Renal - Physiology Flashcards
1
Q
Fluid compartments
- Potassium location
- % of body weight
- Total body water
- ICF
- ECF
- Plasma volume measured by…
- Extracellular volume measured by…
- Osmolarity
A
- Potassium location
- HIKIN’: HIgh K INtracellular.
- 60–40–20 rule (% of body weight):
- 60% total body water
- 40% ICF
- 20% ECF
- Plasma volume measured by radiolabeled albumin.
- Extracellular volume measured by inulin.
- Osmolarity = 290 mOsm/L.
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2
Q
Glomerular filtration barrier
- Responsible for…
- Composed of…
- Pathology of the charge barrier
A
- Responsible for filtration of plasma according to size and net charge.
- Composed of…
- Fenestrated capillary endothelium (size barrier)
- Fused basement membrane with heparan sulfate (negative charge barrier)
- Epithelial layer consisting of podocyte foot processes
- Pathology of the charge barrier
- The charge barrier is lost in nephrotic syndrome, resulting in albuminuria, hypoproteinemia, generalized edema, and hyperlipidemia.
3
Q
Renal clearance
- Cx equation
- Cx vs. GFR
- Cx < GFR
- Cx > GFR
- Cx = GFR
A
- Cx = (Ux * V) / Px = volume of plasma from which the substance is completely cleared per unit time.
- Cx = clearance of X (mL/min).
- Ux = urine concentration of X (mg/mL).
- V = urine flow rate (mL/min)
- Px = plasma concentration of X (mg/mL).
- Cx vs. GFR
- Cx < GFR: net tubular reabsorption of X.
- Cx > GFR: net tubular secretion of X.
- Cx = GFR: no net secretion or reabsorption.
4
Q
Glomerular filtration rate
- Inulin clearance
- GFR equations
- Normal vs. reduced GFR
- Creatinine clearance
A
- Inulin clearance
- Can be used to calculate GFR because it is freely filtered and is neither reabsorbed nor secreted.
- GFR
- = (Uinulin × V) / Pinulin = Cinulin
- = Kf [(PGC – PBS) – (πGC – πBS)].
- GC = glomerular capillary
- BS = Bowman space
- πBS normally equals zero.
- Normal vs. reduced GFR
- Normal GFR ≈ 100 mL/min.
- Incremental reductions in GFR define the stages of chronic kidney disease
- Creatinine clearance
- An approximate measure of GFR.
- Slightly overestimates GFR because creatinine is moderately secreted by the renal tubules.
5
Q
Effective renal plasma flow
- Effective renal plasma flow (ERPF)
- ERPF equation
- RBF equation
A
- Effective renal plasma flow (ERPF)
- Can be estimated using para-aminohippuric acid (PAH) clearance because it is both filtered and actively secreted in the proximal tubule.
- Nearly all PAH entering the kidney is excreted.
- Underestimates true renal plasma flow (RPF) by ~10%.
- Can be estimated using para-aminohippuric acid (PAH) clearance because it is both filtered and actively secreted in the proximal tubule.
- ERPF = (UPAH × V) / PPAH = CPAH.
- RBF = RPF / (1 - Hct).
6
Q
Filtration
- Equations
- Filtration fraction (FF)
- Normal FF
- Filtered load (mg/min)
- Filtration fraction (FF)
- Estimations
- GFR
- RPF
A
- Equations
- Filtration fraction (FF) = GFR / RPF.
- Normal FF = 20%.
- Filtered load (mg/min) = GFR (mL/min) × plasma concentration (mg/mL)
- Filtration fraction (FF) = GFR / RPF.
- Estimations
- GFR can be estimated with creatinine clearance.
- RPF is best estimated with PAH clearance.
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7
Q
Changes in glomerular dynamics
- For each effect (increased/decreased)
- RPF
- GFR
- FF (GFR / RPF)
- Afferent arteriole constriction
- Efferent arteriole constriction
- Increased plasma protein concentration
- Decreased plasma protein concentration
- Constriction of ureter
A
- Afferent arteriole constriction
- RPF: Decreased
- GFR: Decreased
- FF (GFR / RPF): No effect
- Efferent arteriole constriction
- RPF: Decreased
- GFR: Increased
- FF (GFR / RPF): Increased
- Increased plasma protein concentration
- RPF: No effect
- GFR: Decreased
- FF (GFR / RPF): Decreased
- Decreased plasma protein concentration
- RPF: No effect
- GFR: Increased
- FF (GFR / RPF): Increased
- Constriction of ureter
- RPF: No effect
- GFR: Decreased
- FF (GFR / RPF): Decreased
8
Q
Calculation of reabsorption and secretion rate (equations)
- Filtered load
- Excretion rate
- Reabsorption
- Secretion
A
- Filtered load = GFR × Px.
