Lecture 29

Question 1

How is the surface area of the small intestine amplified?

Answer 1

• Folds of Kerchring
• Villi and crypts of Lieberkuhn
• Microvilli

Question 2

How is the surface area of the large intestine amplified?

Answer 2

• Semilunar folds
• Crypts, but no villi
• Microvilli

Question 3

What can lead to diarrhoea?

Answer 3

Decreased reabsorption

Increased secretion

Question 4

Where is active sodium reabsorption happening? What about active potassium secretion?

Answer 4

Sodium absorption: Small and large intestine

Potassium secretion: Large intestine

Question 5

Compare the substances that are absorbed in the small and large intestine

Answer 5

Absorption of non-electrolyte nutrients occurs mainly in the small intestine, whereas both the small and large intestine absorb water and electrolytes (sodium and chloride)

Question 6

Compare the net amounts absorbed in the small and large intestine

Answer 6

The small intestine absorbs net amounts of water, Na+, Cl- and K+ and secretes HCO3-
The large intestine absorbs net amounts of water, Na+, Cl-, and secretes both K+ and HCO3-

Question 7

What drug blocks sodium potassium ATPases?

Answer 7

Digitalis

Question 8

What is digitalis prescribed for? How does it affect the GI tract?

Answer 8

Heart conditions

Causes GI symptoms

Question 9

What is required in transcellular movement of water and solutes?

Answer 9

Must move across 2 membranes in series

Solutes cross at least one active membrane

Question 10

What is paracellular movement?

Answer 10

Passive movement via tight junctions

Question 11

What is the mode of water movement?

Answer 11

Osmosis mainly paracellular

Question 12

What is water movement coupled to?

Answer 12

Solute movement

Question 13

Where does absorption of water occur primarily?

Answer 13

Jejunum

Question 14

What is meant by solvent drag? What is solvent drag responsible for?

Answer 14

Solute dissolved in fluid and moves with it as fluid moves through paracellular pathway. Responsible for considerable Na+ and urea absorption in the jejunum

Question 15

What controls absorption and secretion in the GI tract?

Answer 15

Enteric nervous system - release of ACh, VIP, other secretagogues
Endocrine system - aldosterone
Paracrine system - 5HT

Question 16

Describe osmotic diarrhoea

Answer 16

Haven’t absorbed nutrients so large osmotic load coming through, so drags fluid from GI tract

Question 17

Describe secretory diarrhoea

Answer 17

Increased secretion due to activation of chloride or sodium channels.

Question 18

What is osmotic diarrhoea caused by?

Answer 18

Macronutrient malabsorption

• Pancreatic disease
• Large intakes of sugar alcohols (sorbitol)
• Fructose intolerance
• Lactose intolerance
• Coeliac disease

Question 19

What is the most common cause of secretory diarrhoea?

Answer 19

E. Coli or cholera toxin
- Enterotoxins produced by bacterial microorganisms raise intracellular cAMP, cGMP or Ca2+
- Leads to stimulation of anion secretion, especially Cl-. To maintain charge balance in lumen, Na+ is carried with it, along with water
Also congenital absence of Cl-HCO3 exchanger
Doesn’t impact nutrient coupled Na+ absorption