Exam 4 (Lecture 43) - Absorption of Electrolytes and Water Flashcards
What are electrolytes?
Positive or negative ions dissolved in solution.
List the electrolytes.
Na+, Cl-, HCO3-, K+
What is the term used to describe and increase or decrease for each electrolyte?
1) Sodium = hypo- and hypernatremia
2) Chloride = hypo- and hyperchloremia
3) Bicarbonate = Acidosis or Alkalosis (metabolic)
4) Potassium = hypo - and hyperkalemia
What type of blood test would you order to test for electrolytes?
Chemistry panel
Majority of GI disorders involve loss of _______ and __________.
Water; electrolytes
Where are water and electrolytes absorbed? Where are they reabsorbed?
Absorbed = Small and large intestines
Reabsorbed = kidneys
Why is absorption/reabsorption of water important?
To maintain normal blood volume and mean arterial pressure (blood pressure)
Why is absorption/reabsorption of electrolytes important?
Vital for numerous physiological functions
Describe the absorption pathway for nutrients, water, and electrolytes.
Lumen of small intestine > Brush border ( of simple columnar epithelial cell) > Enterocyte > Basolateral membrane (into the lateral space) > Venous side of blood capillary > Hepatic portal vein > Liver > Cd. VC
Why is Na+ important?
1) Depolarization phase of action potential required for cardiac and skeletal muscle contraction
2) ECF (interstitial fluid and blood) and intracellular fluid balance
What effect will hyponatremia have on heart rate and skeletal muscles?
- Heart = Bradycardia
- Skeletal muscles = Cramping
Describe the three mechanisms of Na+ absorption.
1) Na+ cotransport proteins
- Secondary active transport pathway
- Glucose and AA absorption
2) Na+/H+ antiport exchanger
- Intracellular H+ is exchanged for luminal Na+ across apical membrane
- Once Na+ enters the enterocyte, it is transported across the basolateral membrane to the lateral space by
the action of the Na+/K+ ATPase pump
3) Simple diffusion
- Na+ channels in the apical membrane
- Large electrochemical gradient for Na+ across the enterocyte membrane
- Very little Na+ absorption occurs by this mechanism
Why is Cl- important?
1) Required for ECF and ICF balance
2) Maintains the ionic balance between the plasma and erythrocytes
Describe the three mechanisms of Cl- absorption.
1) Paracellular Cl- absorption
- Major mechanism of Cl- absorption
- Cl- from the gut lumen passes directly into the lateral spaces through the tight junctions
2) Coupled Na+/Cl- absorption
- Net movement of Cl- and Na+ across the apical membrane
3) HCO3- Dependent Cl- absorption
- Net movement of HCO3- into the gut lumen; increasing luminal pH
- Important in the large intestine of herbivores
- Large concentrations of acids from fermentation are created and require buffering
Why is HCO3- important? How is HCO3- measured? How is TCO2 calculated?
1) Acid-base balance and normal blood pH
2) HCO3- mEq/L and TCO2 mmol/L
3) Total CO2 (TCO2) = 0.23 x pCO2 + HCO3-
Describe the mechanism of HCO3- absorption.
1) Partially absorbed by the neutralization of HCl from the stomach
2) Remains in the intestine after the neutralization of stomach acid
3) Remaining HCO3- is absorbed primarily in the ileum and colon
Why is K+ important?
Required for repolarization phase of action potentials causing cardiac and skeletal muscle relaxation
What effect will hyperkalemia have on heart rate and skeletal muscles?
- Heart = Bradycardia
- Skeletal muscles = Weakness
Why is a bright orange sticker used when K+ is added to the IV fluid bag?
This is used to write down the date, time, and how many mEq/L were added so that there isn’t more K+ added to the IV fluids before there needs to be.
Describe the two mechanisms of K+ absorption.
1) Paracellular passive diffusion
- Primary mechanism of K+ absorption using concentration gradient
- K+ absorption is directly coupled to H2O absorption
- Movement of H2O out of the intestinal lumen results in an increase in the luminal K+ concentration, which
in turn drives K+ absorption
2) H+/K+ ATPas pump
Where are the major mechanisms of electrolyte absorption located in the GI tract?
Sodium cotransport?
Bicarbonate absorption?
1) Sodium cotransport = Duodenum and Upper GI tract
2) Bicarbonate absorption = Ileum and Colon
Water absorption in small intestine and large intestine occurs via Starling’s law and the Villous Vascular System.
Water moves in direction necessary to keep ingesta _______.
Iso-osmotic
Starling’s law: name the two pressures responsible for water movement.
1) Oncotic Pressure
2) Hydrostatic Pressure
Define oncotic (osmotic) pressure.
Force exerted by plasma proteins (albumin) that draws water into the capillary lumen
Define hydrostatic pressure.
Pressure created by the osmotic effect of absorbed solutes
