L55, 56 Digestive functions of liver & bile, absorption of carbs, ions, proteins and fats

Question 1

L55

What are the main functions of the liver?

Answer 1

The liver functions in metabolism (carbohydrates, lipids, proteins), detoxification, bile production, storage (glycogen, vitamins), synthesis (plasma proteins like albumin), and immune defence via Kupffer cells.

Question 2

L55

Where is the liver located in the body?

Answer 2

The liver lies in the right upper quadrant of the abdomen, beneath the diaphragm, and is protected by the rib cage.

Question 3

L55

What are the two sources of blood supply to the liver?

Answer 3

The hepatic artery (oxygen-rich blood) and the portal vein (nutrient-rich blood from the gastrointestinal tract).

Question 4

L55

How does blood leave the liver?

Answer 4

Through hepatic veins, which drain into the inferior vena cava.

Question 5

L55

What is the basic structural unit of the liver?

Answer 5

The classical liver lobule – hexagonal in shape, with a central vein and portal triads at each corner.

Question 6

L55

What makes up the portal triad?

Answer 6

A branch of the hepatic artery, portal vein, and bile duct.

Question 7

L55

What are Kupffer cells?

Answer 7

Specialised macrophages in the liver sinusoids responsible for removing pathogens and debris.

Question 8

L55

How is bile formed and transported in the liver?

Answer 8

Bile is secreted by hepatocytes into bile canaliculi, which drain into bile ducts, then to the common hepatic duct.

Question 9

L55

What is the direction of bile flow in relation to blood flow in the liver lobule?

Answer 9

Bile flows in the opposite direction to blood – from the centre of the lobule toward the periphery.

Question 10

L55

How does the liver regulate blood glucose?

Answer 10

Through glycogenesis (formation of glycogen), glycogenolysis (breakdown of glycogen), and gluconeogenesis (formation of glucose from non-carbohydrates).

Question 11

L55

What proteins does the liver synthesise?

Answer 11

Albumin, clotting factors, and transport proteins like transferrin.

Question 12

L55

What is the role of the liver in fat metabolism?

Answer 12

The liver synthesises and breaks down triglycerides, cholesterol, and lipoproteins.

Question 13

L55

What is the liver’s role in detoxification?

Answer 13

The liver metabolises drugs and toxins using phase I (oxidation/reduction) and phase II (conjugation) reactions, making substances easier to excrete.

Question 14

L55

What is cirrhosis?

Answer 14

Chronic liver damage leading to fibrosis and nodular regeneration, disrupting normal liver architecture and function.

Question 15

L55

What is portal hypertension and what can it lead to?

Answer 15

Increased pressure in the portal vein, often due to cirrhosis, leading to complications like varices, ascites, and splenomegaly.

Question 16

L55

What is the hepatic acinus and how does it differ from the classical lobule?

Answer 16

The hepatic acinus is diamond-shaped and based on blood flow between two central veins. It divides into three zones (1–3) reflecting oxygen and nutrient gradients.

Question 17

L55

What are the functional zones of the hepatic acinus and their significance?

Answer 17

Zone 1 (periportal): Closest to the portal triad, receives most oxygen, active in oxidative metabolism and gluconeogenesis.

Zone 2 (mid-zone): Intermediate functions.

Zone 3 (centrilobular): Closest to the central vein, least oxygenated, more prone to ischaemic damage and drug-induced injury.

Question 18

L55

What is the composition of bile?

Answer 18

Bile contains bile salts, bile pigments (mainly bilirubin), cholesterol, phospholipids, and electrolytes.

Question 19

L55

What is the function of bile?

Answer 19

Bile emulsifies fats in the small intestine to aid digestion and absorption of lipids and fat-soluble vitamins; it also facilitates excretion of bilirubin and excess cholesterol.

Question 20

L55

Can the liver regenerate?

Answer 20

Yes. The liver has a remarkable regenerative capacity, capable of restoring mass and function after partial hepatectomy or mild injury.

Question 21

L55

Besides Kupffer cells, what other immune functions does the liver have?

Answer 21

The liver contains dendritic cells, natural killer (NK) cells, and lymphocytes which contribute to immune surveillance and tolerance, especially to gut-derived antigens.

Question 22

L55

What blood tests are used to assess liver function?

Answer 22

Liver Function Tests (LFTs) include ALT, AST, ALP, bilirubin, albumin, and prothrombin time.

Question 23

L55

What does a raised ALT or AST suggest?

Answer 23

Hepatocellular damage — ALT is more specific to liver injury.

Question 24

L55

What does a raised ALP suggest?

Answer 24

Cholestasis or bile duct obstruction, though ALP is also found in bone.

Question 25

# L55 Why is bilirubin measured in liver tests?

Answer 25

To assess the liver’s ability to conjugate and excrete bilirubin — raised levels cause jaundice.

