Body Fluids, Clearance and Glomerular Hemodynamics Flashcards
what contains the ICF
- blood cells
- cells
what comprises the ECF
- interstitial fluid
- plasma (serum)
adult male is composed of what percent water
- 60%
adult female is composed of what percent water
- 50%
formula for total body water
- body weight x fraction of body water
how much of the total body water is extracellular fluid
- 1/3
how much of the total body water is intracellular fluid
- 2/3
how much of the extracellular fluid is interstitial fluid
- 3/4
how much of the extracellular fluid is plasma
- 1/4
how much of the blood volume is hematocrit
- 45%
what are the major ions in ECF
- Na+ and Cl-
is the major intracellular cation
- K+
what are the major intracellular anions
- organic ions
- Pi
protein concentration of plasma versus ECF
- plasma has higher protein
concentration of osmolarity
- mOsm/L
concentration of osmolality
- mOsm/kg
what is tonicity (effective osmolality)
- osmolality of solutes that do not freely cross the cell membrane
osmolality of ICF and ECF
- 275-295 mOsm
ECF shows transient changes in osmolality and tonicity due to
- alterations in salt and water intake
calculation of total osmolality
- total osm = 2 x Na + glucose/18 + BUN/2.8 + EtOH/3.7
calculation of toxicity or effective osmolality
- 2 x Na + glucose/18
formula for net excretion
excretion = filtration + secretion - reabsorption
normal GFR for males
120 +/- 25 ml/min
what is GFR
- rate at which plasma is filtered at glomerulus
normal GFR for females
95 +/- 25 ml/min
GFR is approximately what percent of renal plasma flow
- 20%
GFR with age
- declines
GFR with disease
- increases or decreases
average renal blood flow
- 1000 ml/min
formula for renal plasma flow
RPF= RBF (renal blood flow) x (1-hematocrit)
definition of urine flow (V)
units
- volume of urine excreted per unit time
- ml/min or L/24 hr
average amount of urine flow
500 mL
18L/day
formula for filtered load
filtered load =GFR x P
GFR x plasma concentration
formula for excreted load
excreted load =V x U
urine flow x urine concentration
formula for reabsorption
filtered load - excreted load
formula for secretion
excreted load - filtered load
what is clearance
units
- volume of plasma completely cleared of a substance per unit time
- ml/min
clearance formula
(VxU)/P
excreted load/plasma concentration
clearance formula requires
- steady state concentration
what does it mean when the clearance rate is 0
- substance is not filtered or secreted so none appears in the urine
- substance is freely filtered but is completely reabsorbed so none appears in the urine
when does clearance = GFR
- if everything that is filtered gets excreted, then mLs of plasma cleared = mLs filtered (GFR)
when does clearance = GFR
- solute is freely filtered
- solute is not reabsorbed
- solute is not secreted
- solute is not metabolized
formula for when filtered load = excreted load
GFR x P = V x U
GFR x plasma concentration = excreted load
creatinine clearance requires what for collection
- one or two samples
- 24h urine collection
formula for creatinine clearance
Cl_Cr = (UxV)/P
plasma creatinine _________ in proportion to the decline in GFR
- increases
plasma creatinine when GFR decreases to half value - on first day
- no change in plasma creatinine
filtered load of creatinine (GFRxP_Cr) when GFR decreases to half value - on first day
- declines to half starting value because plasma creatinine is still the same
creatinine clearance when GFR decreases to half value - on first day
- decreased because excreted load is half normal
plasma creatinine when GFR decreases to half value - on day 4
- doubled due to initial fall in filtered and excreted load
filtered load of when GFR decreases to half value - on day 4
- now back to normal
what is renal plasma flow?
renal plasma flow is estimated using
- plasma cleared of solute in one pass through the kidney
- para-amino hippuric acid (PAH)
how much of the para-amino hippuric acid is excreted
what is the maximum clearance you can have?
