filtration & clearance (6) Flashcards
define “glomerular filtration”
“the process by which plasma is filtered across the glomerular capillaries to form a protein free ultrafiltrate in bowman’s space”
what is the first step in urine formation?
separation of an ultrafiltrate at the glomerulus
what drives the net efflux of plasma ultrafiltrate
Differences in oncotic & hydrostatic pressure (starling forces) across the glomerular capillaries
what is the approx GFR in a human in ml/min?
what is the GFR in L/day?
125 mL/min
180 L/day
how often can the entire ECF be recycled through the kidneys?
every 2 hours
what is greater: the filtration coefficient in the glomerular capillaries or the systemic capillaries
the glomerular filtration coefficient is 200x greater than the coefficient in the systemic capillaries
what is something unique tot he glomerular capillaries that is not seen in the systemic capillaries
This small decrease in pressure occurs from the beginning of the capillary to the end despite a decrease in plasma volume and is due to post capillary efferent arteriole constriction
what are the 2 reasons that oncotic pressure increases along the length of the glomerular capillary?
due to plasma filtration
and due to plasma protein concentration
what would cause the oncotic pressure of bowman’s capsule to increase?
nephritic syndrome
what are the 3 barriers that the ultrafiltrated has to cross to get into bowman’s space?
- the endothelial cells of the glomerular capillaries
- capillary basement membrane
- the podocytes on the visceral epithelial layer
what two barriers will block anion filtration?
the capillary basement membrane and the capillary podocytes
what are 4 examples of “freely filterable solutes”
water, NaCl, glucose and inulin
how much of person’s blood goes to the kidenys?
20%
how much of renal blood flow is renal plasma flow?
about 55%
how can filtration rate be determined?
GFR/RPF
what range should urine output be in?
1 ml/min to 10 ml/min
at what level of plasma flow does GFR reach its maximum?
at 600 ml/min
tell me about what results from an increase in plasma flow through the glomeruli
- increase in surface area of the glomerular capillaries
- filtration of the plasma increases until all the glomerular surface area is filtering plasma and a maximal rate of glomerular filtration is achieved
if the renal blood flow is decreased to zero, how much is the kidney able to filter
NONE. come on ppl- gotta know this
what is the result of afferent arteriolar constriction?
decrease in RPF
decrease in glomerular capillary hydrostatic pressure
when is the surface area of glomerular capillary mediating filtration depend on flow?
at low renal plasma filtration levels
what is the result of efferent arteriolar constrictin?
decrease in RPF
increase in glomerular capillary hydrostatic pressure
what value can provide an index of the number of functioning nephrons in the kidneys?
GFR
at what GFR does renal failure begin at?
20 ml/ min
loss of 85% of the nephrons
what is the “renal clearance” of a substance?
virtual volume of plasma from which a solute is completely removed from the plasma by the kidney per unit time
renal clearance of a solute can be used to measure the GFR if what 4 properties are present
- Freely filtered at the glomerulus
- Not reabsorbed in any segment of the nephrons
- Not secreted in any segment of the nephrons
- Not synthesized by the kidney (not metabolized by the kidney)
what is the exogenous solute used to measure GFR?
inulin
what is the endogenous solute used to measure GFR?
creatinine
what is inulin?
- inulin is a fructose polymer
- given via IV infusion to maintain constant plasma (inulin) and measured very accurately in plasma & urine
what is a normal creatinine plasma level?
1 mg/ 100 mL
what does it mean if the creatine level is higher than normal?
that the creatinine clearance is going down and could indicate renal failure
what does it mean if a solute has a clearance ratio to inulin that is less than 1?
means that the concentration of that solute in the urine is less than that in the plasma
means that the solute is being reabsorbed
what does it mean if a solute has a clearance ratio to inulin that is greater than 1?
means that the solute is being secreted in addition to being filtered in the kidneys
define the fractional excretion of water
The fraction of the glomerular filtrate NOT absorbed from the tubular fluid along the nephrons and therefore appearing as urine
how can fractional excretion of water be estimated?
from plasma to urine inulin concentration ratio
what % of filtered water is excreted in the urine if there is a 100x more concentration level of inulin in the urine over plasma
1%
what is the fractional excretion of water in a time of dehydration?
less than 1 %
in L/min, what is renal blood flow
1.2 L/min
describe the importance of autonomic innervations in kidney auto-regulation
tricked ya! autonomic innervations are not important and kidney auto-regulation can still occur in their absence.
auto-regulation is considered “intrinsic” to the kidneys
what cells provide tubuloglomerular feedback? what are they sensing?
macula densa cells sensing an increase or decrease in GFR to cause an increase/decrease in resistance (constriction) of an afferent arteriole to return GFR levels to normal