Question 26

# L55 What are liver function tests (LFTs) and why are they done?

Answer 26

LFTs are blood tests that assess liver health and function. They help diagnose liver disease, monitor progression, and assess response to treatment.

Question 27

# L55 What does ALT (alanine aminotransferase) indicate?

Answer 27

ALT is a cytosolic enzyme primarily found in hepatocytes. Raised ALT suggests hepatocellular injury and is liver-specific.

Question 28

# L55 What does AST (aspartate aminotransferase) indicate?

Answer 28

AST is found in liver, cardiac muscle, and skeletal muscle. Elevated AST suggests hepatocellular injury but is less specific than ALT.

Question 29

# L55 What does a high AST:ALT ratio suggest?

Answer 29

An AST:ALT ratio >2:1 is often associated with alcoholic liver disease.

Question 30

# L55 What does alkaline phosphatase (ALP) indicate?

Answer 30

ALP is raised in cholestasis (bile flow obstruction) and may also be elevated in bone disease. ALP is produced by bile duct epithelial cells.

Question 31

# L55 What does gamma-glutamyl transferase (GGT) indicate?

Answer 31

GGT is raised in cholestasis and is also a marker of alcohol use. A raised ALP with raised GGT supports hepatic origin.

Question 32

# L55 What does raised bilirubin suggest?

Answer 32

Impaired uptake, conjugation, or excretion of bilirubin by the liver, or increased production (e.g. haemolysis). Causes jaundice when levels are high.

Question 33

# L55 What is the difference between conjugated and unconjugated bilirubin?

Answer 33

Unconjugated: Bound to albumin, not water-soluble, raised in haemolysis or Gilbert’s syndrome. Conjugated: Water-soluble, raised in cholestasis or hepatocellular dysfunction.

Question 34

# L55 Why is albumin measured in LFTs?

Answer 34

Albumin reflects the liver’s synthetic function. Low levels suggest chronic liver disease, malnutrition, or nephrotic syndrome.

Question 35

# L55 Why is prothrombin time (PT) important in liver disease?

Answer 35

PT assesses clotting factor production (which are made by the liver). A prolonged PT indicates impaired liver synthesis and correlates with liver failure severity.

Question 36

# L55 What does serum ammonia indicate in liver disease?

Answer 36

Ammonia accumulates when the liver fails to convert it to urea. High levels are associated with hepatic encephalopathy.

Question 37

# L55 Why is urea often low in liver failure?

Answer 37

Because the liver cannot synthesise urea from ammonia, leading to hyperammonaemia and reduced blood urea nitrogen.

Question 38

# L55 What is hepatic encephalopathy and how is it related to liver function?

Answer 38

A decline in brain function due to accumulation of toxins (especially ammonia) that the liver fails to clear. Symptoms range from confusion to coma.

Question 39

# L55 What are the types of jaundice and how do they relate to liver function?

Answer 39

Pre-hepatic: Due to haemolysis (↑ unconjugated bilirubin) Hepatic: Due to liver cell damage (mixed conjugated/unconjugated) Post-hepatic: Due to obstruction of bile flow (↑ conjugated bilirubin)

Question 40

# L55 What does a liver ultrasound help detect in liver disease?

Answer 40

Structural abnormalities like cirrhosis, fatty liver, biliary obstruction, and liver tumours.

Question 41

# L55 Why might an AST rise in muscle injury?

Answer 41

AST is not liver-specific. It can rise in myocardial infarction or skeletal muscle damage, so context is key.

Question 42

# L55 Which enzyme is the most specific indicator of hepatocellular injury? A. AST B. ALT C. ALP D. GGT

Answer 42

Answer: B. ALT

Question 43

# L55 Which cell type in the liver is responsible for phagocytosis and immune surveillance? A. Hepatocytes B. Kupffer cells C. Stellate cells D. Endothelial cells

Answer 43

Answer: B. Kupffer cells

Question 44

# L55 In the hepatic acinus model, which zone is most susceptible to ischaemic damage? A. Zone 1 B. Zone 2 C. Zone 3 D. Central vein

Answer 44

Answer: C. Zone 3

Question 45

# L55 What is the role of bile salts in digestion? A. Breaking down proteins B. Neutralising stomach acid C. Emulsifying fats D. Absorbing glucose

Answer 45

Answer: C. Emulsifying fats

Question 46

# L55 Which of the following would most likely cause a raised conjugated bilirubin level? A. Gilbert’s syndrome B. Haemolytic anaemia C. Obstructive jaundice D. Crigler-Najjar syndrome

Answer 46

Answer: C. Obstructive jaundice

Question 47

# L55 An isolated rise in alkaline phosphatase (ALP) with normal ALT and AST could suggest: A. Cirrhosis B. Acute hepatitis C. Bone disease D. Alcoholic liver disease

