Fluid from the body enters the intestinal lumen during digestion.
This fluid is isosmotic with the blood and contains a high quantity, about 142 mEq/L, of sodium.
A healthy individual secretes 2000–3000 milligrams of sodium per day into the intestinal lumen.
Nearly all of this is reabsorbed so that sodium levels in the body remain constant.
In a diarrheal illness, sodium-rich intestinal secretions are lost before they can be reabsorbed.
This can lead to life-threatening dehydration or electrolyte imbalances within hours when fluid loss is severe.
The objective of therapy is the replenishment of sodium and water losses by ORT or intravenous infusion.

Sodium absorption occurs in two stages.
The first is via intestinal epithelial cells (enterocytes).
Sodium passes into these cells by co-transport with glucose, via the SGLT1 protein.
From the intestinal epithelial cells, sodium is pumped by active transport via the sodium-potassium pump through the basolateral cell membrane into the extracellular space.

The sodium–potassium ATPase pump at the basolateral cell membrane moves three sodium ions into the extracellular space, while pulling into the enterocyte two potassium ions.
This creates a "downhill" sodium gradient within the cell.
SGLT proteins use energy from this downhill sodium gradient to transport glucose across the apical membrane of the cell against the glucose gradient.
The co-transporters are examples of secondary active transport.
The GLUT uniporters then transport glucose across the basolateral membrane.
Both SGLT1 and SGLT2 are known as symporters, since both sodium and glucose are transported in the same direction across the membrane.

The co-transport of glucose into epithelial cells via the SGLT1 protein requires sodium.
Two sodium ions and one molecule of glucose (or galactose) are transported together across the cell membrane via the SGLT1 protein.
Without glucose, intestinal sodium is not absorbed.
This is why oral rehydration salts include both sodium and glucose.
For each cycle of the transport, hundreds of water molecules move into the epithelial cell to maintain osmotic equilibrium.
The resultant absorption of sodium and water can achieve rehydration even while diarrhea continues.
Fluid from the body enters the intestinal lumen during digestion. This fluid is isosmotic with the blood and contains a high quantity, about 142 mEq/L, of sodium. A healthy individual secretes 2000–3000 milligrams of sodium per day into the intestinal lumen. Nearly all of this is reabsorbed so that sodium levels in the body remain constant. In a diarrheal illness, sodium-rich intestinal secretions are lost before they can be reabsorbed. This can lead to life-threatening dehydration or electrolyte imbalances within hours when fluid loss is severe. The objective of therapy is the replenishment of sodium and water losses by ORT or intravenous infusion.
Sodium absorption occurs in two stages. The first is via intestinal epithelial cells (enterocytes). Sodium passes into these cells by co-transport with glucose, via the SGLT1 protein. From the intestinal epithelial cells, sodium is pumped by active transport via the sodium-potassium pump through the basolateral cell membrane into the extracellular space.
The sodium–potassium ATPase pump at the basolateral cell membrane moves three sodium ions into the extracellular space, while pulling into the enterocyte two potassium ions. This creates a "downhill" sodium gradient within the cell. SGLT proteins use energy from this downhill sodium gradient to transport glucose across the apical membrane of the cell against the glucose gradient. The co-transporters are examples of secondary active transport. The GLUT uniporters then transport glucose across the basolateral membrane. Both SGLT1 and SGLT2 are known as symporters, since both sodium and glucose are transported in the same direction across the membrane.
The co-transport of glucose into epithelial cells via the SGLT1 protein requires sodium. Two sodium ions and one molecule of glucose (or galactose) are transported together across the cell membrane via the SGLT1 protein. Without glucose, intestinal sodium is not absorbed. This is why oral rehydration salts include both sodium and glucose. For each cycle of the transport, hundreds of water molecules move into the epithelial cell to maintain osmotic equilibrium. The resultant absorption of sodium and water can achieve rehydration even while diarrhea continues.
Oral rehydration therapy