Physician Associate GIT 2 - Lower GIT PDF 2024-2025

Physician Associate 2024-2025 Copyright © 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc. 1 Anatomy of Lower GI Year 1 PA Dr Hayder Lazim MBChB, MSc, PhD, FHEA [email protected] 2  Learning outcome B...

Physician Associate 2024-2025 Copyright © 2014, 2010, 2006 by Mosby, Inc., an imprint of Elsevier Inc. 1 Anatomy of Lower GI Year 1 PA Dr Hayder Lazim MBChB, MSc, PhD, FHEA [email protected] 2  Learning outcome By the end of this lecture, you will be able to describe and discuss: o The anatomy of the small and large intestine o The blood supply of the small and large intestine o The portal vein o The peritoneum and the major peritoneal folds 3 GIT 4 Small intestine 5  Small intestine Comprises the jejunum and ileum Together measure between 4 - 7 m It lies in the central abdomen, below the transverse colon 6  Small intestine In the living, the jejunum can be distinguished from the ileum by the following features: The jejunum occupy mainly the upper left part of the abdominal cavity. The jejunum makes up the upper two fifths of this length The ileum occupy the lower right part of the abdominal cavity and the pelvic cavity The jejunum begins at the duodenojejunal junction The ileum ends at the ileocecal junction # 7  Small intestine The jejunum is wider and thicker walled and redder than the ileum. Its mucous membrane is thrown into permanent circular folds (plicae circulares), which give it a characteristic appearance in radiographic contrast studies The jejunum less fat in its mesentery, which allows the surgeon to distinguish it from the ileum at operation. 8  Small intestine The jejunal mesentery is attached to the posterior abdominal wall above and to the left of the aorta, whereas the ileal mesentery is attached below and to the right of the aorta. 9  Small intestine  The jejunal mesenteric vessels form only one or two arcades, with long and infrequent branches (vasa recta) passing to the intestinal wall. The ileum receives numerous short terminal vasa recta that arise from a series of three or four or even more arcades.  Aggregations of lymphoid tissue (Peyer patches) are present in the mucous membrane of the lower ileum along the antimesenteric border. In the living, these may be visible through the wall of the ileum from the outside. 10  Barium study Barium meal and follow-through, demonstrating stomach and small intestine showing circular folds of duodenal mucosa and featureless ileum: 1. Stomach 2. Jejunum 3. Loops of ileum 11  Lactose Intolerance The absorptive cells of the small intestine fail to produce enough lactase, which, is essential for the digestion of lactose. Undigested lactose in chyme causes fluid to be retained in the feces; bacterial fermentation of the undigested lactose results in the production of gases. Symptoms include diarrhea, gas, bloating, and abdominal cramps after consumption of milk and other dairy products. The hydrogen breath test is often used to aid in diagnosis of lactose intolerance. The hydrogen is absorbed from the intestines and carried through the bloodstream to the lungs, where it is exhaled. 12 Large intestine 13  Large intestine 1.5 m long Extends from the ileocaecal junction to the anus The caecum, appendix, ascending, transverse, descending and sigmoid colon, rectum and anal canal The longitudinal muscle is collected into three bands, the teniae coli. Fatty tags, the appendices epiploicae The large intestine is sacculated in large folds termed haustra 14  The cecum Is a blind sac, about 8 cm in diameter In the right iliac fossa The ileocaecal orifice The base of the appendix is attached to the posteromedial surface of the cecum about 2.5 cm below the ileocecal junction 15 Appendix (Vermiform Appendix) Is a narrow, muscular tube containing a large amount of lymphoid tissue. 8 - 13 cm It has a complete peritoneal covering, which is attached to the mesentery of the small intestine by a short mesentery of its own, the mesoappendix. McBurney’s point 16  The ascending colon lies in the right lateral region It is about 15 cm long Extending from the caecum to the hepatic flexure of the colon under the right lobe of the liver. Right paracolic gutter of peritoneum along its right side which leads to the right subphrenic space. 17  The transverse colon Extends from the hepatic flexure to the splenic flexure across the abdomen. It is about 50 cm long. It hangs downward, suspended by the transverse mesocolon from the pancreas The left colic flexure is higher than the right colic flexure and is suspended from the diaphragm by the phrenicocolic ligament ? 18  The transverse colon The transverse mesocolon (mesentery of the transverse colon) suspends the transverse colon from the anterior border of the pancreas Barium swallow, Barium meal, Barium follow-through, Barium enema? 19  The descending colon The narrowest part of the colon About 30 cm long lies in the left lateral region Left lies the left paracolic gutter (of peritoneum) It extends downward from the left colic flexure, to the pelvic brim, where it becomes continuous with the sigmoid colon. 