Question 1

In the mouth and stomach, salivary a-amylase initiates the digestion of which nutrients?

Accepted Answer

Salivary a-amylase is an enzyme that initiates carbohydrate digestion in the mouth and stomach. Pepsin breaks down protein-forming chains in the stomach. Thirty percent of fats are broken down by gastric lipase. Fiber is not broken down and contributes to stool volume.

Question 2

Which gastric cells secrete hydrochloric acid and intrinsic factor?

Accepted Answer

The parietal cells (oxyntic cells) secrete hydrochloric acid and intrinsic factor. The chief cells secrete pepsinogen. The pyloric gland mucosa in the antrum synthesizes and releases the hormone gastrin from G cells. D cells secrete somatostatin.

Question 3

Which gastric hormone inhibits acid and pepsinogen secretion, as well as decreases the release of gastrin?

Accepted Answer

Somatostatin inhibits the secretion of acid and pepsinogen and decreases gastrin release. The hormones gastrin and motilin stimulate gastric emptying. Histamine stimulates acid secretion by activating histamine receptors (H₂ receptors) on acid-secreting parietal cells. Acetylcholine stimulates pepsin secretion.

Question 4

Which statement best describes the gastrointestinal tract?

Accepted Answer

The gastrointestinal tract is a hollow tube that extends from the mouth to the anus. The esophagus is a muscular tube that transports food from the mouth to the stomach. The stomach is a baglike structure that secretes digestive juices, mixes and stores food, and propels partially digested food (chyme) into the duodenum. The small intestine is 5 m long and has three segments.

Question 5

What is the formation of water-soluble molecules to facilitate the absorption of the byproducts of lipid hydrolysis accomplished by?

Accepted Answer

The products of lipid hydrolysis must be made water soluble if they are to be efficiently absorbed from the intestinal lumen. The formation of water-soluble molecules known as micelles accomplishes this process. Phospholipase cleaves fatty acids from phospholipids. Triglycerides are covered with phospholipids, lipoproteins, and cholesterol to become particles called chylomicrons. Colipase is a coenzyme needed for optimal functioning of lipase.

Question 6

Exposure to which substance protects the mucosal barrier of the stomach?

Accepted Answer

Prostaglandins and nitric oxide protect the mucosal barrier by stimulating the secretion of mucus and bicarbonate and by inhibiting the secretion of acid. Acetylcholine stimulates pepsin secretion. Helicobacter pylori are bacteria found in the stomach. Bile is secreted by the liver.

Question 7

The student asks the professor why water and electrolytes are transported in both directions through tight junctions and intercellular spaces rather than across cell membranes. What response by the professor is best?

Accepted Answer

The epithelial cell membranes of the small intestine are formed of lipids and are hydrophobic or tend to repel water. Therefore, water and electrolytes are transported in both directions-toward the capillary blood or toward the intestinal lumen-through the tight junctions and intercellular spaces rather than across cell membranes.

Question 8

Glucose transport enhances the absorption of which electrolyte?

Accepted Answer

Sodium passes through the tight junctions and is actively transported across cell membranes. Sodium and glucose share a common active transport carrier (sodium-glucose ligand transporter 1 [SGLT1]) so that sodium absorption is enhanced by glucose transport.

Question 9

Which cells in the stomach secrete histamine?

Accepted Answer

Enterochromaffin-like cells secrete histamine. The parietal cells (oxyntic cells) within the glands secrete hydrochloric acid, intrinsic factor, and gastroferrin. The chief cells secrete pepsinogen. D cells secrete somatostatin.

Question 10

What is the primary source of physiologic iron?

Accepted Answer

The primary source of iron is heme from animal protein. A small portion of iron comes from recycling of old red blood cells.

Question 11

What effect is a result of inhibiting the parasympathetic nervous system with a drug such as atropine?

Accepted Answer

The sympathetic and parasympathetic divisions of the autonomic nervous system control salivation. Because cholinergic parasympathetic fibers stimulate the salivary glands, atropine (an anticholinergic agent) inhibits salivation and makes the mouth dry. Atropine (and similar drugs) does not cause saliva to become thinner, change the pH of saliva, or inhibit digestive enzymes.

Question 12

Which water-soluble vitamin is absorbed by passive diffusion?

