7 - Absorption and Nutrient Processing in the Gastrointestinal Tract

Question 1

What are the major regions of the gastrointestinal tract?

Answer 1

Oesophagus, stomach, small intestine (duodenum, jejunum, ileum), and colon

Question 2

What is the function of the oesophagus in the gastrointestinal tract?

Answer 2

Transit of food from the mouth to the stomach

Question 3

What are the main functions of the stomach?

Answer 3

Storage of food, secretion of hydrochloric acid (H⁺), secretion of pepsin, and production of intrinsic factor

Question 4

What are the main functions of the small intestine?

Answer 4

Digestion of fats, proteins, and carbohydrates; absorption of nutrients; transport of water and electrolytes

Question 5

What are the main functions of the colon?

Answer 5

Storage of waste and absorption of water and electrolytes

Question 6

What organs are connected by the biliary tree?

Answer 6

Liver, gall bladder, pancreas, and duodenum

Question 7

Why are biliary tree organs located near the duodenum?

Answer 7

To allow efficient delivery of digestive secretions into the intestine

Question 8

What enters the duodenum from the stomach?

Answer 8

Acidic fatty chyme through the pylorus

Question 9

What do Brunner’s glands secrete in the duodenum?

Answer 9

Mucus and bicarbonate to neutralise stomach acid

Question 10

What is the role of bile in the duodenum?

Answer 10

Assists fat digestion and cholesterol absorption

Question 11

What is the function of pancreatic juice in the duodenum?

Answer 11

Digests proteins, carbohydrates, and lipids

Question 12

What effect do pancreatic secretions have on intestinal pH?

Answer 12

Increase pH toward neutral

Question 13

Which hormones are released from the duodenum?

Answer 13

Cholecystokinin (CCK) and secretin

Question 14

What substances are found in pancreatic juice?

Answer 14

Bicarbonate, proteases (inactive precursors), amylases, lipases, and nucleases

Question 15

What macromolecules are digested by pancreatic enzymes?

Answer 15

Proteins, carbohydrates, lipids, and nucleic acids

Question 16

Where is bile produced and stored?

Answer 16

Produced in the liver and stored in the gall bladder

Question 17

What are the functions of bile?

Answer 17

Fat emulsification, aiding lipid digestion and absorption, and cholesterol absorption

Question 18

Through which structure does bile enter the duodenum?

Answer 18

Hepatopancreatic sphincter (sphincter of Oddi)

Question 19

What hormone is released in response to fat in the duodenum?

Answer 19

Cholecystokinin (CCK)

Question 20

What are the effects of CCK on the biliary system?

Answer 20

Gall bladder contraction and relaxation of the sphincter of Oddi

Question 21

What does secretin stimulate in bile secretion?

Answer 21

Alkaline bile secretion from bile ducts

Question 22

What is the effect of parasympathetic (vagal) stimulation on bile release?

Answer 22

Gall bladder contraction, sphincter relaxation, and increased bile formation

Question 23

What is the effect of sympathetic stimulation on bile release?

Answer 23

Gall bladder relaxation and reduced bile secretion

Question 24

What are the main functions of the intestinal epithelium?

Answer 24

Provide large surface area, maintain barrier, and allow nutrient/water transport

Question 25

What processes maintain intestinal epithelium integrity?

Answer 25

Stem cell proliferation, migration, differentiation, and tight junction formation

Question 26

What structures increase surface area in the small intestine?

Answer 26

Circular folds, villi, and microvilli

Question 27

What cells are found in villi and what is their function?

Answer 27

Enterocytes; they absorb nutrients

Question 28

What is the brush border?

Answer 28

Microvilli on epithelial cells that increase surface area

Question 29

Where do intestinal epithelial cells originate?

Answer 29

Stem cell zone in intestinal crypts

Question 30

What types of intestinal cells exist?

Answer 30

Colonocytes, goblet cells, endocrine cells, and proliferative cells

Question 31

How does intestinal cell renewal occur?

Answer 31

Proliferation in crypts → migration → shedding at villus tip

Question 32

How much fluid enters the gut daily?

Answer 32

About 9 litres

Question 33

How much fluid is absorbed by the small intestine?