Answer 47

Answer: C. Bone disease

Question 48

# L55 Which two tests together help distinguish hepatic from bone sources of raised ALP? A. AST and ALT B. GGT and ALP C. Bilirubin and albumin D. PT and ALT

Answer 48

Answer: B. GGT and ALP

Question 49

# L55 A patient with chronic liver disease presents with oedema and low oncotic pressure. Which blood test result best explains this? A. Low ALT B. High GGT C. Low albumin D. High ammonia

Answer 49

Answer: C. Low albumin

Question 50

# L55 Which of the following best reflects the liver’s synthetic function? A. GGT B. Prothrombin time C. ALT D. Bilirubin

Answer 50

Answer: B. Prothrombin time

Question 51

# L55 What is the likely cause of encephalopathy in advanced liver failure? A. Hyperkalaemia B. Elevated urea C. Hyperammonaemia D. Hypoglycaemia

Answer 51

Answer: C. Hyperammonaemia

Question 52

# L55 A 45-year-old man with a history of alcohol misuse has an AST:ALT ratio of 3:1. What is the most likely diagnosis? A. Viral hepatitis B. Autoimmune hepatitis C. Alcoholic liver disease D. Biliary atresia

Answer 52

Answer: C. Alcoholic liver disease

Question 53

# L55 A 60-year-old woman has a raised ALP, GGT and conjugated bilirubin. Which condition is most likely? A. Gilbert’s syndrome B. Acute hepatitis C. Primary biliary cholangitis D. Haemolytic anaemia

Answer 53

Answer: C. Primary biliary cholangitis

Question 54

# L55 Which liver structure is the site of nutrient-rich blood entering from the intestines? A. Hepatic artery B. Hepatic vein C. Portal vein D. Central vein

Answer 54

Answer: C. Portal vein

Question 55

# L55 In which situation would the measurement of serum ammonia be most useful? A. Suspected hepatitis B B. Biliary colic C. Suspected hepatic encephalopathy D. Fatty liver disease

Answer 55

Answer: C. Suspected hepatic encephalopathy

Question 56

# L55 What is the primary function of stellate (Ito) cells in the liver under normal physiological conditions? A. Producing albumin B. Storing vitamin A C. Phagocytosing bacteria D. Secreting bile salts

Answer 56

Answer: B. Storing vitamin A

Question 57

# L55 What key event causes stellate cells to contribute to liver fibrosis? A. Hepatic ischaemia B. Exposure to alcohol C. Activation following liver injury D. Inhibition of bile secretion

Answer 57

Answer: C. Activation following liver injury

Question 58

# L55 Which zone of the hepatic acinus receives the most oxygenated blood? A. Zone 1 B. Zone 2 C. Zone 3 D. Portal triad

Answer 58

Answer: A. Zone 1

Question 59

# L55 Which of the following is least likely to be a direct consequence of hepatic dysfunction? A. Coagulopathy B. Hyperglycaemia C. Encephalopathy D. Hypoalbuminaemia

Answer 59

Answer: B. Hyperglycaemia

Question 60

# L55 What is the most likely explanation for prolonged PT in liver failure? A. Malabsorption of calcium B. Platelet destruction C. Decreased synthesis of clotting factors D. Increased bilirubin

Answer 60

Answer: C. Decreased synthesis of clotting factors

Question 61

# L55 A patient has elevated unconjugated bilirubin but normal liver enzymes and no signs of haemolysis. What is the likely diagnosis? A. Gilbert’s syndrome B. Obstructive jaundice C. Hepatitis A D. Cirrhosis

Answer 61

Answer: A. Gilbert’s syndrome

Question 62

# L55 A 35-year-old woman presents with fatigue and pruritus. LFTs show raised ALP and GGT, with positive antimitochondrial antibodies. What is the likely diagnosis? A. Autoimmune hepatitis B. Primary biliary cholangitis C. Wilson’s disease D. Haemochromatosis

Answer 62

Answer: B. Primary biliary cholangitis

Question 63

# L55 In acute liver failure, what would you expect to happen to urea levels and why? A. Increase due to GI bleeding B. Decrease due to impaired ammonia conversion C. Stay the same D. Increase due to protein catabolism

Answer 63

Answer: B. Decrease due to impaired ammonia conversion

Question 64

# L55 Which of the following best differentiates between intrahepatic and extrahepatic cholestasis? A. ALT B. ALP C. GGT D. Imaging (e.g. ultrasound)

Answer 64

Answer: D. Imaging (e.g. ultrasound)

Question 65

# L55 In hepatocellular injury, which pattern of LFT results is typical? A. High ALP, high GGT, normal ALT B. High ALT, high AST, mild ALP rise C. Normal ALT, raised bilirubin D. Low albumin, normal enzymes

Answer 65

Answer: B. High ALT, high AST, mild ALP rise

Question 66

# L56 Where does carbohydrate absorption primarily occur?

Answer 66

In the small intestine, especially the jejunum.

