Absorption mechanisms Practice Questions
40 free Absorption mechanisms practice questions for the Physiology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which mechanism is primarily responsible for glucose absorption in the small intestine?
- A Facilitated diffusion via GLUT2
- B Secondary active transport with sodium
- C Simple diffusion through lipid membrane
- D Endocytosis
Correct answer: Secondary active transport with sodium
Glucose absorption occurs mainly via the sodium-glucose co-transporter (SGLT1). This is a secondary active transport process driven by the sodium gradient.
Which part of the gastrointestinal tract is the major site for nutrient absorption?
- A Stomach
- B Duodenum
- C Jejunum
- D Ileum
Correct answer: Jejunum
The jejunum has extensive surface area and transporters for nutrient absorption. Most carbohydrates, proteins, and lipids are absorbed here.
Fructose is absorbed from the intestine mainly by:
- A Sodium-dependent co-transport
- B Active transport using ATP
- C Facilitated diffusion
- D Simple diffusion
Correct answer: Facilitated diffusion
Fructose absorption occurs via facilitated diffusion using the GLUT5 transporter. It does not require sodium or ATP.
Which form of protein digestion product is absorbed most efficiently?
- A Individual free amino acids
- B Dipeptides and tripeptides
- C Large intact polypeptides
- D Whole undigested proteins
Correct answer: Dipeptides and tripeptides
Dipeptides and tripeptides are absorbed efficiently via peptide transporters. They are then broken down into amino acids inside enterocytes.
Which mechanism is responsible for fat absorption from the intestine?
- A Sodium-dependent active transport
- B Facilitated diffusion via carriers
- C Micelle-mediated diffusion
- D Simple pinocytosis
Correct answer: Micelle-mediated diffusion
Fatty acids and monoglycerides are absorbed by micelle-mediated diffusion. Bile salts are essential for this process.
Which vitamin is absorbed along with dietary fats?
- A Vitamin B12
- B Vitamin C
- C Vitamin A
- D Folic acid
Correct answer: Vitamin A
Vitamin A is a fat-soluble vitamin. Its absorption depends on bile and normal fat digestion.
Absorption of vitamin B12 requires which factor?
- A Bile salts
- B Intrinsic factor
- C Pancreatic lipase
- D Calcium ions
Correct answer: Intrinsic factor
Vitamin B12 absorption requires intrinsic factor secreted by gastric parietal cells. The complex is absorbed in the ileum.
Which mineral is absorbed primarily in the duodenum?
- A Iron
- B Zinc
- C Sodium
- D Copper
Correct answer: Iron
Iron is absorbed mainly in the duodenum. Its absorption is enhanced in the ferrous form and acidic environment.
Which transporter is responsible for sodium absorption in the intestine?
- A Na⁺/K⁺ ATPase
- B SGLT1
- C ENaC
- D H⁺/K⁺ ATPase
Correct answer: ENaC
ENaC channels allow sodium absorption in the distal intestine. They play a role in fluid and electrolyte balance.
Water absorption in the intestine occurs mainly by:
- A Symport
- B Facilitated diffusion
- C Osmosis
- D Endocytosis
Correct answer: Osmosis
Water is absorbed passively by osmosis. It follows the osmotic gradient created by solute absorption.
Which carbohydrate digestion product is absorbed via facilitated diffusion?
- A Glucose
- B Galactose
- C Fructose
- D Starch
Correct answer: Fructose
Fructose absorption occurs via facilitated diffusion. It uses the GLUT5 transporter on enterocytes.
Which structure increases the absorptive surface area of the small intestine the most?
- A Rugae
- B Plicae circulares
- C Villi
- D Microvilli
Correct answer: Microvilli
Microvilli provide the greatest increase in surface area. They form the brush border of enterocytes.
Which mechanism is responsible for calcium absorption in the intestine?
- A Simple diffusion across the membrane
- B Vitamin D-dependent active transport
- C Facilitated diffusion via GLUT carriers
- D Non-selective endocytosis of calcium
Correct answer: Vitamin D-dependent active transport
Calcium absorption is regulated by vitamin D. It involves active transport especially in the duodenum.
Which fatty acid absorption pathway leads to chylomicron formation?
- A Short-chain fatty acids
- B Medium-chain fatty acids
- C Long-chain fatty acids
- D Volatile fatty acids
Correct answer: Long-chain fatty acids
Long-chain fatty acids are re-esterified and packed into chylomicrons. These enter the lymphatic system.
