ABDOMINAL CAVITY the third lecture Abdominal cavity – third part Small intestine (small bowel) Large intestine (large bowel) Lymphatic drainage of the intestine Innervation of the intestine Unpaired visceral branches of the aorta Small intestine Consists of: - duodenum - jejunum - ileum Extends from the pylorus to the ileocecal junction Duodenum First and shorter part of the small intestine The widest and most fixed part Pursues a C-shaped course around the head of the pancreas Begins at the pylorus on the right side and ends at the duodenojejunal junction (duodenojejunal flexure) on the left side (at the level of the L2 vertebra, 2 to 3 cm to the left of the midline) Duodenum Divides into four parts: superior (1st), descending (2nd), horizontal (3rd), ascending (4th). Superior (first) part of duodenum Short, aproximately 5cm Lies anterolateraly to the body of L1 vertebra Ascends from the pylorus and is overlapped by the liver and gallbladder The first 2 cm, immediately distal to the pylorus has a mesentary and is mobile- - ampulla (duodenal cap) Ampulla superiorly attached by the hepatoduodenal ligament and the greater omentum inferiorly Relationship of the duodenum Superior (1st part)- L1 vertebra anterior: peritoneum gallblader quadrate lobe of liver posterior: common bile duct, gastroduodenal artery, portal vein, inferior vena cava superior: neck of gallblader inferior: neck of pancreas Descending (2nd) part of the duodenum Runs inferiorly Curving around the head of the pancreas Initially lies to the right and parallel to the inferior vena cava The common bile and pancreatic ducts enter its posteromedial wall (the eminence- the major duodenal papilla) Entirely retroperitoneal (secondary retroperitoneal) Relationship of the duodenum Descending (2nd part)- L2/L3 vertebra anterior: transverse colon, transverse mesocolon, coils of small intestine posterior: hilum of right kidney, renal vessels, ureter, psoas major medial: head of pancreas, pancreatic duct, common bile duct The inferior (horizontal) part of the duodenum Runs transversely to the left, passing over the inferior vena cava, aorta and L3 vertebra Is crossed by the superior mesenteric artery and vein and the root of the mesentery of the jejunum and ileum The anterior surface- covered with peritoneum Superiorly – the head and uncinate process of pancreas Posteriorly- separated from the vertebral column by the right psoas major, inferior vena cava, aorta and the right testicular/ovarian vessels Relationship of the duodenum Horizontal (3rd) part, anterior to L3 vertebra anterior: superior mesenteric artery superior mesenteric vein, coils of small intestine posterior: right psoas major, right ureter, inferior vena cava, abdominal aorta superior: head and uncinate process of pancreas, superior mesenteric artery superior mesenteric vein The ascending part (fourth) of the duodenum Runs superiorly and along the left side of the aorta to reach the inferior border of the body of the pancreas Curves anteriorly to join the jejunum at the duodenojejunal junction, takes the form of an acute angle – the duodenojejunal flexure (supported by the ligament of Treitz) Two or three inconstant folds and fossae are around the duodenojejunal junction If the loop of intestine enters this fossa, it may strangulate Ligament of Treitz Supports the duodenojejunal flexure Suspensory muscle Composed of a slip of skeletal muscle from diaphragm and a fibromuscular band of smooth muscle from the third and fourth parts of the duodenum Contraction of this muscle widens the angle of the flexure, facilitating movement of the intestinal contents Passes posterior to the pancreas and splenic vein and anterior to the left renal vein Relationship of the duodenum Ascending (4th)part, left of L3 vertebra anterior: the root of mesentery, coils of jejunum posterior: left psoas major, left margin of aorta medial: head of pancreas superior: body of pancreas Abdominal aorta Unpaired visceral branches: celiac trunk superior mesenteric artery inferior mesenteric artery Arteries of the duodenum From the celiac trunk (via the gastroduodenal artery) and the superior mesenteric artery The anastomosis between them occurs approximately at the level of entry of the common bile duct The pancreaticoduodenal arteries (superior and inferior) lie in the curve between the duodenum and the head of the pancreas Veins of duodenum Follow the arteries and drain into the portal vein or through the superior mesenteric and splenic veins Lymphatic vessels of the duodenum Anterior- drain into the pancreaticoduodenal lymph nodes located along the superior and inferior pancreatico- duodenal arteries Anterior- also drain into the pyloric lymph nodes that lie along the gastroduodenal artery Posterior- drain into the superior