Anatomy of Small Intestine PDF

By: Dr. Shahnaz Sabetkam Assistant Professor of Anatomical Sciences Kyrenia University  Small Intestine Finishes chemical digestion Responsible for absorbing most of the nutrients. Ingested nutrients spend at least 12 hours in the small...

By: Dr. Shahnaz Sabetkam Assistant Professor of Anatomical Sciences Kyrenia University  Small Intestine Finishes chemical digestion Responsible for absorbing most of the nutrients. Ingested nutrients spend at least 12 hours in the small intestine. thin-walled tube about 6 meters in length. Extends from the pylorus of the stomach to the cecum of the large intestine occupies a significant portion of the abdominal cavity. 26-5 Small Intestine Small Intestine  The Small Intestine – Structural Features The intestinal wall Mucosa has transverse folds, plicae circulares. Plicae have small projections, villi. Both increase surface area of mucosa for absorption. Each villus has a lymphatic capillary, a lacteal. The Small Intestine – Structural Features 9  Small Intestine Digestion in the small intestine Most enzymatic digestion and absorption occurs in the small intestine. Digestive enzymes and buffers are released by: Pancreas Liver Gall bladder  Small Intestine Longest portion of the alimentary canal Site of most enzymatic digestion and absorption Three subdivisions Duodenum Jejunum Ileum  Sectional Differences of Small Bowel Has three parts 1. The duodenum first segment of the small intestine. approximately 25 centimeters long originates at the pyloric sphincter major duodenal papilla 2. The jejunum middle region of the small intestine. approximately 2.5 meters makes up approximately two-fifths of the small intestine’s total length. primary region for chemical digestion and nutrient absorption 3. The ileum is the last region of the small intestine. about 3.6 meters (10.8 feet) in length forms approximately three-fifths of the small intestine. 26-12 terminates at the ileocecal valve sphincter that controls the entry of materials into the large intestine. Sectional Differences of Small Bowel 13  The Small Intestine: Gross Anatomy Plays Important role in digestion and absorption. Mucosa of SI produce few enzymes, and buffer to neutralize chime. Divided into three part: Duodenum: Receives chime from stomach, bile from gall bladder, and digestive secretion from pancreas. Digestion continues in duodenum, Jejunum and ileum: digestion and absorption takes place here. Ilieocecal sphincter Transition between small and large intestine  The Duodenum Extends from pylorus to duodenojejunal junction Has a “C” shaped course around the head of the pancreas Receives digestive enzymes and bile. Main pancreatic duct and common bile duct enter duodenum. Sphincters control entry of bile and pancreatic juices.  The Duodenum The first The shortest of the small intestine The widest The most deeply lying, The least accessible, Anterior surface is covered in peritoneum. Posterior surface is not covered in peritoneum.  Head of pancreas Supr arenal gland Hepati c portal vein (of portal triad ) Superior mesenteric vessels Hepa ti c artery proper (of portal triad) Transverse mesocolon and its Celi ac trunk cut edges (Common) bile duct (of portal triad) Splenic artery Transverse colon (cut) Right free margin of le sser omen tum (he patoduodenal ligament) Left coli c (splenic) Suprarenal flexure gland Ki dney Right coli c (hep ati c) fle xure Psoas major musc le - -:- - - - S uperi or (1st) part of duodenum Descending (2 nd) part of duoden um Duodenojejunal flexure and jej unum (cut) Infe rior (ho rizontaI, or 3 rd)  Parts of the Duodenum Divided into four parts: Superior: The first Descending: The second Horizontal: The third Ascending: The fourth Only the first 2 cm of the superior part is intraperitoneal, whereas the rest of the duodenum is retroperitoneal. Parts of the Duodenum  The Duodenum( superior part) Superior part: Duodenal ampulla or cap Pylorus protrudes in it. Lesser omentum attaches to its upper margin. Greater omentum attaches to its lower margin.  The Duodenum( descending part) Descending part: The anterior surface is covered with peritoneum. Except along the attachment line of the transverse mesocolon. The head of the pancreas is in direct contact with it. The common bile duct and the main pancreatic duct open into its lumen. Major duodenal papilla and minor duodenal papilla are present at its interior surface.  