Answer 33

Approximately 8.5 litres

Question 34

How much fluid is absorbed by the large intestine?

Answer 34

Approximately 0.4 litres

Question 35

How much fluid is lost in faeces?

Answer 35

About 0.1 litres

Question 36

What does the duodenum absorb?

Answer 36

Calcium, magnesium, and iron

Question 37

What does the jejunum absorb?

Answer 37

Monosaccharides, disaccharides, vitamins, electrolytes, and amino acids

Question 38

What does the ileum absorb?

Answer 38

Vitamin B12, bile salts, fats, and water

Question 39

What does the colon absorb?

Answer 39

Water, electrolytes, and short-chain fatty acids

Question 40

What are villi responsible for?

Answer 40

Nutrient and electrolyte absorption

Question 41

What are intestinal crypts responsible for?

Answer 41

Secretion of water and electrolytes

Question 42

What is transcellular transport?

Answer 42

Movement through epithelial cells using transport proteins

Question 43

What is paracellular transport?

Answer 43

Movement between cells via tight junctions

Question 44

What are the functions of tight junctions?

Answer 44

Maintain cell contact, regulate permeability, and preserve barrier integrity

Question 45

Name proteins involved in tight junctions

Answer 45

Occludin, tricellulin, claudins, JAMs, ZO-1, and actin

Question 46

What is osmosis?

Answer 46

Passive movement of water toward higher solute concentration

Question 47

What is passive diffusion?

Answer 47

Movement down a concentration gradient without energy

Question 48

What is facilitated diffusion?

Answer 48

Movement via channels/carriers down a gradient

Question 49

What is active transport?

Answer 49

Movement against a gradient using ATP

Question 50

How is water absorbed in the intestine?

Answer 50

Passively following solutes

Question 51

How is sodium absorbed in the large intestine?

Answer 51

Actively via ENaC channels

Question 52

What follows sodium absorption in the colon?

Answer 52

Chloride and then wate

Question 53

What enzymes digest starch in the lumen?

Answer 53

Salivary and pancreatic α-amylases

Question 54

What are the products of starch digestion?

Answer 54

α-limit dextrins, maltotriose, and maltose

Question 55

What monosaccharides are produced at the brush border?

Answer 55

Glucose, galactose, and fructose

Question 56

How are glucose and galactose absorbed?

Answer 56

Via SGLT1 (sodium-linked active transport)

Question 57

How is fructose absorbed?

Answer 57

Via GLUT5 (facilitated diffusion)

Question 58

How do monosaccharides exit enterocytes?

Answer 58

Via GLUT2

Question 59

What ion is secreted by crypt cells?

Answer 59

Chloride (Cl⁻)

Question 60

What stimulates intestinal secretion?

Answer 60

VIP, bacterial toxins, fatty acids, bile acids, and laxatives

Question 61

What is the mechanism of secretory diarrhoea?

Answer 61

↑ cAMP → ↑ Cl⁻ secretion → Na⁺ and water follow

Question 62

What does oral rehydration solution contain?

Answer 62

Sodium chloride, glucose, sodium bicarbonate, potassium chloride in 1 L water

Question 63

How does oral rehydration therapy work?

Answer 63

Uses sodium-glucose co-transport to enhance water absorption

Question 64

What are bile acids derived from?

Answer 64

Cholesterol

Question 65

What property makes bile acids effective in digestion?

Answer 65

Amphipathic nature

Question 66

What are the functions of bile acids?

Answer 66

Solubilise lipids and facilitate absorption

Question 67

What happens to lipids in the stomach?

Answer 67

Form large droplets and are mechanically emulsified

Question 68

What happens to lipids in the duodenum?

Answer 68

Broken down by pancreatic lipase into monoglycerides and fatty acids

Question 69

What role do bile salts play in lipid digestion?

Answer 69

Prevent re-aggregation and form micelles

Question 70

What is the function of micelles?

Answer 70

Increase lipid solubility and deliver lipids to enterocytes

Question 71

How do absorbed lipids enter circulation?

Answer 71

Enter lacteals → lymph → thoracic duct → left subclavian vein