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How is the surface area of the small intestine amplified?

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


How is the surface area of the large intestine amplified?

- Semilunar folds
- Crypts, but no villi
- Microvilli


What can lead to diarrhoea?

Decreased reabsorption
Increased secretion


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

Sodium absorption: Small and large intestine
Potassium secretion: Large intestine


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

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)


Compare the net amounts absorbed in the small and large intestine

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-


What drug blocks sodium potassium ATPases?



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

Heart conditions
Causes GI symptoms


What is required in transcellular movement of water and solutes?

Must move across 2 membranes in series
Solutes cross at least one active membrane


What is paracellular movement?

Passive movement via tight junctions


What is the mode of water movement?

Osmosis mainly paracellular


What is water movement coupled to?

Solute movement


Where does absorption of water occur primarily?



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

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


What controls absorption and secretion in the GI tract?

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


Describe osmotic diarrhoea

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


Describe secretory diarrhoea

Increased secretion due to activation of chloride or sodium channels.


What is osmotic diarrhoea caused by?

Macronutrient malabsorption
- Pancreatic disease
- Large intakes of sugar alcohols (sorbitol)
- Fructose intolerance
- Lactose intolerance
- Coeliac disease


What is the most common cause of secretory diarrhoea?

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