Digestive System and Fluid Loss

GI Fluid Production

• The GI tract produces and processes large amounts of fluids daily:
  • Saliva: 1.5 liters.
  • Gastric secretions (HCl, enzymes): 1.5 liters.
  • Bile: 1 liter.
  • Pancreatic enzymes, bicarbonate buffer: 1 liter.
• Most of these fluids are reabsorbed in the small and large intestines, leaving about 150 mL of undigested material and bacteria to be excreted.

Causes of Fluid and Electrolyte Imbalances

• Dehydration occurs with excessive vomiting or diarrhea:
  • Leads to hypovolemia (low blood volume).
  • Results in low blood pressure and poor tissue perfusion.
  • Causes intracellular dehydration, impairing cell function.
  • Can be fatal if not managed.
• Electrolyte loss:
  • Sodium and chloride lost through vomiting (gastric HCl).
  • Sodium and potassium lost via diarrhea.
  • Loss causes alkalosis if HCl is lost, or acidosis if bicarbonate is lost.

Causes of Acid-Base Imbalances

• Alkalosis:
  • Due to loss of HCl during persistent vomiting.

• Metabolic acidosis:
  1. From loss of bicarbonate in diarrhea.
  2. Also occurs during malnutrition when cells rely on fat breakdown, producing ketones (ketoacidosis).
     • Malnourished cells cannot function properly, risking organ failure.
       • Cells revert to fat and protein breakdown, further increasing acidity.
  3. Lactic acid buildup may occur if cells switch to anaerobic respiration due to insufficient oxygen or glucose.

• Note:  The kidneys are typically able to maintain tight control of blood pH, maintaining blood pH homeostasis.
  • Metabolic acidosis typically only occurs if nephrons aren’t able to keep up with ensuring the excretion of excess H⁺ and reabsorption of bicarbonate (HCO₃^–).
  • Likewise nephrons typically are able prevent alkalosis by ensuring the reabsorption of H⁺ and excretion of bicarbonate.

Impact on Cell and Organ Function:

• Incorrect pH impairs cellular enzyme activity.

Summary

• GI illnesses and dehydration can produce dangerous electrolyte and pH disturbances.
• Managing hydration and electrolytes are crucial to prevent morbidity and mortality.