Question 67

# L55 How are glucose and galactose absorbed?

Answer 67

Via SGLT1 (Sodium-Glucose Linked Transporter 1), a secondary active transporter using the Na⁺ gradient.

Question 68

# L56 How is fructose absorbed?

Answer 68

Via GLUT5, a facilitated diffusion transporter.

Question 69

# L56 Which transporter exports all monosaccharides to the blood?

Answer 69

GLUT2 on the basolateral membrane.

Question 70

# L56 What are the final digestion products of proteins?

Answer 70

Amino acids, dipeptides, and tripeptides.

Question 71

# L56 How are amino acids absorbed?

Answer 71

Via sodium-dependent active transport systems.

Question 72

# L56 How are di- and tripeptides absorbed?

Answer 72

Via PEPT1, a proton-dependent transporter.

Question 73

# L56 What happens to absorbed di/tripeptides in enterocytes?

Answer 73

They are hydrolysed to free amino acids before entering the bloodstream.

Question 74

# L56 Where is Na⁺ absorbed and by what mechanisms?

Answer 74

Throughout the small intestine and colon via: Na⁺/H⁺ exchangers (NHE3) Sodium channels (ENaC, especially in the colon) Na⁺-glucose and Na⁺-amino acid cotransporters

Question 75

# L56 How is Cl⁻ absorbed?

Answer 75

Through passive diffusion or Cl⁻/HCO₃⁻ exchangers, coupled with Na⁺ absorption.

Question 76

# L56 How is K⁺ absorbed?

Answer 76

Mainly by passive diffusion in the small intestine and secreted in the colon if needed.

Question 77

# L56 How is calcium absorbed and regulated?

Answer 77

Actively in the duodenum (via TRPV6) under control of vitamin D, and passively throughout the small intestine.

Question 78

# L56 How is iron absorbed?

Answer 78

Fe³⁺ is reduced to Fe²⁺ (ferrous) by duodenal cytochrome b, then absorbed via DMT1 (divalent metal transporter 1). Stored as ferritin or exported by ferroportin.

Question 79

# L56 How much water is absorbed in the GI tract?

Answer 79

About 8–9 liters/day, mostly in the small intestine.

Question 80

# L56 What drives water absorption?

Answer 80

Osmotic gradients created by solute (e.g. Na⁺, glucose) absorption.

Question 81

# L56 Where is water absorption maximal?

Answer 81

In the jejunum, though it continues in the ileum and colon.

Question 82

# L56 Is water absorption passive or active?

Answer 82

Entirely passive, following solute movement.

Question 83

# L56 What is the role of SGLT1 in carbohydrate absorption?

Answer 83

SGLT1 transports glucose and galactose into enterocytes using a Na⁺ gradient (secondary active transport).

Question 84

# L56 What powers the Na⁺ gradient used by SGLT1?

Answer 84

The Na⁺/K⁺ ATPase on the basolateral membrane.

Question 85

# L56 How is fructose absorbed in the small intestine?

Answer 85

Through GLUT5, via facilitated diffusion.

Question 86

# L56 What transporter helps export monosaccharides from enterocytes into the blood?

Answer 86

GLUT2 on the basolateral membrane.

Question 87

# L56 How does GLUT2 contribute during high carbohydrate intake?

Answer 87

GLUT2 may be recruited to the apical membrane to enhance glucose/fructose absorption.

Question 88

# L56 What are the final digestion products of proteins?

Answer 88

Free amino acids, dipeptides, and tripeptides.

Question 89

# L56 How are amino acids absorbed?

Answer 89

Via Na⁺-dependent or Na⁺-independent amino acid transport systems (classified by charge and size).

Question 90

# L56 How are di- and tripeptides absorbed?

Answer 90

Via the H⁺-dependent PepT1 transporter.

Question 91

# L56 What happens to absorbed peptides inside enterocytes?

Answer 91

They are hydrolysed into amino acids by intracellular peptidases.

Question 92

# L56 What else is absorbed by PepT1 apart from peptides?

Answer 92

Certain drugs like beta-lactam antibiotics (e.g., cefadroxil).

Question 93

# L56 How is sodium absorbed in the small intestine?

Answer 93

Via Na⁺/glucose, Na⁺/amino acid cotransporters, and Na⁺/H⁺ exchangers (NHE3).

Question 94

# L56 How is sodium absorbed in the colon?

Answer 94

Through ENaC, regulated by aldosterone.

Question 95

# L56 How is chloride absorbed?

Answer 95

By passive diffusion and via Cl⁻/HCO₃⁻ exchangers, often coupled with Na⁺ absorption.

Question 96

# L56 How is potassium handled in the gut?

Answer 96

Absorbed passively in the small intestine, secreted or absorbed in the colon depending on needs.

