Lecture 32: Glomerular Function Flashcards
Normal urine is made mostly of (6)
water, electrolytes (sodium, potassium), drugs/toxins, metabolites and acids
The kidney has a variety of functions including (5)
- filtration
- excretion
- salt and water homeostasis
- pH regulation
- hormone synthesis
What is meant by the drug and toxins that are present in the normal urine composition?
drugs like aspirin
plant toxins
What would happen in we didn’t remove drugs in our urine?
Drugs like aspirin need to removed otherwise if we kept taking them, they would accumulate in the blood and have bad side effects
What is filtration fraction?
how much blood that reaches the kidneys is actually filtered
What is filtered load?
how much of a substance is actually filtered
What is clearance?
clearing a substance from the blood
What is the main role of kidneys?
filters blood
What happens during filtration?
liquids are extracted to form a plasma-like filtrate
Where does filtration occur?
at the glomerulus
What three things define renal filtration?
- renal blood flow
- filtration barrier
- driving forces
Define renal blood flow
the amount of blood that flows into a kidney
What does the renal corpuscle consist of?
the glomerulus/glomerular capillaries and the glomerular capsule
How does the nephron control its own perfusion?
by sensing the NaCl level in the DCT and then cells in the juxtaglomerular complex adjust the afferent and efferent arterioles to adjust the perfusion of the glomerular capillary
What is perfusion?
the delivery of blood to a capillary bed
What percentage of the cardiac output does the renal output take up?
20-25%
Where does filtration take place?
in the glomerulus/glomerular capillary
What three things is the filtration membrane composed of?
- fenestrated endothelium
- basement membrane
- podocytes with foot processes and filtration slits
What is freely filtered by the filtration barrier?
small substances
What is not filtered by the filtration barrier?
large substances
Define a small substance that is filtered by the filtration barrier
one which has a low molecular mass
Define a large substance that is not filtered by the filtration barrier
one which has a high molecular mass
One of the things that defines renal filtration is driving forces. What are the driving forces? What do these come down to?
pressure gradients between the glomerular capillary and the capsular space and this comes down to the permeability of the glomerular capillary and the surface area of the glomerular capillary
What are the four forces that determine the net filtration pressure?
- glomerular hydrostatic pressure (GHP)
- blood colloid osmotic pressure (BCOP)
- capsular hydrostatic pressure (CsHP)
- capsular colloid osmotic pressure
Define glomerular hydrostatic pressure
fluid in the glomerular capillary exerting a pushing force across the barrier that favours filtration
Define blood colloid osmotic pressure (BCOP)
Proteins and other osmotically active solutes act like magnets and “pull” water towards them
Define capsular hydrostatic pressure (CsHP)
the pushing force in the opposite direction to the glomerular hydrostatic pressure due to fluid in the capsule and the fact that the capsule is embedded in the in a tissue and unable to expand
How can you calculate renal clearance? What is the unit?
Cs = (Us x V)/Ps in mL/min
In the equation for renal clearance, what does Us stand for? What is the unit?
the concentration of substance in the urine (mg/L or mol/L)
In the equation for renal clearance, what does V stand for?
volume of urine produced per unit time (mL/min or L/hr)
In the equation for renal clearance, what does Ps stand for?
concentration of the substance in the plasma (mg/L or mol/L)
What does the equation for renal clearance describe?
the rate at which the substance is cleared by the kidneys per unit time
What is the glomerular filtration rate (GFR)?
The volume of filtrate formed by both kidneys per minute
We can estimate GFR using
renal clearance
to be used as a measure of GFR, a substance must
- not be reabsorbed from the tubule
- not be secreted into the tubule
- not be metabolised
What are two main substances that we can use renal clearance to estimate GFR?
- inulin
- creatinine
What is inulin?
- a polysaccharide not metabolised by the body
What is creatinine?
a waste product produced by muscles
Creatinine is filtered freely at the glomerulus but is not ______, _______ or ________
reabsorbed
secreted
metabolised
How is plasma creatinine an indicator for kidney function?
if plasma creatinine is low, both kidneys are working
What is the filtration fraction and how can it be calculated?
how much blood reaching the kidney is actually filtered
it can be calculated by the glomerular filtration rate/renal plasma flow
How much is the renal plasma flow?
about half the volume of blood
Define filtered load
the amount of a particular substance filtered per minute
How can you calculate filtered load?
the glomerular filtration rate x solute plasma concentration
Define capsular colloid osmotic pressure
The pressure if proteins entered the capsular space. It is therefore usually zero because normally no proteins enter the capsular space
