hypertonic solution, retain fluid or expell fluid

remember that the gi track is an enclosed tube. when a hypertonic tube feeding gets sloshed into it peristaltic action washes it down, down, down. what do we know about hypertonic fluids? they are solutions with higher osmolality. usually, something with a lot of carbohydrate or salt in it will do that. and, if the tube has somehow gone past the pyloric sphincter (which has the ability to slow down what gets passed into the intestines) its like a roller coaster ride for these hypertonic tube feedings that get directly deposited into the duodenum. so, what happens when hypertonic meets gi track? the body naturally wants to achieve homeostasis. it starts sending water into the intestine to dilute this tube feeding to a more isotonic state that it would rather have. the body always wants to achieve a normal state. in so doing, the contents of the intestine increase dramatically. the other problem is that the ph of this hypertonic tube feeding is on the acidic side making it pretty irritating to the lining of the small intestine. the first thing the intestinal track wants to do is get this tube feeding out of it and so its motility increases. so, you have some increased intestinal motility and increased fluid coming along. and, it all starts moving down the pipe rather quickly. that is the pathophysiology of dumping syndrome. in about 2 hours it is all literally going to "blow" meaning this person is going to have diarrhea.

osmotic laxatives work the same way because they pull fluid into the intestinal track to dilute down the electrolyte content.

it's all about the osmolality with the added bonus of the physical irritability caused by the hypertonicity of the solutions. try tasting some oral fleet's enema solution. i've had to take it for colonoscopy preps and it burns the back of my throat. i also have had gastric bypass surgery. if i eat too much ice cream which is loaded with pure sugar i get dumping syndrome. i can hear the gurgling in my gut and i know i am going to dump. i also get the symptoms of hyperglycemia in about an hour because so many calories get absorbed into my blood stream at one time (i don't have a pyloric valve to contain it all in my stomach anymore so it all goes directly into the jejunum where all that galactose and added sugar is absorbed directly and rapidly into the blood stream) and diarrhea in about 2 to 3 hours. depending on how much of a pig i was will determine how sick i will feel.

other stuff that will give you dumping syndrome are eating too many sugar free candies that are sweetened with things like sorbitol. they are also sugars that are very irritating to the lining of the intestinal track, have high osmolarities and act just like laxatives if you eat enough of them at one time.

so in what situation does an ingested hypertonic solution cause excess fluid to be retained in the body or fluid to be taken from the body into the gi tract?

What still confuses me is when it is said that eating a diet high in sodium can cause Fluid retention. This says a totally opposite thing! I know there must be some A&P to explain that.

Water follows sodium. Think of water and sodium as partners holding hands. Where one goes, the other is tagging along. A diet high in sodium causes the person to retain fluid. Symptoms of hypernatremia, which is systemic, are the symptoms of overhydration:

• Elevated blood pressure (hypertension)
  
• Elevated pulse (tachycardia)
  
• Elevated temperature
  
• Elevated respiratory rate, possible dyspnea
  
• Increased body weight
  
• Bounding peripheral pulses
  
• Moist mucous membranes
  
• Moist respiratory secretions
  
• Crackles in lungs on auscultation
  
• Fever
  
• Edema (may be pitting)
  
• Dry skin
  
• Weakness
  
• Restlessness/agitation
  
• Disorientation
  
• Delusions
  
• Hallucinations
  
• Lethargic when undisturbed
  
• Irritable when stimulated
  
• Muscle irritability
  
• Diminished or absent DTRs
  
• High pitched cry in infants
  
• Seizures
  
• Coma (due to swelling of brain cells)
  
• Respiratory arrest due to increased osmotic pressure