GFR Flashcards
What are the three layers of the glomerular capillary filtration barrier?
capillary endothelium, glomerular basement membrane, podocyte epithelium
what is the purpose of the glycocalyx to the barrier function of the endothelial surface layer?
governs transcapillary fluid exchange and acts as a biomechanical sensor; prevents albumin from passing through
What cannot pass the filtration barrier? What can?
large molecules (proteins), cells cannot
water, small solutes (glucose, amino acids, electrolytes)
What is the tamm-horsfall protein?
most abundant protein excreted in urine; secreted in the loop of henle
Damage in which parts of the filtration barrier can result in hematuria and proteinuria?
The basement membrane and glycocalyx
What causes proteinuria?
damage to the glomerular basement membrane, which causes the loss of negative charge, which then permits the passage of albumin into the filtrate
How does proteinuria influence fluid oncotic and hydrostatic pressure?
capillary oncotic pressure would decrease due to the less protein in the blood
How does the anatomical arrangement of the kidney influence nephron function?
the cortex has tubules and vessels that are intertwined whereas the medulla has vessels organized in parallel arrays; blood flow is greater in the cortex than in the medulla; filtration might occur more in the cortex?
What is the equation for filtered load?
filtered load of X = plasma concentration of X*GFR
what is the equation for urinary excretion?
amount filtered - amount reabsorbed + amount secreted = amount excreted in the urine
what is the equation for tubular reabsorption?
glomerular filtration - urinary excretion + amount secreted
What is the urinary concentration of x? (Ux)
the concentration of that substance x in the urine in a given volume
What is urine flow rate? (V)
the rate at which urine is produced (urine volume/time)
what is the urine excretion rate?
the urinary concentration of x (Ux)* the urine flow rate (V)
What is renal clearance (C)? What is the equation?
the volume of plasma completely cleared of a substance by the kidneys per unit time; C=(Ux*V)/Px
What is the glomerular filtrate?
the volume of plasma filtered into the combined nephrons of both kidneys per unit of time
what is the capillary filtration coefficient?
permeability * surface area
What is the filtration fraction (FF)?
GFR/RPF; it is the fraction of RBF that is filtered across the glomerulus
How does the RBF and GFR change during severe hemorrhage or renal artery stenosis?
RBF decreases so GFR increases to maintain homeostasis
How can you use renal clearance to estimate GFR?
GFR is directly proportional if:
- the substance is freely filterable
- neither reabsorbed nor secreted
- not synthesized broken down or accumulated by the kidney
- physiologically inert
compare and contract the use of inulin and creatinine clearances as a measure of GFR
You can use inulin to estimate GFR because its renal clearance is directly proportional; creatinine is also freely filtered but 10% of it is secreted, so its not an ideal marker
how does sympathetic stimulation increase blood pressure through: 1. arterial resistance vessels, 2. juxtraglomerular granular cells 3. tubular epithelial cells
- SNS targets alpha1 receptors on vessels vessels and causes vasoconstriction (afferent>efferent)
- SNS targets beta1 receptors on juxtaglomerular cells and causes renin release and RAAS
- SNS targets tubular epithelial cells to increase sodium resorption through the sodium/potassium pump
What are the acute effects of SNS on
- RBF
- GFR
- renin secretion
- sodium resorption?
- decreased RBF
- GFR is stabilized
- renin secretion increases
- stimulates sodium resorption in PCT and DCT
What are the chronic effects of SNS on
- urinary output
- sodium excretion
- water intake?
- decreased urinary output
- decreased sodium excretion
- increased water intake
