Small Intestine @NotesMed.com @NotesMed.com Small Intestine • Consists of: – Duodenum – Jejunum – Ileum • Extends: Distal end of the pyloric canal to the ileocaecal valve • Length:-About 6 meters • Duodenum extends up to the duodenojejunal junction • The remaining small intestine is often referred to as the ‘small bowel’ – the proximal two-fifths is referred to as the jejunum – the distal three fifths as the ileum @NotesMed.com Duodenum • The term “duodenum” is the Latin corruption of Greek word “do-deka- daktulos” meaning 12 fingers. • Shortest, widest and most fixed part of small intestine • Extend: from the pylorus to duodenojejunal flexure. • Length:- 10 inches (25 cm) long. @NotesMed.com @NotesMed.com Duodenum • It begins at the pylorus which lies on the transpyloric plane about 2.5 cm to the right of the median plane and ends at the duodenojejunal junction which lies about 2.5 cm to the left of the median plane and little below the transpyloric plane. • The main function of the duodenum is digestion • C- shaped structure, adjacent to the head of the pancreas • Lies in the abdominal cavity above the level of the umbilicus; opposite to the first, second and third lumbar vertebrae @NotesMed.com @NotesMed.com PARTS AND RELATIONS • Four parts: – Superior (first) part, 5 cm (2 inches) long – Descending (second) part, 7.5 cm (3 inches) long. – Horizontal (third) part, 10 cm (4 inches) long. – Ascending (fourth) part, 2.5 cm (1 inch) long @NotesMed.com Superior (first) part • Extent: Pylorus to superior duodenal flexure • Features: – It develops from the foregut. – It is only partly retroperitoneal. – It is freely mobile and distensible. – It has no circular folds in the mucous membrane of itsinitial 2.5 cm—seen as the duodenal cap in barium meal radiographs. – It is the site for duodenal ulcer. – It is supplied by the branches of coeliac trunk/artery. @NotesMed.com Superior (first) part • Relations – Anteriorly: Quadrate lobe of the liver and gallbladder. – Posteriorly: Portal vein, gastroduodenal artery, and common bile duct (CBD). – Superiorly: Epiploic foramen being separated from it by the portal vein and bile duct. – Inferiorly: Head and neck of the pancreas. @NotesMed.com @NotesMed.com Descending (second) part • Extent: superior duodenal flexure(L1) to inferior duodenal flexure (L3) • Features – Its upper half develops from the foregut and lower half from the midgut. – It lies behind the transverse mesocolon. – It receives the bile duct, the chief and accessory pancreatic ducts. – It is the only part of the intestine supplied by double rows of vasa recta, arising from anterior and posterior pancreaticoduodenal arterial arcades. @NotesMed.com Descending (second) part • Relations : – Anteriorly: Gallbladder and right lobe of the liver, transverse colon, transverse mesocolon (commencement), and coils of the small intestine. – Posteriorly: Right kidney and right renal vessels, right edge of the inferior vena cava (IVC), and right psoas major muscle. – Medially: Head of the pancreas. – Laterally: From below upward; ascending colon, right colic flexure, and right lobe of the liver. @NotesMed.com Horizontal (third) part • Extents: Inferior duodenal flexure to front of aorta(L3) • Relations: – Anteriorly: Root of the mesentery, superior mesenteric vessels, and coils of the jejunum. – Posteriorly: Right psoas major, right ureter, IVC, abdominal aorta, and right gonadal vessels. – Superiorly: Head of the pancreas with its uncinate process. – Inferiorly: Coils of the jejunum. @NotesMed.com Ascending (fourth) part • Extent: Front of aorta to duodeno-jejunalflexure(L2) • Relations: – Anteriorly: Transverse colon and transverse mesocolon. – Posteriorly: Left psoas major muscle, left sympathetic chain, left gonadal vessels, and inferior mesenteric vein. – Superiorly: Body of the pancreas. – On to the left: Left kidney and left ureter. – On to the right: Upper part of the root of mesentery. @NotesMed.com INTERIOR OF THE DUODENUM (second part) • Circular folds: • Major duodenal papilla: – Well-marked conical projection on the posteromedial wall and situated 8–10 cm distal to the pylorus. • Minor duodenal papilla: – Small conical projection situated 2 cm proximal (and ventral) to the major duodenal papilla. • Arch of plica semicircularis: – Is forms an arch above the major duodenal papilla like a hood (cf. monk’s hood) • Plica longitudinalis: – It is a vertical tortuous fold of the mucous membrane extending downward from the major duodenal papilla. @NotesMed.com SUSPENSORY MUSCLE OF DUODENUM (LIGAMENT OF TREITZ) • Fibromuscular band, which suspends the duodenojejunal flexure from the right crus of the diaphragm. • Its upper end is attached on to the right crus of the diaphragm and the lower end attached on to the posterior surface of the duodenojejunal flexure. • This band contains: – Striated muscle fibres in the upper part. – Elastic fibres in the middle part. – Non-striated muscle fibres in the lower part. @NotesMed.com DUODENAL RECESSES (FOSSAE) • Duodenojejunal junction, small pocket like pouches of peritoneum called duodenal recesses – Superior duodenal recess – Inferior duodenal recess – Paraduodenal recess – Retroduodenal recess @NotesMed.com ARTERIAL SUPPLY • Superior pancreaticoduodenal artery • Inferior pancreaticoduodenal artery • Supraduodenal artery of “Wilkie” • Retroduodenal branches of the gastroduodenal artery • Leash of branches of the hepatic artery. • Branches from the right gastroepiploic artery. • Artery from the first jejunal branch of the superior mesenteric artery @NotesMed.com VENOUS DRAINAGE • Splenic vein. • Superior mesenteric, and • Portal veins. @NotesMed.com LYMPHATIC DRAINAGE • Pancreaticoduodenal nodes- Coeliac and mesenteric group of lymph node NERVE SUPPLY • Sympathetic nerves: T6–T9 segments of the spinal cord. • Parasympathetic nerves: from both the vagi through coeliac and superior mesenteric plexuses. @NotesMed.com @NotesMed.com Duodenum Small intestine proper Short in length (25 cm) Long in length (<6 m) Supplied by two rows of vasa Supplied by single row of vasa recta recta Presence of Brunner glands in Absence of glands in submucus submucus coat coat @NotesMed.com.