Kingdom of Bahrain Arabian Gulf University College of Medicine and Medical Sciences

1. Kingdom of BahrainArabian Gulf UniversityCollege of Medicine and Medical Sciences GI System – Review Problem (6) – Small and Large Bowel Ali Jassim Alhashli, BSc www.alhashli.com

2. Anatomy and Embryology of Small Bowel • Embryology: • 4th week: primitive gut tube (from endoderm) will divide into: foregut, midgut and hindgut. • Endoderm: becomes intestinal epithelium and glands. • Mesoderm: becomes connective tissue, muscle and wall of intestine. Notice that the junction between foregut and midgut is at the opening of common bile duct. • 5th week: midgut loop herniates through the umbilical ring. • 10th week: midgut rotates a total of 270 degrees counterclockwise around the axis of superior mesenteric artery (SMA) and returns back to abdominal cavity.

3. Anatomy and Embryology of Small Bowel

4. Anatomy (continued): • Jejunum and ileum: • Jejunum is the first 40% of small intestine distal to ligament of Treitz. • Ileum is the second 60% of small intestine distal to ligament of Treitz. • Mesentery attaches both jejunum and ileum to posterior abdominal wall. • Arterial supply: SMA. • Venous drainage: SMV. • How to differentiate between jejunum and ileum on gross inspection? • Jejunum: larger diamter, thicker wall, more prominent plicacircularis, few aracades, long vasa recta. • Ileum: smaller diameter, thinner wall, less prominent plicacircularis, more arcades and short vasa recta. • Lymphatic drainage of small bowel: • It participates in absorption of fat. • Bowel wall → mesenteric lymph nodes → through lymphatic vessels to cyternachyli (a retroperitoneal organ between aorta and IVC) → thoracic duct → left subclavian vein. • Innervation: • Parasympathetic: vagus nerve; for peristalsis and enhancement of bowel secretions. • Sympathetic: plexus at the base of SMA; inhibiting peristalsis and bowel secretions. • Enteric nervous system: • Meissner plexus: submucosa. • Auerbach plexus: between inner circular and outer longitudinal muscle of the wall. Anatomy and Embryology of Small Bowel

5. Anatomy and Embryology of Small Bowel

6. Anatomy and Embryology of Large Bowel • Embryology: • Midgut: from ampulla of Vater to mid-transverse colon. Midgut is supplied by SMA. • Hindgut: rest of the colon to proximal anus. Hindgut is supplied by IMA. • Distal anus from ectoderm. Blood supply from branches of internal pudendal artery. • Dentate line marks the transition between proximal anus and ectoderm. • Anatomy: • Colon: • It extends from ileocecal valve to the rectum and consists of: cecum, ascending colon, transverse colon, descending colon and sigmoid colon (1-1.5 meters in length). • Colon is characterized by the presence of: • Haustra • Taenia coli: 2 distinct bands of longitudinal muscle converging at the appendix. • Fat appendages. • Intraperitonealvs retroperitoneal parts of the colon: • Intraperitoneal: cecum, transverse colon and sigmoid colon. • Retroperitoneal: ascending colon, descending colon and posterior parts of hepatic and splenic flexures.

7. Anatomy and Embryology of Large Bowel

8. Anatomy and Embryology of Large Bowel • Anatomy (continued): • Rectum: • Length: 15 cm. • Fascia: • Waldeyer’s fascia: extending from S4 vertebra (in sacrum) to the rectum. • Denovillier’s fascia: anterior to lower third of the rectum. • Pelvic floor: • Formed by levatorani which is composed of the following muscle: pubococcygeus, iliococcygeus and puborectalis. Levatorani is innervated by S4. • Anus: • Anal canal extends from pelvic floor to anal verge (junction between anoderm and perianal skin). • Dentate line: separates proxminal anus in which epithelium is columnar from distal anus in which the epitheliam is squamous (from ectoderm). • Columns of Morgagni: 12-14 columns, superior to dentate line, separated by crypts, perianal glands discharge their secretions at the base of these columns. • Anal sphincter: • Internal anal sphincter: made of smooth muscle, involuntary, contracted at rest. • External anal sphincter: made of striated muscle, voluntary.

