Kidney function Flashcards
Potassium excretion can vary between 1 and 80%. Why does this not have a marked effect on water balance?
K+ conc. in plasma is so low compared relatively to Na+, variations are insufficient to cause effect
If a patient is dehydrated, filtrate present in which part of the nephron has the highest osmolarity, and why?
Tip of Loop of Henle. In PCT and descending loop, water is reabsorbed in large amounts - higher filtrate osmolarity. In ascending loop and DCT, solutes are reabsorbed so osmolarity is lower
How will consumption of distilled water affect osmolarity?
Decreases plasma osmolarity
Which of: glucose, urea, salt and ethanol as no effect on ADH production?
Urea
Why does urea have no effect on ADH production
Urea has limited effect on blood osmolality as it is a small molecule freely filtered - easy diffusion mean it does not contribute to osmotic pressure
Why do ethanol, salt and glucose affect ADH production
Ethanol is a direct inhibitor of hypothalamus
Salt increases water retention and bp, stimulating ADH
Glucose filtered, leads to water retention, requiring ADH to control
What would urine osmolarity of a patient with hepatic cirrhosis be like and why?
High osmolarity
Hepatic cirrhosis mimics SIADH by: retaining water in body, leads to vasodilation, causing a drop in blood pressure. As a response, body releases ADH to remove more water from tubular fluid, leading to higher urine osmolarity
What would urine osmolarity of a patient with loss of function UT-B1 transporter?
Low osmolarity
UT-B1 function is to move urea into vasa recta. In abnormal function, more urea stays in blood. As urea is a freely filtered molecule with no effect on osmolarity by itself, it’s increased presence will decrease the osmolarity of the interstitial fluid - less water reabsorption means more dilute urine, lower urine osmolarity
Why do most diuretics increase potassium excretion?
Increase in flow rate in collecting duct (as less water has been reabsorbed), directly stimulates potassium excretion
