Ch 3 sodium and water

Question 1

define osmolarity

Answer 1

number of particles of solute per litre of solution

Question 2

define osmolality

Answer 2

number of particles of solute per kilogram of solvent

Question 3

normal osmolality for dogs

Answer 3

290-310mOsm/kg

Question 4

normal osmolality for cats

Answer 4

290-330mOsm/kg

Question 5

formula for calculated plasma osmolality

Answer 5

2Na + glucose/18 + BUN/2.8

Question 6

define abnormal osmolal gap

Answer 6

difference between measured and calculated osmolality of more than 10mOsm/kg

Question 7

causes of increased osmolal gap

Answer 7

large quantities of unmeasured solute (lactic acid, sulphates, phosphates, acetylsalicylic acid, mannitol, ethylene glycol and its metabolites, ethanol, isopropyl alcohol, methanol, radiographic contrast solution, paraldehyde, sorbitol, glycerol, propylene glycol or acetone) OR pseudohyponatremia (hyperlipemia, marked hyperglycaemia, hyperproteinemia)

Question 8

specific gravity refers to what ratio

Answer 8

weight of a volume of liquid to weight of an equal volume of distilled water

Question 9

how can you roughly estimate urine osmolality from USG?

Answer 9

multiply last two digits by 36

Question 10

situations where estimating urine osmolality from USG is misleading

Answer 10

proteinuria, glucosuria - substances with high molecular weights have a greater effect on USG than on osmolality

Question 11

formula for effective osmolality (tonicity)

Answer 11

Posm - BUN/2.8

Question 12

in table form, describe the relative effect of pure water loss, hypotonic fluid loss, isotonic fluid loss, hypertonic fluid loss and isotonic fluid loss with water replacement on ECF volume and total solute concentration, and ICF volume and total solute concentration

Answer 12

Question 13

MOA of furosemide

Answer 13

loop diuretic, inhibits the luminal Na-K-2Cl cotransporter in the thick ascending limb of the loop of Henle

Question 14

what percentage of excreted sodium is reabsorbed in the loop of Henle and by what mechanisms

Answer 14

~25%, mostly by Na+-H+ antiporters and Na+-K+-2Cl- cotransporters in the thick ascending loop of Henle, also by passive reabsorption in the thin descending and ascending limbs

Question 15

what percentage of excreted sodium is reabsorbed in the distal convoluted tubule and connecting segment and by what mechanism(s)?

Answer 15

~5%, via the Na+-Cl- cotransporter in the early distal tubule

Question 16

MOA of thiazide diuretics

Answer 16

inhibits the Na+-Cl- cotransporter in the distal convoluted tubule

Question 17

what percentage of excreted sodium is reabsorbed in the proximal tubules and by what mechanism(s)?

Answer 17

~67%, in the early proximal tubule it is cotransported with glucose, amino acids and phosphate and also reabsorbed exchange for H+ via the luminal Na+-H+ antiporter, in the late proximal tubule it is reabsorbed with Cl- by luminal Na+-H+ antiporters and luminal Cl–anion- antiporters, resulting in net NaCl reabsorption

Question 18

what percentage of excreted sodium is reabsorbed in the collecting ducts, and by what mechanism(s)

Answer 18

~3%, enters passively through Na+ channels in the luminal membranes of the principal cells

Question 19

MOA of K+-sparing diuretics

Answer 19

blocks Na+ channels in the principal cells in the collecting ducts

Question 20

aldosterone effect on renal sodium handling

Answer 20

increases number and activity of open sodium channels in the luminal membranes of the principal cells in the collecting ducts

Question 21

1. low pressure mechanoreceptors (volume receptors) in the cardiac atria and pulmonary vessels and high-pressure baroreceptors (pressure receptors) in the aortic arch and carotid sinus
2. juxtaglomerular apparatus repond to changes in perfusion pressure