Glomerular Filtration and Renal Clearance Flashcards
What is the selectively of the filtration barrier determined by?
Molecular size of intravascular components
Electrical charge of filtration barrier components (all negative)
What is the capillary endothelium filled with?
Negatively charged glycoprotein
What is the basement membrane made up of?
Collagen, proteoglycans
Physical barrier, electrostatic repulsion
What is the key selective barrier in filtration?
Filtration silts
What is the composition of the ultra-filtrate?
Most ions and low molecular weight components
Exclusion of larger plasma proteins
Positively charged marcomolecules
What is typical renal blood flow?
20% of total CO
What is typical renal plasma flow?
605ml/min
What is typical GFR?
125ml/min
What is the average excretion rate?
1ml/min
What does GFR equal to?
Kf x NFP
What is the filtered load?
Total amount of any substance freely filtered from renal glomerular capillaries into Bowman’s space
calculated by GFR x [X] in plasma
How can GFR be altered?
Constriction and dilation of AA and EA
What does a rise in blood pressure cause in relation to GFR?
Increased excretion of salt and water
How do kidneys regulate their blood flow?
Adjusting vascular resistance in response to changes in arterial pressure
What is normal blood pressure?
90mmHg
What are 2 mechanisms responsible for regulation of RBF and GFR?
Myogenic mechanism
Tubuloglomerular feedback
Regulate tone of AA
Describe the myogenic mechanism.
Vascular smooth muscle contracts when stretched
Fast acting - protects from short-term fluctuations in blood pressure
Describe the tubuloglomerular feedback.
Macula densa cells act as salt sensors
High levels of Na+ -> decrease in GFR by AA constriction
What uptakes NaCl across macula densa cells?
NKCC2 channel -> increased ATP and adenosine
What does ATP and adenosine bind to on AA?
ATP - P2X receptors
ADO - adensoine A1 receptors
What does receptor binding lead to?
Increase in Ca2+ -> vasoconstriction of AA -> GFR decreases
What 2 neurotransmitters causes vasoconstriction?
Norepinephrine and epinephrine bind to alpha 1 adrenoreceptors
What 2 vasoactive factors cause vasoconstriction?
Angiotensin 2
Endothelin
What 2 vasoactive factors cause vasodilation?
Nitric Oxide
Prostaglandins
What is renal clearance?
Volume of plasma from which that substance is completely removed by kidneys per unit time
What is the equation for clearance (mL/min)?
(urine conc. of X)(mg/mL) x (urine volume per unit time)(mL/min) / Plasma conc. of X mg?mL
How is PAH cleared?
Freely filtered, not reabsorbed, fully secreted
Clearance = renal plasma flow (605ml/min)
How is Inulin cleared?
Freely filtered, not reabsorbed, secreted, synthesized or metabolized
Clearance = GFR (125ml/min)
How are glucose and AA cleared?
Freely filtered, fully reabsorbed, not scereted
Clearance = 0ml/min
Which substance’s clearance is used for routine GFR assessment?
Creatinine
How is creatinine cleared?
Freely filtered, not reabsorbed but small amount secreted by proximal tubule
What measurement is more common to use as an indicator of GFR?
Plasma creatinine
What is a strong indicator of renal disease?
Rising plasma creatinine
