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Memorize this‌ Renal Physiology Percent of total body weight that is Total Body Water (TBW)
60%
TBW is highest in
newborns and adult males
TBW is lowest in
adult females and adults with large amounts of adipose tissue
ICF comprises how much of TBW
2/3
Major cations of ICF
K+ and Mg2+
Major anions of ICF
protein and organic phosphates
ECF comprises how much of TBW
1/3
ECF is composed of
interstitial fluid and plasma
Major cation of ECF
Na+
Major anions of ECF
Cl- and HCO3-
How much of ECF is plasma?
1/4
How much of ECF is interstitial fluid?
3/4
An ultrafiltrate of plasma (has little protein)
interstitial fluid, bowman space
Steady state Osmolarities of ECF and ICF
Equal (about 295 mOsm/Kg water)
How equality of Concentration between compartments is achieved?
Water shifts (first response). Volume compartments change. Increase in ECF volume; decrease in hematocrit Decrease in ECF volume; increase in hematocrit Increase in ECF volume, ECF Osmolarity, serum Na+ conc.; decrease in ICF volume, Hct decreased
Isomotic volume expansion Isomotic volume contraction Hyperosmotic volume expansion
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Hyperosmotic volume contraction Hypoosmotic volume expansion Hypoosmotic volume contraction Clearance Clearance equation
Increase in ECF osmolarity, serum Na+ conc.; decrease in ECF volume, ICF volume, Hct aprox. = Increase in ECF volume, ICF volume; decrease in ECF osmolarity, serum Na+, Hct aprox. = Increase in ICF volume and Hct; decrease in ECF volume, ECF osmolarity, serum Na+ volume of plasma cleared of a substance per unit time đ?‘ˆâˆ—đ?‘‰ đ??ś= đ?‘ƒ
RBF is what percent of cardiac output
25%
RBF is directly proportional to
Pressure difference between renal artery and renal vein
RBF is inversely proportional to
Resistance of the renal vasculature
Vasoconstriction of renal arterioles (both) does this
Decrease RBF
Causes vasoconstriction
Sympathetic nervous system and angiotensin II
At low concentrations angiotensin II preferentially constricts
Efferent arterioles
Constriction of efferent arterioles
increases GFR
ACE inhibitors
Dilate efferent arterioles, reduce hyperfiltration and occurrence of diabetic nephropathy
Vasodilation of renal arterioles does this
Increase RBF
Reduce vasodilation
Prostaglandins E2 and I2, bradykinin, nitric oxide, dopamine
How RBF is maintained
Changing renal vascular resistance
Range of blood pressures in which RBF remains constant
80-200 mmHg
Myogenic mechanism Tuboglomerular feedback
Renal afferent arterioles contract in response to stretch Macula densa sense increased Na+ load and cause constriction of afferent arterioles
Used to measure RPF
Clearance of PAH
PAH is
Para-aminohippuric acid
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PAH underestimates RBF by
10%
Measurement of RBF Used to measure GFR
đ?‘…đ??ľđ??š = Clearance of Inulin
đ??şđ??šđ?‘… đ?‘…đ?‘ƒđ??š
Filtration fraction (FF) Normal filtration fraction If filtration fraction increases If filtration fraction decreases Glomerular hydrostatic pressure
đ?‘…đ?‘ƒđ??š 1 − đ??ťđ?‘?đ?‘Ą
0.2 Protein concentration in blood in peritubular capillaries increases and reabsorption increases in the proximal tubule Protein concentration in blood in the peritubuar capillaries decreases and reabsorption decreases in the proximal tubule Increased by dilation of afferent arterioles and/or constriction of efferent arterioles
Increase in glomerular hydrostatic pressure causes
Increase in GFR
GFR equation
GFR=Kf[(Pgc-Pbs)-(PIgc-PIbs)]
Filtered load
GFR*[Plasma]
Excretion rate
[Urine]*V
Reabsorption Rate
Filtered load - Excretion rate
Secretion rate
Excretion rate - Filtered load
Reabsorbs glucose from tubular fluid into blood Reabsorptive rate at which the carriers are saturated Tm for glucose (no reabsorption)
Na+-glucose cotransport in the proximal tubule Maximum Transport (Tm), Tubular maximum “reabsorption� 350 mg/dl
Plasma concentration at which glucose first Threshold appears in the urine Threshold for glucose
250 mg/dl
Region between threshold and Tm
Splay
Where secretion of PAH occurs
Proximal tubule
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Substances with highest clearances
Filtered and Secreted
Substances with lowest clearances
Not Filtered or Completely Reabsorbed
Substances with clearance equal to GFR
Freely filtered but not reabsorbed or secreted đ??śđ?‘Ľ đ??şđ??šđ?‘…
Clearance Ratio Na+ is removed here How much Na+ is reabsorbed in the proximal tubule? Na+ is reabsorbed in early proximal tubule with
Along Entire Nephron 67% (aprox.) Glucose, Phosphate, Amino acids, and Lactate
via cotransport with Na+ is reabsorbed in early proximal tubule via countertransport with
H+
Acetazolamide
Carbonic Anydrase Inhibitor
Na+ is reabsorbed in late proximal tubule via cotransport with
Cl-
Glomerulotubular Balance ECF volume contraction causes ECF volume expansion causes How much Na+ is reabsorbed in thick ascending limb of loop of Henle Mechanism of Na+ reabsorption in thick ascending limb
Constant fractional reabsorption of Na+ and H2O Increase in proximal tubular reabsorption Decrease in proximal tubular reabsorption 15-25% Na+-K+-2Cl- cotransporter
Loop diuretics inhibit
Na+-K+-2Cl- cotransporter
Furosemide
Loop Diuretic
Ethacrynic acid
Loop Diuretic
Bumetanide
Loop Diuretic
True or false: False Thick ascending limb is permeable to water Potential (electrical) difference in thick Lumen-Positive potential difference ascending limb
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How much of Na+ is reabsorbed in the distal tubule and collecting duct?