mesenteric nodes Efferent lymphatic vessels- drain into the celiac lymph nodes (form the intestinal lymphatic trunk) The nerves of duodenum From the vagus and sympathetic nerves through the celiac and superior mesenteric plexuses on the pancreaticoduodenal arteries Jejunum and ileum The jejunum begins at the duodenojejunal flexure The ileum ends at the ileocecal junction – the union of the terminal ileum and the cecum Together: 6 to 7 meters long The jejunum constituting approximately two-fifths and the ileum approximately three-fifths No clear line of the demarcation between the jejunum and the ileum The differences between jejunum and ileum Color: deeper red (paler pink) Caliber: 2-4cm (2-3cm) Wall: thick and heavy (thin and light) Circular folds (plicae circulares): large, tall and closely packed (low and sparse, absent in distal part) Lymphoid nodules (Peyer’s patches): few (many) The differences between jejunum and ileum Vascularity: greater (less) Vasa recta (straight arteries): long (short) Loops of arcades: a few large (many short) Jejunum and ileum The layers of small intestine Intestinal villi - tiny projections of the mucous membrane - increase the internal absorptive surface area of the intestinal wall Lacteals Specialized lymphatic vessels in the intestinal villi Absorb fat Drain in turn into lymphatic vessels between the layers of the mesentery Ileal (Meckel’s) diverticulum The most common problem that occurs in the digestive system Congenital disease A remnant of the proximal part of the embryonic yolk stalk 50 cm from the ileocecal junction (30-60 cm in infants) Occurs in 1 out of every 50 people Diffucult to diagnose Symptoms are mistaken for appendicitis or a peptic ulcer The mesentery of the small intestine A fan-shaped fold of peritoneum- attaches the jejunum and ileum to the posterior abdominal wall Extends from the duodenojejunal juction on the left side of the L2 vertebra to the ileocolic junction and the right sacroiliac joint The average breadth of the mesentery from its root to the intestinal border is 20 cm The root of the mesentery Crosses: Ascending and horizontal parts of the duodenum Abdominal aorta Inferior vena cava Right ureter Right psoas major Right testicular/ovarian vessels Superior mesenteric artery Arises from the abdominal aorta at the level of the L1 vertebra, approximately 1 cm inferior to the celiac trunk Runs between the layers of the mesentery, Sends 15 to 18 branches to the jejunum and ileum. Arterial arcades (arches, loops) - the union of the branches, give rise to straight arteries (the vasa recta) Relations of superior mesenteric vein and artery in root of mesentery Lies anterior and to the right of the superior mesenteric artery in the root of mesentery of the small intestine Superior mesenteric vein Ends posteriorly to the neck of the pancreas Unites with the splenic vein to form the portal vein Lymph vessels and nodes of the small intestine The lymphatic vessels pass between the layers of the mesentery The lymph nodes are close to the intestinal wall (juxta- intestinal), among the arterial arcades (mesenteric) and along the proximal part of the superior mesenteric artery (superior, central) Efferent vessels from mesenteric lymph nodes drain to the superior mesenteric (central) lymph nodes From the terminal ileum through ileocolic lymph nodes Innervation of the small intestine Presynaptic sympathetic fibers reach celiac and superior mesenteric ganglia (prevertebral) through greater and lesser splanchnic nerves Parasympathetic fibers (presynaptic nerves) derive from posterior vagal trunk and synapse with intrinsic postsynaptic neurons in the wall (Auerbach plexus- myenteric plexus) Referred site – umbilical region Innervation of the small intestine Sympathetic stimulation – reduces motility and secretion of the intestine and acts as vasoconstrictor (reducing or stopping digestion and making blood (and energy) available for fleeing or fighting Parasympathetic stimulation increases motility and secretion of the intestine, restoring digestive activity Large intestine Consists of: Cecum with appendix Colon: ascending, transverse, descending, sigmoid Rectum and anal canal The large intestine The differences between small and large intestine Teniae coli (omental, mesocolic, free)- three thickned bands of muscle Haustra- sacculations of the colon between the teniae Omental appendices- small fatty projections of the omentum Caliber- the internal diameter is much longer Semilunar folds (internal surface) The cecum The first part of the large intestine Continuous with the ascending colon A blind intestinal pouch Approximately 7.5cm in both length and breadth Lies in the right lower quadrant (iliac fossa) Lies inferior to the junction of the terminal ileum and the cecum Ileocecal