Week 7 Lecture Notes on the Small and Large Intestine PDF

Small Intestine longest part of alimentary canal extends from pyloric orifice to ileocecal junction most food digestion and absorption take part in small intestine parts: duodenum jejunum ileum https://sites.google.com/view/grossanatomyi...

Small Intestine longest part of alimentary canal extends from pyloric orifice to ileocecal junction most food digestion and absorption take part in small intestine parts: duodenum jejunum ileum https://sites.google.com/view/grossanatomyii/week-7-lecture-notes 6/21/24, 2:17 PM Page 18 of 38  Duodenum C-shaped tube, about 10 inches long, that curves around head of pancreas à located in epigastric and umbilical regions begins at pyloric orifice and ends at duodenojejunal flexure its initial segment is intraperitoneal (like stomach) à remaining of duodenum is secondary retroperitoneal (only its anterior surface is covered by peritoneum) divided into 4 parts: 1st (superior), 2nd (descending), 3rd (inferior, horizontal or transverse) and 4th (ascending) important anatomical relations: gastroduodenal artery passes posterior to 1st part of duodenum à a peptic ulcer in posterior wall of 1st part of duodenum can erode gastroduodenal artery or one of its branches causing a massive hemorrhage gallbladder is anterior to 1st part and upper portion of 2nd part of duodenum à inflammation of gallbladder can create adhesions or even a fistula between gallbladder and duodenum superior mesenteric artery and vein pass anterior to 3rd part of duodenum à an aneurysm of SMA can compress 3rd part of duodenum causing intestinal obstruction internal structure: in approximately the first 2cm, duodenal mucosa is smooth (duodenal ampulla/cap) remaining of duodenum à mucosal surface has numerous folds à circular folds (plicae circulares) major duodenal papilla à small elevation located approximately half-way down posteromedial wall of 2nd part of duodenum, created by hepatopancreatic ampulla (of Vater) à has small orifice at its tip (opening of hepatopancreatic ampulla) that releases bile and pancreatic enzymes into duodenum minor duodenal papilla (inconstant) à located in 2nd part of duodenum, about 2cm above major duodenal papilla à marks opening of accessory pancreatic duct https://sites.google.com/view/grossanatomyii/week-7-lecture-notes 6/21/24, 2:17 PM Page 19 of 38  Jejunum and Ileum jejunum begins at duodenojejunal flexure and ileum ends at ileocecal junction each has peculiar features, but there is a gradual change from one to the other (no sharp boundary between them) coils of jejunum and ileum are intraperitoneal and freely movable à attached to posterior abdominal wall by mesentery of small intestine, which allows branches of superior mesenteric vessels, lymph vessels and nerves to reach jejunum and ileum root of mesentery of small intestine extends inferiorly and to the right from left side of L2 to right sacroiliac joint https://sites.google.com/view/grossanatomyii/week-7-lecture-notes 6/21/24, 2:17 PM Page 21 of 38  Differences Between the Jejunum and Ileum coils of jejunum lie in upper part of infracolic compartment à coils of ileum are in lower part of infracolic compartment and pelvic cavity jejunum has larger diameter and thicker walls than ileum in jejunum circular folds are larger and more numerous than in ileum jejunal arteries form less number of arcades than ileal arteries à straight arteries (vasa recta), which originate from last series of arcades, are longer in jejunum than ileum aggregated lymphoid follicles/nodules (Peyer’s patches) are present in ileum along its antimesenteric border (not present in jejunum) ileum has more mesenteric fat than jejunum Large Intestine extends from ileocecal junction to anus ileal (ileocecal) orifice is located in medial wall of cecum à guarded by 2 mucosal folds (superior and inferior ileocecal lips, formerly known as ileocecal valve) à play little or no role in preventing reflux from cecum to ileum (major role is played by circular muscle at end of ileum) mainly concerned with absorption of water and electrolytes and storage of undigested materials until they can be eliminated from body as feces parts: cecum with vermiform appendix, ascending colon, transverse colon, descending colon, sigmoid colon, rectum and anal canal https://sites.google.com/view/grossanatomyii/week-7-lecture-notes 6/21/24, 2:17 PM Page 22 of 38  Differences between large and small intestines: teniae coli à 3 bands of longitudinally arranged smooth muscles fibers, approximately equally spaced around circumference of large intestine à named according to their relations to peritoneal attachments of transverse colon (omental tenia, mesocolic tenia and free tenia) large intestine has fatty appendices (epiploic/omental appendices) à not present in small intestine wall of small intestine is smooth à wall of large intestine is sacculated (haustra) https://sites.google.com/view/grossanatomyii/week-7-lecture-notes 6/21/24, 2:17 PM Page 25 of 38  Vermiform Appendix narrow muscular tube containing large amount of lymphoid tissue intraperitoneal à has small mesentery (mesoappendix) that contains appendicular vessels McBurney’s point à located at junction of lateral and middle thirds of a line joining right ASIS to umbilicus à area of greatest tenderness in appendicitis 3 teniae coli converge at base of appendix (useful in locating appendix during surgery) position of appendix is variable à retrocecal (most common), hanging down into pelvis against right pelvic wall (pelvic), below cecum (subcecal), projecting upward anterior or posterior to terminal part of ileum (preileal or postileal) sensory fibers carrying pain from appendix terminate in spinal cord at level of T10 à pain referred around umbilicus https://sites.google.com/view/grossanatomyii/week-7-lecture-notes 6/21/24, 2:17 PM Page 29 of 38  Pancreas exocrine and endocrine gland exocrine part produces enzymes involved in digestion of proteins, fats and carbohydrates endocrine part (pancreatic islets [of Langerhans]) produces hormones (main