Where is the largest number of hormone-producing cells found in the body?
The small intestine is the body’s largest reservoir of hormone-producing cells. Multiple specialized cells within the intestinal mucosa respond to luminal stimuli and secrete over 30 peptide hormones which regulate the functions of the intestine, other organs in the gastro-entero-pancreato-biliary system, the heart, and the brain (See Schwartz 10th ed., p. 1145.)
Which of the following features is characteristic of the ileum, as opposed to the jejunum?
A. The presence of valvulae conniventes
B. The presence of Peyer patches
The entire small intestine contains valvulae conniventes, also known as plicae circularis. The jejunum has larger vasa recta, a larger diameter, and a less fatty mesentery. The ileum contains prominent lymphoid follicles called Peyer patches. (See Schwartz 10th ed., p. 1138.)
Within the intestine, epithelial cells originate from stem cells, proliferate in the crypts, and migrate up the villus in 2 to 5 days. This process replaces cells that are removed due to apoptosis or exfoliation. This rapid turnover makes the small intestine susceptible to
The high cellular turnover rate of enterocytes makes the small intestine susceptible to damage by inhibitors of proliferation such as radiation and cytotoxic chemotherapy. (See Schwartz 10th ed., p. 1138.)
A pocket- or sock-like outpouching on the anti-mesenteric side of the distal ileum, called a Meckel diverticulum, is caused by
A. Excessive traction on the intestine during childbirth.
B. Increased intraluminal pressure.
C. A persistent vitelline duct.
D. A mutation of the c-Mec gene.
The embryonic gut communicates with the yolk sac by mean of the vitelline duct. Failure of this structure to obliterate by the end of gestation can result in a Meckel diverticulum. (See Schwartz 10th ed., p. 1139.)
How much fluid normally enters the adult small intestine each day?
Eight to nine liters of fluid enters the small intestine daily, of which over 80% is absorbed. This includes 2 L from oral intake, 1.5 L of saliva, 2.5 L of gastric juice, 1.5 L of biliopancreatic secretions, and 1 L of fluid secreted by the small intestine. (See Schwartz 10th ed., p. 1140.)
How are the digestion products of carbohydrates, such as glucose, galactose, and fructose, absorbed through the intestine?
A. By passive diffusion across enterocyte plasma membranes.
B. By facilitated diffusion via specific transporters such as sodium-glucose cotransporter 1 (SGLT1), glucose transporter 2 (GLUT2), and glucose transporter 5 (GLUT5).
C. By endocytosis of enterocytes on the villus.
D. By facilitated diffusion through tight junctions between enterocytes.
The three terminal products of carbohydrate digestion are transported through the enterocyte brush border membrane via facilitative transporter proteins such as the sodium-glucose cotransporter 1 (SGLT1), glucose transporter 2 (GLUT2), and glucose transporter 5 (GLUT5). There is evidence of overexpression of these transporters, particularly SGLT1, in diabetes and obesity, and new therapeutic approaches for these conditions are designed to inhibit these transporters. (See Schwartz 10th ed., p. 1141.)
What does the “enterohepatic circulation” refer to?
A. The superior mesenteric-portal venous circuit.
B. The secretion of cholesterol in the bile and its reabsorption in the distal ileum.
C. The secretion of bile acids by the liver and their reabsorption in the distal ileum.
D. The secretion of cholecystokinin by the jejunum and its stimulation of bile flow.
Bile acids act as detergents which increase the solubility of lipid micelles which are taken up by the brush border membrane of the jejunum, where over 90% of fat is absorbed. The bile acids themselves remain in the intestinal lumen and are reabsorbed in the distal ileum where they enter the portal venous circulation and are re-secreted in the bile. (See Schwartz 10th ed., p. 1143.)
The secretin-glucagon family of gut hormones includes all of the following structurally related peptides EXCEPT
B. Glucose-dependent insulinotropic polypeptide (GIP)
C. Glucagon-like peptide-1 (GLP-1)
D. Vasoactive intestinal polypeptide (VIP)
Peptide hormones produced by enteroendocrine cells of the intestine are grouped into families based on their amino acid structural similarity. The secretin-glucagon family of hormones includes glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine (PHI), growth hormone-releasing hormone (GHRH), and pituitary adenylyl cyclase-activating peptide (PACAP). (See Schwartz 10th ed., p. 1145.)
The most common cause of small bowel obstruction is
D. Postoperative adhesions
Intra-abdominal adhesions related to prior abdominal surgery accounts for 75% of cases of small bowel obstruction. Cancer-related small bowel obstruction is almost always due to extrinsic compression or entrapment of the bowel by a primary or metastatic tumor; primary small bowel malignancies are rare. (See Schwartz 10th ed., p. 1146.)
