Glossary of 13. Electrolytes and Fluid Balance
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- What is the normal body water distribution?
- Intracellular = 66%
Extracellular = 33%
- What primarily determines the body H2O distribution?
- Osmotic pressure
- What is Osmotic pressure?
- The force that moves water between body compartments.
- What type of ions contribute to the osmotic pressure?
- Colloids and nondiffusible ions.
- What is the normal Osmolality of the body?
- 285-298 mOsm/kg
- What instrument is used to measure body osmolality?
- a Thermistor - to measure the vapor point of blood.
- How can the body's osmolality be estimated instead of measuring with thermistor?
- Calculate the Osmolal Gap
- What's the osmolality gap calculation?
- 1.86Na + Glu/18 + BUN/2.8 +9
- What 5 things stimulate Aldosterone secretion?
- -Decreased Blood volume
- What determines the H2O distribution between the vasculature and interstitium?
- Starling's forces
- What is the Starling equation in a nutshell?
- NFP=K x (Forces Out - In)
- What are forces out in a capillary?
- What are forces in for a capillary?
- Colloid osmotic
- What force is higher in:
- Arterioles: Hydrost. > osmotic
Venules: Osmotic > Hydrost.
- When all is said and done, what force is greater for water movement?
- Filtration > reabsorption; so water has to return via lymphatic system.
- What's the anion gap?
- The difference between the measured cations and anions.
- What 4 conditions can cause an increased anion gap?
- 1. Diabetic ketoacidosis
2. Decreased Calcium/Mg
- What 3 things can cause a decreased anion gap?
What's most common?
- 1. Lab error - most common
2. Multiple myeloma
3. Increased Ca/Mg
- List 5 roles of electrolytes:
- 1. Maintain osmotic pressure
2. Maintain pH
3. Regulate muscle function
4. Participate in redox
5. Participate in enzyme catalysis
- What is the major extracellular cation?
- Where is most Na reabsorbed?
- in the proximal tubule
- How would the following hormonal conditions affect Na?
- Addisons = Hyponatremia
Cushing's = Hypernatremia
- What specimens are tested for Sodium levels?
- Are sodium levels affected by hemolysis?
- What is the major intracellular cation?
- What is the major controller of Na after reabsorption in the prox tubules?
- How does Aldosterone function?
- To increase Na reabsorption and H2O also
- What hormone counteracts Aldosterone?
- Atrial Natiuretic Factor ANF
- Where does ADH act on the kidney?
- Collecting ducts
- What 2 important Receptors affect sodium levels?
- What do osmoreceptors detect?
Where are they located?
- -increased osmolarity
- What happens when increased osmolarity is detected?
- Stimulates the release of ADH to increase H2O reabsorption and thus decrease osmolarity
- What do Baroreceptors detect?
Where are they located?
- Detect changes in blood pressure
-located in smooth muscle of vasculature
- What results when baroreceptors detect increased blood pressure?
- -Stimulates ADH release from brain
-ADH stimulates RAS to start
- How does the RAS result in increased Na/H2o reabsorption?
- Because renin is a stimlator of aldosterone release
- What are 3 types of hyponatremia?
- What type of pH is generally associated with hyponatremia?
- Metabolic acidosis
- Why does acidosis cause low Na?
- Because of sodium wasting - have to excrete Na+ to reabsorb HCO3- and have the charges balance.
- What causes a dilutional hyponatremia?
- -Excessive water reabsorption
- What is hormonal hyponatremia?
- Addison's disease
- How would increased ADH affect body sodium levels?
- Increased ADH = too much H2O reabsorption, so dilutional hyponatremia.
- How would decreased ADH affect body sodium levels?
- Not enough H2O so hypernatremia
- What type of Ca and K levels are usually seen with hypernatremia?
- What hormonal problem usually causes hypernatremia?
- What is the general reason for most hypernatremia conditinos?
- Disproportionate loss of water vs. sodium.
- How do urine sodium levels change in:
- Hypernatremia = hyponatruria
Hyponatremia = hypernatruria
- So back to this.. what is the major INTRACELLUAR cation?
- How is K kept inside cells?
- By the Na/K pump - ATPase
- What affects body potassium levels (hormone)?
- How doe aldosterone regulate K?
- Increased Aldosterone causes increased K excretion
- How does the body respond to hypokalemia?
-Tachycardia (slowed heartrate)
- How does the body respond to hyperkalemia?
- -Weak, numb, tingly
- What hormonal disorder causes hypokalemia?
- What hormonal disorder causes hyperkalemia?
- What are 3 causes of hypokalemia?
- 1. Decreased dietary intake
2. Increased loss of K-rich fluids
3. Redistribution from extra to intracellular fluid
- What are 2 things that make K go from extracellular fluid to intracellular?
- 1. Insulin therapy
2. Alkalosis (decreased H+ buffering by Hgb so more room for K+)
- What are 3 causes of hyperkalemia?
- 1. IV infusion
2. Redistribute from intra-> extracellular fluid
3. Decreased excretion
- What would make K go from intracellular to ECF?
- Acidosis - need space inside the cells to buffer extra H+
- What hormonal disorder would cause decreased K excretion?
- What is the body potassium in:
- Hyperkaluria = hypokalemia
Hypokaluria = hyperkalemia
- What 4 preanalytical variables falsely increase potassium measurement?
- 1. Clenching in phlebotomy
2. Clotting (don't use serum)
4. Delay in centrifugn
- What are 2 methods used to measure sodium and potassium?
- 1. Flame emission spec
- What membrane is used for Na?
- What membrane is used for K?
- Valinomycin - ion-exchange
- What is the principle of ISE measurement?
- Potentiometric - a change in potential as the ions interact with the membrane
- What error can occur in ISE?
What causes it?
- Electrolyte exclusion effect - caused by other electrolytes in the fluid being measured.
- How can you avoid EEE?
- By using the direct ISE method where there is no dilution. (Indirect uses high ionic strength diluent)
- What is the major extracellular anion?
- How is chloride reabsorbed in the kidneys?
- Passively AND via active pumps
- What are 3 causes of hypochloremia?
- 1. Salt losing nephritis
2. Prolonged vomiting
- Why does alkalosis cause hypochloremia?
- Because there is base excess, so to counter the negative charge more chloride ions are lost.
- What 3 conditions are associated with hyperchloremia?
- 1. Dehydration
2. Acute renal failure
3. Metabolic acidosis
- What 3 methods are used for Cl measurement?
- 1. Mercurimetric titration
3. Coulometric - Amperometric
- What type of electrode is used in coulometric measurement of Cl?
- Silver chloride.
- What is the principle of amperometric measurement for Cl?
- -The electrode generates Cl ions which bind with pt. Cl -> Cl2
-Free Ag ions shut down the system.
- What is the other major anion measured in electrolyte measurements?
- Bicarbonate - HCO3-
- What specimens are analyzed for HCO3 measurement?
- Serum or plasma
- What special care needs to be taken for CO2 measurement?
- Anaerobic conditions
- What are 3 methods for tCO2 measurement?
- 1. Continuous flow
2. pCO2 electrode
- What is the principle of the continuous flow method?
- 1. Acid buffer converts all CO2 to gas
2. Gas diffuses across membrane
3. pH buffer changes and detected with an indicator
- How does the pCO2 electrode work?
- As CO2 gas is detected in WB, the pH changes; rate of change is measured.
- What enzymatic method is used for CO2 measurement?
- 2 step method; phosphoenolpyruvate produces oxaloacetate; then measure
oxaloacetate + NADH by detecting NADH decrease
- What wavelength is NADH detected at?
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