ones are insulin and glucagon) elongated organ that lies in epigastric and left hypochondriac regions à deeply located on posterior abdominal wall, behind peritoneal sac (most of it is secondary retroperitoneal) https://sites.google.com/view/grossanatomyii/week-7-lecture-notes 6/21/24, 2:17 PM Page 31 of 38  Parts: head, neck, body and tail head: lies within concavity of duodenum uncinate process à tongue-like process of lower part of head that extends to the left, posterior to superior mesenteric vessels neck: slightly constricted part between head and body located anterior to origins of portal vein and superior mesenteric artery body: longest part à extends to the left and slightly superiorly tail: located within splenorenal ligament à comes in contact with hilum of spleen (only part of pancreas that is intraperitoneal) anatomical relations: anteriorly: lesser sac, stomach, root of transverse mesocolon posteriorly: common bile duct, origin of portal vein, IVC, abdominal aorta with origin of superior mesenteric artery, splenic vein, left kidney, left suprarenal gland superiorly: splenic artery ducts: principal (main) pancreatic duct: begins in tail and runs length of organ à opens into 2nd part of duodenum (together with common bile duct) on major duodenal papilla accessory pancreatic duct: drains upper part of head à opens into 2nd part of duodenum on minor duodenal papilla two ducts usually communicate with each other https://sites.google.com/view/grossanatomyii/week-7-lecture-notes 6/21/24, 2:17 PM Page 32 of 38  Marginal Artery continuous arterial channel that skirts inner margin of colon from ileocecal junction to rectosigmoid junction formed by anastomoses between branches of ileocolic, right colic, middle colic, left colic and sigmoid arteries can serve as a source of collateral circulation to a part of colon after its chief arterial supply has been obstructed or ligated https://sites.google.com/view/grossanatomyii/week-7-lecture-notes 6/21/24, 2:17 PM Page 33 of 38  *There is no video about this next section. Read these notes and refer to the photos.* Portal Vein drains blood from most of alimentary canal (from lower ⅓ of esophagus to upper ½ of anal canal), spleen and pancreas à terminates in liver begins posterior to neck of pancreas by union of superior mesenteric and splenic veins runs superiorly and to the right à passes posterior to 1st part of duodenum à runs within hepatoduodenal ligament (posterior to proper hepatic artery and common bile duct) à divides into right and left terminal branches at porta hepatis https://sites.google.com/view/grossanatomyii/week-7-lecture-notes 6/21/24, 2:17 PM Page 34 of 38  tributaries: splenic vein à begins at hilum of spleen à runs to the right, posterior to pancreas, and inferior to splenic artery à joins superior mesenteric vein posterior to neck of pancreas to form portal vein à receives tributaries that correspond with branches of splenic artery (short gastric, left gastroepiploic, pancreatic veins) as well as inferior mesenteric vein tributaries: inferior mesenteric vein à drains territory supplied by inferior mesenteric artery (receives left colic, sigmoid and superior rectal veins) à ascends on posterior abdominal wall, posterior to peritoneum à usually terminates by joining splenic vein posterior to pancreas, but may end at junction of splenic and superior mesenteric veins or drain into superior mesenteric vein superior mesenteric vein à ascends in root of mesentery of small intestine on right side of SMA à passes anterior to 3rd part of duodenum and uncinate process of pancreas à joins splenic vein posterior to neck of pancreas to form portal vein à receives tributaries that correspond with branches of SMA (inferior pancreaticoduodenal, jejunal, ileal, ileocolic, right colic and middle colic veins) and right gastroepiploic vein tributaries: right and left gastric veins à collect blood from lesser curvature of stomach à drain directly into portal vein superior pancreaticoduodenal veins à drain into portal vein or superior mesenteric vein cystic veins à drain gallbladder directly into liver or join portal vein paraumbilical veins à very small veins that run along round ligament of liver à connect veins of anterior abdominal wall with portal vein (usually its left branch) https://sites.google.com/view/grossanatomyii/week-7-lecture-notes 6/21/24, 2:17 PM Page 35 of 38  Portal-Systemic Anastomoses in normal conditions, portal venous blood passes through liver and drains into IVC, which then carries it to heart (direct route) other routes of communication exist between portal and systemic (SVC, IVC) circulations à become important if direct route is blocked causing portal hypertension (ex.: cirrhosis of liver) à in patients with portal hypertension, portal-systemic anastomoses become enlarged (varicose veins) and can rupture and bleed sites of portal-systemic anastomoses: in lower part of esophagus, esophageal veins that drain into left gastric vein (portal circulation) anastomose with esophageal veins that drain into azygos venous system (systemic circulation, SVC) à enlargement of these veins in portal hypertension causes esophageal varices sites of portal-systemic anastomoses: in walls of rectum and anal canal à tributaries of superior rectal vein (portal circulation) anastomose with tributaries of middle and inferior rectal veins (systemic circulation, IVC) à enlargement of these veins in portal hypertension causes internal hemorrhoids (most hemorrhoids are NOT associated with portal hypertension) in anterior abdominal wall à paraumbilical veins (portal circulation) anastomose with superficial veins of anterior abdominal wall which drain superiorly into axillary vein or inferiorly into femoral vein (systemic circulation) à enlargement of these veins in portal hypertension causes caput Medusae wherever non-peritoneal areas of intestines, liver and pancreas (portal circulation) are in contact with body wall (systemic circulation) https://sites.google.com/view/grossanatomyii/week-7-lecture-notes 6/21/24, 2:17 PM Page 37 of 38