U: Disorders Of Water Balance

Front 1

What is the major determinant of extracellular fluid osmolality?

What brain area senses small increases in the osmolality via osmoreceptors?
- what does it release in these cases?
- what does this cause?
- an increase in osmolality of ~1-2% causes the above phenomenon. When does thirst kick in?

Back 1

Sodium

Hypothalamus
- ADH from the post. pituitary
- ^ water reabs. in CT
- ~2-3%

Front 2

Can a decrease in ECFV perpetrate ADH release?
- sensitivity?
- receptor?

Blood pressure drop?

Drugs/Vomiting/Stress?

Back 2

yes
- low
- baroreptor

yes; same.

yes
- N/A
- direct neural (?); note that this is not a physiologic response

Front 3

Hyponatremia is a decrease in plasma sodium concentration < ____.

Back 3

135mEq/L

Front 4

Since intracellular fluid (ICF) always has the same osmolality as extracellular fluid (ECF), it follows that the osmolality of intracellular fluid is also _______ in subjects with hyponatremia.
- why does this happen?

Back 4

decreased
- results from osmotic movement of water from the extracellular to the intracellular compartment.

Front 5

What accounts for the neurological sx in pts with hyponatremia?
- what are the three potential causes of hyponatremia (re: general cause theory)
- in pts with hyponatremia, is total body Na increased, normal, or decreased?

Back 5

swelling of the brain cells; pts with hyponatremia always have swollen cells to some degree.
- pure water retention, retention of more water than sodium, or loss of sodium in excess of water compared to the proportion normally present in plasma
- depends on the etiology; see above (normal, increased, decreased; respectively)

Front 6

CHF, cirrhosis of the liver, and occasionally in kidney dz accompanied by large losses of protein in the urine.... what condition occurs?
- What causes this?

Back 6

hyponatremia with an increase in ECFV
- non-osmotic ADH release --> excessive retention of water.

Front 7

What is the primary indication that ECFV is increased?

Back 7

swelling (edema)

Front 8

In the proximal tubule, the active reabsorption of sodium is followed by what type of water abs?

How about in later nephron segments?

Back 8

isoosmotic

they are reabsorbed independently; water through the effects of ADH

Front 9

dry mucous membranes, decreased skin turgor, weight loss, changes in pulse and blood pressure...
- what are these typical manifestations of re: body water?

Back 9

ECFV depletion.

Front 10

Explain the pathogenesis of Hyponatremia with a decrease in ECFV.
- what is the tx?

Back 10

pt loses more water than salt via diarrhea/sweat --> hypernatremic --> ADH --> water retained --> normoosmolic, but stlil \ECFV.... if the loss continues, eventually non-osmotic stim of ADH will cause massive water retention which will dilute the Na. These pts will simultaneously have \ECFV b/c the volume of retained water isn't enough to compensate for the lack of sufficient sodium.
- replacement of NaCl (isotonic sodium cholride solution)

Front 11

What is the most common form of hyponatremia seen in adults?
- pathogenesis?
- most common cause?

Back 11

the one associated with clinically normal extracellular fluid volume.
- most commonly the body becomes unable to dilute urine appropriately for some reason --> some of the water that doesn't go to the ICF signals osmotic secretion of salt into the urine --> rapidly returns to normal ECF volume.
--> the ECFV doesn't ^ becuase the ICFV takes most of the excess water.
- non-osmotic nonphysiological release of ADH (SIADH; caused by things like tumors, CNS dz, Lung dz, Drugs)

Front 12

(1) Hyponatremia accompanied by hypoosmolality in plasma. (2) A normal ECF volume as judged by good skin turgor and no edema. (3) Absence of other known causes of hyponatremia with clinically normal ECF volume (indicated above). (4) Urinary sodium excretion that is normal if the subject consumes a normal amount of sodium. (5) A urine osmolality that is not as dilute as it should be, considering the presence of hypoosmolality of plasma.

...consider what?

Normally, A plasma osmolality below approximately 270 mOsm/kg H2O should be accompanied by a urinary osmolality of less than ___ mOsm/kg H2O.

Back 12

SIADH

100

Front 13

While the non-emergent tx for SIADH is water restriction, what is done in more acute senarios?

Back 13

The rapid correction involves promoting prompt renal excretion of water by infusing a concentrated solution of sodium chloride, which is then excreted in a larger volume of water than that at which it was infused.

Front 14

Which condition has the following:
- hyponatremia NOT caused by retention of ingested water
- caused by ICF --> ECF movement
+ shrunken cells
- hyperosmolality of body fluids (ECF)
- *Decrease* in ECF volume with more water loss than sodium... would typically cause hypernatremia but not in this condition.... why not?

Tx?

Back 14

severe hyperglycemia (or some other large solute that can't get into the cells) that causes ECF hyperosmolality.
- hypernatremia doesn't happen b/c all of the water comes out of the ICF to replace that being lost to dilute urination.

insulin; and admin of IV fluids.

Front 15

What is Pseudohyponatremia?

Back 15

technical problem w/ analysis that causes an underestimate of the plasma sodium concentration via an OVERestimation of the amount of water in the sample.
...the pt really doesn't have a deficit in water excretion though; instead they have a metabolic problem characterized by ^^of large molecules in plasma (lipids/proteins)