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4# Digestion & absorption in the GI tract
Q1. Digestion is best defined as:
Absorption of nutrients into blood
Breakdown of large molecules into smaller ones by hydrolysis
Transport of nutrients into enterocytes
Oxidation of nutrients inside cells
Explanation:
Digestion refers to enzymatic hydrolysis of large food molecules into smaller absorbable units.
Q2. The first step of carbohydrate digestion occurs in the:
Stomach
Duodenum
Mouth
Jejunum
Explanation:
Carbohydrate digestion begins in the mouth by salivary amylase.
Q3. Salivary amylase mainly breaks starch into:
Maltose, maltotriose, and dextrin
Glucose only
Sucrose and lactose
Fructose
Explanation:
Salivary amylase hydrolyzes starch into maltose, maltotriose and dextrins.
Q4. The optimal pH for salivary amylase activity is approximately:
2
4
5
6.7
Explanation:
Salivary amylase works best near neutral pH (~6.7).
Q5. Salivary amylase stops functioning when gastric pH falls below:
6
4
3
2
Explanation:
Salivary amylase becomes inactive when gastric pH drops below 4.
Q6. Which brush border enzyme digests lactose?
Sucrase
Maltase
Lactase
Dextrinase
Explanation:
Lactase breaks lactose into glucose and galactose.
Q7. The most common disaccharidase deficiency is:
Sucrase deficiency
Maltase deficiency
Isomaltase deficiency
Lactase deficiency
Explanation:
Lactase deficiency leads to lactose intolerance causing diarrhea and flatulence.
Q8. Protein digestion begins in the:
Mouth
Stomach
Jejunum
Ileum
Explanation:
Protein digestion begins in the stomach by the enzyme pepsin.
Q9. The optimal pH for pepsin activity is:
6
4
1–2
8
Explanation:
Pepsin functions best in strongly acidic conditions (pH 1–2).
Q10. Pepsin primarily digests proteins into:
Short polypeptides
Amino acids
Fatty acids
Glucose
Explanation:
Pepsin breaks proteins into smaller polypeptides and peptones.
Q11. Which pancreatic enzyme acts as an exopeptidase?
Trypsin
Chymotrypsin
Elastase
Carboxypeptidase
Explanation:
Carboxypeptidase removes amino acids from the terminal end of peptides.
Q12. Lingual lipase is secreted by:
Salivary glands
Ebner glands
Pancreas
Stomach glands
Explanation:
Lingual lipase is secreted by Ebner glands of the tongue.
Q13. The majority of fat digestion occurs in the:
Small intestine
Stomach
Mouth
Colon
Explanation:
Most fat digestion occurs in the small intestine via pancreatic lipase.
Q14. Emulsification of fat droplets is mainly caused by:
Lipase
Pepsin
Bile salts and lecithin
Amylase
Explanation:
Bile salts and lecithin break fat into small droplets increasing surface area for lipase.
Q15. Glucose and galactose absorption occurs by:
Simple diffusion
Facilitated diffusion
Active transport with H+
Secondary active transport with Na+
Explanation:
Glucose and galactose are absorbed by Na+ dependent cotransport (SGLT).
Q16. Fructose absorption occurs mainly via:
Active transport
Facilitated diffusion
Simple diffusion
Pinocytosis
Explanation:
Fructose is absorbed by facilitated diffusion through GLUT transporters.
Q17. Dipeptides and tripeptides are absorbed with:
Na+
Cl-
H+
Ca2+
Explanation:
Dipeptides and tripeptides are absorbed via H+ dependent cotransporters.
Q18. Short chain fatty acids (<10–12 C) are absorbed:
Directly into blood
Into lymph
Into chylomicrons
Into bile
Explanation:
Short chain fatty acids diffuse directly into portal blood.
Q19. Long chain fatty acids are transported from enterocytes mainly as:
Albumin complexes
Free fatty acids
Micelles
Chylomicrons
Explanation:
Long chain fatty acids are re-esterified into triglycerides and transported as chylomicrons.
Q20. Chylomicrons enter circulation through:
Portal vein
Lymphatic lacteals
Hepatic artery
Inferior vena cava
Explanation:
Chylomicrons enter lymphatic vessels (lacteals) before reaching systemic circulation.
Q21. Calcium absorption occurs mainly in the:
Ileum
Colon
Upper small intestine
Stomach
Explanation:
Most calcium absorption occurs in the duodenum and upper jejunum.
Q22. Calcium absorption is enhanced by:
Oxalate
Phosphate
Bicarbonate
Vitamin D
Explanation:
Vitamin D increases calcium binding proteins and enhances absorption.
Q23. Approximately how much water is absorbed daily in the GI tract?
1 L
9 L
15 L
20 L
Explanation:
About 2 L ingested + 7 L secreted fluids are absorbed daily.
Q24. The major site of water absorption in colon is:
Distal colon
Sigmoid colon
Proximal colon
Rectum
Explanation:
Most water absorption in large intestine occurs in proximal colon.
Q25. Kupffer cells in liver mainly function in:
Immunity
Bile production
Protein synthesis
Detoxification
Explanation:
Kupffer cells are macrophages responsible for liver immune defense.
Q26. The liver stores iron mainly as:
Hemoglobin
Transferrin
Hemosiderin
Ferritin
Explanation:
Iron is stored in hepatocytes mainly as ferritin.
Q27. The liver acts as a blood reservoir containing approximately:
200 ml
450 ml
1 L
2 L
Explanation:
The liver can store about 450 ml of blood (~10% of total blood).
Q28. Which vitamin can be synthesized by colonic bacteria?
Vitamin A
Vitamin C
Vitamin K
Vitamin D
Explanation:
Colonic bacteria synthesize vitamin K as well as some B vitamins.
Q29. Which substance can be absorbed in small quantities from the stomach?
Glucose
Proteins
Fatty acids
Alcohol
Explanation:
The stomach absorbs small amounts of alcohol and some drugs like aspirin.
Q30. Humans cannot digest cellulose because:
No cellulose-digesting enzyme is secreted
Cellulose is toxic
Cellulose is absorbed directly
It requires bile salts
Explanation:
Humans lack cellulase enzymes, though colonic bacteria can digest small amounts.