renal physiology- glomelural filtration Flashcards
what is a renal corpuscle?
- glomerulus (tuft of capillaries)
- Bowmans capsule
describe the capillaries in the glomerulus?
-fenestrated capillaries
what cannot pass through the glomerulus?
- formed elements (platelets, RBC, WBC) as they are too big
- negatively charged molecules as the GBM is negatively charged
what can pass through the glomerulus?
- electrolytes (sodium ,potassium)
- H20
- small proteins
- nutrients
- waste products
as they are small enough to pass through the fenestrated pores of the glomerulus
what feeds the glomerulus and what drains the glomerulus?
feeds- afferent arteriole
drains- efferent arteriole
what are the three layers in the glomerular basement membrane?
- lamina rara interna (faces endothelial cells made up of negatively charged heparin sulphate)
- lamina densa (type 4 collagen and laminins)
- lamina rara externa (faces podocytes made up of negatively charged heparin sulphate)
why does negatively charged albumin not enter the glomerulus?
- as the glomerular basement membrane Is negatively charged as well meaning they will repel each other
- GBM has 3 layers; lamina rara externa, lamina densa, lamina rara interna
- lamina rara externa and interna are made up of heparin sulphate which is negatively charged
what is found between podocytes?
nephrin
what is the space between the podocytes called?
-the filtration slit (approx 35-30nm in diameter)
what does the nephrin do?
- spans the filtration slit (slit diaphragm)
- only allows molecules less than 7 to 9 nm to pass between the podocytes
what do the juxtaglomelural cells secrete?
-renin
what occurs if a macromolecule that was not supposed to get through the glomerulus gets through and gets stuck in the slit diaphragm?
-the mesangial cells will go through phagocytosis and destroy it
role of mesangial cells?
- phagocytose molecules stuck in the slit diaphragm
- can cause vessels to contract controlling amount of blood that got into the afferent arteriole and into the capillaries
- have gap junctions that connect to the juxta glomerular cells and can stimulate release of renin
what is the normal glomerular filtration rate?
125 ml/min
- 1,200ml/min comes in the afferent arteriole
- 625ml/min passes into the GBM while 575ml/min passes into the efferent arteriole
- only 20% of stuff that attempts to get through the GBM actually manages to get through and and filtered
- 20% of 625 is 125ml/min
what is the NFP (net filtration pressure) made up of?
- pressure pushing things out
- pressure pulling things in
role of glomolerular hydrostatic pressure?
-pressure that tries to push the plasma components out of the capillary and into Bowman’s space
average pressure of GHP (glomerular hydrostatic pressure)?
55mm/ Hg
role of COP (colloid osmotic pressure)?
- plasma proteins trying to keep the water from leaving the capillaries and going into Bowmans capsule
- pushes things into the capillary
- exerted by albumin
average COP?
30mmHg
what is CHP?
- capsular hydrostatic pressure
- the Bowman’s space decreases in diameter like a funnel, this can cause a build up of liquid and pressure (just like a funnel) causing a pressure that pushes up the way and back into the capillaries
what is the average value of CHP?
15mmHg
what causes things to be pushed out and pushed into the bowmans capsule?
GHP- tries to push things out of the capillary and into the bowmans capsule (55mmHg)
COP- tries to pull things into the capillaries from the Bowmans capsule, mediated by albumin, as it wants to keep water in plasma (30mmHg)
CHP- This tries to pull things into the capillaries from Bowmans capsule. Bowmans capsule is shapes like a funnel as it goes down, causing a backlog of fluid and increase in pressure causing CHP,
what is the net filtation pressure (NFP)?
10mm/Hg
NFP= pressure of things getting pushed out - pressure pulling in NFP= (GHP)- (COP-+ CHP) NFP= (55)- (30 + 15) NFP= 10mm/Hg
what is the NFP directly proportional to?
GFR
increase in NFP= increase in GFR
what affects the GFR?
- NFP
- surface area of glomerulus (larger SA, larger GFR)
- permeability of glomerulus
what affect does diabetic nephropathy have on GBM and why?
- diabetic nephropathy may increase the thickness of GBM due to deposition of proteins
- this will decrease GFR
what affect may glomerulonephritis have on basement membrane?
- glomerulonephritis can destroy basement membrane and make it very permeable
- this can increase GFR
what is KF?
- filtration coefficiant
- this is the surface area of glomerulus and the permeability of glomerulus
how can GFR be calculated using NFP and KF?
GFR= NFP x KF
role of BP on GHP?
increase in BP increases GHP
decrease in BP decreases GHP
role of proteins on COP?
increase in proteins increase in COP
decrease in proteins dereases COP
-this is because the proteins hold on to blood (albumin mediated) and COP wants H2O to stay in the blood
what affect does renal calculi and hydronephrosis have on CHP?
this would increase CHP as it causes fluid to get pushed back up increasing pressure and decreasing GFR