20  The sigmoid colon 10 to 15 in. (25 to 38 cm) long Mobile and hangs down into the pelvic cavity Form of a roughly S-shaped loop Lies in the left iliac region extending from the pelvic brim to the front of the 3rd sacral vertebra, where it becomes the rectum. It is attached to the pelvic wall by an inverted V- shaped mesentery, the sigmoid mesocolon ? The apex of the inverted V-shaped mesentery overlies the left ureter, the bifurcation of the left 21 common iliac artery and the left sacroiliac joint.  The rectum About 13 cm long. Extends from the sigmoid colon to the anal canal. The lower part of the rectum is dilated to form the rectal ampulla. Begins in front of the 3rd sacral segment, curving forwards with a loop to the left to the tip of the coccyx. No mesentery; its upper third is covered by peritoneum on its front and sides, the middle on its front only and its lower third lies extraperitoneally. The three teniae coli of the sigmoid colon come 22 The rectum 23  External differences between the small and large intestines The small intestine (with the exception of the duodenum) is mobile, whereas the ascending and descending parts of the colon are fixed. The caliber of the full small intestine is smaller than that of the filled large intestine. The small intestine (with the exception of the duodenum) has a mesentery that passes downward across the midline into the right iliac fossa. 24 Differences between Small and Large Intestines 25  External differences between the small and large intestines The longitudinal muscle of the small intestine forms a continuous layer around the gut. In the large intestine (with the exception of the appendix), the longitudinal muscle is collected into three bands, the teniae coli. The small intestine has no fatty tags attached to its wall. The large intestine has fatty tags, called the omental appendices (appendices epiploicae; epiploic appendages). The wall of the small intestine is smooth, whereas that of the large intestine is sacculated in large folds termed haustra. 26 Differences between Small and Large Intestines 27  Internal differences between the small and large intestines The mucous membrane of the small intestine has permanent folds, called plicae circulares, which are absent in the large intestine. The mucous membrane of the small intestine has villi, which are absent in the large intestine. Aggregations of lymphoid tissue called Peyer patches are found in the mucous membrane of the small intestine; these are absent in the large intestine. 28 Differences between Small and Large Intestines 29  General arrangement of abdominal viscera Abdominal viscera: 1. liver; 2. oesophagus; 3. stomach; 4. spleen; 5. gallbladder; 6. first part of duodenum; 7. head of pancreas; 8. duodenojejunal flexure; 9. transverse colon; 10. ascending colon; 11. descending colon; 12. sigmoid colon; 13. terminal ileum; 14. appendix 30 31 32 Blood supply of the small and large intestine 33  Blood supply and organs of the GI Tract The GI tract is divided based on vascular supply into 3 parts (embryology): Coeliac trunk – foregut - from the lower 1/3 of the esophagus down as far as the middle of the second part of the duodenum Superior mesenteric - midgut - from the middle of the second part of the duodenum as far as the distal one third of the transverse colon. Inferior mesenteric - hindgut - the large intestine from the distal one third of the transverse colon to halfway down the anal canal. 34  Superior mesenteric artery Arises just below the coeliac trunk (L1) Runs down behind the neck of the pancreas Passes anterior to third part of duodenum Runs between layers of ‘The Mesentery’ Ends by anastomosing with ileal branch of its own ileocolic branch 35 Superior mesenteri c artery 36  Superior mesenteric artery o Inferior pancreaticoduodenal artery - anastomose with the superior pancreaticoduodenal artery o Middle colic artery - branches supply the right two-thirds of the transverse colon o Right colic artery- ascending and descending branches-supplies the ascending colon - anastomoses with the ileocolic and middle colic arteries. o Jejunal and ileal arteries, 15–20 in number, arising from the left of the artery within the small bowel mesentery - side-to-side anastomoses between these branches, and tiers of arterial arcades are formed o Ileocolic artery, which descends to the right, dividing to supply the caecum, appendix and lower ascending colon.  Anterior and posterior cecal arteries  The appendicular artery is a branch of the posterior cecal artery 37  Inferior mesenteric artery Arises about 1.5inches above the bifurcation of the aorta Runs down and to the left, crossing the left common iliac artery Becomes the Superior Rectal Artery (Which anastomoses with the middle and inferior rectal arteries) 38  Inferior mesenteric artery o Left colic artery - transverse and descending colon - anastomoses with the middle colic and sigmoid arteries. o Sigmoid arteries - supply the sigmoid and lower descending colon. o Superior rectal artery, which is the continuation of the inferior mesenteric artery - supplies the rectum and upper anal canal. 