Gastrointestinal Bleeding case 6

A 2-year-old child is seen in the emergency department because of bright red blood per rectum. This is the third time this has happened, and on the previous episode, no lesion was identified on colonoscopy. During this visit, the child is scheduled for small bowel barium studies,

which show an outpouching of the distal ileum about 2 feet proximal to the cecum.

Q 1

Which of the following is the most likely diagnosis?

/ A. Abnormally located appendix

/ B. Crohn disease

/ C. Diverticulosis

/ D. Meckel diverticulum

/ E. Potter syndrome

Q 2

The prevalence of this patient's anatomic anomaly in the US population is which of the following?

/ A. 2%

/ B. 6%

/ C. 15%

/ D. 40%

/ E. 80%

Q 3

This patient's anatomic anomaly is thought to be embryologically derived from which of the following?

/ A. Mesonephric duct

/ B. Mullerian duct

/ C. Paramesonephric duct

/ D. Vitelline duct

/ E. Wolffian duct

Q 4

Which of the following is the most common type of ectopic tissue seen in this patient's anatomic anomaly?

/ A. Endometrial tissues

/ B. Gastric mucosa

/ C. Jejunal mucosa

/ D. Pancreatic tissue

/ E. Rectal mucosa

Q 5

The ulceration that was the source of bleeding in this patient is most likely related to acid secretion by which of the following cell types?

/ A. Chief cells

/ B. Mucous neck cells

/ C. Parietal cells

/ D. Surface epithelial cells

/ E. Zymogenic cells

Q 6

The acid-secreting cells are stimulated by which of the following hormones?

/ A. Cholecystokinin

/ B. Gastric inhibitory peptide

/ C. Gastrin

/ D. Secretin

/ E. Vasoactive intestinal polypeptide

Q 7

Stimulation of which receptor on the acid-secreting cell leads to increased acid secretion?

/ A. Epinephrine receptor

/ B. Histamine-1 receptor

/ C. Histamine-2 receptor

/ D. Prostaglandin E2 receptor

/ E. Somatostatin receptor

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Gastrointestinal Bleeding case 6 answers

A1

The correct answer is D. This patient has a Meckel diverticulum. Meckel diverticula can be asymptomatic through life, or may come to medical attention because of a bleeding peptic ulcer, acute inflammation, rupture, strangulation, or intussusception of the Meckel diverticulum. Diagnosis, as in this case, may be difficult because the ileum is difficult to visualize. In some cases, small bowel barium studies may successfully identify the lesion.

While the appendix (choice A) can have variations in location, these tend to involve the side of the cecum into which it opens. Also, the appendiceal lumen remains narrow in aberrant locations.

Crohn disease (choice B) can involve the distal ileum and cause gastrointestinal bleeding, but would not cause an isolated outpouching of the ileum.

Diverticulosis (choice C) refers to acquired diverticula, and is usually a disease of older individuals.

Potter syndrome (choice E) refers to the cluster of bilateral renal agenesis, oligohydramnios, limb deformities, facial deformities, and pulmonary hypoplasia.

A2

The correct answer is A. The usually cited prevalence for Meckel diverticulum is 2%, although it actually varies from 0.2% to 4%. Many medical students remember five "2s" associated with Meckel diverticulum: 2 inches long, 2 feet from the ileocecal valve, 2% of the population, commonly presents in the first 2 years of life, and may have 2 types of epithelium.

A3

The correct answer is D. The vitelline duct or yolk stalk embryologically connects the midgut to the yolk sac. The duct usually disappears by the seventh gestational week, but if it fails to obliterate, several lesions can be produced, including Meckel diverticulum, a persistent vitelline duct that drains as a fistula through the anterior abdominal wall at the umbilicus, a fibrous band, or a vitelline duct cyst. The other ducts are genital ducts.

The mesonephric (wolffian) duct (choices A and E) develops into seminal vesicles, epididymis, ejaculatory duct, and ductus deferens; the paramesonephric (mullerian) duct (choices B and C) develops into the fallopian tube, uterus, and part of the vagina.

A4

The correct answer is B. Meckel diverticula often have ectopic tissues in them, the most common of which is heterotopic gastric mucosa. The tissues listed in the other choices can also be seen, as well as colonic mucosa.

A5

The correct answer is C. In gastric mucosa, whether in the stomach, or in an ectopic location, it is the parietal cells that secrete acid. This acid secretion is particularly likely to cause peptic ulceration in a Meckel diverticulum or the adjacent ileum, because the secretion of protective mucus is likely to be markedly inadequate in this setting, and the distal small intestinal mucosa is not equipped to handle an acid environment.

The chief cells, also called zymogenic cells (choices A and E) secrete pepsinogen.

The mucous neck cells and surface epithelial cells (choices B and D) secrete mucus.

A6

The correct answer is C. The polypeptide hormone gastrin is secreted by the duodenum and pyloric antrum. Its release is stimulated by the presence of digested protein in the stomach and duodenum. Gastrin stimulates acid secretion from the parietal cells of the gastric glands and pepsinogen secretion from the chief cells.

Cholecystokinin (choice A) is secreted by the endocrine cells of the duodenum and proximal jejunum, and stimulates pancreatic enzyme synthesis and secretion, increases gall bladder emptying, and decreases gastric emptying.

Gastric inhibitory peptide (choice B) inhibits gastrin release and gastric acid secretion, and causes insulin release from the endocrine pancreas.

Secretin (choice D) is produced in the crypts of Lieberkühn of the duodenum, and stimulates pepsinogen secretion from the stomach, and fluid and bicarbonate release from the pancreas.

Vasoactive intestinal polypeptide (choice E) induces smooth muscle relaxation, modifies the composition of pancreatic juice and bile, and inhibits gastric acid secretion and absorption from the intestinal lumen.

A7

The correct answer is C. Acid secretion by parietal cells can be stimulated by the gastrin receptor, the histamine-2 (H2) receptor, and the acetylcholine receptor. Drugs with anti-H2 receptor activity are used to treat peptic ulcer disease. The histamine that stimulates the H2 receptors is probably derived from enterochromaffin cells.

Epinephrine and histamine-1 receptors (choices A and B) do not appear to have a physiologic role in gastric acid secretion.

Substances capable of reducing gastric acid secretion include prostaglandin E₂(choice D), secretin, and somatostatin (choice E).