8%
Reabsorption of Na+ in early distal tubule
Na+ - Cl- cotransporter
Thiazide Diuretics Inhibit
Na+ - Cl- cotransporter in early distal tubule
True or false: early distal tubule is impermeable to water Two cell types in late distal tubule and collecting duct
True Principal cells and Alpha-Intercalated cells
Principal cell reabsorb
Na+ and H2O
Principal cells secrete
K+
Effect of aldosterone on principal cells
increase Na+ reabsorption and K+ secretion
Effect of ADH on principal cells
increase H2O permeability
K+-sparing diuretics
Decrease K+ secretion by Principal cells DT
Spironolactone
K+- Sparing Diuretic
Triamterene
K+- Sparing Diuretic
Amiloride
K+ - Sparing Diuretic
Alpha-Intercalated Cells Secrete
H+
Alpha-Intercalated Cells Reabsorb
K+ via H+/ K+- ATPase
Effect of Aldosterone on alpha-intercalated cells
Increase H+ secretion
Location of most of body's K+
ICF
Shift of K+ out of cells causes
Hyperkalemia
Shift of K+ into cells causes
Hypokalemia
When K+ excretion equals K+ dietary intake K+ balance Filtration of K+
Occurs Freely
How much K+ is reabsorbed across Proximal Tubule
67%
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How much K+ is reabsorbed across Thick Ascending Limb Reabsorption of K+ in thick ascending limb is done via Action of K+ in Distal Tubule and Collecting Duct Hyperaldosteronism Hypoalsosteronism
20% Na+-K+-2Cl- cotransporter Either Secreted or Reabsorbed Increases K+ secretion and causes Hypokalemia Decreases K+ secretion and causes Hyperkalemia
Effect of acidosis on K+ secretion
Decreases
Effect of alkalosis on K+ secretion
Increases
Effect of thiazide and loop diuretics on K+ secretion Effect of excess of anions in the lumen on K+ secretion How much of the filtered urea is reabsorbed in Proximal Tubule? Impermeable to Urea Effect of ADH on Urea How does urea excretion vary with urine flow rate? How much of phosphate is reabsorbed in the proximal tubule? How is phophate reabsorbed in proximal tubule? True or false: distal segments do not reabsorb phosphate Effect of PTH on phosphate Reabsorption How much of plasma Ca++ is filtered across glomerular capillaries? How much of filtered Ca++ is reabsorbed in Proximal Tubule and Thick Ascending Limb? Effect of Loop Diuretics on Ca++ Reabsorption How much of filtered Ca++ is reabsorbed in the Distal Tubule and Collecting Ducts? Effect of Thiazide Diuretics on Ca++ Reabsorption
Increases Increases 50% Distal Tubule, Cortical and Outer Medullary Collecting Ducts Increases Permeability in Inner Medullary Collecting Ducts Inversely 85% Via Na+- Phosphate cotransport True Inhibits 60% 90% Inhibits 8% Increases
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Where is Mg++ Reabsorbed? Where do Mg++ and Ca++ compete for Reabsorption What happens to urine when ADH levels are high? Effect of ADH on NaCl Reabsorption in Thick Ascending Limb
Proximal Tubule (PT), Thick Ascending Limb (TAL), Distal Tubule (DT) Thick Ascending Limb (TAL) Becomes Concentrated Increases