Renal II Flashcards
Define: Clearance
the volume of plasma from which a substance is completely cleared ,by the kidneys per unit time
What does the principle of renal clearance emphasize?
the excretory function of the kidneys
it considers only the rate at which a substance is excreted into the urine and not its return to the systemic circulation through the renal vein
Basic Clearance Formula
Cx = (UxV)/Px
Ux = urine concentration of x (mg/ml)
V = urine volume (mL/min)
Px = Plasma concentration of x (mg/mL)
If a substance is present in urine at concentration of 100 mg/mL and urine flow rate is 1 mL/min and the substance has a concentration of 1 mg/mL in plasma, what is the clearance of the substance?
(100 mg/mL X 1 mL/min)/ 1 mg/ml = 100 ml/min
100 mL of plasma is completely cleared of the substance/min
Equation to find GFR using Clearance
GFR = (UwV)/Pw
urinary clearance of w is equal to the GFR
What criteria needs to be met in order for GFR = (UwV)/Pw to be valid?
- W must be
- freely filtrable
- not reabsorbed
- not secreted
- not synthesized by tubules
- not broken down by tubules
What fits the required criteria and can be used to determine GFR using clearance?
Inulin → a polysaccharide
GFR = renal clearance of inulin
Clearance of inulin (Cin) = GFR
What is the issue with using inulin to measure GFR?
inulin is not naturally occurring
What is used in place of inulin in clinical settings? why?
Creatinine
creatinine is freely filterable and not reabsorbed like inulin
there is a direct relationship between plasma creatinine and GFR within limits
What is the relationship between Creatinine and GFR?
a small amount of creatinine is secreted → clearance of creatinine is slightly higher than real GFR
if plasma creatinine is raised, it indicates that renal function, especially GFR, is impaired
GFR decreases → plasma creatine increases
large increase in creatinine → small drop in GFR
What is normal plasma creatinine?
10 mg/L
What happens to plasma creatinine if GFR decreases 50%?
plasma creatinine rises but stabilizes at 20 mg/L
Para-aminohippurate (PAH)
filtered at glomerulus, not reabsorbed, almost totally secreted
PAH approximates renal plasma flow
Equation: Clearance of PAH
CPAH = (UPAHV)/PPAH = ERPF
ERPF = effective renal plasma fluid
What happens to 10-15% of total renal plasma flow?
it supplies non-filtering and non-secreting portions of the kidneys such as (peripelvic fat), and this plasma cannot lose its PAH by secretion
ERPF
0.9RBF
Equation: RBF
RBF = RPF/(1-hematocrit)
hematocrit = % of blood cells
Define: Diffusion
occurs from an area of higher concentration to one of lower concentration (down concentration gradient)
affected by the electrical potential difference across the cell membranes of the renal tubule cells
Define: Facilitated Diffusion
depends on interaction of solute with a specific protein in the membrane that facilitates its movement across the membrane
utilizes transporters to move proteins
Define: Primary Active Transport
the movement of molecules through a mechanism which is directly coupled to energy derived from metabolic processes (consumes ATP)
occurs against the concentration gradient (low to high)
utilizes ATP-dependent transporters or through endocytosis
Define: Endocytosis
transport process where there is invagination of a part of the cell membrane until it completely pinches off and forms a vesicle in the cytoplasm
Define: Secondary Active Transport
occurs when the energy from the downhill movement of a solute provides energy for the uphill movement of another solute
Define: Solvent Drag
occurs when water is reabsorbed and solutes which have been dissolved in the water is reabsorbed with water
Two types of transport mechanisms in reabsorption
Paracellular
Transcellular