Water & Electrolyte Movement In The GI Tract Flashcards
What is the most abundant substance in chyme?
Water
What happens in the small intestine?
Water reabsorption
What % of water is reabsorbed in small intestine?
80%
How much ingested & secreted water enters small intestine per day & how much passes into large intestine?
8000ml - small intestine
1500ml - large intestine
Which part of the gut reabsorbs most water?
Jejunum
Where does water reabsorption happen?
Small intestine
Is water reabsorbed in the stomach and how much?
Yes abundantly small amounts
Why are small amounts of water reabsorbed in the stomach?
Has a much smaller SA available for diffusion and lacks the solute-absorbing mechanisms that create the osmotic gradient necessary for absorbing water
How much fluid is reabsorbed? (%)
98%
What happens to the 2% of fluid and how many ml is that?
200ml being excreted in stools
Describe the epithelial membranes of the small intestine in terms of water
They are very permeable to water & net water diffusion occurs across the epithelium whenever a water concentration difference is established by the active absorption of solutes
What accounts for the most actively transported solutes?
Na+
Why does Na+ account for the most actively transported solutes?
Because it constitutes the most abundant solute in chyme- it is actively transported from the lumen in the cell membranes of the ileum & jejunum
What is luminal membrane transport variably coupled with?
Glucose, amino acids or other substances
The contents of the colon are….
Iso-osmotic
What does iso-osmotic in the colon mean?
Conc in lumen of colon = that of blood
What ions are reabsorbed in the colon?
K+ and Cl-
What happens in k+ reabsorption in the colon?
In general, K+ reabsorption is by passive diffusion
The net movement begin determined by the potential difference between the lumen and intestinal capillaries
What can diarrhea result in to do with k+?
Severe hypokalaemia (loss of K+)
What happens in Cl- reabsorption in the colon?
It is actively reabsorbed in exchange for bicarbonate resulting in intestinal contents becoming more alkaline
