RENAL PHYSIOLOGY II Flashcards
how is the filtration happen in glomerulus?
freely-filtered –> not very selective and creates a plasma-like filtrate of the blood
what determines glomerular filtration?
- filtration barrier
- renal blood flow
- driving forces
how selective is the filtration barrier?
- small substances and glucose are freely-filtered
- large substances (haemoglobin and albumin) are not filtered
what is the stats of renal blood flow and how does that affect the glomerulus filtration?
- 20% CO —> RBF approximately 1100-1200mL/min
—> high flow for filtration rather than metabolism
what are the 2 driving forces within glomerular filtration and what does each do?
hydrostatic pressure
- due to volume of fluid
- ‘pushes’ fluid away
colloid osmotic pressure
- osmotic pressure due to protein
- ‘pulls’ fluid towards
which pressure favour and oppose filtration?
- positive pressure favour filtration
- negative pressure oppose filtration
what are the 4 forces that drives the filtration?
- glomerular hydrostatic pressure (+50)
- blood colloid osmotic pressure (-25)
- capsular hydrostatic pressure (-15)
- capsular colloid osmotic pressure = 0
which is the major force that favours filtration in glomerulus?
glomerular hydrostatic pressure (GHP)
what is the filtration fraction and what is the number for that?
filtration fraction = glomerular filtration rate / renal plasma flow
GFR = 125mL/min
RPF = 625mL/min
—> 20% of the RPF is filtered and 80% remains in the glomerular capillaries (to travel to efferent aterioles and then peritubular capillaries)
how much is the amount of plasma filtered per day by kidneys?
180L
even though 180L of plasma is filtered per day, the urine excreted per day is only ______1______, therefore the process needs to be _____2______ and it is _______3_______ with the ability declines slowly from age 30
1: 1.5L
2: tightly regulated
3: varies from person to person
what is renal filtered load?
- filtered load = amount of a particular substance filtered per unit of time
- filtered load of renal = GFR s solute plasma concentration
what is renal clearance?
the volume of plasma that is cleared of a substance by the kidneys per unit time
what is the renal clearance indicate?
- quantify how much a substance is handled by the kidneys
- estimate glomerular filtration rate (GFR)
what is the clearance of creatinine?
clearance of creatinine = volume of plasma filtered per min = GFR
what is the clearance of medication and toxins?
clearance of medication and toxins = volume of plasma flow through the kidneys per min = RPF
what is the clearance of creatinine?
clearance of sodium = very small
what is the clearance of glucose?
clearance of glucose = 0 (all is reabsorbed —> no plasma has been “cleared” of glucose)
what is the equation of clearance
Cx = (Ux x V) / Px
how do we estimate the GFR using the clearance
because we have creatinine and inulin, which is freely- filtered but not reabsorbed or secreted –> use there stats to estimate the GFR
what is creatinine and what is inulin?
creatinin:
- waste product of muscles
- already in body so most commonly used clinically
inulin
- polysaccharide which is not metabolised by body
- not found in body and must be injected
- food high in inulin: wheat, shalots and red onions, bulb of leeks
what is the relationship between GFR and plasma creatinine indicate?
- low plasma creatinine <—> GFR high => normal kidney function of both kidneys
- fairly normal plasma creatinine <—> one kidney working with GFR 60mL/min
- high plasma creatinine <—> kidneys ability to clear waste is reduced
