Human Digestive System Practice Questions

Correct answer: Salivary amylase

Salivary amylase, also known as ptyalin, is secreted by the salivary glands and begins the digestion of starches into simpler sugars like maltose in the mouth. Pepsin and trypsin digest proteins, while lipase breaks down fats. Chemical digestion of carbohydrates pauses once the food reaches the highly acidic environment of the stomach.

Correct answer: Peristalsis

Peristalsis is an involuntary series of wave-like muscle contractions and relaxations that moves food along the mechanical pathways of the digestive system. Mastication refers to chewing, and deglutition is the medical term for swallowing. Segmentation involves localized contractions that mix food in the small intestine rather than moving it forward.

Correct answer: Epiglottis

The epiglottis is a leaf-shaped flap of cartilage located behind the tongue that folds over the glottis during swallowing to seal off the windpipe. This mechanism directs food safely into the esophagus instead of the respiratory tract. Sphincters act as muscular valves between digestive organs, while the uvula helps seal the nasopharynx during swallowing.

Correct answer: Parietal cells

Parietal cells, located in the gastric glands of the stomach, secrete hydrochloric acid which lowers the gastric pH to activate pepsinogen. Chief cells secrete the inactive enzyme precursor pepsinogen itself. Mucous cells secrete protective mucus, and G cells produce the hormone gastrin.

Correct answer: Emulsifying fat globules into smaller droplets

Bile salts do not chemically digest lipids; instead, they act as detergents to emulsify large lipid droplets into a fine suspension of smaller droplets. This mechanical process drastically increases the surface area available for pancreatic lipase to break down the fats chemically. Bile is produced by the liver and stored in the gallbladder.

Correct answer: Small intestine

The small intestine is highly adapted for both final chemical breakdown and nutrient absorption due to its immense length and specialized internal structures. Virtually all carbohydrates, proteins, and lipids are absorbed into the bloodstream or lymphatic system through its walls. The stomach primarily breaks down proteins mechanically and chemically, while the large intestine focuses on water recovery.

Correct answer: Duodenum

The duodenum is the shortest and first section of the small intestine where crucial chemical mixing occurs. It receives chyme from the stomach through the pyloric sphincter and blends it with bile and pancreatic juice. The jejunum and ileum follow the duodenum, while the cecum is the beginning of the large intestine.

Correct answer: Absorbing dietary fats and fat-soluble vitamins

Lacteals are specialized lymphatic capillaries found at the center of each intestinal villus. Because lipids are too large to directly enter regular blood capillaries, they are packaged into chylomicrons and absorbed into lacteals instead. Amino acids and simple sugars, conversely, enter the blood capillaries directly.

Correct answer: Enterokinase

Enterokinase (also known as enteropeptidase) is an enzyme bound to the mucosal membrane of the duodenum that cleaves a peptide from trypsinogen to form active trypsin. Once activated, trypsin initiates a cascade by activating other pancreatic proteases like chymotrypsin. Pepsin operates exclusively in the highly acidic environment of the stomach.

Correct answer: Increasing internal surface area for absorption

These structural features collectively amplify the inner surface area of the small intestine by roughly 600-fold compared to a simple flat tube. This expansive surface area maximizes the contact between digested nutrients and transport proteins on epithelial cells. Microvilli form the microscopic 'brush border' where final nutrient breakdown occurs.

Correct answer: Cholecystokinin

Cholecystokinin (CCK) is secreted by enteroendocrine cells in the duodenum in response to fatty and protein-rich chyme. It triggers gallbladder contraction to release bile and stimulates the pancreas to release digestive enzymes. Secretin stimulates the secretion of bicarbonate ions, while gastrin increases gastric acid release.

Correct answer: Absorption of water and electrolytes

The large intestine absorbs remaining water, salts, and certain vitamins produced by symbiotic bacteria before eliminating undigested wastes. It does not perform significant chemical breakdown or absorb macronutrients like proteins or lipids. Liquid waste is gradually condensed into solid feces as it traverses the colon.

Correct answer: Pyloric sphincter

The pyloric sphincter acts as a gateway regulating the flow of chyme from the pylorus of the stomach into the duodenum of the small intestine. It prevents large fragments of food from passing through until they are properly liquidized. The ileocecal valve separates the small intestine from the large intestine.

Correct answer: Bicarbonate ions

Pancreatic juice contains a high concentration of sodium bicarbonate, which acts as a chemical base to buffer the strong acid in chyme. This neutralization raises the pH of the duodenum to an optimal level (around pH 7-8) for pancreatic enzymes to function properly. Bile salts are produced by the liver, not the pancreas.

Correct answer: Chyme

Chyme is the semi-fluid, highly acidic mass of semi-digested food that passes from the stomach into the duodenum. A bolus is the ball of food formed in the mouth after chewing and mixing with saliva. Micelles are temporary lipid aggregations that assist in fat absorption within the small intestine.

Correct answer: Hepatic portal vein

The hepatic portal vein forms a unique circulatory pathway that routes absorbed monosaccharides, amino acids, and other nutrients straight to the liver for metabolic processing and detoxification before entering general circulation. The hepatic artery supplies oxygenated blood to liver tissues, whereas the inferior vena cava returns blood back to the heart.

Correct answer: Vitamin C

Vitamin C (ascorbic acid) is a vital cofactor required for the synthesis of collagen, a structural protein found in connective tissues throughout the body, including the gums and intestinal walls. Without it, tissues weaken, leading to bleeding and poor wound healing. Vitamin K is essential for blood clotting, while B12 is needed for red blood cell maturation.

Correct answer: Liver

The liver plays an indispensable role in protein metabolism by breaking down toxic ammonia, a byproduct of amino acid deamination, into safer urea via the ornithine cycle. The kidneys subsequently filter this urea out of the bloodstream and excrete it in urine. The pancreas primarily focuses on digestive enzymes and blood sugar hormones.

Correct answer: Submucosa

The submucosa is a thick layer of loose connective tissue that lies immediately beneath the mucosa, containing larger blood vessels, lymphatics, and the submucosal plexus (Meissner's plexus). The mucosa is the innermost layer facing the lumen, the muscularis externa contains the smooth muscle layers for motility, and the serosa forms the outermost protective covering.

Correct answer: Gastroesophageal reflux disease

Gastroesophageal reflux disease (GERD) occurs when the lower esophageal sphincter (cardiac sphincter) relaxes inappropriately or weakens, allowing highly acidic gastric contents to rise into the esophagus and irritate its lining. Chronic untreated reflux can lead to esophageal inflammation or strictures. Celiac disease is an autoimmune reaction to gluten affecting the small intestine.