Small intestine
It is approximately 1.5 cm in diameter in newborns after 35 weeks of gestational age, and 2.5–3 cm (1 inch) in diameter in adults. On abdominal X-rays, the small intestine is considered to be abnormally dilated when the diameter exceeds 3 cm. On CT scans, a diameter of over 2.5 cm is considered abnormally dilated. The surface area of the human small intestinal mucosa, due to enlargement caused by folds, villi and microvilli, averages 30 square meters.
Intestinal gland
As estimated from the image in panel A, there are about 100 colonic crypts per square millimeter of the colonic epithelium. The length of the human colon is, on average 160.5 cm (measured from the bottom of the cecum to the colorectal junction) with a range of 80 cm to 313 cm. The average inner circumference of the colon is 6.2 cm. Thus, the inner surface epithelial area of the human colon has an area, on average, of about 995 sq cm, which includes 9,950,000 (close to 10 million) crypts.