Module 7
TRUE or FALSE: 1L of 5% glucose will have a higher osmolarity than its molarity, but 1L of 5% NaCl will have an equal osmolarity and molarity.
False.
Which of the following will lead to an INCREASE in GFR?
Increasing afferent arteriolar resistance; Increasing efferent arteriolar resistance; Increasing ultrafiltration coefficient; Increasing hydrostatic pressure of Bowman’s capsule; Increasing colloid osmotic pressure of the glomerular capillaries; Increasing Filtration Fraction
Potential answer choices: Increasing efferent arteriolar resistance; Increasing ultrafiltration coefficient
The proximal tubule is the only site along the nephron that reabsorbs glucose (TRUE/FALSE?) It does so via carrier-mediated transport (TRUE/FALSE?)
Both are true statements.
What are the top 2 sites for K+ reabsorption along the nephron?
1) Proximal, 2) thick ascending limb
You want to measure total body water in a patient. You inject intravenously 10 mL of a solution of antipyrine with a concentration of 150 mg/mL. After equilibrium, the concentration of antipyrine in the blood is 0.03 mg/mL. You’d like to calculate the total body water. How would you set-up this calculation?
Use conservation of mass to solve for the unknown total body water volume:
(Known indicator volume) * (Known indicator concentration) = (Unknown total body water volume) * (Known indicator concentration in body)
Under hypertonic conditions, water will move from the (cell/solution) to the (cell/solution).
Cell; solution
What substances can be used to estimate GFR? RBF?
GFR: Inulin (only filtered, not reabsorbed or secreted); Creatinine (overestimates GFR, slightly secreted)
(SELECT ALL) Which components of the RAAS system are always circulating in the bloodstream?
Angiotensin II, Angiotensinogen, Renin, ACE, Angiotensin I
Angiotensinogen; Angiotensin I; ACE
K+ movement in the proximal tubule is exclusively (paracellular/transcellular), while movement in the thick ascending limb travels both paracellularly and transcellularly.
Paracellular
You need to measure Bart Simpson’s interstitial fluid volume. What indicators can you use to calculate this? How would you set-up these calculations?
Plasma volume = blood volume * (1-HCT). To measure blood volume, need 125I-albumin or 51Cr-red blood cells.
Interstitial fluid volume = ECF - plasma volume. To measure ECF, need 22Na, inulin, or thiosulfate.
Where do the greatest changes to filtrate osmolarity occur along nephron?
Loop of Henle (normally), Collecting tubule/duct (in the presence of ADH)
What sites along the nephron are impermeable to paracellular Na+ transport?
Thin descending loop; distal convoluted tubule; collecting tubule
In response to low effective circulating volume, angiotensin II will (upregulate/downregulate) several channels, including the basolateral Na+/K+ pump and Na+/HCO3- cotransporter; and apical Na/H+ exchanger.
Upregulate
MATCHING: Match the cell type to its function (K+ reabsorption or K+ secretion):
alpha-intercalated cells, beta intercalated cells, principal cells
K+ reabsorption: principal cells, alpha intercalated cells.
K+ secretion: beta intercalated cells
Lisa Simpson is found to have the following glomerular Starling forces: a glomerular capillary hydrostatic pressure of 55 mmHg, a Bowman’s space hydrostatic pressure of 15 mmHg, and a glomerular capillary oncotic pressure of 30 mmHg. The ultrafiltration coefficient is 1.
You are asked to calculate the net ultrafiltration pressure for this patient. How would you set-up these calculations?
Net ultrafiltration pressure = Kf * [(Capillary hydrostatic pressure + Bowman’s space oncotic pressure) - (Bowman’s space hydrostatic pressure + capillary oncotic pressure)]
OR,
NUP = Kf * [(forces of filtration) - (forces of reabsorption)]
The countercurrent (multiplier/exchanger) is responsible for creating the osmotic gradient in the renal medulla.
Countercurrent multiplier
What triggers the release of aldosterone, and where does this hormone act along the nephron?
Triggers: RAAS, angiotensin II; high potassium levels; low sodium levels; ACTH (permissive role)
Site of action: principal cells of the late distal tubule and collecting tubules
What triggers the release of ADH, and what senses these triggers for ADH release?
Potential triggers: dehydration; high blood salt concentration; low effective circulating volume (i.e. low blood pressure)
Sensed by osmoreceptors in the hypothalamus.
Activation of the RAAS system will decrease K+ (reabsorption/secretion), causing (hyperkalemia/hypokalemia).
Secretion; hypokalemia
Marge Simpson presents to clinic with the following lab values:
GFR =100 mL/min
PNa = 140 mEq/L
Urine rate flow = 1 mL/min
Urine Na+ concentration = 100 mEq/L
You are tasked to calculate the rate of Na+ filtration, excretion, reabsorption, and secretion. How would you set-up these calculations?
Filtration = GFR * PNa
Excretion = Urine Flow Rate * Urine Na+ Concentration
Reabsorption = (Filtration [Na+]) - (Excretion [Na+])
Secretion = (Excretion [Na+]) - (Filtration [Na+])
If a patient’s maximum urine osmolarity decreases from 1200 mOsm/L to 300 mOsm/L, then the obligatory urine volume will (increase/decrease) in order to maintain solute excretion.
Increase.
Homer Simpson has hypernatremia. You are his provider and want to prescribe medication to help him but want to avoid prescribing a loop diuretic. Your options are: a thiazide diuretic (blocks Na+/Cl- cotransporter) or amiloride (blocks epithelial Na+ channels). What are some pros and cons of each medication as compared to loop diuretics?
Pro: amiloride is K+ sparing
Cons: both medications increase Ca2+ reabsorption; both medications produce less diuresis
What channels will ADH act on, and where are these channels located along the nephron?
Increases # of UT-A1 channels (apical side of medullary collecting duct); increases # of AQP-2 channels (apical side of distal & collecting tubules)
Homer Simpson is prescribed furosemide.
Where along the nephron does this medication act? How will this drug impact ion movement?
Acts on the thick ascending limb to block the Na+/K+/2Cl- cotransporter. Blocks the reabsorption of Na+, Cl-, and K+. Since NH4+ can replace K+ for reabsorption, also reduces NH4+ reabsorption. Secondary effects include reducing Ca2+ and Mg2+ reabsorption.
Homer Simpson weighs 150kg and receives an infusion (2.0L of 3% NaCl). His plasma osmolarity is normal pre-infusion (i.e., 280 mOsm/L). After the infusion, Homer feels better, but you are a PHY 504 so you need to calculate Homer’s new fluid compartment osmolarities and volumes (ECF, ICF, TBW). How would you set-up these calculations?
Determine pre-infusion fluid/osmolarity:
1) Calculate TBW, ICF and ECF (assume ICF is 40% of body weight and ECF is 20% body weight). TBW is ECF + ICF.
2) Calculate total mOsm in ECF, ICF, and TBW (volume * plasma osmolarity). To accomplish this, you need to convert 3% NaCl from grams/L to mmol/L, then to mOsm/L!
Determine post-infusion fluid/osmolarity:
1) Calculate new plasma osmolarity: Add infusion volume to TBW volume. Add infusion osmoles to TBW osmolarity. Divide new TBW mOsm/new TBW L for new plasma osmolarity.
2) Calculate new ECF volume: Add infusion osmoles to ECF. Divide new ECF mOsm/new plasma osmolarity for new ECF volume.
3) Calculate new ICF volume: new TBW volume - new ECF volume. OR, unchanged ICF mOsm/new plasma osmolarity.