deck_603758 Flashcards
Kidney excretion =
filtered + secreted - reabsorbed
Filtration Fraction =
GFR/RPF (about 1/5)
properties causing filtration at glomerulus ?
elevated capillary hydrostatic pressure more permeable capillary (glomerular cap’s)
cause of reabsorption in the peritubular capillary?
high osmotic pressure generated by filtration upstream, and a low hydrostatic pressure generated by high resistance in the efferent arteriole (upstream) lossof fluid due to filtration
fluid breakdown in body
60% total weight2/3 = ICF1/3 = ECF of which is 25% plasmaless in obese peoplemore in skinny males
Concentration =
M/V
Total Body Water markers
Tritiated water Deuterated water Antipyrine
Extracellular fluid markers
Inulin Mannitol radioactive Na
Plasma fluid markers
Evan’s Blue (T-1824) 125I albumin
Intracellular Volume =
TBW-ECF
renal clearance =
VOLUME of plasma completely cleared of X per unit time([Ux] x V) / [Px] Ux: urine concentration V: urine flow ratePx: plasma concentration
GFR estimated by:
inulin clearancealso creatinine clearance reflects GFR
RPF =
PAH clearanceAssumed 100% of PAH is voided from plasma through the kidney via filtration and secretionReality Only 90% of PAH is excreted, so PAH clearance = effective RPF… underestimate of true RPF
Assumption for inulin and GFR
inulin is: freely filtered, not reabsorbed, not secreted, not syn via kidney, not degraded by kidney, doesn’t alter kidney function
BUN/Pcr
indicates reason for abnormal serum creatinine and BUN<20:1 = dehydration/prerenal failure10:1 with elevated BUN and Pcr = intrinsic renal failure
FEna diagnostic purpose
Fractional Excretion of Na values for PR and ATN/ARF have little overlap… best for diagnostic differentiationPR –> low FEnaATN –> higher FEna
Plasma Osmolarity Estimation
2x[Na] + glucose/18 + BUN/2.8usually about 300mosm/kg
Effects on body volumes:Diarrhea
Diarrhea (isosmotic):- ECFICF and Osmolarity unchanged
Effects on body volumes:Water Deprivation
Water Deprivation (hyperosmotic):- Both ECF and ICF+ osmolarity
Effects on body volumes:Adrenal insufficiency
Adrenal insufficiency (Hyposmotic): - ECF and osmolarity+ ICF
Effects on body volumes:Infusion of Isotonic Na
Isotonic increase: + ECFUnchanged ICF and Osmolarity
Effects on body volumes:NaCl Intake
Hyperosmotic increase:+ ECF and Osmolarity- ICF
Effects on body volumes:SIADH/drinking lots of water
Hyposmotic increase:+ ECF and ICF- Osmolarity
GFR =
Kf x (Pc - Pbs - oncotic Pc) aka net filtration Pnet filtration usually 6mmhg (45 - 29 - 10)
Physiological Regulation of GFR
Pgc –> determined by BP and Resistance of afferent and efferent arterioles
Constriction of Afferent arteriole
- RPF- Pgc –> - GFRex) symp activation or high Angio II
Constriction of Efferent arteriole
-RPF+ Pgc –> +GFRex) low Angio II (efferent preference)
Renal Autoregulations
Maintain RPF during change in BP via afferent and efferent arteriole constrictionMyogenic mechanism –> afferenttubuloglomerular feedback –> afferentAngio II –> efferent
Renal Failure and types
diminished GFRPrerenalIntrinsicPostrenal
Prerenal failure
GFR falls due to compromised blood flow/pressure to kidneysex) dehydration, heart failure
Post renal failure
GFR falls due to obstruction downstream of kidney
Intrinsic Renal Failure
Decreased GFR from vascular occlusion (Pgc), glomerular damage (Kf), Tubular damage, Nephritis
Determinants of Protein Filtration
Size and ChargeIncrease size –> decrease filtrationmore - charge –> decrease filtration
Causes of Proteinuria
- loss of filter charge barrier2. loss of filter size barrier3. proximal tubule disfunction - less reabsorption4. Overload
Nephrotic Syndrome
Collection of diseases defined by proteinuria, hypoproteinemia, edema, hyperlipidemia
Proximal tubule
site of most reabsorption –> 2ndary pumps driven by primary Na-K pump. reabsorbs: Na, Glucose, AA’s, phosphate, lactate, early reabsorb of Na couple with HCO3- and late with Cl-
Proximal tubule secretion
secretes organic acids and bases2 non specific carriers: 1) Anion carrier 2) cation carrier
late proximal tubule
Primary reabsorption of NaCl driven by [Cl] gradient from lumen to blood.transcellular and paracellular transport
Glomerulotubular Balance
Increase GFR –> increase reabsorption (compensates for high GFR)driven by: peritubular oncotic pressure rise; Tubular hydrostatic P rise; Peritubular hydrostatic P decrease
Thin descending limb
permeable to water and relatively impermeable to ions –> H2O reabsorption
Thin ascending limb
impermeable to water; Na reabsorption passively