39  The rectum The superior, middle, and inferior rectal arteries The superior rectal artery is a direct continuation of the inferior mesenteric artery The middle rectal artery is a small branch of the internal iliac artery. The inferior rectal artery is a branch of the internal pudendal artery in the perineum. It anastomoses with the middle rectal artery at the anorectal junction. 40  The Marginal Artery Anastomoses of the colic arteries to form a single arterial trunk Begins at ileocaecal junction where is anastomoses with ileal artery and ends at superior rectal 41 Portal vein 42 The Formation of the Portal Vein From the lower end of the oesophagus to the upper end of the anal canal, blood from the gastrointestinal tract drains into the liver The superior mesenteric vein joins the splenic vein to form the portal vein; the inferior mesenteric vein enters the splenic vein to the left of this 43  Portal-Systemic Anastomoses Small communications exist between the portal and systemic systems: 1. Oesophageal 2. Rectal 3. Paraumbilical 4. Retroperitoneal (colic) o Important if the direct route becomes blocked 44  Oesophageal Varices Portal hypertension, commonly caused by cirrhosis Dilated veins in lower third of oesophagus Can lead to life-threatening variceal haemorrhaging 45  Caput Medusae Distended and engorged paraumbilical veins Radiation of the veins from the umbilicus across the abdomen to joint the systemic veins Appearance like that of Medusa who had venomous snakes in place of hair (greek mythology) 46 Peritoneum 47  Peritoneum o The peritoneum (peri- around) is the largest serous membrane of the body lining of the abdominal and pelvic cavities o The peritoneum is divided into:  the parietal peritoneum, which lines the wall of the abdominal cavity  the visceral peritoneum, which covers some of the organs in the cavity o Peritoneal cavity between the two layers of peritoneum  Potential Space  A ‘closed’ cavity in males  Communication with the exterior via the vagina, uterus and uterine tubes in females 48  Peritoneum Divided into two parts: the greater sac and the lesser sac. The greater sac is the main compartment and extends from the diaphragm down into the pelvis. The lesser sac is smaller and lies behind the stomach. The greater and lesser sacs are in free communication with one another through an oval window called the opening of the lesser sac, or the epiploic foramen 49  Peritoneal Reflections o Intraperitoneal  When an organ is completely covered with visceral peritoneum Visceral  e.g. Stomach, jejunum, ileum, peritoneu m  Organs are attached to each other or to the abdominal wall by peritoneal folds, known as a mesentery Peritoneal Mesentery o Retroperitoneal Parietal  When an organ lies behind the peritoneum, only partially covered peritone um  e.g. Pancreas, ascending and descending colon Visceral peritoneu o Extraperitoneal m  Lying outside the peritoneum Parietal peritoneu  May be fat, tissue etc m 50  Major peritoneal folds o The greater omentum (fat skin), the largest peritoneal fold, drapes over the transverse colon and coils of the small intestine like a “fatty apron” o The falciform ligament (falc- sickle-shaped) attaches the liver to the anterior abdominal wall and diaphragm o The lesser omentum arises as an anterior fold in the serosa of the stomach and duodenum, and it connects the stomach and duodenum to the liver o A fan-shaped fold of the peritoneum, called the mesentery (mes- middle), binds the jejunum and ileum of the small intestine to the posterior abdominal wall o Two separate folds of peritoneum, called the mesocolon , bind the transverse colon (transverse mesocolon) and sigmoid colon (sigmoid mesocolon) of the large intestine to the posterior abdominal wall 51  Major peritoneal folds 52  Innervation of the Peritoneum Parietal Sensitive to pain, temperature, touch and pressure Innervated by T7-L1 as it lines anterior abdominal wall and peripheral diaphragm Central tendon of diaphragmatic parietal peritoneum is supplied by the phrenic nerves Visceral Sensitive only to stretch and tearing NOT touch, pressure or temperature Overdistension of the viscera leads to the sensation of pain 53  Peritonitis A common cause of peritonitis , an acute inflammation of the peritoneum, is contamination of the peritoneum by infectious microbes, which can result from accidental or surgical wounds in the abdominal wall, or from perforation or rupture of abdominal organs. If bacteria gain access to the peritoneal cavity through an intestinal perforation or rupture of the appendix, they can produce an acute, life-threatening form of peritonitis. 54 Your turn! 55 Your turn! 56  Lecture contents We o Understand the anatomy of the small and large intestine o Understand the blood supply of the both small and large intestine o Understand the portal vein o Understand the peritoneum and the major peritoneal 57  All images are copyright their owners Images will be removed if requested Icons madebybythe Freepik from creator Flaticon.com Content © Edge Hill University Medical School James’ Place provides suicidal crisis support www.jamesplace.org.uk for men Text JP to 85258 www.mind.org.uk Here to make sure no one has to face 86463 a mental health problem alone 0300 123 3393 [email protected] www.samaritans.org We support anyone who needs help. 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