Control of ECF and Osmolality

Question 1

Hyponatremia

Answer 1

Pna<135 typically due to water retention

Question 2

3 types of hyponatremia

Answer 2

psuedonatremia, isotonic or hypertonic hyponatremia, and Hypotonic hyponatremia

Question 3

What is psuedonatremia?

Answer 3

Artifactual reading due to a measurement problem, generally due to hyperlipidemia or hyperproteinemia

Question 4

What is Isotonc or hypertonic hyponatremia?

Answer 4

the presence of unmeasured effective osmoles (mannitol) is causing the shift of H2O from ICF to ECF (hyperglycemia, contrast)

Question 5

What is Hypotonic hyponatremia?

Answer 5

Effective osmolality of the plasma is LOW, TRUE hyponatremia

Question 6

Hypotonic hyponatremia has 3 classes

Answer 6

Hypovolemic (volume depletion, low BP), Euvolemic, and Hypervolemic (ECF volume expansion, edema)

Question 7

Hyponatremia is secondary to

Answer 7

defect in renal water clearance (since low Posm, low ADH, high H2O excretion)

Question 8

Reasons for defect in renal water clearance?

Answer 8

Excessive water drinking (psychiatric issue) usually due to medications

Question 9

Psuedohyponatremia

Answer 9

Na levels appear high when measured in total plasma, but normal when measured in plasma water

Question 10

Isotonic or Hypertonic Hyponatremia causes

Answer 10

presence of effective osmole

Question 11

Syndrome of Inappropriate ADH (SIADH)

Answer 11

euvolemia; plasma ADH is inappropriately HIGH; presistant ADH and persistant reabsorption of H2O

Question 12

Tricyclic antidepressants and morphine can cause SIADH

Answer 12

stimulate ADH and can cause hyponatremia

Question 13

Presentation of patient with SIADH

Answer 13

hyponatremia, (-) free water clearance, despite need to excrete

Question 14

Treatment for SIADH hyponatremia

Answer 14

H2O restriction, blockade of ADH at the collecting duct

Question 15

Nephrogenic Syndrome of Inappropriate Antidiuresis

Answer 15

SIADH like symptoms described by a GAIN OF FUNCTION of the ADH receptors (V2)

Question 16

Exertion and Hyponatremia

Answer 16

prolonged exercise (>4hr) loss of electrolytes through sweat and excessive intake of HYPOTONIC fluids, ALSO during exercise ADH is inappropriately secreted

Question 17

Hypernatremia

Answer 17

pna >145, often the result of unreplaced water loss

Question 18

Body’s defense against hypernatremia

Answer 18

ADH and thirst

Question 19

Diabetes insepidus

Answer 19

excretion of large volumes of HYPOTONIC urine due to a defect in ADH (inability to resorb water properly)

Question 20

Central diabetes insepidus

Answer 20

decreased production of ADH from pituitary (stroke, tumor, drug-induced, genetic)

Question 21

Nephrogenic Diabetes insepidus

Answer 21

kidneys inability to respond to ADH (drug-induced [LITHIUM] or defect in V2 receptor)

Question 22

In a normal patient, water deprivation will result in

Answer 22

ADH secretion, water retention, and concentrated urine

Question 23

In a patient with Central DI, water deprivation will result it

Answer 23

no ADH, water still lost, Uosm will remain < Posm

Question 24

Central DI, patient when given endogenous ADH

Answer 24

ADH, will cause water retention, and urine concentration

Question 25

Nephrogenic DI, patient is given endogenous ADH

Answer 25

urine concentration remains dilute, no response to ADH

Question 26

under euvolemic conditions, the excretion of Na is

Answer 26

equal to intake of Na

Question 27

regulation of Na reabsorption occurs at the

Answer 27

proximal tubule and loop of Henle, Fine tuning occurs at distal tubule and collecting duct

Question 28

Autoregulation of GFR and Na excretion

Answer 28

despite positional changes, changes in BP, etc, GFR is regulated to remain constant and provide a constant filtered load of Na

Question 29

Tubuloglomerular feedback TGF

Answer 29

Autoregulatory mechanism; macula densa sense NaCl flow and controls afferent arteriole

Question 30

Glomerular tubular balance

Answer 30

fraction of Na reabsrobed in the proximal tubule is always 67%, even if GFR increases (then absolute reabsorption increases)

Question 31

What two mechanisms regulate Glomerular tubular balance

Answer 31

Na-solute symport and starling forces in the peritubular capillaries

Question 32

Na-solute transport increases with an

Answer 32

increase in Filtered load (increased GFR increases the filtration of other solutes (glucose, aa) and the reabsorption increases for these solutes as well as Na

Question 33

If filtration fraction increases (H2O and electrolytes lost from blood)

Answer 33

then the reabsorptive pressure of the peritubular capillaries will be greater (decreased Pc and increased oncotic P) and Na is more likely to be reabsorbed

Question 34

Load dependent Na transport in the loop of Henle

Answer 34

if a large amount of Na arrives at ascending limb, a large amount will be transferred, if a small amount arrives a small amount will be transferred; this way a constant amount arrives at distal tubule

Question 35

Regulators of Na excretion

Answer 35

Aldosterone, ANP, SNS

Question 36

total Na and ECF volume is controlled by

Answer 36

Aldosterone, ANP, SNS, and ADH

Question 37

SNS effect on kidney

Answer 37

Increased renin release (beta-1), RAAS, directly increases Na absorption at the proximal tubule

Question 38

RAAS effects

Answer 38

increased Na reabsorption directly, via AT1 receptors by increasing # of Na/H symporters
Stimulates aldosterone release from adrenal cortex
Increases the FF by increasing GFR (constriction of efferent)
Systemic arterial vasoconstriction (increase BP, TPR, MAP)
ADH release –> water retention (increased ECF, MAP)
Negative feedback to Renin release

Question 39

ADH stimulation

Answer 39

high plasma osmolality, Ang II, decreased baroreceptor stretch

Question 40

Atrial Natriuretic Peptide (ANP)

Answer 40

increases Na excretion in response to increased ECF or hypertension

Question 41

ANP increases Na excretion through

Answer 41

increased GFR, reduced Na reabsorption in proximal tubule, and in the collecting duct