Which amino acid transport mechanism is sodium-dependent?
- A Facilitated diffusion
- B Primary active transport
- C Secondary active transport
- D Passive diffusion
Correct answer: Secondary active transport
Most amino acids are absorbed by sodium-dependent secondary active transport. The sodium gradient drives uptake.
Which vitamin is absorbed by simple diffusion?
- A Vitamin B1
- B Vitamin B12
- C Vitamin C
- D Vitamin D
Correct answer: Vitamin D
Vitamin D is fat-soluble and absorbed by simple diffusion. Its absorption depends on bile-mediated fat digestion.
Which segment of the intestine absorbs bile salts?
- A Duodenum
- B Jejunum
- C Ileum
- D Colon
Correct answer: Ileum
Bile salts are actively reabsorbed in the terminal ileum. This process is part of enterohepatic circulation.
Which absorption mechanism explains oral rehydration therapy effectiveness?
- A Glucose-driven sodium absorption
- B Passive diffusion of water alone
- C Active chloride secretion into lumen
- D Bicarbonate secretion by enterocytes
Correct answer: Glucose-driven sodium absorption
Glucose enhances sodium absorption via SGLT1. Water follows osmotically, improving hydration.
Which nutrient absorption is impaired in celiac disease?
- A Fat-soluble vitamins
- B Only dietary glucose
- C Only dietary iron
- D Only ingested water
Correct answer: Fat-soluble vitamins
Celiac disease damages intestinal villi. This reduces absorption of fats and fat-soluble vitamins.
Which transport protein moves absorbed glucose into portal circulation?
- A SGLT1
- B GLUT5
- C GLUT2
- D Na⁺/K⁺ ATPase
Correct answer: GLUT2
GLUT2 transports glucose from enterocytes into portal blood. It works by facilitated diffusion.
Which of the following transporters is responsible for the uptake of glucose and galactose across the apical membrane of the enterocyte against their concentration gradient?
- A GLUT2
- B GLUT5
- C SGLT1
- D SGLT2
Correct answer: SGLT1
SGLT1 (Sodium-Glucose Linked Transporter 1) utilizes the sodium gradient created by the Na+/K+ ATPase to co-transport glucose or galactose into the cell. This is a primary example of secondary active transport in the small intestine.
Fructose is absorbed from the intestinal lumen into the enterocyte via which specific mechanism?
- A Primary active transport
- B Facilitated diffusion through GLUT5
- C Secondary active transport with sodium
- D Solvent drag through tight junctions
Correct answer: Facilitated diffusion through GLUT5
Unlike glucose, fructose absorption is sodium-independent and occurs via facilitated diffusion using the GLUT5 transporter. Because it is a passive process, it cannot move fructose against a concentration gradient.
How do short-chain and medium-chain fatty acids (fewer than 12 carbons) typically enter the systemic circulation?
- A Packaged into chylomicrons and transported via lacteals
- B Bound to bile salts and absorbed into the lymphatic system
- C Directly into the portal blood as free fatty acids
- D Via facilitated diffusion through the GLUT2 transporter
Correct answer: Directly into the portal blood as free fatty acids
Short- and medium-chain fatty acids are more water-soluble than long-chain fatty acids. They bypass the complex process of re-esterification and chylomicron formation, moving directly into the portal venous blood.
The absorption of most dietary lipids occurs in the small intestine. After entering the enterocyte, long-chain fatty acids and monoglycerides are re-esterified and packaged into which of the following?
- A Micelles
- B Chylomicrons
- C Very Low-Density Lipoproteins (VLDL)
- D High-Density Lipoproteins (HDL)
Correct answer: Chylomicrons
Once inside the enterocyte, lipids are reconstituted into triglycerides and combined with apoproteins and cholesterol to form chylomicrons. These large particles are then exported via exocytosis into the central lacteals of the villi.
Which mechanism best explains the absorption of Vitamin B12 (Cobalamin) in the terminal ileum?
- A Micelles within the intestinal lumen
- B Chylomicrons for lymphatic export
- C Very Low-Density Lipoproteins (VLDL)
- D High-Density Lipoproteins (HDL)
Correct answer: Chylomicrons for lymphatic export
Vitamin B12 must bind to Intrinsic Factor (produced by gastric parietal cells) to be protected from digestion. This complex is then recognized by specific receptors (cubilin) in the terminal ileum and absorbed via endocytosis.
