Small intestine Dr. Suhasini P tayde Associate prof Department of Anatomy • The small intestine is divided into the duodenum, jejunum, and ileum. Together these can extend up to six meters in length of which 2/5 is jejunum and lower 3/5 is ilieum . • coils are packed in infracolic compartment of greater sac. • Extent • It starts a duodenojejunal junction to the ileum. • mesentry Mesentery －Two-layered fold of peritoneum that attach the intestines to the posterior abdominal wall 1- Mesentery of small intestine suspends the small intestine from the posterior abdominal wall Broad and a fan-shaped It has root[attched] and free margin Root of mesentery is 15 cm long and contains superior mesenteric vessels, free margin is about 6 meters long Directed obliquely from left side of L2 vertebra to right sacroiliac joint It crosses following structures 3rd part of duodenum Abdominal aorta Inferior vena cava Right gonadal vessels and right ureter Mesentery of small intestine Contents of the mesentery - The jejunal and ileal branches of the superior mesenteric artery &veins - Nerve plexuses - Lymphatic vessels - The lymphatic nodes, - connective tissue - Fat parts of Small intestines • Duodenum: secretes mucous enzymes and hormones and is a site of entry for bile and pancreatic juices • Jejunum: nutrient absorption • ileum: central portion of the abdominal cavity; pH 7-8; absorbs B12 and bile salts • The jejunum is the second part of the small intestine. • It begins at the duodenojejunal flexure and is found in the upper left quadrant of the abdomen. • The jejunum is entirely intraperitoneal as the mesentery proper attaches it to the posterior abdominal wall. • The jejunum represents the proximal two-fifths of the jejunum-ileum continuum • The wall of the jejunum is thicker and its lumen is wider than in ileum • The jejunum contains more prominent circular folds of Kerckring • The ileum is the last and longest part of the small intestine. • It is found in the lower right quadrant of the abdomen, although the terminal ileum can extend into the pelvic cavity. • The ileum terminates at the ileal orifice (ileocecal junction) where the cecum of the large intestine begins. • Distinguising features • The diameter and thickness of the wall of the jejunum are greater than that of ileum • The arterial arches in the mesentry of jejnum are less in number hence,the vasa recta are longer • In the case of ileum ,the arterial arches are • . more and vasa recta are short. • There are transparent windows in the mesentry of jejunum due to absence of fat. • The mucosa has large circular • Ileum contains less and smaller folds and large numerous villi in circular folds and villi but more jejunum lymphatic follicles • The small intestine has four tissue layers: 1.The serosa is the outermost layer of the intestine. The serosa is a smooth membrane consisting of a thin layer of cells that secrete serous fluid. 2.The muscularis is a region of muscle adjacent to the submucosa membrane. It is responsible for gut movement, or peristalsis. 3.The submucosa is the layer of dense, irregular connective tissue or loose connective tissue 4.The mucosa • Peyer’s Patches • Peyer’s patches are organized lymph nodules. They are aggregations of lymphoid tissue that are found in the antimesentric margin of ileum • They may ulcerate in typhoid fever. it gives rise to longitudinal oriented ulcers • Intestinal Villi • intestinal villi (singular: villus) are tiny, finger-like projections that protrude from the epithelial lining of the mucosa. • Villi increase the internal surface area of the intestinal walls. • Functional importance of arterial arcade • is that they provide abundant collateral circulation when some of vasa recta may be constricted during peristalsis Large intestine • The large intestine extends from ileoceacal junction to the anus in the perineum.it is one and half meters in length. • Parts of large intestine are • Caecum 6cm • Appendix 2 to 20cm asending colon, • Transverse colon, • Descending colon • Sigmoid colon • Rectum and anal canal the large intestine has several distinct characteristics; appendices appendices teniae coli and haustra. epiploic appendages are fat filled pouches of peritoneum that are attached externally to the walls of entire large intestine except caecum,appendix and rectum. Taeniae coli are three longitudinal bands of smooth muscle located underneath the peritoneum that extend along certain sections of the large intestine. Taeniae are absent in the vermiform appendix and in the rectum Haustra are sacculations are dilated parts in between taeniae. • The portion of the large intestine located between the cecum and rectum is termed the colon. • The main functions of the colon include fluid and electrolyte reabsorption. • The ascending colon travels through the right iliac fossa, right flank, and right hypochondriac region. 15 cm long • It begins from the caecum and ends at the right colic (hepatic) flexure. The ascending colon is retroperitoneal. • It is 15cm in length. Transverse colon • The transverse colon is the second major part of the colon. • It extends between the right and left colic (splenic) flexures, spanning the right hypochondriac, epigastric and left hypochondriac regions of the abdomen. • It is 50cm in length • The transverse colon is intraperitoneal.it is suspended by transverse mesocolon and attaches to the posterior abdominal wall. Descending colon • The descending colon extends between the left colic flexure and sigmoid colon. • It is narrower ,longer more deeply placed than asending colon 25cm long. • It travels through the left hypochondriac region, left flank and left iliac fossa. • The left paracolic gutter is located between the descending colon and the lateral abdominal wall. • Sigmoid colon • The S-shaped sigmoid colon travels from the left iliac fossa until the third sacral vertebra (rectosigmoid junction).40 cm long. It is connected to the pelvic wall by the sigmoid mesocolon. • Rectum • The rectum stretches between the rectosigmoid and anorectal junction . • Anal canal • The anal canal forms the terminal part of the gastrointestinal tract. It extends from the anorectal junction to the anus. • Arteries • The large intestine receives arterial blood predominantly from the superior and inferior mesenteric arteries. • right two-thirds of the transverse colon receives branches from middle colic arteries from superior mesenteric arteries. • The inferior mesenteric artery supplies the hindgut derivates, namely the left third of the transverse colon, descending colon, sigmoid, colon, rectum and the upper part of the anal canal via three branches: left colic, sigmoid, and superior rectal arteries. • The superior and inferior mesenteric branches supplying the colon anastomose to form the marginal artery of Drummond. This runs along the inner margin of the large intestine. • the large intestine flows mostly into the superior and inferior mesenteric veins. • Lymphatic drainage • Lymphatics are arranged in four groups • Epicolic nodes • Paracolic nodes • Intermediate colic nodes • Preterminal nodes Large intestine Small intestine • About 6.5meters long,narrow • About 1.5 meters long,wider more moveble except duodenum fixed • Villi-presence of villi more • Absence of villi in postnatal life numerous n longer in jejunum n • Crypts of lieberkuhn are duodenum longer,numerous with goblet • Crypts are lined by absorptive cells,paneth cells absent cells,goblet cells and paneth cells • Presence of taeniae • Circular folds are present coli,sacculations amd appendices epiploicae.