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46 Cards in this Set
- Front
- Back
How is water balance, and therefore serum Na+, maintained in setting of increased water intake?
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Excretion of dilute urine
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What are the ways to lose water?
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Fixed Water Excretion / total insensible losses: 0.5 L/day
- Stool (0.1 L/day) - Sweat (0.1 L/day) - Pulmonary (0.3 L/day) Variable Water Excretion: - Urine (1.0 - 1.5 L/day) |
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What is osmolarity?
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Total solute / ECF volume
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What are the approximate concentrations of K+ and Na+ intracellularly?
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K+: 140 mEq/L
Na+: 10 mEq/L |
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What are the approximate concentrations of K+ and Na+ extracellularly?
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K+: 4 mEq/L
Na+: 140 mEq/L |
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What is the primary determinant of extracellular fluid osmolarity?
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** Na+ concentration (140 mEq/L)
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How does a hypertonic osmolarity return to isotonicity?
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- Stimulates hypothalamic receptors
- ↑ Thirst → ↑ Water intake - ↑ ADH release → Renal water retention Causes return to isotonicity |
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How does a hypotonic osmolarity return to isotonicity?
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- Inhibits hypothalamic receptors
- ↓ Thirst → ↓ Water intake - ↓ ADH release → Renal water excretion Causes return to isotonicity |
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What receptors control stimuli for ADH release? How?
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- Osmoreceptors: ↑ plasma Osm → ↑ ADH
- Baroreceptors: ↑ volume depletion → ↑ ADH |
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How does osmolarity relate to ADH release? What receptors control this?
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- As plasma osmolarity increases above 280, ADH release into plasma increases
- Controlled by osmoreceptors |
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How does blood volume relate to ADH release? What receptors control this?
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- As % blood volume depletion increases above 5%, ADH release into plasma increases
- Controlled by baroreceptors |
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Where is the tubular fluid the most concentrated (highest osmolarity?
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- Loop of Henle
- Medullary collecting duct (depending on amount of ADH) |
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Where is the tubular fluid the least concentrated (highest osmolarity?
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- Distal Tubule
- Cortical Collecting Tubule / Duct |
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How does ADH affect urine osmolarity?
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- The more ADH there is, the greater the urine osmolarity (up to 1200)
- The less ADH there is, the lower the urine osmolarity (as low as 50) |
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Why did the woman in the water drinking contest die?
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- Her serum Na+ was estimated to be 114 mEq/L (normal is 135 - 145 mEq/L)
- She overrode her decrease thirst mechanism, so continued to dilute her Na+ / hypotonic fluid |
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What are the signs and symptoms of Hyponatremia?
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- Nausea / vomiting
- Weakness - Headache - Lethargy - Seizures - Respiratory depression - Death |
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What factors alter water balance?
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- ADH (appropriate or inappropriate)
- Water intake - Altered renal water handling |
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What can cause inappropriate secretion of ADH?
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- Cancer (eg, small cell lung)
- CNS disease - Pulmonary disease - Drugs: narcotic, anti-emetics, SSRIs - HIV |
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How is ECF osmolarity regulated?
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Tightly by changes in thirst and ADH secretion
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How does the kidney prevent hypo-osmolarity d/t increased water intake?
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Excretes a dilute urine (osm < 100 mOsm/kg)
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What effects can inappropriately elevated ADH have?
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- Hyponatremia
- Hypo-osmolarity since urinary dilution is impaired (osm > 300 mOsm/kg) |
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What is the GFR? Normal values?
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-Amount of plasma filtered through glomeruli per unit time
- Normal: ~90 - 125 mL/min |
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What is BUN? Function?
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- Blood Urea Nitrogen, nitrogenous waste product of protein metabolism
- Less accurate indicator of GFR than creatinine d/t variation in protein intake, catabolic rate, tubular reabsorption - Useful in conjunction w/ creatinine in differential diagnosis of renal disease |
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Why is BUN less accurate of an indicator of GFR than creatinine?
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BUN levels vary d/t:
- Protein intake - Catabolic rate - Tubular reabsorption |
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What is Creatinine? Why is it useful for estimating GFR?
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- Breakdown product of skeletal muscle
- Production remains constant over time - Filtered at glomerulus |
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Why is creatinine less accurate of an indicator of GFR than inulin?
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- Creatinine is also secreted in nephron
- Creatinine clearance therefore overestimates GFR |
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What are the limitations of creatinine for determining GFR?
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- Creatinine is also secreted in nephron
- Creatinine clearance therefore overestimates GFR - Differences in individual muscle mass affect creatinine clearance |
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How can you very roughly estimate GFR if you know creatinine?
