A patient undergoes surgical removal of the stomach (total gastrectomy) but keeps their small intestine intact. Which prediction about their digestion is most accurate?
AThey will be unable to digest proteins and carbohydrates because the stomach is the primary site of chemical digestion
BThey will be unable to absorb glucose and amino acids because the stomach is the primary absorptive organ
CChemical digestion and absorption can proceed in the small intestine, though they will need dietary modification to compensate for lost churning, acidification, and controlled metering
DDigestion will be unaffected because the accessory organs (liver, pancreas) compensate entirely for the missing stomach
The stomach is a holding, homogenizing, and metering organ — not the primary site of chemical digestion or absorption. The small intestine, with its brush border enzymes, massive surface area (villi + microvilli), and pancreatic enzyme supply, performs the vast majority of both. After gastrectomy, patients retain this machinery and can digest and absorb most nutrients, though they face challenges with rate control (the pyloric valve is gone), vitamin B12 absorption (intrinsic factor is lost), and iron absorption. The misconception that digestion 'happens in the stomach' reverses the actual division of labor.
Question 2 Multiple Choice
During a meal, the small intestine contracts in short, non-propulsive segments that churn the luminal contents back and forth without moving them forward. What is the functional purpose of this pattern?
ATo propel chyme toward the colon as rapidly as possible, maximizing throughput
BTo prevent backflow from the large intestine by creating pressure waves in both directions
CTo mix digesta and increase contact time between nutrients and the absorptive mucosa, maximizing absorption
DTo break down large food particles mechanically before pancreatic enzymes arrive
Segmentation is the 'mixing and slowing' motion of the small intestine — rhythmic contractions that churn without net propulsion. Its biological purpose is to maximize contact between chyme and the absorptive surface (villi and microvilli) and to keep contents near the brush border enzymes long enough for digestion and uptake to complete. This is the opposite of peristalsis, which propels. The small intestine needs to *slow* transit during active absorption; segmentation achieves this. Between meals, the migrating motor complex takes over as a housekeeping sweep.
Question 3 True / False
The liver is the primary source of the digestive enzymes that break down fat in the small intestine.
TTrue
FFalse
Answer: False
The liver produces bile salts — not enzymes. Bile salts are detergents (emulsifiers) that break dietary fat into small droplets, dramatically increasing the surface area available for enzymatic attack. The actual enzymes that chemically digest fat (pancreatic lipases, phospholipases) are produced by the pancreas and delivered to the duodenum. The gallbladder stores and concentrates bile between meals and releases it in response to cholecystokinin when fat arrives in the duodenum. The liver's role in digestion is bile synthesis, not enzymatic digestion.
Question 4 True / False
The enteric nervous system can coordinate peristaltic contractions in the gut even when all neural connections to the brain and spinal cord are severed.
TTrue
FFalse
Answer: True
The enteric nervous system (ENS) is a semi-autonomous neural network embedded in the gut wall, containing approximately as many neurons as the spinal cord. It includes its own sensory neurons (detecting luminal distension), interneurons, and motor neurons that complete the peristaltic reflex circuit entirely locally: mechanoreceptors detect a bolus, ascending excitatory neurons trigger contraction behind it, descending inhibitory neurons trigger relaxation ahead. The autonomic nervous system modulates the ENS (parasympathetic enhances, sympathetic inhibits) but is not required to run the basic circuit. An isolated gut segment can still peristalse.
Question 5 Short Answer
Why is the small intestine, rather than the stomach, the primary site of both chemical digestion and nutrient absorption?
Think about your answer, then reveal below.
Model answer: The small intestine is where all major enzymatic systems converge: pancreatic enzymes (proteases, lipases, amylase, nucleases) arrive via the pancreatic duct; bile salts emulsify fats; and the brush border itself carries peptidases and disaccharidases. The enormous surface area created by villi and microvilli (brush border) maximizes absorptive capacity — estimated to increase the absorptive surface ~600-fold over a simple tube. The stomach's pH (~2) is hostile to pancreatic enzymes and incompatible with most absorption, and it lacks the specialized transporters. The stomach's role is preparation: churning food into chyme, acidifying it, and metering it into the duodenum where real digestion occurs.
Understanding the small intestine as the primary digestive site explains why surgical procedures and diseases affecting the small intestine (Crohn's disease, celiac disease, short-bowel syndrome) have severe nutritional consequences, while stomach removal is more manageable. The stomach is important but replaceable in function; the small intestine is not. This also explains why pancreatic insufficiency (loss of enzyme supply to the duodenum) causes dramatic malabsorption — the stomach cannot compensate.