Question 97

# L56 How is calcium absorbed?

Answer 97

Via: - Active transport in the duodenum: TRPV6 → calbindin → PMCA/NCX (vitamin D-dependent). - Passive diffusion throughout small intestine (paracellular).

Question 98

# L56 What regulates active calcium absorption?

Answer 98

1,25-dihydroxyvitamin D₃ (calcitriol).

Question 99

# L56 How is iron absorbed and transported?

Answer 99

Fe³⁺ is reduced to Fe²⁺, absorbed via DMT1; stored as ferritin or exported via ferroportin with help from hephaestin.

Question 100

# L56 What regulates ferroportin activity?

Answer 100

Hepcidin, a liver hormone that decreases iron export during inflammation or iron overload.

Question 101

# L56 How much water is absorbed daily by the GI tract?

Answer 101

Approximately 8–9 liters/day.

Question 102

# L56 Where does most water absorption occur?

Answer 102

Jejunum > ileum > colon.

Question 103

# L56 How is water absorbed?

Answer 103

Passively via osmosis, driven by solute (especially Na⁺) absorption.

Question 104

# L56 What channels assist water absorption?

Answer 104

Aquaporins (AQP3, AQP7) present on enterocytes.

Question 105

# L56 How does defective water absorption lead to diarrhea?

Answer 105

Unabsorbed solutes (e.g., lactose in intolerance) retain water in the lumen, causing osmotic diarrhea.

Question 106

# L56 How does aldosterone affect intestinal absorption?

Answer 106

Increases Na⁺ absorption by upregulating ENaC in the colon.

Question 107

# L56 What GI disorder impairs nutrient absorption due to villus atrophy?

Answer 107

Celiac disease – damages absorptive surfaces.

Question 108

# L56 Why do people with lactase deficiency get diarrhea?

Answer 108

Undigested lactose creates an osmotic load, pulling water into the lumen.

Question 109

# L56 What transporter is defective in cystic fibrosis affecting gut secretions?

Answer 109

CFTR – impairs Cl⁻ and water secretion, thickening mucus.

Question 110

# L56 What role does SGLT1 play in nutrient absorption?

Answer 110

SGLT1 (Sodium-Glucose Linked Transporter 1) facilitates active transport of glucose and galactose in the small intestine, using the sodium gradient created by Na⁺/K⁺ ATPase.

Question 111

# L56 How does GLUT2 function in glucose absorption?

Answer 111

GLUT2 facilitates the passive transport of glucose, galactose, and fructose from enterocytes into the portal circulation.

Question 112

# L56 How is fructose absorbed in the intestine?

Answer 112

Fructose is absorbed by facilitated diffusion via the GLUT5 transporter.

Question 113

# L56 What is the primary mechanism for protein absorption in the small intestine?

Answer 113

Proteins are absorbed as di- and tri-peptides via PepT1 (proton-dependent oligopeptide transporter) and as free amino acids via various sodium-dependent transporters.

Question 114

# L56 What role does gastric acid play in iron absorption?

Answer 114

Gastric acid reduces ferric (Fe³⁺) to ferrous (Fe²⁺) iron, enhancing solubility and uptake in the duodenum via DMT1.

Question 115

# L56 How is vitamin B12 absorbed?

Answer 115

Vitamin B12 binds intrinsic factor in the stomach, and the complex is absorbed in the terminal ileum via receptor-mediated endocytosis.

Question 116

# L56 Which hormones regulate nutrient absorption in the GI tract?

Answer 116

Hormones like CCK, secretin, GIP, and motilin regulate GI motility and secretion, indirectly affecting nutrient absorption.

Question 117

# L56 What diseases can impair nutrient absorption?

Answer 117

Conditions like celiac disease, Crohn's disease, pancreatic insufficiency, and bile acid malabsorption can significantly impair absorption.

Question 118

# L56 How do bile acids assist in nutrient absorption?

Answer 118

Bile acids emulsify fats, aiding in micelle formation for absorption of lipids and fat-soluble vitamins (A, D, E, K).

Question 119

# L56 What transporter is involved in calcium absorption?

Answer 119

TRPV6 facilitates calcium entry into enterocytes; it is regulated by vitamin D, which also upregulates calbindin and PMCA1b.

Question 120

# L56 What triggers the insertion of GLUT2 into the apical membrane?

Answer 120

High luminal glucose concentrations (post-meal) can stimulate translocation of GLUT2 to the apical membrane for rapid glucose uptake.

Question 121

# L56 How does secretory diarrhea occur in diseases like cholera?

Answer 121

Cholera toxin activates adenylate cyclase → ↑cAMP → activates CFTR → excessive Cl⁻ secretion → water follows → severe watery diarrhea.

Question 122

# L56 What’s the function of NHE3 in the intestine?

Answer 122

NHE3 (Na⁺/H⁺ exchanger) allows Na⁺ absorption in exchange for H⁺ secretion — also helps regulate pH and bicarbonate balance.