A closed-loop obstruction is particularly dangerous because
A. Intraluminal pressure rises high enough to cause ischemia and necrosis.
B. The obstruction is painless.
C. Bacterial overgrowth results in sepsis.
D. The obstructive segment is not apparent on imaging studies.
A closed-loop obstruction, in which an intestinal segment is obstructed both proximally and distally, as in a volvulus, is particularly dangerous because intraluminal pressure rises quickly and can cause venous congestion and arterial obstruction which leads to necrosis of the intestinal wall and perforation. It classically presents with “pain out of proportion to the physical exam,” and is usually apparent on CT scan which frequently shows a U-shaped or C-shaped dilated bowel loop associated with a radial distribution of mesenteric vessels converging toward a torsion point. (See Schwartz 10th ed., p. 1147.)
Therapy of a small bowel obstruction usually consists of prompt surgical correction. In patients with no evidence of closed-loop obstruction, and in whom there is no fever or leukocytosis or tachycardia, a period of careful observation with nasogastric decompression may be successful in all of the following conditions EXCEPT
A. Partial small bowel obstruction.
B. Obstruction in the early postoperative period.
C. Obstruction due to Crohn disease.
D. Obstruction due to an internal hernia.
Partial small bowel obstruction and early postoperative obstruction can mimic ileus, and may respond to nonoperative therapy. Crohn disease usually responds to medical therapy, although recurrent obstruction is an indication for surgical correction. Obstruction due to an internal hernia requires prompt surgical intervention to avoid strangulation and necrosis. (See Schwartz 10th ed., p. 1149.)
Interventions which may reduce the incidence and duration of postoperative ileus include all of the following EXCEPT
B. A m-opioid receptor antagonist
C. Intravenous erythromycin
D. Avoiding excess intra- and postoperative fluid administration
Epidural analgesia (with reduced systemic narcotic administration), avoiding excess intra- and postoperative fluid administration, and administration of alvimopan, a mu-opioid receptor antagonist, have all been associated with reduced incidence and/or duration of postoperative ileus. Prokinetic agents such as metoclopramide and erythromycin are rarely useful. (See Schwartz 10th ed., p. 1153.)
Risk factors for the development of Crohn’s disease include all of the following EXCEPT
A. Having a family member with Crohn’s disease
C. Having Chinese ancestry
D. Having Ashkenazi Jewish ancestry
The risk of having Crohn’s disease is two- to fourfold higher in Ashkenazi Jewish families, 15 times higher in family members of a patient with Crohn’s disease, and is increased in higher socioeconomic groups, and among smokers. The incidence in China is 1% of the incidence in the United States, although this number is increasing. (See Schwartz 10th ed., p. 1153.)
The primary genetic defect associated with Crohn’s disease is a mutation of the NOD2 gene on chromosome 16. This gene encodes for a protein product which
A. Mediates the innate immune response to microbial pathogens
B. Activates stellate cells to produce collagen
C. Regulates the rate of crypt-to-villus enterocyte migration
D. Mediates the production of enterocyte alkaline phosphatase
The protein product of the NOD2 gene mediates the innate immune response to microbial pathogens. A variety of defects in immune regulatory mechanisms such as overresponsiveness of mucosal T cells to enteric flora-derived antigens can lead to defective immune tolerance and sustained inflammation. (See Schwartz 10th ed., p. 1153.)
In the resection of a stenotic area of intestine in a patient with Crohn’s disease, the best approach is
A. A resection margin of 2 cm from gross disease.
B. A resection margin of 12 cm from gross disease.
C. A resection margin 2 cm from microscopic disease on frozen section.
D. A resection margin 12 cm from microscopic disease on frozen section.
There are no differences in the recurrence rates for resection with a 2-cm margin or a 12-cm margin from gross disease. The additional bowel lost may contribute to eventual short gut syndrome in a patient who requires multiple resections, so minimizing bowel loss is a priority. There is no benefit to achieving frozen section negative margins in the resection of Crohn’s strictures; positive margin resections have the same recurrence rate as negative margin resections. The effort to obtain a frozen section negative margin carries the risk of removing more intestine than is necessary. (See Schwartz 10th ed., p. 1157.)
The failure of an enterocutaneous fistula to heal on a regimen of total parenteral nutrition and antisecretory therapy may be due to which of the following?
A. A foreign body in the fistula tract.
B. Epithelialization of the fistula tract.
C. Downstream obstruction of the fistulized segment of intestine.
Factors which prevent healing of an enterocutaneous fistula include foreign body, epithelialization of the fistula tract, downstream obstruction, radiation enteritis, associated infection (abscess or sepsis), malignancy, and a short (<2 cm) fistula tract. (See Schwartz 10th ed., p. 1158.)
Which primary malignancy of the small intestine is most common?
A. Adenocarcinoma of the duodenum
B. Carcinoid tumor of the ileum
C. Lymphoma of the jejunum
D. Gastrointestinal stromal tumor (GIST) of the duodenum
Adenocarcinomas of the duodenum are the most common primary small bowel malignancy and account for 35 to 50% of the total. Lymphoma and gastrointestinal stromal tumors (GISTs) of the small bowel are the least common and each accounts for 10 to 15% of the total. (See Schwartz 10th ed., p. 1159.)
