Lab 5 - Renal Flashcards
What is a urine specific gravity test?
Speciifc gravity is a measure of the weight of particles int he urine.
The more concentrated the urine the higher the specific gravity
What specific gravity values represent normal kidney function?
1.002 - 1.035
Anything above 1.020 indicates de-hydartion
How do you calculate urine production (mL/min)?
Divide the total urine volume by the time since you last collected urine.
What are the mechanisms in the kidney to concentrate urine?
Counter current mechanism in juxtamedullary Loop of Henle and neighbouring vas recta creates the hyperosmotic gradient in the medulla. This gradient faciliates water leaving the CD for reabsorption into the blood when AQP are present.
What is the fast system?
ADH - has to be fast because changes in osmolarity (glucose) are serious
What is the slow system?
Aldosterone - slow because changes in NaCl not serious implications
What is the bodies repsonse to dehydration?
Fast response:
Dehydration > Increase ECF osmolarity >altered actovity of hypothakamic osmoreceptors > Increased activity of ADH neurons > Increased secretion of ADH > Increased AQP2 channels inserted into apcial memrbane of collecting ducts in kidney > increased water permeability to facilliatte increased water reabsorption into bloodstream = decreased urine output.
Explain the control response (no drinking):
Urine output and specific gravity did not change.
Explain the water response:
Increase in urine output
Decrease in speciifc gravity (less concentrated urine)
BECAUSE this happens when there is an intake of hypotonic fluid:
Decrease in ECF osmolarity > altered activity of hypothalamic osmoreceptors > decreased actvity of ADH neurons > Secretion of ADH > Decrease in AQP2 channels inserted into apical membrane of collecting duct in kidney > Decrease in water permaebility and water reabsorption = increase urine output
Explain the Exercise + water response:
Slight delayed increase in urine production (slight because some water and ions lost through sweat) and Decrease in speicifc gravity.
Because:
HITT exercise causes increase in SNS activity causing renal and splanchnic vasoconstriction thus decrease in blood flow to kidneys, glomerular filtration rate and urine production.
But also secretion of ADH causing increased water reabsorption at the CD.
leading to delayed diuresis.
Explain the response to a sports drink (glucose and NaCl):
Increase in urine production (delayed) and decrease in specific gravity.
Delayed because: initially there is no change in ECF osmolarity so no mechanism to initiate diuresis. But then glucose blood is detected by beta cells in pancreas which increases insulin released from beta cells and glucose is removed from the blood by brain, liver, skeletal muscle and adipose tissue - and water follows. This then causes a decrease in ECF osmolarity, ADH release and water reabsorption resulting in increased urine output.
Why do sports drinks have both glucose and NaCl?
Designed to replace the water and ions lost in sweat. The presece of glucose can increase the rate of NaCl and water absorption in GI tract via SGLT1 transporters.
Where in the renal tubule is glucose reabsorbed?
PCT and TDL
Is there noramlly glucose in the urine?
No
Explain the repsonse to drinking an isotonic NaCl solution (salt water):
Very minimal change in rate of urine production over the hour and same speciifc gravity.
This is because it used the slow system (aldosterone). The fluid enteres the ECF but ECF osmolarity same as ICF so there is no gradient thus no net movement of water into the cells.
ECF volume increase = plasma volume increased = stimulation of barorecptors in carotid arteries and aortic arch.
