Renal and Formulas Flashcards
Clearance Formula
Cx = Ux * V/Px
Clearance = Urine Concentration x Flow rate/Plasma Concentration
Filtered Load Formula
Filtered load = GFR * Px
Glomerular Filtration Rate x Plasma concentration
Ohm’s Law
Q = DeltaP/R
Flow Rate = Pressure Change / Radius
Ultrafiltration Pressure Definition
Net Filtration Pressure of Glomerulus, caused by oncotic and hydrostatic pressure differences across the filtration membrane.
Ultrafiltration Pressure Formula
UP = (Pgc + πbs) - (Pas + πgc)
Filtration pressure is the difference between the sum of the glomerular capillaries’ hydrostatic pressure and the oncotic pressure of the filtrate (pressure pushing out of the capillaries and pulling into the capule) and the filtrate hydrostatic pressure (pushing back into the capillaries) and glomerular capillaries oncotic pressure (pulling back into the capillaries)
Compliance Equation
Compliance = ΔV / ΔP - Change in volume per change in pressure.
Dalton’s law of partial pressures
Px = Pb * F
Partial pressure of x in a mixed gas = the pressure of the gas * the fraction of the mixture that gas makes up.
Relationship between GFR and ultrafiltration pressure (UP)
GFR = UP * Kf (ultrafiltration coefficient)
Fractional excretion relationship
FE = (Ux * V) / (Px * GFR)
Fractional Excretion = (urinary concentration x urine flow rate) / (Plasma concentration * GFR)
Relationship between dead space, tidal volume, and alveolar ventilation
Va = (Vt - Vd) * RR
Alveolar ventilation = (Tidal Volume - Dead Space) * Respiratory Rate
Alveolar Gas equation - Arterial Oxygen pressure = ?
PAO2 = FIO2(PB-PH20) - PACO2
Pressure of Arterial O2 = Fraction of Inspired 02 * (Barometric Pressure - Partial Pressure of H20) - Pressure of Arterial CO2
Laplace’s Law
P = 2T/r
Collapsing pressure is inversely proportional to radius, meaning that small alveoli are harder to open than large ones.
Relationship between flow, pressure, and radius (Poiseuille’s Law)
Q = (Π* ΔP * r^4) / (8nL)
Big picture - as radius increases, flow increases by a factor of 4.
Fick’s Law of Diffusion
V = (AD (P1-P2)) / Δ x
Flow rate = area x diffusion coeffecient x pressure difference / thickness
High renin level effects on glomerulus
ATII constricts Afferent Arteriole, leading to decreased GFR
Low renin level effect on glomerulus
ATII dilates Afferent arteriole, leading to increased GFR
Chemical signals that dilate the afferent arteriole
low ATII, prostaglandins, ANP, NO - anything that lowers BP basically.
Chemical signals that constrict the afferent arteriole
High ATII, NE, ADH - anything that raises BP.
Effects of charge and size on glomerular filtration
The filtration membrane is negatively charged, and the slits are very small, so bigger and more negatively charged molecules don’t go through, while smaller and more positively charged molecules cross more easily.
Determinants of GFR
Permeability, surface area, pressure
Myogenic regulation of GFR in response to increased BP
As BP rises, the smooth muscle of the afferent arteriole “pushes back” by contracting, causing a decrease in GFR. This happens quickly.
Tuboglomerular regulation of GFR in response to increased BP
As BP rises, the macula densa senses increased NaCl, and releases ATP. This becomes adenosine, which acts as a paracrine signal, causing increased intracellular calcium release and constriction in the afferent arteriole, leading to decreased GFR.
Sympathetic stimulation effect on afferent arteriole
constriction
Natriuretic Peptides - Function?
Released in response to sudden increase in BP, cause Afferent arteriole to dilate, increasing GFR. They also cause increased blood flow to the vasa recta, decreasing the osmolarity of the medulla and leading to more dilute urine to decrease volume.