Accepted Answer

Of the options available, only Vitamin B₆ is the water-soluble vitamin absorbed by passive diffusion. B₁ and folic acid are absorbed by active transport. Vitamin K requires micelle formation with bile salts and lipid diffusion.

Question 13

Food enters the stomach via which orifice or sphincter?

Accepted Answer

Each end of the esophagus is opened and closed by a sphincter. The upper esophageal sphincter (cricopharyngeal muscle) prevents entry of air into the esophagus during respiration. The lower esophageal sphincter (cardiac orifice) prevents regurgitation from the stomach. The lower esophageal sphincter is located near the esophageal hiatus-the opening in the diaphragm where the esophagus ends at the stomach. The gastric sphincter controls the release of food from the stomach to the small intestine and is also known as the pyloric sphincter. The fundal sphincter is not a structure in the GI system.

Question 14

Where in the small intestines are lymphocytes, plasma cells, and macrophages produced?

Accepted Answer

The lamina propria, which is a connective tissue layer of the mucous membrane, lies beneath the epithelial cells of the villi and contains lymphocytes, plasma cells, which produce immunoglobulins and macrophages. Together the microvilli create a mucosal surface known as the brush border. The villi and microvilli greatly increase the surface area available for absorption. Between the bases of the villi are the crypts of Lieberkühn (intestinal glands), which extend to the submucosal layer. Undifferentiated cells arise from stem cells at the base of the crypt and move toward the tip of the villus, maturing to become columnar epithelial secretory cells (water, electrolytes, and enzymes) and goblet cells (mucus).

Question 15

The ileum and jejunum are suspended by folds of the peritoneum that contain an extensive vascular and nervous network. What are these folds called?

Accepted Answer

The ileum and jejunum are suspended in loose folds from the posterior abdominal wall by a peritoneal membrane called the mesentery. The mesentery facilitates intestinal motility and supports blood vessels, nerves, and lymphatics. The duodenum begins at the pylorus and ends where it joins the jejunum at a suspensory ligament called the Treitz ligament. Intrinsic reflexive activity is mediated by the myenteric plexus (Auerbach plexus) and the submucosal plexus (Meissner plexus) of the enteric nervous system. The lamina propria (a connective tissue layer of the mucous membrane) lies beneath the epithelial cells of the villi and contains lymphocytes and plasma cells, which produce immunoglobulins and macrophages.

Question 16

Saliva contains which immunoglobulin (Ig)?

Accepted Answer

Saliva contains only IgA, which helps prevent infection.

Question 17

Which pancreatic enzyme is responsible for the breakdown of carbohydrates?

Accepted Answer

Salivary and pancreatic amylases breakdown starches to oligosaccharides by splitting a-1,4-glucosidic linkages of long-chain molecules. Trypsin is involved in protein hydrolysis. Gastric lipase aids in the digestion of fat. Chymotrypsin works with trypsin.

Question 18

What process is capable of increasing both intrathoracic and intraabdominal pressure, thereby facilitating defecation?

Accepted Answer

The Valsalva maneuver consists of inhaling and forcing the diaphragm and chest muscles against the closed glottis and increases both intrathoracic and intraabdominal pressure. This pressure is transmitted to the rectum thereby facilitating defecation. Relaxation of the internal anal sphincter creates the urge to defecate. Peristalsis moves the products of digestion along in the gastrointestinal tract. The ileogastric reflex inhibits gastric motility when the ileum becomes distended.

Question 19

Which enzyme breaks down protein-forming polypeptides in the stomach?

Accepted Answer

Pepsin, a proteolytic enzyme, breaks down protein-forming polypeptides in the stomach. Acetylcholine stimulates pepsin secretion. The hormones gastrin and motilin stimulate gastric emptying. Secretin stimulates pancreas to secrete alkaline pancreatic juice and liver to secrete bile; decreases gastrointestinal motility; inhibits gastrin and gastric acid secretion.

Question 20

A professor has taught a class of students about the characteristics of vitamin B₁₂. Which statement by a student demonstrates a need for more education?

Accepted Answer

Most vitamin B₁₂ (cobalamin) is bound to intrinsic factor (making it resistant to digestion) and is absorbed in the terminal ileum, although a small amount of the vitamin is absorbed in its free (unbound) form. Vitamin B₁₂ is not necessary for platelet maturation. When a student makes this statement, the professor knows the student needs more education.

Quiz 41: Structure and Function of the Digestive System