9. Anatomy and Embryology of Large Bowel

10. Anatomy and Embryology of Large Bowel • Blood supply: • Arterial supply: • SMA: • Supplies cecum, ascending colon and proximal 2/3 of transverse colon. • Via: ileocolic, right colic and middle colic arteries. • IMA: • Supplies: distal third of transverse colon, descending colon, sigmoid colon and superior rectum. • Via: left colic, sigmoidal and superior rectal arteries. • Notice that splenic flexure represents “watershed” area between the areas supplied by SMA and IMA. • Internal iliac artery: • Supplies: middle and distal rectum. • Via: middle and inferior rectal arteries. • Internal pudendal artery: • Supplies the anus. • Venous drainage: • SMV: drains cecum, ascending colon and transverse colon. • IMV: drains descending colon, sigmoid colon and superior rectum. • Internal iliac veins: drain middle and inferior rectum. • Middle rectal vein: drains upper anus. • Inferior rectal vein: drains lower anus.

11. Anatomy and Embryology of Large Bowel

12. Anatomy and Embryology of Large Bowel • Innervation: • Sympathetic: inhibits peristalsis. • Parasympathetic: stimulates peristalsis. • Lymphatic drainage of anal canal: • Above dentate line: internal iliac lymph nodes. • Below dentate line: inguinal lymph nodes. • Histology: • Colon and rectum: mucosa, submucosa, inner circular muscle layer and outer longitudinal muscle layer. • Anus: anoderm.

13. Physiology of Large Bowel • What are the functions of colon and rectum? • Absorption of water and electrolytes from stool. • Storage of feces. • Motility: • Segmental contraction (most common): localized simultaneous contractions of longitudinal and circular muscle of the colon. • Retrograde movement (from transverse colon to cecum): prolonging the time of presence of colon contents to increase the absorption of water and electrolytes. • Mass movement: • Antegrade propulsion of luminal contents. • Duration = 30 seconds, frequency: 3-4 times/day (especially after waking up or eating), rate = 0.5-1 cm/second. • Neuronal control of the colon: • Extrinsic: sympathetic and parasympathetic. • Intrinsic: Meissner’s plexus and Auerbach’s plexus. • Process of defecation: • Mass movement will push feces to be stored in the rectum. • Rectum will distend causing relaxation of internal sphincter. • Relaxation of external sphincter leads to propulsion of feces through anal canal. • Increased intra-abdominal pressure aids in the propulsion of feces.

14. Physiology of Large Bowel

15. Duodenal atresia: • Definition: failure of duodenum to recanalize during fetal development. Mostly occurs at the site of ampulla of Vater. • Associate conditions: • Down syndrome. • Imperforate anus. • Esophageal atresia. • Polyhydramnios. • Small for gestational age. • Signs and symptoms: • Abdominal distention. • Bilious vomiting. • Diagnosis: • AXR: double bubble sign (air in stomach and duodenum). • Treatment: • Fluid replacement. • Gastric decompression. • Broad-spectrum antibiotics. • Surgery: • Duodenal atresia: side-to-side anastomosis. • Jejunoilealatresia: end-to-end anastomosis. Duodenal Atresia

16. Meckel’sDiverticulum • Meckel’sdiverticulum (true diverticulum): • Definition: persistent vitelline duct which does not obliterate. It contains heterotopic epithelium (gastric or pancreatic). • Epidemiology: it is more common in males > 2 years of age. • Rule of 2’s: • 2 feet away from ileocecal valve. • 2 inches (length). • 2% of population. • Symptomatic in 2% of patients. • 2 types of tissues (gastric and pancreatic). • Under 2 years of age. • Signs and symptoms: • Most important: intermittent painless rectal bleeding. • Intestinal obstruction. • Diverticulitis. • Diagnosis: Mickel’s scan (scintigraphy). • Treatment: surgical resection.

17. Volvulus • Definition: twisting of a segment of bowel around its mesenteric axis especially occurring in elderly. • Location: • Most common: sigmoid (75%). • Cecum (25%). • Risk factors: • Old age. • Chronic constipation. • Hypermobilececum. • Psychotropic drugs. • Signs and symptoms: • Abdominal distention. • Crampy abdominal pain. • Constipation/obstipation. • Nausea and vomiting. • Diagnosis: • AXR: kidney bean appearance. • Barium enema: bird’s beak at areas of colonic narrowing. • Treatment: • Cecalvolvulus: right hemicolectomy. • Sigmoid volvulus: • Acute setting: decompression with rigid sigmoidoscopy. • Surgery (emergent if there is strangulation of perforation)