Question 123

# L56 What happens to undigested lactose in lactase deficiency?

Answer 123

It remains in the lumen, draws water osmotically, and is fermented by bacteria → gas + diarrhea (osmotic + fermentative symptoms).

Question 124

# L56 What is the fate of bile salts after lipid digestion?

Answer 124

Reabsorbed in the terminal ileum via ASBT (apical sodium-dependent bile acid transporter) and returned to the liver (enterohepatic circulation).

Question 125

# L56 How do enterocytes prevent iron overload?

Answer 125

By storing excess iron as ferritin, and regulating export through ferroportin, which is inhibited by the hormone hepcidin.

Question 126

# L56 What transporters are involved in amino acid absorption?

Answer 126

Multiple systems like system B⁰ (neutral AAs, Na⁺-dependent), system X⁻ (acidic AAs), system L (large neutral AAs, Na⁺-independent).

Question 127

# L56 What enzyme is essential for disaccharide digestion at the brush border?

Answer 127

Disaccharidases like sucrase, lactase, and maltase; deficiency leads to malabsorption syndromes.

Question 128

# L56 What conditions affect B12 absorption?

Answer 128

Pernicious anemia (loss of intrinsic factor), terminal ileum diseases (e.g., Crohn’s), or resection → B12 deficiency.

Question 129

# L56 What role do intracellular enzymes play in nutrient absorption?

Answer 129

They hydrolyse absorbed di/tripeptides into amino acids and re-esterify absorbed lipids for chylomicron formation.

Question 130

# L56 How is folate absorbed in the intestine?

Answer 130

Folate is absorbed primarily in the jejunum via a proton-coupled folate transporter (PCFT) in its monoglutamate form.

Question 131

# L56 What is the role of intracellular calbindin in calcium absorption?

Answer 131

Calbindin binds Ca²⁺ and shuttles it across the enterocyte cytoplasm to the basolateral membrane, preventing cytotoxicity and aiding efficient transport.

Question 132

# L56 What is the role of the Na⁺/K⁺ ATPase in all absorptive processes?

Answer 132

It maintains the Na⁺ gradient that drives nearly all secondary active transport of glucose, amino acids, bile salts, and ions.

Question 133

# L56 How does the colon secrete potassium?

Answer 133

Through apical BK (big potassium) channels, especially during high flow or aldosterone stimulation.

Question 134

# L56 How does the intestinal microbiota influence absorption?

Answer 134

Microbes ferment undigested carbohydrates into short-chain fatty acids (SCFAs) like butyrate, which are absorbed and contribute to colonic health and energy.

Question 135

# L56 What are the consequences of terminal ileum resection?

Answer 135

Malabsorption of bile salts (→ steatorrhea), and vitamin B12 deficiency (→ megaloblastic anemia).

Question 136

# L56 What type of diarrhea results from defective ENaC channels?

Answer 136

Secretory diarrhea due to impaired Na⁺ absorption, as seen in congenital chloride diarrhea or pseudohypoaldosteronism.

Question 137

# L56 What nutrient absorption is pH-dependent in the duodenum?

Answer 137

Iron — acidic pH helps reduce Fe³⁺ to Fe²⁺, which is more absorbable via DMT1.

Question 138

# L56 Which transporter is responsible for glucose and galactose absorption at the apical membrane of enterocytes? A. GLUT2 B. GLUT5 C. SGLT1 D. PepT1

Answer 138

Answer: C. SGLT1 ✅ Explanation: SGLT1 is a sodium-dependent glucose transporter located at the apical membrane, co-transporting Na⁺ with glucose or galactose into enterocytes.

Question 139

# L56 Fructose is absorbed in the small intestine by which transporter? A. SGLT1 B. GLUT5 C. GLUT2 D. Na⁺/Glucose cotransporter

Answer 139

Answer: B. GLUT5 ✅ Explanation: GLUT5 specifically facilitates facilitated diffusion of fructose across the apical membrane.

Question 140

# L56 Which condition would impair carbohydrate absorption due to an enzyme deficiency? A. Cystic fibrosis B. Lactase deficiency C. Zollinger-Ellison syndrome D. Pernicious anemia

Answer 140

Answer: B. Lactase deficiency ✅ Explanation: Without lactase, lactose cannot be digested into absorbable monosaccharides, leading to osmotic diarrhea.

Question 141

# L56 Which transporter facilitates absorption of di- and tri-peptides into enterocytes? A. SGLT1 B. PepT1 C. DMT1 D. FATP

Answer 141

Answer: B. PepT1 ✅ Explanation: PepT1 uses a proton gradient to co-transport small peptides into the enterocyte.

