Flashcards in Disorders of Water Metabolism Deck (19):
1. List the components of water balance (both input and output).
intake is managed by GI absorption and thirst (often modified by ADH)
65% of water that is filtered is reabsorbed in the PCT
ascending limb is the most important limb in nephron for water balance although no water is reabsorbed here
distal tubule has more Na reabsorption
collecting duct is important for last bit of water reabsorption, largely governed by ADH
2. Explain what controls the secretion of antidiuretic hormone. Discuss physiologic stimuli.
the main controller at higher volumes is osmolality
at very low volumes ADH is triggered by strongly by the perceived drop in pressure
3. Explain the interaction between circulating volume and plasma osmolality.
hypo-osmotic circulating volume will cause water to travel to the ICF compartment
hyper-osmotic circulating volume will cause water to travel into the ECF compartment, specifically the intravascular compartment
4. Explain the interaction between circulating volume and plasma osmolality.
osmolality of is inversely proportionate to ICF volume
osmolality is a window into ICF volume
most of the tonicity in molecules that contribute to osmolality is represented by Na+ an therefore Na+ is a reasonable approximation of osmolality (glucose and urea are disregarded in MOST cases)
5. Describe the clinical conditions that are associated with excess or decreased antidiuretic hormone secretion.
central DI (not make ADH): neurosurgery, trauma, various infection(affecting the posterior pituitary)
nephrogenic DI: receptor (lithium, hypokalemia, hypercalcemia, interstitial diseases to the kidney)
differentiated by water deprivation test
6. Compare and contrast a water diuresis and a solute diuresis.
aldosterone will cause solute diuresis and solutes will be followed by water, this can be encouraged by blocking of Na channels by diuretic agents
water diuresis occurs when aquaporins are not inserted into luminal side of the collecting ducts, largely controlled by ADH
osmolality= total osmoles/ total water
Name the two major disorders of water balance.
hyponatremia (too much water)
hypernatremia (too little water)
What is the normal range of serum [Na+]?
145-135, usually symptoms and treatment occur below 130 or above 150 (meq/L)
What is the action of ADH binding in the kidney
ADH binds with V2 receptors to cause insertion of AQP in the luminal side
Describe non-physiologic stimuli for ADH release.
any disease of the CNS
nausea or pain
What detects blood osmolarity in order to regulate ADH levels?
remember, ADH and osmolality move in the same direction when the body is working normally
What are the clinical and laboratory signs of sodium imbalance?
clinical: confusion, seizure, coma, death
lab(+++++): serum and urine osmolality, serum Na
What are the clinical and laboratory signs of ECF fluid balance?
clinical (+++) orthostatic hypotension, tachycardia, low BP, dry mucous membranes, weight loss
lab: hemoconcentration, high uric acid, urine Na and Cl
When working with a patient who is hyponatremic, what are 3 important questions to remember?
1. What is the serum osmolality?
2. What is the ECF volume status
3. In hyponatremia with normal ECF, is the kidney behaving normally?
In a hyponatriumic state, what would account for hyperosmotoic or isosmotic serum?
high serum osmolaltiy and low serum Na implies water is being dragged from ICF (ie. glucose in blood)
if there is significant volume of plasma occupied by a substance other than water, plasma sodium will appear low
In a patient with hyponatremia with normal ECF volume, what is likely the cause if the kidney is working normally vs. not (increased ADH).
if kidney is working appropriately, the patient is likely drinking lots of water, if the patient has inappropriate secretion of ADH, they will urinate frequently, a dilute urine
How would you treat different causes hyponatremia based on ECF status?
low ECF, give salt and water
normal ECF, restrict water intake
high ECF, remove salt and water (diuretics)