18. Intussusception: • Definition: telescoping of one portion of the bowel into the other. Common site is ileocecal valve. • Epidemiology: • It is the most common cause of intestinal obstruction in males under 2 years of age. • Causes: • Idiopathic. • Hypertrophy of Peyer’s patches after viral infection (enterovirus in summer; rotavirus in winter). • Meckel’sdiverticulum. • Polyp. • Lymphoma. • Henoch-Schonleinpurpura. • Cystic fibrosis. • Signs and symptoms: • Intermittent colicky abdominal pain. • Currant-jelly stool. • Bilious vomiting. • Sausage-like mass in RUQ. • Diagnosis and treatment: • Abdominal x-ray and ultrasound: target sign. • Barium enema (both diagnostic and theraputic): • It will show: coiled spring appearance. • Rule of 3’s: • Barium column should not exceed a height of 3 feet. • 3 attempts. • 3 minutes/ each attempt • Recurrence: • Reduction with barium: 10% • Surgical reduction: 5% Intussusception

19. Lactose tolerance: • Etiology: lactose is a disaccharide which is composed of (glucose + galactose) and is found in diary products. In patients with lactose intolerance, there is deficiency of the enzyme lactase thus there will be malabsorption of lactose. • Clinical manifestations: • Osmotic diarrhea. • Abdominal pain. • Bloating and flatulence. • NOTICE THAT PATIENTS WILL NOT HAVE WEIGHT LOSS. • Diagnosis: • ↑stool osmolality (due to presence of lactose) and increased osmolar gap. • Confirmation: by removing diary products from diet and resolution of symptoms within 24-36 hours. • Treatment: • Avoid lactose in the diet. • Lactase supplements can be given. • Irritable Bowel Syndrome (IBS): • Definition: it is an idiopathic disorder in which there is increased peristalsis and segmentation contractions of the bowel. • Etiology: unknown. • Clinical manifestations: • 20% of patients having constipation ONLY. • A large number of patients will have diarrhea alternating with constipation. • All patients will have abdominal pain. • Diagnosis: Rome criteria which must be present for ≥ 3 months • Diarrhea alternating with constipation. • Abdominal pain relieved with defecation. • Fewer symptoms at night. • Treatment: • High-fiber diet to increase the bulk of the stool. • Those with predominant diarrhea: antidiarrhea such as (loperamide can be used). • Antispasmodic agents can be tried → if they do not work → try tricyclic antidepressants. Lactose Intolerance and IBS

20. Lactose Intolerance and IBS

21. Etiology: major causes of fat malabsorption are • Celiac disease (most common). • Chronic pancreatitis. • Tropical sprue. • Whipple disease (rarest). • Clinical manifestations: • Triad of: • Chronic diarrhea in the form of steatorrhea (greasy, fatty, foul-smelling stool which is not easily flushed). • Weight loss. • Malabsorption of fat-soluble vitamins (A, D, K and E). • If the disease is affecting duodenum (such as in celiac disease) → there will be malabsorption of iron leading to iron-deficiency anemia. • If the disease is affecting terminal ileum → this can result in megaloblastic anemia due to vitamin B12 deficiency. • 10% of patients with celiac disease might also have a vesicular rash on the extensor surfaces of their body known as dermatitis herpetiformis. • Patients with chronic pancreatitis will have a history of repeated pancreatitis due to alcohol or gallstones. • Diagnosis: • Celiac disease: • Initial: anti-endomysial antibodies and anti-transglutaminase antibodies. • Most accurate: small bowel biopsy which will show atrophy of villi, lymphocytic infiltration and crypts elongation. • Chronic pancreatitis: • Abdominal X-ray/ CT-scan showing calcification of the pancreas. • Most accurate (although rarely done) is secretin test in which secretin will be injected in the blood but there will be no release of bicarbonate or enzymes in the duodenum. • Tropical sprue and whipple disease: diagnosed by bowel biopsy to find organisms. In whipple disease, the presence of T.whippellii in in macrophages will give foamy macrophages that are Periodic-Acid-Schiff (PAS) stain positive. • Treatment: • Celiac disease: gluten-free diet. If a patient has dermatitis herpetiformis → dapsone. • Chronic pancreatitis: replacement of pancreatic enzymes and fat-soluble vitamins. • Tropical sprue/ whipple disease: treated with timethoprim/sulfamethoxazole or doxycycline. Malabsorption Syndromes

