Physio 2 Flashcards
what exists in the same concentration in plasma and ultrafiltrate?
organic and inorganic anionic and cationic solutes
glomerular filtration rate (GFR)
125 ml/min or 180 L per day. filters entire ECF volume every 2 hours.
filtration rate formula
Kf[(Pgc-Pbs)-(piGC-piBS)]
Kf is the filtration coefficient of the glomerular capillary and is the product of capillary hydraulic conductivity and the surface area available for filtration. (Pgc-Pbs) is the difference in hydrostatic pressure inside the glomerular capillary and bowmans space. The pi is the difference in oncotic pressure in the same areas. O
how does Pgc change over the course of the glomerular capillary?
about 45-50 mmHg at the beginning and about 41-47mmHg at the end. decrease occurs despite a decrease of plasma volume, and is due to post capillary efferent arteriole constriction
changes in piGC over course of glomerular capillary
25 mmHg at the beginning and 35 mmHg at the end. due to plasma filtration and concentration of the plasma protein
glomerular barrier to filtration
endothelial cells of the glomerular capillaries restrict passage of cellular elements into bowmans space. capillary basement membrane restricts filtration of solutes larger than 1 kDa. an anionic charge favors filtration of cations and restricts filtration of anionic proteins. Podocytes of visceral epithelial layer of bowman’s capsule have foot processes covering capillaries. foot processes are separated by filtration slits where anionic charge further restricts filtration of anionic proteins, but not smaller organic/inorganic anions
what does removal of negative charge from the glomerular barrier do?
increases the passage of anions. this occurs in nephrotic serum nephritis
renal hemodynamics
GFR remains constant and the rate and volume of urine excretion varies according to the rate and volume of fluid consumed, which changes the volume and solute concentration of the ECF
what happens when RPF increases?>
GFR increases and filtration fraction decreases.
FF = GFR / RPF
fluid reabsorption in the post glomerular peritubular capillaries
starling forces drive reabsorption from the interstitial space into the peritubular capillaries. peritubular capillary oncotic pressure difference driving fluid absorption exceeds the peritubular capillary hydrostatic pressure difference opposing fluid absorption
pathway of fluid reabsorption
lumenal tubular fluid -> tubule cell -> interstitial fluid -> peritubular capillary plasma
what can measuring the GFR show?
can provide an index of the number of functioning nephrons in kidney disease. renal failure begins when GFR decreases to below 20 ml/min or a loss of function of 85% of the nephrons.
renal clearance of a substance
virtual volume of plasma from which a solute is completely removed from the plasma by the kidney per unit of time. measured as ml/min.
GFR calculation
GFR = Us x V/Ps
Us x V is amount of solute excreted / time
Ps x GFR is amount of solute filtered / time
Amount of solute filtered / time = amount of solute excreted / time
solutes used to measure GFR
exogenous: Insulin. given by IV infusion, measured accurately in plasma and urine
endogenous: creatinine. in the absence of strenuous exercise or disease, a constant amount of creatinine / time diffuses from skeltal muscle to plasma
solute clearance from the plasma by the kidney
formula: Cs - (Us x V)/Ps
clearance ratios
a solute clearance less than the clearance of insulin/creatinine indicates that the solute is not freely filtered at the glomerulus, or , if freely filtered, net solute reabsorption has occurred. solute clearance greater than insulin / creatinine shows net solute secretion
fractional excretion of water
fraction of the glomerular filtrate not reabsorbed from the tubular fluid along the nephron and therefore appearing as urine.
FEh20 = V / GFR
fractional excretion of solute
fraction of filtered solute that appears in the urine. estimated as a ratio of clearance to GFR
autoregulation of renal blood flow
maintained relatively constant over MAPs which maintains a constant GFR. due to myogenic response of renal vasculature in response to pressure changes. tubuloglomerular feedback at the macula densa cells sensing an increase or decrease in GFR and providing increased or decreased resistance. Autoregulation of renal blood flow is intrinsic to kidney and occurs in the absence of autonomic innervation to the kidneys
glomerular filtration
process by which plasma is filtered across the glomerular capillaries to form a protein-free ultrafiltrate in bowman’s space. driven by differences in starling forces drive the net efflux.
