<unk> ze The length of the<unk>  can vary greatly, from as short as to as long as , also depending on the measuring technique used. The typical length in a living person is 3m–5m. The length depends both on how tall the person is and how the length is measured. Taller people generally have a longer<unk>  and measurements are generally longer after death and when the bowel is empty. +<unk>  bowel dilation on CT scan in adults 4 cm Severely dilated 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<unk>  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<unk> l mucosa, due to enlargement caused by folds, villi and microvilli, averages 30 square meters. Parts The<unk>  is divided into three structural parts. * The duodenum is a short structure ranging from 20 cm (7.9 inches) to 25 cm (9.8 inches) in length, and shaped like a "C". It surrounds the head of the pancreas. It receives gastric chyme from the stomach, together with digestive juices from the pancreas (digestive enzymes) and the liver (bile). The digestive enzymes break down proteins and bile emulsifies fats into micelles. The duodenum contains Brunner's glands, which produce a mucus-rich alkaline secretion containing bicarbonate. These secretions, in combination with bicarbonate from the pancreas, neutralize the stomach acids contained in gastric chyme. * The jejunum is the midsection of the<unk> , connecting the duodenum to the<unk> . It is about 2.5 m long, and contains the circular folds, and intestinal villi that increase its surface area. Products of digestion (sugars, amino acids, and fatty acids) are absorbed into the bloodstream here. The suspensory muscle of duodenum marks the division between the duodenum and the jejunum. * The<unk> : The final section of the<unk> . It is about 3 m long, and contains villi<unk> milar to the jejunum. It absorbs mainly vitamin B12 and bile acids, as well as any other remaining nutrients. The<unk>  joins to the cecum of the large intestine at the ileocecal junction. The jejunum and<unk>  are suspended in the abdominal cavity by mesentery. The mesentery is part of the peritoneum. Arteries, veins, lymph vessels and nerves travel within the mesentery. Blood supply The<unk>  receives a blood supply from the celiac trunk and the superior mesenteric artery. These are both branches of the aorta. The duodenum receives blood from the coeliac trunk via the superior pancreaticoduodenal artery and from the superior mesenteric artery via the inferior pancreaticoduodenal artery. These two arteries both have anterior and posterior branches that meet in the midline and anastomose. The jejunum and<unk>  receive blood from the superior mesenteric artery. Branches of the superior mesenteric artery form a series of arches within the mesentery known as arterial arcades, which may be several layers deep. Straight blood vessels known as vasa recta travel from the arcades closest to the<unk>  and jejunum to the organs themselves. Microanatomy Micrograph of the<unk>  mucosa showing the intestinal villi and crypts of Lieberkühn. The three sections of the<unk>  look<unk> milar to each other at a microscopic level, but there are some important differences. The parts of the intestine are as follows: This cross section diagram shows the 4 layers of the<unk>  wall. Layer Duodenum Jejunum<unk>  Serosa 1st part serosa, 2nd–4th adventitia Normal Normal Muscularis externa Longitudinal and circular layers, with Auerbach's (myenteric) plexus in between Same as duodenum Same as duodenum Submucosa Brunner's glands and Meissner's (submucosal) plexus No BG No BG Mucosa: muscularis mucosae Normal Normal Normal Mucosa: lamina propria No PP No PP Peyer's patches Mucosa: intestinal epithelium<unk> mple columnar. Contains goblet cells, Paneth cells<unk> milar to duodenum ? Gene and protein expression About 20,000 protein coding genes are expressed in human cells and 70% of these genes are expressed in the normal duodenum. Some 300 of these genes are more specifically expressed in the duodenum with very few genes expressed only in the<unk> . The corresponding specific proteins are expressed in glandular cells of the mucosa, such as fatty acid binding protein FABP6. Most of the more specifically expressed genes in the<unk>  are also expressed in the duodenum, for example FABP2 and the DEFA6 protein expressed in secretory granules of Paneth cells. Development The<unk>  develops from the midgut of the primitive gut tube. By the fifth week of embryological life, the<unk>  begins to grow longer at a very fast rate, forming a U-shaped fold called the primary intestinal loop. The loop grows so fast in length that it outgrows the abdomen and protrudes through the umbilicus. By week 10, the loop retracts back into the abdomen. Between weeks<unk> x and ten the<unk>  rotates anticlockwise, as viewed from the front of the embryo. It rotates a further 180 degrees after it has moved back into the abdomen. This process creates the twisted shape of the large intestine. File:Sobo 1906 399.First stage of the development of the intestinal canal and the peritoneum, seen from the<unk> de (diagrammatic). From colon 1 the ascending and transverse colon will be formed and from colon 2 the descending and<unk> gmoid colons and the rectum. File:Sobo 1906 400.Second stage of development of the intestinal canal and peritoneum, seen from in front (diagrammatic). The liver has been removed and the two layers of the ventral mesogastrium (lesser omentum) have been cut. The vessels are represented in black and the peritoneum in the reddish tint. File:Sobo 1906 401.Third state of the development of the intestinal canal and peritoneum, seen from in front (diagrammatic). The mode of preparation is the same as in Fig 400
Small intestine
Large intestine
Stomach
Liver
Gastrointestinal tract
Gastric mucosa
Lung
Kidney