vascular, and has more developed mucosal folds than the jejunum. The ileum joins the cecum, the first portion of the large intestine, at the ileocecal sphincter (or valve). The jejunum and ileum are tethered to the posterior abdominal wall by the mesentery. The large intestine frames these three parts of the small intestine. Parasympathetic nerve fibers from the vagus nerve and sympathetic nerve fibers from the thoracic splanchnic nerve provide extrinsic innervation to the small intestine.