- 90% excreted in one pass
- plasma flow
clearance of PAH is equal to
90% of renal plasma flow
the extraction ratio of PAH is equal to
0.9
formula for filtration fraction
FF = GFR/RPF
glomerular filtration rate/renal plasma flow
what is being filtered versus what is continuing on into the rest of the kidney
what is the usual value of filtration fraction
- 20%
glomerular ultrafiltration depends upon
- special anatomic properties of filtration barrier
- high hydrostatic pressure in glomerular capillaries
glomerular filtration filters based on
- size and charge
are blood cells filtered in glomerulus
why
- no
- they are too big
what is the size of molecules that can pass through the filtration barrier?
<40 angstroms
what charge of molecules can pass through filtration barrier
why
- positively and neutrally charged
- basement membrane is negatively charged
are albumin and other plasma proteins filtered by the healthy kidney
- no
GFR starling forces
GFR = Kf (PGC-PBS)-(πGC-πBS)
PGC = hydrostatic pressure in glomerular capillaries PBS= hydrostatic pressure in interstitium (bowman's space) Kf = filtration coefficient πGC = osmotic pressure in plasma πBS = osmotic pressure in interstitium
GOOD COCK WITHOUT THE BULLSHIT
what is the normal value of πBS
- 0
which reins higher in glomerular capillaries - PGC or oncotic pressure?
why?
- PGC
- favors filtration
effect on COP due to loss of protein free fluid
- COP increases
angiotensin II release in hypovolemia
result
- increases
- efferent arteriole constriction
filtration rate in hypovolemia
- increases
THIS IS COUNTERINTUITIVE
colloid oncotic pressure in hypovolemia
result
- increases
- drives reabsorption of what you have filtered
proximal reabsorption in hypovolemia
- increases
angiotensin II release in hypervolemia
result
- decreases
- efferent arteriole dilation
filtration rate in hypervolemia
- decreases
colloid oncotic pressure in hypervolemia
- decreases
proximal reabsorption in hypervolemia
- decreases
diabetes insipidus is a disorder of
- ADH
result of diabetes insipidus
- unable to concentrate urine
- large volume of dilute urine
renal plasma flow in regard to PAH formula
clearance PAH/extraction ratio
if Cx < GFR
- net tubular absorption of X
if Cx>GFR
- net tubular secretion of X
RPF of para-amino hippuric acid (PHA) formula
RPF=(UxV)/(P) / extraction ratio
extraction ratio = 0.9
GFR over differences in mean arterial pressure
- doesn’t change
RAAS process in response to low BP
- BP drops so hydrostatic pressure goes down
- stretch on afferent arteriole goes down which releases renin
- sympathetic system releases renin
- deliver low Na+ and Cl- distally and that causes renin release
- increases angiotensin II production and aldosterone production
- angiotensin II causes efferent arteriole vasoconstriction
- fluid will back up in the glomerular capillary
what releases renin
- smooth muscle cells in afferent arteriole of JG apparatus
Afferent Constriction:
predict
GFR, RPF, FF
GFR: decreased
RPF: decreased
FF: same
Efferent constriction
predict
GFR, RPF, FF
GFR: increases
RPF: decreases
FF: increases
Afferent dilation
predict
GFR, RPF, FF
GFR: increases
RPF: increases
FF: same
Efferent dilation
predict
GFR, RPF, FF
GFR: decreases
RPF: increases
FF: decreases
Increased serum protein
predict
GFR, RPF, FF
GFR: decreases
RPF: same
FF: decreases
Urinary obstruction
predict
GFR, RPF, FF
GFR: decreases
RPF: same
FF: decreases
Angiotensin blockade
predict
GFR, RPF, FF
GFR: decreases
RPF: increases
FF: decreases
Angiotensin blockade same as efferent dilation
NSAIDs
predict
GFR, RPF, FF
GFR: decreases
RPF: decreases
FF: same
NSAIDs effect same as afferent constriction