Question 142

# L56 After absorption into enterocytes, small peptides are further processed by: A. Brush-border enzymes B. Cytosolic peptidases C. Pancreatic enzymes D. Bile salts

Answer 142

Answer: B. Cytosolic peptidases ✅ Explanation: Once inside enterocytes, di- and tri-peptides are hydrolyzed into amino acids by intracellular enzymes.

Question 143

# L56 What drives most amino acid transport across the apical membrane of enterocytes? A. Proton gradient B. Na⁺ gradient C. ATP hydrolysis D. Osmotic pressure

Answer 143

Answer: B. Na⁺ gradient ✅ Explanation: Amino acid absorption is largely secondary active, using the Na⁺ gradient established by Na⁺/K⁺ ATPase.

Question 144

# L56 Which transporter is key for apical iron uptake in enterocytes? A. Ferritin B. Ferroportin C. DMT1 D. PCFT

Answer 144

Answer: C. DMT1 ✅ Explanation: Divalent Metal Transporter 1 (DMT1) transports Fe²⁺ across the apical membrane into the enterocyte.

Question 145

# L56 Calcium absorption is enhanced by which vitamin and binding protein? A. Vitamin C and albumin B. Vitamin B12 and ferritin C. Vitamin D and calbindin D. Vitamin K and transferrin

Answer 145

Answer: C. Vitamin D and calbindin ✅ Explanation: Vitamin D induces synthesis of calbindin, which helps shuttle Ca²⁺ across the enterocyte.

Question 146

# L56 What is the primary function of the Na⁺/K⁺ ATPase in nutrient absorption? A. Synthesizes glucose B. Drives passive Cl⁻ absorption C. Maintains sodium gradient for co-transport D. Pumps glucose directly into the blood

Answer 146

Answer: C. Maintains sodium gradient for co-transport ✅ Explanation: It actively expels Na⁺ to maintain low intracellular Na⁺, enabling secondary active nutrient uptake.

Question 147

# L56 Water absorption in the small intestine primarily occurs via: A. Osmosis following active solute transport B. Passive diffusion of water channels C. Active pumping through aquaporins D. Aldosterone-stimulated channels

Answer 147

Answer: A. Osmosis following active solute transport ✅ Explanation: Solute absorption, especially Na⁺, creates osmotic gradients that drive water uptake.

Question 148

# L56 In the colon, sodium is absorbed primarily through: A. Na⁺/H⁺ exchanger B. SGLT1 C. ENaC (Epithelial Na⁺ Channel) D. CFTR

Answer 148

Answer: C. ENaC (Epithelial Na⁺ Channel) ✅ Explanation: ENaC in the colon, regulated by aldosterone, allows passive Na⁺ entry across the apical membrane.

Question 149

# L56 Aldosterone increases: A. Water secretion B. Cl⁻ absorption C. ENaC expression D. Glucose transporter activity

Answer 149

Answer: C. ENaC expression ✅ Explanation: Aldosterone enhances ENaC expression and Na⁺/K⁺ ATPase activity to increase sodium reabsorption.

Question 150

# L56 What structure is essential for solubilizing dietary fats for absorption? A. Chylomicron B. Liposome C. Micelle D. Bilirubin

Answer 150

Answer: C. Micelle ✅ Explanation: Micelles, formed by bile salts, ferry lipids to the brush border for absorption.

Question 151

# L56 After lipid absorption, triglycerides are reassembled and exported as: A. LDL B. HDL C. Chylomicrons D. Micelles

Answer 151

Answer: C. Chylomicrons ✅ Explanation: Lipids are packaged into chylomicrons in enterocytes for lymphatic transport.

Question 152

# L56 Which part of the intestine reabsorbs bile salts? A. Duodenum B. Jejunum C. Ileum D. Colon

Answer 152

Answer: C. Ileum ✅ Explanation: Bile salts are actively reabsorbed in the terminal ileum by ASBT transporters.

Question 153

# L56 Which hormone reduces iron export by degrading ferroportin? A. Secretin B. Hepcidin C. Aldosterone D. Gastrin

Answer 153

Answer: B. Hepcidin ✅ Explanation: Hepcidin inhibits iron absorption by inducing degradation of ferroportin.

Question 154

# L56 A patient with terminal ileum resection is at risk for which two deficiencies? A. Calcium and iron B. Vitamin B12 and bile salts C. Vitamin C and protein D. Glucose and water

Answer 154

Answer: B. Vitamin B12 and bile salts ✅ Explanation: The terminal ileum is the exclusive site for both B12-intrinsic factor complex and bile salt absorption.

Question 155

# L56 Cholera toxin causes diarrhea by: A. Inhibiting glucose absorption B. Inhibiting ENaC C. Increasing CFTR-mediated Cl⁻ secretion D. Blocking aquaporins

Answer 155

Answer: C. Increasing CFTR-mediated Cl⁻ secretion ✅ Explanation: Cholera toxin raises cAMP, stimulating CFTR and leading to secretory diarrhea.

