Lecture 32 Flashcards
Filtration by the nephron?
Ultrafiltration
Creates a plasma-like filtrate of the blood.
Renal blod flow to and from the glomerulus?
Afferent and efferent arterioles supply the glomerulus with blood for filtration.
What is the filtration membrane composed of?
Fenestrated endothelium, basement membrane, and podocytes with foot processes and filtration slots.
How does the size of substances affect filtration?
Small substances with low molecular weight will be able to pass through the membrane (freely filtered)
What are the driving forces of glomerular filtration determined by?
Forces/pressure gradients between glomerular capillary/ capsular space.
Permeability of glomerular capillary.
Surface area of glomerular capillary
What are the four forces (pressures) determining net filtration pressure ?
GHP
BCOP
CsHP
CsCOP
What is GHP?
glomerular hydrostatic pressure = Blood pressure (+50mmHg)
What is BCOP?
blood colloid osmotic pressure = albumin (-25mmHg)
What is CsHP?
capsular hydrostatic pressure = corpuscle embedded in tuissue (-15mmHg)
What is CsCOP)?
capsular colloid osmotic pressure = no protein in capsular space (+ 0 mmHg)
Equation for clearance?
(Cs) = Us x V / Ps (in mL/min)
What is Us?
concentration of S in urine (mg/L or mol/L)
What is V?
volume of urine produced per unit time (mL/min or L/hour)
What is Ps?
concentration of S in plasma (mg/L or mol/L)
What is the purpose of this equation?
the equation describes the clearance via the kidneys for all substances that can be detected in plasma and urine!!!
What is the Glomerular Filtration Rate?
GFR is the amount of fluid filtered per unit time. • normally ~180 L/day or 125 mL/minute
What factors determine whether a substance can be used as a measure of GFR?
- not be reabsorbed from the tubule
- not be secreted into the tubule
- not be metabolised
What two substances are often used as a measure of GFR?
Inulin and creatinine
What is Inulin?
- polysaccharide not metabolised by body
* not found in body, must be injected
What is Creatine?
- waste product produced by muscles
* already in the body so most commonly used clinically
Why is measuring the renal clearance of Creatine ideal for clinically estimating GFR?
creatinine is filtered freely at the glomerulus but is not reabsorbed, secreted or metabolised!!!!
What is the relationship between GFR and Creatinine?
plasma creatinine is an indicator for kidney function; plasma creatinine is low, if both kidneys are working (125 mL/min)
What is filtration factor?
GFR/RPF
What is the filtered load?
Amount of a particular substance solute filtered per minute
GFR x solute plasma conc
