Session 2 pierce Flashcards
what are the three layers of the glomerular filtration barrier, and what is the sizes that allow for things to filter through
Capillary endothelium
Glomerular basement membrane
Podocyte epithelium
molecules less than 20 A are freely filtered
molecules greater than 42 are not filtered
anything inbetween may or may not be filtered
what is the glycocalyx and what is its function with filtration, what happens if this is lost
glomerular endothelium that forms a sticky biogel in the endothelial lumen that helps with filtration
-made of glycoproteins that alter filtration based on charge (negative)
it enhances filtration of cationic dextrans
decreases filterabillity of anionic dextrans
Nephrotoxic serum nephritis will destroy the glycocalyx leading to increased filtration of anions (proteins)
what is freely filtered and what is not freely filtered
Freely filtered:
- water
- small solutes, glucose, amino acids, electrolytes
- concentrations equal on both sides of the membrane
Not freely filtered:
- Large molecules (proteins)
- formed elements (cells)
- Miniscule amounts of protein are filtered
equation for urinary excretion
Urinary excretion = amount filtered - amount reabsorbed + amount secreted
Ue = F + S - R
use this equation determine any number of theses
what is the significance of what goes into the kidney must come out, eqation
the arterial input into the kidney = the venous output out of the kidney + the urine output
X in artery = X in vein + X in ureter
What is the urine excretion rate of x and what does each variable mean
x = Ux times V
Ux = the concentration of that substance in the urine
V = Urine flow rate, the rate at which urine is produced. Dependant on fluid intake and fluid homeostasis. Normally if fluid intake is increased, urine flow will increase
what is renal clearance
The rate at which substances are removed or cleared from plasma
-Renal clearance means the rate of removal by the kidneys
Renal clearance (C) is the volume of plasma completely cleared of a substance by the kidneys per unit of time
Renal clearance is the ratio of urinary excretion (Ux times V) to plasma concentration (Px)
units are volume per unit time
clearance is a flow rate removed from the blood
what is the equation for renal clearance
Cx = (Ux times V)/Px
clearance of a substance = concentration of X in urine times the urine flow rate divided by the concentration of X in the plasma
what is Glomerular filtrate
(GF) volume of plasma filtered into the combined nephrons of both kidneys per unit of time
The fluid filtered across the glomerular capillaries into bowmans space
- protein free
- cell free
- similar to plasma (plasma ultrafiltrate), isosmotic to the plasma
- 20 % of the RBF or RPF
what is the glomerular filtration rate
roughly 20 percent of RBF
- Balance of starling forces (hydrostatic and oncotic forces
- Capillary filtration coefficient (Kf): Permeabillity x surface area
-Averages 125 mL/day
FF = GFR/RPF
FF is normally 20 percent
what percentage of the RPF is normally absorbed
99 percent
what is the filtration fraction
The fraction RPF that is filtered across the glomerulus
- changes with ultrafiltration pressure
- influenced by blood pressure
as FF increases the oncotic pressure of the efferent arteriole increases, to facilitate reabsorption of tubular fluid
- this is because as more solution is being filtered out it leaves more concentrataed stuff behind
- this will increase the oncotic pressure in the efferent arteriole as we move down the arteriole
how is filtered load and filtration fraction not the same? what is the equation for filtered load
Filtered load is a rate in mg/min
filtration fraction is the ratio of the GFR/RBF
Filtered load = GFR times Px
how to determine the percentage of the filtered load of something reabsorbed per day and what are the variables at play
Filtered load = GFR times Px
Reabsorption = Filtered load - excretion
Ecretion = V times the Ux
variables:
- GFR
- PLasma concentration
- Urine concentration
- Urine flow rate
when can we use renal clearance to estimate GFR and what are the conditions
Filtered amount = excreted amount
that would mean GFR = Ux times V divided by Px
(equation for clearance but with GFR)
GFR is directly proportional to renal clearance if:
- substance must be freely filtered into glomeruli
- must be neither absorbed or secreted by renal tubules
- not be synthesized or broken down or accumulate in kidney
- must be physiologically inert (not toxic and without effect on renal function)
Examples of substance that can be used to calculate GFR and meets the clearance conditions
