Gastrointestinal tract
The small intestine begins at the duodenum and is a tubular structure, usually between 6 and 7 m long. Its mucosal area in an adult human is about 30 m. Its main function is to absorb the products of digestion (including carbohydrates, proteins, lipids, and vitamins) into the bloodstream. There are three major divisions:
Large intestine
The average inner diameter of sections of the colon in centimeters (with ranges in parentheses) are cecum 8.7 (8.0-10.5), ascending colon 6.6 (6.0-7.0), transverse colon 5.8 (5.0-6.5), descending/sigmoid colon 6.3 (6.0-6.8) and rectum near rectal/sigmoid junction 5.7 (4.5-7.5).