Renal Phys Flashcards
What’s the 60/40/20 rule?
Total body water is 60% of body weight (42L).
ICF is 40% of body weight. (28L)
ECF is 20% of body weight. (14L)
What portion of total body weight is intravascular/total blood volume?
7% (~5L)
How is the ECF divided between plasma and interstitial fluid?
plasma is 25% of ECF (3L)
interstitial fluid is 75% of ECF (11L)
Does total body fluid increase or decrease with age?
Decreases (from 75% in neonate to 50% in old age)
Do adult men or women have a higher total body fluid volume %?
Men; women have more fat and therefore less water
What’s the average osmolarity of body fluids? Do ICF and ECF have the same?
~300mOsm/L; ECF and ICF have about the same osmolarity but solute composition is different
What’s a normal GFR?
125mL/min
What percentage of the CO perfuses the kidneys?
20%
What ion determines the ECF volume?
Na
If the ECF volume expands, how does the kidney respond to correct it?
increase output of sodium and water in the urine by decreasing reabsorption
What does it mean to be in sodium balance?
dietary intake and urinary output are equal
Are the following causes of edema via increased hydrostatic or decreased oncotic pressures? congestive heart failure, liver disease, nephrotic syndrome, pulmonary edema
CHF, pulm edema - inc hydrostatic
liver, kidney - dec oncotic
In the renal handling formula, Excretion =
Filtration - Reabsorption + Secretion
What happens to sodium in the proximal tubule?
about 66% is reabsorbed isosmostically with water
What percentage of filtered sodium is reabsorbed in the loop of Henle?
25%
The ascending limb of the loop of Henle is impermeable to water and resorbs solutes in excess of water. This dilutes the tubular fluid to what approximate osmolarity?
~100mOsm/L
Why is it important that water not be reabsorbed in the loop of Henle?
allows urine to be diluted in relation to plasma; sets up the concentration gradient in the medulla that allows for urine concentrating when volume depleted
What happens with sodium and water in the distal tubule?
~6% Na reabsorbed in early distal tubule; late distal tubule regulated by aldosterone
early distal tubule impermeable to water and helps dilute tubular fluid further; late distal tubule controlled by ADH
Why is the functioning of the collecting duct important?
sensitive to ADH and travels through the medulla allowing the kidney to reabsorb water to defend against ECF contraction
What fraction of plasma is filtered to form the ultra filtrate? How is this determined?
20%; ration of GFR/RPF (RPF = renal plasma flow)
How frequently is the entire ECF of a 70kg adult seen by the kidney?
entire ECF is filtered every 2 hours
How can GFR be approximated using lab values?
GFR = Cin (clearance of inulin) = UV/P
U - conc in urine
V - urine flow rate
P - plasma conc
How can the fractional excretion of water be estimated?
V/GFR = Pin / Uin
creatinine is a good surrogate for inulin
How is the fractional excretion of any substance estimated?
FEx = (UxPcreat) / (UcreatPx)