Oral rehydration therapy (ORT) is highly effective for treating secretory diarrhea because it exploits which physiological principle?
- A The inhibition of chloride secretion by high luminal glucose concentrations
- B Coupled sodium-glucose absorption creating an osmotic gradient for water
- C The direct stimulation of the Na+/K+ ATPase pump by luminal potassium
- D The ability of fructose to bypass the damaged SGLT1 glucose transporters
Correct answer: Coupled sodium-glucose absorption creating an osmotic gradient for water
In many diarrheal diseases, the SGLT1 transporter remains functional. Providing both sodium and glucose ensures their co-transport into enterocytes, which draws water back into the body via osmosis, even when other secretory mechanisms are overactive.
Iron is absorbed in the duodenum primarily in the ferrous ($Fe^{2+}$) state. Which protein is responsible for the export of iron across the basolateral membrane into the blood?
- A Ferritin
- B Ferroportin
- C Divalent Metal Transporter 1 (DMT1)
- D Transferrin
Correct answer: Ferroportin
Ferroportin is the only known iron exporter in enterocytes, regulated by the hormone hepcidin. Once iron enters the blood, it is oxidized to $Fe^{3+}$ and binds to transferrin for transport.
Which transport protein is the primary mediator for the absorption of dipeptides and tripeptides in the small intestine?
- A SGLT1
- B PepT1
- C GLUT2
- D ASBT
Correct answer: PepT1
PepT1 is a $H^+$-dependent co-transporter that moves dipeptides and tripeptides into the enterocyte. This mechanism is highly efficient and often accounts for more protein absorption than the transport of individual free amino acids.
Calcium absorption is regulated by 1,25-dihydroxyvitamin D3. What is the role of calbindin in this process?
- A It acts as a calcium-sensing receptor on the apical membrane
- B It shuttles calcium across the cytosol to the basolateral membrane
- C It pumps calcium into the lumen against its concentration gradient
- D It binds calcium in the lumen to form an absorbable complex
Correct answer: It shuttles calcium across the cytosol to the basolateral membrane
Calbindin is an intracellular binding protein that prevents free calcium levels from rising too high inside the enterocyte while facilitating its movement to the basolateral side. Its synthesis is directly stimulated by active Vitamin D.
Bile salts are essential for lipid digestion, but they are not absorbed with the fats in the upper small intestine. Where and how are they primarily recovered?
- A Simple diffusion in the duodenum
- B Active transport in the terminal ileum
- C Facilitated diffusion in the ascending colon
- D Receptor-mediated endocytosis in the jejunum
Correct answer: Active transport in the terminal ileum
The majority of bile salts are reabsorbed via the Apical Sodium-dependent Bile acid Transporter (ASBT) in the terminal ileum. This process is the critical step in the enterohepatic circulation.
The 'solvent drag' mechanism contributes significantly to the absorption of which of the following?
- A Ferritin, an iron storage protein
- B Ferroportin, a basolateral exporter
- C Divalent Metal Transporter 1 (DMT1)
- D Transferrin, a plasma carrier
Correct answer: Ferroportin, a basolateral exporter
Solvent drag occurs when the bulk flow of water through paracellular pathways (tight junctions) carries small, dissolved solutes along with it. This is a major pathway for sodium and urea absorption in the small intestine.
Which form of dietary folate is the most common, and how is it modified prior to absorption?
- A Monoglutamate; converted to polyglutamate within the liver
- B Polyglutamate; trimmed to monoglutamate at the brush border
- C Methylfolate; absorbed directly without any further modification
- D Folic acid; requires binding to intrinsic factor for its uptake
Correct answer: Polyglutamate; trimmed to monoglutamate at the brush border
Dietary folate mostly exists as polyglutamates. The enzyme folate conjugase on the brush border must strip the extra glutamate residues to form monoglutamate, which is the only form transported into the enterocyte.
In the colon, short-chain fatty acids (SCFAs) like butyrate are produced by bacterial fermentation. How are they primarily absorbed?