Inulin, amount excreted is equal to amount filtered
Creatinine
- dependant on age and muscle mass
- however small amount approximately 10 percent of creatinine is secreted)
- not quite ideal
What are the three main ways sympathetics increase Bloodpressure via kidneys, the cells they function on, and their receptors
Arterial resistance
- vasoconstriction
- alpha 1
JG cells
- renin release + RAAS
- B1
Na-K-ATPase
- increased Na+ reabsorption
- alpha 1
what are the forces causing filtration by the glomerular capillaries
Starlings equation
Forces favoring filtration:
- Pgc
- nBC
Forces opposing filtration:
- Pbc
- ngc
net is positive = filtration
net is negative = no filtration
what are the three physical factors that contribute to GFR
-Hydraulic conductivity (permeabillity of the fenestrated endothelium) Lp
-Surface area for filtration
(Lp x Sf) = ultrafiltration coefficient Kf
-Capillary ultrafiltration pressure Puf
GFR = Kf x Puf
how to calculate the ultrafiltration pressure (Puf) and how does it change
Puf = Pgc - Pbc - ngc (starlings equation)
nbc = oncotic pressure in bowmans capsule is normally 0 Pgc = Hydrostatic pressure in gc Pbc = HYdrostatic pressure in bowmans capsule ngc = oncotic pressure in glomerular capillary
the Pgc can change based on
- Renal arterial blood ressure
- afferent arteriolar resistance
- efferent arteriolar resistance
What determines the Ultrafiltration coefficient (kf)
Hydraulic conductivity x Surface area = Kf
damage to kidney can effect the surface area and permeabillity
Glomerular mesangial cells can affect the surface area by contracting to decrease the SA or relaxing to increase SA
where are the changes of hydrostatic pressures in the renal vasculature
Renal artery = high
Afferent arteriole = steep drop
glomerular capillary = relatively high pressure but is maintained throughout
-helps to filter more fluid
Efferent arteriole: steep drop
Pgc, GFR, and RBF when vasoconstriction of the afferent arteriole
Pgc: decrease
GFR: decrease
RBF: decrease
Pgc, GFR, and RBF when vasoconstriction of the efferent arteriole
Pgc: increase
GFR: increase
RBF: decrease
Pgc, GFR, and RBF when vasodilate the efferent arteriole
Pgc: decrease
GFR: decrease
RBF: increase
Pgc, GFR, and RBF when vasodilate the afferent arteriole
Pgc: increase
GFR: increase
RBF: increase
what are some vasoconstrictors
sympathetics (catecholamines)
-more alpha 1 on afferent arteriole than efferent
endothelin
ATP/adenosine
Angiotensin II
-primarily constricts the efferent arteriole which raises GFR
what are some vasodilators
- prostaglandins
- Brdykinin
- Nitric oxide
- Dopamine
- Atral natriuretic peptide
- Ace inhibitor (tends to lower GFR)
Mechanisms of Glomerulartubular balance
Increase reabsorption rate within the renal tubules when GFR rises (kidney compensates)
- Change in pressure in the efferent arteriole leads to an increase in GFR leaving more filtered at glomerulus, higher oncotic presssure in the efferent arteriole and peritubular capillary (PTC) (this promotes Na+ reabsorption)
- Increased delivery of solutes to proximal tubule leads to an increase reabsorption of Na+ due to the lots of solutes
- also with increased GFR there is an increase shear due to fluid flow that the apical microvilli will upregulate apical sodium transporters to increase Na absorption
what are the two Autoregulation methods of the Kidney via the RBF and the GFR
Local reflex: between vascular smooth muscle cells (myogenic reflex)
- blood vessels resist stretch during periods of high blood pressure
- calcium signaling
- Afferent arteriolar constriction and efferent arteriolar dilation
Tubuloglomerular feedback
- Juxtaglomerular apparatus (macula densa cells, juxtaglomerular cells and extraglomerular mesangial cells
- senses tubular Na+ concentration
- signals between the macula densa and JG cells to maintain constant Na delivery to the distal tubule and constant gfr
- renin release
when does the macula densa signal
increase delivery of NaCl to macula densa
- Increase ATP/adenosine
- vasoconstricts afferent arteriole
- decrease GFR
summary of the Tubuloglomerular feedback
Macula densa senses NaCl
- JG cells secrete renin
- mesangial cell will transduce the message
What is fractional excretion
what percentage of whatever has been filtered actually gets excreted
FEx = Amount x excreted/amount of X filtered
FEx = ((Ux)(V))/((Px)(GFR))
FEx = ((Ux)(Pcr))/((Px)(Ucr)) (clearance of creatinine
FEx will be lower than 100 percent if reabsorption occurs
FEx will be higher than 100 percent if secretion occurs