Adenocarcinoma of the duodenum is associated with what hereditary oncologic syndrome?
A. Hereditary nonpolyposis colorectal cancer (HNPCC)
B. Familial adenomatous polyposis (FAP)
C. Peutz-Jeghers syndrome
D. Von Hippel-Lindau (VHL) syndrome
Duodenal carcinoma is a late manifestation of the familial adenomatous polyposis (FAP) syndrome. After resolution of the colonic disease by total colectomy, patients with FAP must be followed with periodic upper gastrointestinal (GI) endoscopy to maintain surveillance for duodenal tumors. Duodenal cancer is the leading cause of death among patients with FAP. (See Schwartz 10th ed., p. 1158.)
Which of the following statements is true regarding GISTs?
A. Most occur in the small intestine.
B. GISTs are usually metastatic when first diagnosed.
C. GISTs typically present with GI hemorrhage.
D. GISTs are usually responsive to cytotoxic chemotherapy.
GISTs are a form of sarcoma which occur most commonly (70%) in the stomach. They more frequently present with GI hemorrhage than other small bowel malignancies. They are usually refractory to conventional cytotoxic chemotherapy, but are not usually metastatic on initial diagnosis. A radical lymphadenectomy is not usually required; a segmental resection of the involved portion of the small intestine is usually sufficient surgical treatment. (See Schwartz 10th ed., p. 1162.)
Methods to prevent radiation enteritis of the small bowel during pelvic irradiation for gynecologic or rectal malignancy include which of the following?
A. Tilt table positioning in Trendelenburg position during radiation therapy treatments.
B. Closure (reapproximation) of the pelvic peritoneum after primary resection.
C. Placement of an absorbable mesh sling to suspend small intestine out of the pelvis during postoperative radiation therapy.
In addition to limiting radiation exposure to less than 5000 cGy, avoiding radiation to the small intestine after pelvic surgery can involve steep Trendelenburg positioning during radiation therapy sessions, closure of the pelvic peritoneum at the level of the sacral promontory to prevent small bowel filling the pelvis, and creating of an absorbable mesh sling to prevent the small intestine from filling the pelvic cavity. (See Schwartz 10th ed., p. 1163.)
What ectopic tissue is commonly found in a Meckel diverticulum?
Approximately 60% of Meckel diverticula contain ectopic tissue, of which over 60% consists of gastric mucosa. Pancreatic acini are next most common, followed by pancreatic islets, endometriosis, and hepatobiliary tissues. Gastric mucosa can ulcerate and bleed, the etiology of which can be hard to determine unless the Meckel diverticulum is known. (See Schwartz 10th ed., pp. 1163–1164).
A patient with recent onset of ascites after an episode of acute pancreatitis undergoes paracentesis, which reveals cloudy white fluid. What therapy is indicated?
C. Total parenteral nutrition (TPN) and octreotide
D. Octreotide and weekly paracentesis
Chylous ascites can develop as a complication of operative procedures or inflammatory conditions such as acute pancreatitis. Lymphatic drainage from damaged lymphatics can heal when the patient is made NPO, and maintained on TPN and octreotide. Medium-chain triglycerides have been advocated as an oral diet, but temporary cessation of oral feeding and octreotide comprise the most successful therapy. (See Schwartz 10th ed., pp. 1169–1170.)
Short bowel syndrome has been arbitrarily defined in adults as having a small intestine of less than what length?
A functional definition, in which insufficient absorptive capacity results in diarrhea, dehydration, and malnutrition is more appropriate, but a standard definition of short bowel syndrome of 200 cm has been used widely. (See Schwartz 10th ed., p. 1171.)
Common causes of short bowel syndrome include all of the following EXCEPT
In adults, the common etiologies of short bowel syndrome include mesenteric ischemia, malignancy, and Crohn’s disease. In pediatric patients, common causes include intestinal atresias, volvulus, and necrotizing enterocolitis. Radiation enteritis usually involves isolated segments of small bowel of less than 50% of total small intestinal length. (See Schwartz 10th ed., p. 1171.)
After an emergency operation for bowel infarction in which more than half of the small intestine was removed and a jejunostomy created, high volume ostomy losses cause recurrent dehydration. Management of this condition includes which of the following?
A. Proton pump inhibitors or histamine-2 receptor antagonists
Reducing gastric secretion with proton pump inhibitors or histamine-2 receptor antagonist, reducing gastroenteropancreatic secretions with octreotide, and inhibiting motility with agents such as loperamide or diphenoxylate, are useful approaches to prevent dehydration as the short gut adapts to its new length. Total parenteral nutrition is also often required. (See Schwartz 10th ed., p. 1171.)