Question 156

# L56 What transporter is involved in folate absorption? A. PepT1 B. PCFT C. ENaC D. DMT1

Answer 156

Answer: B. PCFT ✅ Explanation: The proton-coupled folate transporter (PCFT) facilitates folate uptake in the jejunum.

Question 157

# L56 Which of the following is most likely to cause osmotic diarrhea? A. Secretin overproduction B. Bacterial overgrowth C. Lactase deficiency D. Low sodium diet

Answer 157

Answer: C. Lactase deficiency ✅ Explanation: Undigested lactose remains in the lumen, drawing water and causing osmotic diarrhea.

Question 158

# L56 Which of the following occurs via paracellular water absorption? A. Water moves through aquaporins only B. Water is actively pumped across the membrane C. Water follows solutes through tight junctions D. Water is co-transported with amino acids

Answer 158

Answer: C. Water follows solutes through tight junctions ✅ Explanation: Paracellular water absorption occurs between cells, driven by osmotic gradients created by solute absorption.

Question 159

# L56 Enterocyte polarity is critical because it ensures: A. Randomized transport of nutrients B. Uniform expression of transporters C. Directional (vectorial) absorption from lumen to blood D. Passive diffusion of all molecules

Answer 159

Answer: C. Directional (vectorial) absorption from lumen to blood ✅ Explanation: Apical and basolateral membranes contain distinct transporters enabling vectorial (directional) movement of substances.

Question 160

# L56 What is the function of brush-border disaccharidases like sucrase-isomaltase? A. Break down starch to maltose B. Hydrolyze dipeptides to amino acids C. Break down disaccharides into absorbable monosaccharides D. Emulsify dietary fats

Answer 160

Answer: C. Break down disaccharides into absorbable monosaccharides ✅ Explanation: These enzymes at the microvilli cleave disaccharides into monosaccharides like glucose, galactose, and fructose.

Question 161

# L56 Which transporter is involved in enterohepatic recirculation of bile salts in the ileum? A. NPC1L1 B. ASBT C. FATP4 D. DMT1

Answer 161

Answer: B. ASBT ✅ Explanation: Apical Sodium-dependent Bile Salt Transporter (ASBT) reabsorbs bile salts in the terminal ileum.

Question 162

# L56 Feedback regulation of bile acid synthesis is mediated by which ileal hormone? A. GLP-1 B. CCK C. FGF19 D. Secretin

Answer 162

Answer: C. FGF19 ✅ Explanation: FGF19 is secreted in response to bile acid reabsorption and suppresses further bile acid synthesis in the liver.

Question 163

# L56 A patient with chronic proton pump inhibitor (PPI) use is at increased risk of which absorption issue? A. Enhanced Ca²⁺ absorption B. Reduced iron and B12 absorption C. Increased bile salt secretion D. Increased folate absorption

Answer 163

Answer: B. Reduced iron and B12 absorption ✅ Explanation: Acid is required to solubilize iron and release B12 from food. PPIs reduce gastric acid and impair both processes.

Question 164

# L56 In celiac disease, villous atrophy primarily impairs absorption in the: A. Ileum B. Colon C. Duodenum and jejunum D. Stomach

Answer 164

Answer: C. Duodenum and jejunum ✅ Explanation: These are the primary sites of nutrient absorption and are most affected in celiac disease, leading to malabsorption.

Question 165

# L56 A child with greasy stools and failure to thrive is diagnosed with cystic fibrosis. Which mechanism explains the malabsorption? A. Villous atrophy B. Decreased brush-border enzymes C. Lack of pancreatic enzymes and bile delivery D. Excess acid in the small intestine

Answer 165

Answer: C. Lack of pancreatic enzymes and bile delivery ✅ Explanation: CF causes thick secretions that block pancreatic ducts, impairing digestion of fats and proteins.

Question 166

# L56 A patient presents with macrocytic anemia. What absorptive defect is most likely? A. Ileal resection B. Duodenal ulcer C. Pancreatic enzyme deficiency D. GLUT5 defect

Answer 166

Answer: A. Ileal resection ✅ Explanation: Vitamin B12 is absorbed in the terminal ileum; its loss leads to B12 deficiency and macrocytic anemia.

Question 167

# L56 Secretory diarrhea is characterized by: A. Reabsorption of water due to lactose breakdown B. Inhibition of chloride secretion C. Active chloride secretion into the lumen D. Increased glucose-driven water reabsorption

Answer 167

Answer: C. Active chloride secretion into the lumen ✅ Explanation: Toxins like cholera activate cAMP, stimulating CFTR to secrete Cl⁻ and cause water loss into the gut lumen. Answer: C. Active chloride secretion into the lumen ✅ Explanation: Toxins like cholera activate cAMP, stimulating CFTR to secrete Cl⁻ and cause water loss into the gut lumen.