Sodium and Water Flashcards
Certain solutes, particularly ____, do not contribute to water shifts across most membranes and are thus known as ineffective osmoles.
urea
____ is the most abundant constituent in the body, comprising ~50% of body weight in women and 60% in men.
Water
The solute or particle concentration of a fluid is known as its _____, expressed as milliosmoles per kilogram of water (mOsm/kg).
osmolality
The major ECF particles are _____
Na +and its accompanying anions Cl – and HCO3–,
Predominant ICF osmoles.
K +and organic phosphate esters (ATP, c tine phosphate, and phospholipids)
Vasopressin secretion, water ingestion, and renal water transport collaborate to maintain human body fluid osmolality between ____ mOsm/kg.
280 and 295
AVP secretion is stimulated as _____ increases above a threshold level of ~285 mOsm/kg
systemic osmolality
there is a linear relationship between osmolality and circulating AVP
AVP has a half-life in the circulation of only ______;
10–20 min
AVP acts on renal, V 2 -type receptors in the ______ and principal cells of the _____, increasing intracellular levels of cyclic AMP and activating protein kinase A (PKA)–dependent phosphorylation of multiple transport proteins.
thick ascending limb of Henle
collecting duct (CD)
The AVP- and PKA-dependent activation of ______transport by the thick ascending limb of the loop of Henle (TALH) is a key participant in the countercurrent mechanism
Na+-Cl –and K+
AVP-induced, PKA-dependent phosphorylation of the aquaporin-2 water channel in ______ stimulates the insertion of active water channels into the lumen of the CD, resulting in transepithelial water absorption down the medullary osmotic gradient
principal cells
Arterial perfusion and circulatory integrity are, in turn, determined by ______, in addition to the modulation of systemic arterial resistance.
renal Na + retention or excretion
Approximately two-thirds of filtered Na+ -Cl – is reabsorbed by the _______, via both paracellular and transcellular mechanisms.
renal proximal tubule
The ____ subsequently reabsorbs another 25–30% of filtered Na+ -Cl – via the apical, furosemide-sensitive Na+ -K+ -2Cl – cotransporter.
TALH
The thiazidesensitive apical Na+ -Cl – cotransporter (NCC) reabsorbs 5–10% of filtered Na+-Cl –in the ____.
DCT
Reabsorb Na⁺ via amiloride-sensitive epithelial Na⁺ channels (ENaC).
Principal Cells
Approximately ____ of fluid enter the gastrointestinal tract daily, 2 L by ingestion and 7 L by secretion
9 L
Evaporation of water from the skin and respiratory tract (so-called _____) constitutes the major route for loss of solute-free water, which is typically 500–650 mL/d in healthy adults.
“insensible losses”
Reabsorb Cl⁻ via SLC26A4 anion exchanger (Cl⁻-OH⁻ and Cl⁻-HCO₃⁻ exchange).
Intercalated Cells
More reliable signs of hypovolemia include a decreased jugular venous pressure (JVP), orthostatic tachycardia (an increase of _____ beats/min upon standing), and orthostatic hypotension (a ______mmHg drop in blood pressure on standing).
> 15–20
> 10–20
______ is the most appropriate resuscitation fluid for normonatremic or hyponatremic patients with severe hypovolemia;
Isotonic, “normal” saline (0.9% NaCl, 154 mM Na+)
Hypernatremic patients should receive a ______, if there has only been water loss (as in DI), or ____ if there has been water and Na+-Cl –loss;
hypotonic solution 5% dextrose
hypotonic saline (1/2 or 1/4 normal saline)
Patients with bicarbonate loss and metabolic acidosis, as occur frequently in diarrhea, should receive ______
intravenous bicarbonate, either an
isotonic solution (150 meq of Na+ -HCO 3 – in 5% dextrose)
or a more hypotonic bicarbonate solution in dextrose or dilute saline.
_____ and _____constitute the two key effectors in the defense of serum osmolality
Water intake
circulating AVP