- A Active transport via the SGLT1 glucose carrier protein
- B Exchange with bicarbonate or via H+-coupled transporters
- C Passive diffusion into the lymphatic lacteals of the villi
- D They are not absorbed at all and are excreted in the feces
Correct answer: Exchange with bicarbonate or via H+-coupled transporters
SCFAs are a vital energy source for colonocytes. They are absorbed via sodium-linked transporters or $H^+$-coupled monocarboxylate transporters (MCTs), often in exchange for bicarbonate.
Water absorption in the small intestine is 'isostatic.' This means that:
- A Water is actively pumped across the apical membrane
- B Water follows solute absorption to keep osmotic equilibrium
- C Water absorption is entirely independent of sodium transport
- D Water moves only through the transcellular pathway
Correct answer: Water follows solute absorption to keep osmotic equilibrium
The intestinal mucosa is highly permeable to water. As solutes (like glucose and $Na^+$) are actively transported into the lateral intercellular spaces, they create an osmotic gradient that pulls water along passively.
Which of the following describes the correct path of a glucose molecule from the intestinal lumen to the blood?
- A SGLT1 (apical) $\rightarrow$ Cytosol $\rightarrow$ GLUT2 (basolateral)
- B GLUT5 (apical) $\rightarrow$ Cytosol $\rightarrow$ SGLT1 (basolateral)
- C Simple diffusion $\rightarrow$ Cytosol $\rightarrow$ Na+/K+ ATPase (basolateral)
- D SGLT1 (apical) $\rightarrow$ Cytosol $\rightarrow$ SGLT1 (basolateral)
Correct answer: SGLT1 (apical) $\rightarrow$ Cytosol $\rightarrow$ GLUT2 (basolateral)
Glucose enters the cell through SGLT1 on the apical membrane using the sodium gradient. It then exits the cell into the interstitial fluid and portal blood through GLUT2 on the basolateral membrane via facilitated diffusion.
A patient with a resection of the distal 50 cm of the ileum is most likely to develop which of the following conditions?
- A Iron deficiency anemia with marked glossitis
- B Megaloblastic anemia with steatorrhea
- C Progressive osmotic glucose intolerance
- D Symptomatic refractory hypercalcemia
Correct answer: Megaloblastic anemia with steatorrhea
The terminal ileum is the exclusive site for Vitamin B12 absorption and the primary site for bile salt reabsorption. Loss of this segment leads to B12 deficiency (megaloblastic anemia) and impaired fat emulsification (steatorrhea) due to a depleted bile salt pool.
Which intestinal structure provides the greatest increase in surface area for absorption?
- A Plicae circulares (Valves of Kerckring)
- B Villi
- C Microvilli (Brush border)
- D Haustra
Correct answer: Microvilli (Brush border)
While all three structures increase surface area, microvilli provide the largest increase (approximately 20-fold). Combined with plicae and villi, the total surface area of the small intestine is increased by roughly 600-fold compared to a simple cylinder.
Absorption of which electrolyte is significantly increased by the action of aldosterone in the distal colon?
- A Potassium
- B Sodium
- C Chloride
- D Bicarbonate
Correct answer: Sodium
Aldosterone increases the number of ENaC (epithelial sodium channels) in the apical membrane of the distal colon. This enhances sodium reabsorption and secondarily promotes potassium secretion.
Zollinger-Ellison syndrome (excess gastrin) causes steatorrhea (fatty stools) primarily because:
- A Gastrin directly inhibits the secretion of pancreatic lipase
- B Low duodenal pH inactivates lipase and precipitates bile salts
- C Gastrin stimulates rapid emptying of the gallbladder into the gut
- D Excess acid destroys the intestinal GLUT5 transporters
Correct answer: Low duodenal pH inactivates lipase and precipitates bile salts
Pancreatic lipase requires a neutral pH to function, and bile salts precipitate in acidic environments. The massive acid output in Zollinger-Ellison syndrome overwhelms the pancreatic bicarbonate, leading to fat malabsorption.
Medium-chain triglycerides (MCTs) are often used in clinical nutrition for patients with malabsorption because:
- A They reach the lymphatic system faster than long-chain triglycerides
- B They are absorbed without micelle formation or pancreatic lipase
- C They are taken up using the apical SGLT1 transporter
- D They stimulate the gallbladder to release more bile salts
Correct answer: They are absorbed without micelle formation or pancreatic lipase
MCTs are more water-soluble and can be hydrolyzed more easily than long-chain triglycerides. They can be absorbed directly by enterocytes even when bile salt or pancreatic enzyme levels are low.