GU 11. Topic 2: The Glomerulus as a Filter

Decreases it

How does a negative charge affect how things can pass thru the glomerular filtration barrier

Increases it

How does a positive charge affect how things can pass thru the glomerular filtration barrier

1) Fenestrated capillary endothelium 2) Basement membrane 3) Filtration slits of *podocytes* (aka. glomerular visceral epithelial cells)

What are 3 layers of glomerular filter from inside to outside? (capillary/blood lumen to Bowman's space)

large plasma proteins (ex. albumin)

the GBM prevents the filtration of

filtration slits

the ___ b/w the podocytes helps retard the filtration of plasma proteins

fenestrated

the endothelium of capillary loops is

0.15/0.20 usually around 20% is filtered! (proportion of the fluid reaching the kidneys which passes into the renal tubules)

the filtration fraction is GFR/RPF and is usually between

basal lamina

the middle element of the filtration barrier

serum albumin

the slit membranes prevent the passage of anything equal to or larger than

basal lamina (basement membrane)

most important barrier to passage of plasma proteins

Yes

Can Na+ pass freely thru the glomerular filtration barrier

No

Can albumin pass freely thru the glomerular filtration barrier

Yes

Can glucose pass freely thru the glomerular filtration barrier

Not really (0.03 filtrate/plasma water)

Can hemoglobin pass freely thru the glomerular filtration barrier

Yes

Can inulin pass freely thru the glomerular filtration barrier

Yes, pretty much (0.75 filtrate/plasma water)

Can myoglobin pass freely thru the glomerular filtration barrier

Yes

Can water pass freely thru the glomerular filtration barrier

Vascular endothelial growth factor (VEGF)

What do podocytes secrete, which maintains the normal permeability of the glomerular fenestrated endothelium

A transmembrane protein that is a structural component of the slit diaphragm, expressed by podocytes

What is nephrin

Increased protein excretion in the urine (can happen if podocytes are injured)

What is proteinuria

Conc. of solute in filtrate / Conc. of solute in plasma (higher ratio means it passes easily! so small cations have a ratio of 1.0!!) (permselectivity of the glomerular barrier for different solutes, as estimated by the ratio of solute concentration in the ultrafiltrate versus the plasma (UFx/Px). The ratio UFx/Px, also known as the sieving coefficient for the solute X (i.e. concentration in ultrafiltrate divided by mean of concentrations in pre and post filter blood) depends on molecular weight and effective molecular radius. )

What ratio is important for pore size when determining the permselectivity of glomerulus to macromolecules

greater

a disease that diminished the density of negative sialic acid moieties in the GBM would result in ___ filtration of plasma proteins

7 g

about ___ of albumin are filtered daily and reabsorbed by the proximal tubule

basal lamina (Basement membrane)

everything except the largest protein molecules can pass through the

negative

fixed charge of glomerular basement membrane

slit diaphragm proteins (ex. nephrin)

form an important part of GFB by forming a zipper-like structure b/w adjacent foot processes

glomerulus

if Mb is present, much of it is filtered at the

anionic proteoglycan clusters w/in Glomerular basement membrane (GBM has a net NEGATIVE charge!!)

main barrier precluding the free passage of albumin across the glomerular capillary walls

albumin

most abundant circulating protein and healthy people excrete <30 mg per day