lecture 32 - renal / urinary physiology Flashcards
what is freely filtered through the filtration barrier
small substances (mostly everything), not large substances (like haemoglobin and albumin)
what is renal blood flow equal to
20% of cardiac output
why is renal blood flow high
for filtration
what are the two types of driving forces and their directions
- hydrostatic pressures = due to volume of fluid, pushes fluid away
- colloid osmotic pressures = due to protein, pulls fluid towards
what does positive pressure favour
filtration
what does negative pressure oppose
filtration
what is glomeruluar hydrostatic pressure
blood pressure = favouring filtration, 50+mmHg
what is blood colloid osmotic pressure
albumin = trying to pull fluid from capsule back into blood, -25mmHg
what is capsular hydrostatic pressure
pressure of filtrate already present = trying to push fluid from capsule into the blood, -15 mmHg
what is the capsular colloid osmotic pressure
no protein in capsular space = 0 mmHg
what is net filtration pressure usually equal to
10 mmHg
what is filtration fraction
how much of the kidneys plasma flow is filtered
what is the filtration fraction equation
glomerular filtration / renal plasma flow
how much of renal plasma is filtered
20%
what is the glomerular filtration rate
the amount of plasma filtered per unit time by the kidneys
what is the glomerular filtration rate normally per day and per minute
180L/day and 125ml/minute
what is the renal filtered load
the amount of a particular substance filtered per unit time
what is the equation of the filtered load
glomerular filtration rate x solute plasma concentration
what is renal clearance
the volume (ml) of plasma that is cleared of a substance by the kidneys per unit time
what can clearance be used for
- quantify how a substance is handled by the kidneys
- estimate glomerular filtration rate
is creatinine and inulin filtered, secreted, reabsorbed, excreted ?
- freely filtered
- not secreted
- not reabsorbed
- all filtered is excreted in urine
what is the clearance of creatinine equal to
volume of plasma filtered per minute (GFR)
is medications and toxins (e.g PAH) filtered, secreted, reabsorbed, excreted ?
- freely filtered
- entirely secreted
- not reabsorbed
- all in blood is excreted in urine
what is the clearance of PAH
volume of plasma flowing through the kidneys per minute
is glucose filtered, secreted, reabsorbed, excreted ?
- freely filtered
- not secreted
- FULLY reabsorbed in proximal tubule
- NONE excreted in urine
what is the clearance of glucose
no plasma is cleared of glucose
is sodium filtered, secreted, reabsorbed, excreted ?
- freely filtered
- not secreted
- almost fully reabsorbed in most parts of the nephron
- small amount excreted in urine
what is the clearance of sodium
very small volume of plasma per minute
what is the clearance equation
concentration of X in urine x volume of urine produced per unit time / concentration of X in plasma
to estimate GFR a substance must be ……
- freely filtered
- not reabsorbed from the tubule
- not be secreted into the tubule
what substances can be used to estimate GFR and what is the more common one
inulin and creatinine
- creatinine most common because already found in the body
if both kidneys are working what will the creatinine levels be like
low in the plasma
if kidneys ability to clear products reduces then what will the creatinine levels in the plasma be like
increase
