Digestive System Tournament
Two onboarding diagrams orient you in the digestive tract from mouth to portal vein. Then eight MCAT-DoK quiz rounds: enteropeptidase as the single gatekeeper of the pancreatic protease cascade, how proton pump inhibitors change protein digestion, starch from chewing to portal glucose, the GI cell-and-hormone map, gastric pH and pepsin, bile salts as detergents rather than enzymes, brush-border vs. pancreatic enzymes, and pernicious anemia.
Where the Digestion fits in Digestion and absorption
Reactome separates the gut into the two jobs it performs in sequence: enzymatic digestion, which cuts macromolecules into absorbable units, and intestinal absorption, which moves those units across the enterocyte. Nothing crosses the brush border until digestion is finished, so the highlighted digestion panel is the gatekeeper for everything to its right. Click the highlighted Digestion panel to enter the tournament.
Click the highlighted Digestion box to continue.
What this tournament tests
Each task maps to a distinct MCAT cognitive demand. The first two orient you in the broader topology; the next eight test the high-yield mechanism, regulation, sequence and quantitative reasoning that consistently appear on test day.
The Bigger Picture
Anchor enzymatic digestion inside Reactome's digestion and absorption map.
Whole-Pathway Overview
Pan and zoom the curated WikiPathways gastric acid production figure before you start answering.
Fill in the Blank
Recall enteropeptidase as the brush-border enzyme that fires the pancreatic protease cascade.
Disruptor
Predict what happens to pepsin and iron absorption when omeprazole raises gastric pH.
Sequence Ordering
Trace starch from salivary amylase through brush-border enzymes, SGLT1, and GLUT2 to the portal vein.
Match the Pairs
Pair each secretory cell or hormone (parietal, chief, G, ECL, CCK, secretin, incretins, somatostatin) with its action.
Numeric Input
Recall the gastric pH at which pepsinogen autoactivates and pepsin works best.
Select All That Apply
Identify TRUE statements about bile salts, colipase, mixed micelles, and enterohepatic circulation.
Odd One Out
Separate membrane-bound brush-border enzymes from secreted pancreatic enzymes.
Pernicious Anemia Disruptor
Link parietal cell loss to intrinsic factor, ileal B12 uptake, and subacute combined degeneration.
Public leaderboard
Your score posts to a global, persistent leaderboard scored by points first, time as tiebreaker.
Digestion in 60 seconds
Digestion is regionally specialized. The mouth starts carbohydrate (salivary amylase) and fat (lingual lipase); the stomach handles protein with pepsin at pH 2 and inactivates amylase; the small intestine does nearly all real digestion and absorption once pancreatic bicarbonate raises the pH. Pancreatic proteases ship as zymogens, and enteropeptidase on the duodenal brush border makes the single activating cut - trypsin then activates everything else, including more trypsinogen.
Acid secretion runs through the parietal cell's H+/K+ ATPase, stimulated by gastrin (CCK-B), histamine (H2, the main amplifier), and acetylcholine (M3) - which is why proton pump inhibitors blunt acid more completely than H2 blockers. In the duodenum, secretin answers acid with bicarbonate and CCK answers fat and amino acids by contracting the gallbladder, releasing pancreatic enzymes, and slowing gastric emptying. Somatostatin shuts the whole system down.
Only monosaccharides and small peptides or amino acids can cross, so brush-border enzymes (maltase, sucrase-isomaltase, lactase) are obligatory - lactase deficiency leaves osmotically active lactose for colonic bacteria to ferment. Apical glucose uptake is secondary active transport via SGLT1 (fructose uses facilitated GLUT5) and basolateral exit is passive through GLUT2. Carbohydrate and protein products drain into the hepatic portal vein; most fat leaves in lymph as chylomicrons.
Fat needs help twice. Bile salts are amphipathic detergents that emulsify - they catalyze nothing - and pancreatic lipase plus colipase do the hydrolysis at the enlarged oil-water interface, with mixed micelles ferrying products across the unstirred water layer. Remember the site-specific absorption facts: iron in the duodenum, folate in the jejunum, and B12 with intrinsic factor plus bile salts in the terminal ileum.
FAQ
Why does the pancreas secrete proteases as inactive zymogens?
Self-protection. Trypsin, chymotrypsin, elastase, and the carboxypeptidases would digest pancreatic tissue if activated in the acinar cell, so they are stored as precursors and activated only after enteropeptidase acts in the duodenum. The pancreas also secretes a trypsin inhibitor (SPINK1) as a second safeguard. Premature intrapancreatic trypsin activation is exactly the central event in acute pancreatitis.
Are bile salts enzymes?
No, and this is a favorite MCAT trap. Bile salts are amphipathic detergents that break large fat droplets into many small ones, hugely increasing the surface area available to lipase. That is emulsification - a physical process with no bond cleavage. The actual hydrolysis is done by pancreatic lipase with colipase, phospholipase A2, and cholesterol esterase.
Why does losing the terminal ileum cause both diarrhea and anemia?
The terminal ileum is the only site that reabsorbs bile salts and the only site that takes up the intrinsic factor-B12 complex. Lose it and bile salts spill into the colon, drawing water and causing bile acid diarrhea while the liver scrambles to resynthesize them from cholesterol. At the same time B12 absorption fails, producing a megaloblastic anemia that takes years to appear because hepatic B12 stores are large.
Why does folate correct the anemia of B12 deficiency but not the neurologic damage?
Both vitamins feed the same thymidine synthesis step, so folate alone can restore DNA synthesis and normalize the blood smear. But B12 is separately required for methylmalonyl-CoA mutase and for myelin maintenance, so demyelination of the dorsal columns and corticospinal tracts continues unchecked - subacute combined degeneration. That is why elevated methylmalonic acid distinguishes B12 from folate deficiency and why you never treat blindly with folate.
Do I need an account to play?
No. The tournament is fully public. You get a randomized handle and your score posts to the public leaderboard at the bottom of this page.
Keep going
What happens to absorbed fat once the enterocyte packages it into a chylomicron and ships it through lymph.
What the liver does with the portal glucose this tract just delivered.
Overview diagram: Reactome Pathway R-HSA-8963743, licensed CC BY 4.0.