Lecture 2: electrolyte imbalance Flashcards
Define a colligative property and how they are measured in lab
Properties dependent on concentration of solute not the identity. Measured by freezing point osmometer (used to be vapour but limited due to volatile substances)
Give a brief overview of the thirst centre
hypothalamus detects osmotic pressure via osmoreceptors, signals for thirst if osmotic pressure is high
give a brief overview of what RAAS does
RAAS modulates vessel tone and blood volume; renin and aldosterone can be measured individually and their results + ratios are informative
give a brief overview of what ADH does
ADH is released by posterior pituitary signaled by hypothalamus.
ADH increases vessel tone and increases aquaporin insertion in the collecting duct leading to more water resorption
give a brief overview of natriuretic peptides
natriuretic peptides include ANP and BNP; they are released when heart and ventricles are stretched due to high blood volume. They directly inhibit aldosterone, and decrease sodium resorption in kidneys
How does the body respond to hyponatremia
Suppresses ADH, and increases urine output
What is the symptom progression of hyponatremia
H2O flows from intravascular to tissues -> cerebral edema -> nausea, malaise -> headaches -> coma
How do you teat acute vs chronic hyponatremia
acute: saline
chronic: SLOWLY with saline to prevent brain damage
What are the 3 categories of hyponatremia
hyponatremia is categorized based on blood volume:
hypovolemia, hypervolemia, euvolemia
What are the hypovolemia causes of hyponatremia
Renal causes: aldosterone deficiency, diuretics, salt-losing kidney disease
non-renal causes: GI (diarrhea, vomiting); skins (burns)
What are the hypervolemia causes of hyponatremia
End stage renal disease, congestive heart failure, cirrhosis, nephrotic syndrome
What are the euvolemic causes of hyponatremia
diuretics or
SIADH: drugs, CNS disturbance (stroke, trauma, surgery), cancer (small cell carcinoma)
What are the 3 causes of pseudohyponatremia and how
- hyperglycemia: dilution due to hyperosmolality
2/3. hyperlipidemia/hyperproteinemia: Electrolyte exclusion effect, (direct methods are unaffected, but they are low throughput); indirect methods are inaccurate because the water fractions in these cases are lower -> pseudohyponatremia
What are the hypovolemia causes of hypernatremia
increased loss + decreased intake of water
What are the hypervolemia causes of hypernatremia
Hyperaldosteronism, Cushings
What are the euvolemic causes of hypernatremia
Diabetes insipidous (opposite of SIADH) (hypotonic urine); insensible losses (concentrated urine)
Describe Diabetes insipidus
(opposite of SIADH)
Absent/insufficient production of ADH (Central)
Absent/insufficient ADH action (nephrogenic)
- causes polyuria and electrolyte imbalance
How is Diabetes insipidus measured
Measure ADH marker: copeptin (can’t measure ADH directly) is 1:1 with ADH
Overview of potassium homeostasis
K+ homeostasis maintained by kidneys and intracellular distribution
- reabsorbed in proximal tubule, secreted in distal tubule as a consequence of aldosterone exchanging K+ with Na using ENaC
What are the causes of Hypokalemia
Increased loss:
- Renal: Cushings, hyperaldosteronism, K wasting diuretic
-non-renal: vomiting, diarrhea
Decreased intake:
- poor diet
Redistribution
- alkalosis
- insulin
- hypothermia
- ….
What are the features of hypokalemia
Weakness, paralysis, confusion, arrhythmias
What are the causes of hyperkalemia
Increased intake: diet, IV, blood transfusion
Decreased loss: ACE inhibitor (prevents aldosterone), Renal failure, K sparing diuretics, aldosterone deficiency
redistribution: tissue damage, metabolic acidosis, beta receptor antagonists
Pseudohyperkalemia
Describe pseudohyperkalemia
Caused by improper storage temperature (low temp), wrong draw order (some tubes have additives), hemolysis, delay in processing blood sample