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GFR ~ 100 / Cr
E.g., Serum Cr of 1 → GFR = 100 E.g., Serum Cr of 2 → GFR = 50 E.g., Serum Cr of 3 → GFR = 33 |
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When is a change in serum creatinine more serious?
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When the change is a greater percentage of the total creatinine it has a greater impact on GFR
E.g., change from 1 to 1.5 is more serious than 3 to 3.5 |
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How can you use inulin values to calculate GFR?
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GFR = Uinulin * V / Pinulin
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What is the Cockcroft-Gault equation used for?
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Estimating GFR from serum creatinine (takes into account age, weight, and gender too)
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What are the ways to calculate Creatinine Clearance?
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- CrCl = U*V/P
- Cockcroft - Gault equation |
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Why are serum creatinine based GFR estimates sometimes inaccurate?
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Extremes in age, BMI, or muscle mass
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Which of the following does not contribute to systemic response to extracellular fluid volume depletion?
- increased reabsorption of Na+ at PT - decreased renal nerve activity - increase ADH secretion - activation of baroreceptors |
Decreased renal nerve activity
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What factors contribute to systemic response to extracellular fluid volume depletion?
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- Baroreceptor activation (increased sympathetic tone)
- Increased renin secretion - Increased AngII / increased Aldosterone = increased tubular Na reabsorption |
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What are the direct tubular effects on Na+ reabsorption?
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Renal sympathetic nerves:
- multiple tubular receptors stimulate Na+ reabsorption Angiotensin II: - tubular receptors - increases activity of PT Na/H counter-transporter Aldosterone: - stimulates Na+ reabsorption in cortical collecting duct principal cells - increases number of luminal Na+ channels and BL Na/K-ATPases |
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What percentage of filtered load of Na+ has its excretion dependent on aldosterone action?
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~2%
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What controls Aldosterone secretion?
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Angiotensin II:
- most important stimulus for aldosterone secretion relating to Na balance - AngII is dependent upon renin secretion and therefore baroreceptors, macula densa, and renal sympathetic tone |
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What is the action of ADH? Where?
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- Binds to V2 receptors on cells in late distal tubule, collecting tubules, and collecting ducts
- Leads to increased Aquaporin-2 (AQP-2) channels on the tubular lumen side to increase reabsorption of H2O - Mediated via ↑cAMP, activation of PKA, and protein phosphorylation |
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What should be done to treat a patient with volume depletion due to nausea, vomiting, and diarrhea?
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- Give normal saline (150 cc/hour IV)
- Anti-emetics - Increase oral fluid intake |
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What does the systemic response to decreased ECF volume involve? Implications?
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- Baroreceptor and sympathetic nerve activation
- Activation of Renin-AngII-Aldo system - Increased ADH - Leads to enhanced renal tubular Na+ and H2O reabsorption (leads to low urine Na+, low FENa, and elevated urine osmolarity) |
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28 yo male w/ 20y hx of CKD d/t vesicoureteral reflux presents w/ weakness, bone pain, headaches, blurred vision, and nausea. BP 220/160. Ill appearing, pale sclera and nail beds, flow murmur LLSB, knobby knees/ankles w/ valgus knee deformity, ↑ DTRs w/ clonus.
Labs: Hct 7 g/dl, serum creatinine 16 mg/dl, BUN 180 mg/dl, Ca 6.5 mg/dl, phosphorus 11 mg/dl, PTH 1200 (11-54 pg/ml) What factor contributes to his parathyroidism? |
Increased serum phosphorus
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What stimulates PTH release?
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- Low Ca2+
- High Phosphorus |
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What are the endocrine functions of the kidney?
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- Renin release from juxtaglomerular cells
- Erythropoetin (epo) produced by renal cortical tubular cells, stimulates RBC production in marrow - 1,25-dihydroxy-vitamin D production formed in proximal tubule cells, regulates calcium and phosphate balance |
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What are the effects of increased PTH?
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- ↑ Vitamin D3 activation → ↑ intestinal Ca2+ reabsorption
- ↑ Renal Ca2+ reabsorption - ↑ Ca2+ release from bones |
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How are calcium and phosphorus affected by kidney disease?
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- ↑ Serum PO4 (increased retention)
- ↓ 1,25-Dihydroxy-Vitamin D - ↓ Serum Ca2+ - Decreased calcitriol production ↓ Ca2+ absorption, hypocalcemia Leads to ↑PTH release (2° Hyperparathyroidism) |