The Duodenum (horizontal part) Horizontal part: Cr osses to the left in front of. L3 vertebra The inferiorvena cava The aorta Continues with the ascending part in front of the aorta. The anterior surface is covered with peritoneum. Except along the attachment line of the mesentery.  The Duodenum (Ascending part) Ascending part: Returns to L2 vertebra. Runs on the left side of the aorta. Forms sharp duodenojejunal flexure The anterior surface is covered with peritoneum. Except along the attachment line of the mesentery.  The Duodenal Vessels Arteries Superior pancreaticoduodenal artery (branch of gastroduodenal artery which is a branch of the common hepatic artery from the celiac trunk) Inferior pancreaticoduodenal artery (branch of superior mesenteric artery) Veins Follow the arteries and drain directly or indirectly (through superior mesenteric or splenic veins) into the portal vein The Duodenal Vessels  The Duodenal Lymphatics Lymphatics Drain into the celiac and superior mesenteric lymph nodes.  The Duodenal Innervation Nerves Parasympathetics comes from vagus. Sympathetic nerves come from celiac and superior mesenteric plexuses (through the thoracic splanchnic nerves). (Oddi Sphincter)  L2 Right Iliac Fossa Mesentery  Jejunum and ileum About 6-7 meters long, the jejunum contstituting the first 2/5 Most of the jejunum lies in the upper left quadrant of the abdomen, whereas most of the ileum lies in the lower right quadrant  Jejunum and ileum They are specialised for Absorption of digested food, Vitamins, Electrolytes Coils of the jejunum and ileum are attached to the posterior abdominal wall with the mesentery Jejunum Ileum Jejunum: The jejenum is slightly wider than the ileum. The mucosa is thrown into circular folds in the jejenum, whereas circular folds in the ileum are small and sparse. Ileum has distinctive lymphoid follicles (Peyer’s patches); such large follicles are absent in the jejenum. Jejunum Ileum Jejunum begins at duodenojejunal flexure, no clear demarcation to ileum. Jejunum has long vas recta, large plicae, thick walls, transparent mesentry. Ileum has short vasa recta, small plicae, thin walls, fat in the mesentery.  Jejunum and ileum Macroscopic differences between jejunum and ileum Jejunum Ileum Color Deeper red Pale pink Caliber 2-4 cm 2-3 cm Wall Thick Thin Vascularity Greater Lesser Vasa recta Long Short Arcades Few large loops Many short loops Fat in mesentery Less More Circular folds Large, heavily packed Small, sparse Lymphoid nodules Few Many  Comparison of Jejunum and Ileum JEJENUM JEJENUM JEJENUM ILEUM ILEUM ILEUM Comparison of Jejunum and Ileum Comparison of Jejunum and Ileum  Mesentery Coils of the jejunum and ileum are attached to the posterior abdominal wall with the mesentery. The root of the mesentery crosses: Ascending and horizontal parts of the duodenum Abdominal aorta IVC Right ureter Right psoas major muscle Right testicular (or ovarian) vessels Mesentery Mesentery  Jejunum and ileum arteries Arteries Superior mesenteric artery supplies both the jejunum and ileum. This artery sends about 15-18 branches which extend within the two layers of the mesentery. The branches unite to form arcades (loops) that gives rise to vasa recta. Jejunum and ileum veins Veins Superior mesenteric vein Drains both the jejunum and ileum. This vein unites with the splenic vein to form the portal vein.  Jejunum and ileum Lymphatics Most of the lymph drains into the superior mesenteric lymph nodes. Lymph from the terminal part of the ileum drains into the ileocolic lymph nodes.  Jejunum and ileum innervation Nerves Parasympathetics Mainly comes through the posterior vagal trunk (right vagus nerve). The presynaptic parasympathetic fibers synapse with the postsynaptic neurons in the myenteric and submucosal plexuses within the wall of small intestine. Sympathetics Presynaptic fibers come through the greater, lesser and least splanchnic nerves (from T5-T12 segments of the spinal cord). These nerves synapse at the ganglia within the celiac and superior mesenteric plexuses.  Jejunum and ileum innervation Nerves Sympathetic stimulation reduces the secretion and motility of the intestine, therefore reducing or stopping the digestion. Parasympathetic stimulation increases the motility and secretion. Regarding the GVA innervation, the intestine are insensitive to almost all tactile stimuli like cutting or burning, however, quite sensitive to distension, which is perceived as colic. Any Questions?