22. Malabsorption Syndromes

23. Inflammatory Bowel Disease (IBD): • Definition: the term includes both Crohn’s Disease (CD) and Ulcerative Colitis (UC). They are discussed together because there are similarities between them: • Etiology: both are of unknown etiology, but CD is thought to be a response to intestinal bacteria while UC is thought to be an autoimmune disease. • Clinical manifestations: they present with diarrhea (± blood), abdominal pain, fever and weight loss. • Diagnosis: • Barium studies: CD reveals (string-sign) while UC reveals (lead-pipe appearance). • Most accurate diagnostic way is: endoscopy. • CD has positive Anti-SaccharomycesCerevisiae Antibodies (ASCA) while UC has positive (ANCA). • Treatment: • Acute exacerbation are treated with steroids. • Long-term management: with anti-inflammatory drugs (such as salicylic acid) and azathioprine. • Features of CD and UC: • CD: diarrhea (usually not bloody); it can involve the whole GI tube from mouth to anus (but commonly affecting terminal ileum); inflammation is transmural (whole-thickness of GI wall); it produces skip lesions (lesions are not continuous); there might be a palpable abdominal mass due to formation of granulomasin bowel wall; extra-intestinal manifestations including joint pain and skin manifestations such as erythemanodosum; barium showing string sign; complications include perforation, fistual and strictures, getting worse with smoking. • UC: diarrhea (usually bloody); it only involves the colon and starting from rectum; inflammation involves only the mucosa, lesions are continuous, barium showing lead-pipe; increased risk for cancer, smoking is protective, surgical resection of affected part is curative. Inflammatory Bowel Disease (IBD)

24. Inflammatory Bowel Disease IBD (continued): • Treatment: • Mainstay of treating IBD is aminosalicylic acid: • CD: pentasa which is released in upper and lower bowel. • UC: asacol which is released in large bowel. • Long-term therapy also includes azathioprine (to reduced the need for steroids). • Acute exacerbations of IBD are treated with high-doses of steroids (the choice is budesonide). • In patients with CD which is refractory to medical therapy mentioned previously, you can try infliximab (but you have to test for tuberculosis by PPD). • Surgery is curative for UC but not very effective in CD. Inflammatory Bowel Disease (IBD)

25. Inflammatory Bowel Disease (IBD) Crohn’s disease-skip lesions Crohn’s disease-string sign

26. Inflammatory Bowel Disease (IBD) Ulcerative colitis-lead pipe

27. Hirschsprung’s disease: • Definition: it is the lack of Auerbach (myenteric) and Meissner (submucosal) plexi thus resulting in intestinal obstruction. • There are 3 types: • Rectal. • Rectosigmoid. • Entire colon. • Signs and symptoms: • Neonates: • Failure to pass meconium (< 24 hours). • Most common cause of mortality is enterocolitis. • Children: • Abdominal distention. • Bilious vomiting. • Chronic constipation. • Diagnosis: • AXR. • Barium enema: look for transition zone which may not appear before 1-2 weeks of age. • Definitive diagnosis: rectal biopsy (showing absence of ganglion cells). • Treatment: • Colostomy proximal to the transition zone. • Surgical resection when age reaches 6-12 months. • Colostomy kept after surgery for 1-3 months. Hirschsprung’s Disease

28. Hirschsprung’s Disease

29. Diverticulosis: • Diverticula: it is a blind tube forming a cavity. • Etiology: • It is occurring more commonly in elderly and might be considered as a normal part of aging. • It occurs mainly due to lack of fiber in the diet which subsequently causes increased intracolonic pressure that results in outpouching of the colonic wall. • Clinical manifestations: patients are usually AYMPTOMATIC, but if they have symptoms they are mainly: • Left lower abdominal pain (which can be colicky). This occurs when diverticula is formed in the sigmoid colon. • Painless bleeding especially if diverticula is formed in the right colon (due to a thinner wall). • Diagnosis: colonoscopy. • Treatment: increasing fiber in the diet. • Diverticulitis: • Definition: infection/inflammation of a diverticula. • Etiology: blockage of diverticula entrance with nuts or corn. • Clinical manifestations: fever and more intense pain. • Diagnosis: • ↑WBCs. • Confirmed by: CT-scan. • Treatment: • Antibiotics: such as ciprofloxacin and metronidazole. • Mild disease: augmentin. Diverticular Disease

30. Diverticular Disease Diverticulosis (barium enema) Diverticulitis CT-scan