- Excretion rate = V × Ux.
- Reabsorption = filtered – excreted.
- Secretion = excreted – filtered.
9
Q
Glucose clearance
- Glucose at a normal plasma level
- At plasma glucose of ~200 mg/dL
- At plasma glucose of ~375 mg/dL
- Glucosuria
- Normal pregnancy
A
- Glucose at a normal plasma level
- Completely reabsorbed in proximal tubule by Na+/glucose cotransport.
- At plasma glucose of ~200 mg/dL
- Glucosuria begins (threshold).
- At plasma glucose of ~375 mg/dL
- All transporters are fully saturated (Tm).
- Glucosuria
- An important clinical clue to diabetes mellitus.
- Normal pregnancy
- Decreases reabsorption of glucose and amino acids in the proximal tubule –> glucosuria and aminoaciduria.
10
Q
Amino acid clearance
- Reabsorption
- Hartnup disease
- Definition
- Findings
- Treatment
A
- Reabsorption
- Sodium-dependent transporters in proximal tubule reabsorb amino acids.
-
Hartnup disease
- Definition
- Autosomal recessive disorder.
- Deficiency of neutral amino acid (e.g., tryptophan) transporters in proximal renal tubular cells and on enterocytes.
- Findings
- Leads to neutral aminoaciduria and decreased absorption from the gut
- Results in pellagra-like symptoms
- Treatment
- Treat with high-protein diet and nicotinic acid.
- Definition
11
Q
Nephron physiology:
Early proximal convoluted tubule (PCT)
- Functions
- Important hormones
- % Na+ reabsorbed
A
- Functions
- Contains brush border.
- Reabsorbs all of the glucose and amino acids and most of the HCO3–, Na+, Cl–, PO43–, K+, and H2O.
- Isotonic absorption.
- Generates and secretes NH3, which acts as a buffer for secreted H+.
- Important hormones
- PTH
- Inhibits Na+/PO43– cotransport → PO43– excretion.
- AT II
- Stimulates Na+/H+ exchange → ↑ Na+, H2O, and HCO3- reabsorption (permitting contraction alkalosis).
- PTH
- % Na+ reabsorbed
- 65–80%
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12
Q
Nephron physiology:
Thin descending loop of Henle
- Functions
A
- Functions
- Passively reabsorbs H2O via medullary hypertonicity (impermeable to Na+).
- Concentrating segment.
- Makes urine hypertonic.
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13
Q
Nephron physiology:
Thick ascending loop of Henle
- Functions
- % Na+ reabsorbed
A
- Functions
- Actively reabsorbs Na+, K+, and Cl-.
- Indirectly induces the paracellular reabsorption of Mg2+ and Ca2+ through (+) lumen potential generated by K+ backleak.
- Impermeable to H2O.
- Makes urine less concentrated as it ascends.
- % Na+ reabsorbed
- 10–20%
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14
Q
Nephron physiology:
Early distal convoluted tubule (DCT)
- Functions
- Important hormones
- % Na+ reabsorbed
A
- Functions
- Actively reabsorbs Na+, Cl-.
- Makes urine hypotonic.
- Important hormones
- PTH
- ↑ Ca2+/Na+ exchange → Ca2+ reabsorption.
- PTH
- % Na+ reabsorbed
- 5–10%
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15
Q
Nephron physiology:
Collecting tubule
- Functions
- Important hormones
- % Na+ reabsorbed
A
- Functions
- Reabsorbs Na+ in exchange for secreting K+ and H+ (regulated by aldosterone).
- Important hormones
- Aldosterone
- Acts on mineralocorticoid receptor → insertion of Na+ channel on luminal side.
- ADH
- Acts at V2 receptor → insertion of aquaporin H2O channels on luminal side.
- Aldosterone
- % Na+ reabsorbed
- 3–5%
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