Intestinal fluid and electrolyte balance

Question 1

How do the small and large intestine increase SA?

Answer 1

SI: villi; microvilli; plicae; crypts of lieuberkeuhn

LI: crypts; semilunar folds; microvilli

Question 2

What is the net movement of electrolytes in the SI and LI?

Answer 2

In the small intestine there is net reabsorption of non electrolyte nutrients, large intestine absorbs water and electrolytes

KEY: SI absorbs small amount of water, Na+, K+ and Cl- and secretes HCO3-; LI absorbs net amount of water, Na+, Cl- and SECRETES K+ and HCO3-

Question 3

Why does sodium move into cells?

Answer 3

Na+/K+ ATPase creates deficiency of Na+ in cells, causing gradient for Na+ to move into through Na+/glucose co transporter and Na+/amino acid cotransporter

SECONDARY ACTIVE TRANSPORT (SGLT andGLUT)

Question 4

What drug will block Na+/K+ ATPase?

Answer 4

Digitalis, patients who take it for heart end up with GI symptoms

Question 5

Where does sodium co transport mainly occur?

Answer 5

Jejunum and ileum

Question 6

What is the other way of moving sodium into the cell?

Answer 6

• Na+/H+ exchangers in duodenum and jejunum (pH dependent)
• Na+/H+ with Cl-/HCO3- exchangers: NaCl into cell and H2CO3 out
• Apical sodium channels in colon due to aldosterone (blood pressure management) Active

Question 7

How does chloride move into the cell?

Answer 7

• Passively through apical channels or paracellularly to balance charge. Normally in jejunum and distal colon
• Also chloride bicarbonate exchangers

Question 8

What are the basolateral channels?

Answer 8

Na+/K+ ATPase; Pottasium channels (into blood); NKCCl (Na+,K+, HCO3- and Cl- into cells)

Question 9

How is Cl- moved out?

Answer 9

Due to NKCC, Cl- accumulation in cell
CFTR in apical membrane causes diffusion out of cell (expressed in repsonse to Ca2+, cAMP, VIP)
Na+ follows paracellularly

Question 10

How is K+ secreted/moved?

Answer 10

• Paracellular pathway
• passively secreted by cell
• active secretion by BK channels (mainly in colon)
• active absorption by K+/H+ exchange

Question 11

What are osmotic and secretory diarrhoea?

Answer 11

Nutrients arent absorbed, so water is dragged out of GI tract
Secretoty diarrhoea isdue to increased secretion of a particular ion (namely Cl-) movement of Na= and H20

Question 12

What causes osmotic diarrhoeas?

Answer 12

Malabsorption
Pancreatic diseases (amylases and lipases don’t work)
lactose intolerance
coeliac disease

Question 13

What causes secretory diarrhoea?

Answer 13

E.coli and cholera toxins increase cAMP, increases CFTR expression. Treated with oral rehydration solution/therapy
Loss of water from extra cellular fluid

Question 14

How does ORS work?

Answer 14

Causes sodium and glucose to go into the cell, causes chloride to follow, water follows.