Glomerular filtration Flashcards
How many layers are glomerular capillary membranes made up of?
Three
What are the layers of the glomerular capillary membranes?
Endothelium
Basement membrane
Podocytes
What type of endothelium do glomerular capillaries have?
Fenestrated, meaning they have holes between endothelial cells
What is the basment membrane of the glomerular capillaries made up of?
Collagen fibres
Glycoproteins that are negatively charged
What is the structure of podocytes?
Give off projections called pedicels
pedicels contain spaces in between them
What are the spaces in between pedicels called?
Filtration slits
What is glomerular filtration?
Refers to the process of fluid and molecules passing from the glomerular capillaries into Bowman’s capsule
What do fluids and molecules pass through as they are filtered from the glomerular capillary into Bowman’s capsule?
Pass through fenestrations between cells in endothelial layer of glomerular capillary
then through gaps in basement membrane
then through filtration slits
What factors determine whether an ion/small molecule can be filtered out of the glomerular capillaries into Bowman’s capsule?
Its size
Its charge
How does size affect whether an ion/small molecule can be filtered out of the glomerular capillaries into Bowman’s capsule?
Large molecules are too big to pass through the glomerular capillary membrane
remain in the glomerular capillaries
Small molecules pass through the glomerular capillary membrane
into Bowman’s capsule
How does charge affect whether an ion/small molecule can be filtered out of the glomerular capillaries into Bowman’s capsule?
Two molecules of the same size, one is positively charged and the other is negatively charged
more of the positively charged molecule passes through the glomerular capillary membrane into Bowman’s capsule
because the negatively charged molecule is repelled by the negatively charged glycoproteins in the basement membrane
What is the glomerular filtrate?
Refers to the fluid and molecules themselves that leave the glomerular capillaries and pass into Bowman’s capsule
What is the glomerular filtrate made up of?
Water
Ions
Small molecules e.g. gluose, amino acids, urea
What are the concentrations of water, ions, small molecules etc. in the glomerular filtrate, compared to the plasma?
They are the same
What parts of the blood do not form part of the glomerular filtrate?
Cells
Proteins e.g. albumin
Why do cells and proteins e.g. albumin not form part of the glomerular filtrate?
They are too large to pass through the glomerular capillary membranes
Also proteins are negatively charged, so they are repelled by the negatively charged glycoproteins in the basement membrane of the glomerular capillaries
What ion/small molecule does not have the same concentration in the glomerular filtrate as it does in the plasma? Why?
Calcium ions
Because of calcium binding proteins in the plasma holding on to it
and themselves not being filtered out
What is proteinuria?
Proteins in the urine
What is a cause of proteinuria to do with the glomerular capillary membrane?
Loss of negatively charges on glycoproteins in basement membrane
smaller negatively charged membranes can pass through glomerular capillary membrane
What is meant by the filtration fraction?
The amount of renal plasma flow that is filtered out of the glomerular capillary into Bowman’s capsule
What is the actual normal filtration fraction?
20%
What is meant by glomerular filtration rate (GFR)?
The amount of fluid and molecules pass from the glomerular capillaries into Bowman’s capsule per unit time
What is the actual normal GFR?
125ml/min
140-180L/day
What are the factors of the GFR?
Hydrostatic and oncotic pressures of glomerular capillaries and Bowman’s capsule
How does glomerular hydrostatic pressure affect the GFR?
Higher glomerular hydrostatic pressure
more fluid pushes out of the glomerular capillary into Bowman’s capsule
increases GFR
How does glomerular hydrostatic pressure change across the length of the glomerular capillary? Why?
It decreases
because fluid is filtered out of the glomerular capillary into Bowman’s capsule
less fluid in glomerular capillary
How does glomerular oncotic pressure affect the GFR?
Higher glomerular oncotic pressure
more force drawing water into the glomerular capillary from Bowman’s capsule
decreases GFR
How does glomerular oncotic pressure change across the length of the glomerular capillary? Why?
It increases
because water is filtered out of the glomerular capillary into Bowman’s capsule, but proteins remain
become more concentrated
How does Bowman’s capsule hydrostatic pressure affect the GFR?
Higher Bowman’s capsule hydrostatic pressure
more fluid pushing out of Bowman’s capsule into glomerular capillary
decreases GFR
What pathological state can cause an increase in Bowman’s capsule hydrostatic pressure?
Obstruction of urinary tract by e.g. stone
What is meant by the net filtration pressure?
The overall pressure gradient between the glomerular capillary and the Bowman’s capsule
