GFR and The Glomerulus Flashcards
What pushes the filtrate out the blood?
Fenestrated capillaries with a more dilated afferent arteriole compared with he efferent
Where is filtration in the nephron?
The Glomerulus
How does blood enter the kidney?
Renal Artery
Outline arterial blood flow in the kidney.
Renal Artery — Segmental artery—lobular artery — arcuate artery — interlobular arteries — afferent arteriorle– glomerulus — efferent arteriole — vasarecta or peritubular capillaries
Outline arterial blood flow in the kidney.
Renal Artery — Segmental artery—lobular artery — arcuate artery — interlobular arteries — afferent arteriole– glomerulus — efferent arteriole — vasa recta or peritubular capillaries
What is the arterial blood flow feature in the capillaries that helps filtration?
Two in series resistance capillary beds (Glomerulus and the Vasa Recta or Peritubular capillaries)
What are the two types of nephrons?
Cortical
Juxtamedullary
Which nephron type is important for setting up the corticomedullary osmotic gradient?
Juxtamedullary (long nephron with glomerulus sitting adjacent to medulla, vasa recta with counter current flow to the tubule flow)
Where do you find peritubular capillaries?
Around cortical nephrons Loop of Henle
What proprotion of out nephrons are cortical?
90%
Contrast the two nephron types.
See Picture
NOTE EA=AE in juxtamedullary not cortical
What is the renal blood flow in L/min
1.1L/min
What is renal plasma flow?
A normal haematocrit (the proportion of blood made up of cells) is 0.45 of total blood volume .
- 1L/min is total blood flow
- 55 (the bit thats left for plasma when cells taken out)x 1.1= 605ml/min of plasma
Where in the kindey are the glomeruli?
Cortex
What percentage of the blood coming into the renal artery will be filtered at any one time?
20%
What is the normal glomerular filtrate per day?
140-180L/day
(125ml/min = approx 0.2 x 605)
What percentage of blood arriving at the kdney will leave the efferent arteriole unfiltered?
80%
What is the renal corpuscle?
Glomerulus + Bowmans Capsule
What is the function of the renal corpuscle?
Produce ultra filtrate
Bowmans Capsule has two layers (parietal and visceral) outline the features of each.
parietal is simple squamous epithelium
Flitration barrier is made up of vascular endothelium and visceral Bowmans capsule
Which part of the nephron must sit close to Bowmans capsule so that the juxtaglomerula appuratus can monitor and adjust kidney function in the dital tubule?
DCT
Describe the filtration barrier of the kidney
See Drawing (ignore colour errors)
What doesnt get filtered out of blood?
Cells and large proteins
What is filtered out at the glomerulus?
Water, salts and small molecules
What is the result of filtration?
100% of plasma glucose, sodium, urea and creatinine are in the ultrafiltrate
What is a normal plasma sodium in mmol.L
140
Creatinine levels should be what?
60-120mmol/L
Whats a normal serum urea?
15mg/dl
Note the units
List the three layers of the filtration barrier.
Capillary endothelium
Basement Membrane
Podocyte Layer
What forms filtration slits?
Pseudopodia
Why is good basement membrane integrity important for normal glomerular filtration?
Glycoproteins and collagen in teh acellular BM.
Glycoproteins are negatively charged and so repel otehr negatively charge molecules (hence proteins don’t filter)
Where does filtate move relative to the enothelium?
Between cells in the fenestrations
The filtration barrier is selective, in what ways?
Selective for small molecules
Repels negatively charge molecules
How might a nephrotoxic lead to increase proteinuria?
Toxic to glycoproteins in basement membrane (strips the negative charge)
Increase negative protein filrtation
Outline to forces acting accross the glomerulus.
How does the kidney autoregulate? (we need constant GFR in variable cardiac output sitautions- you dont want to urinate lots when exercising)
Myogenic mechanism
Tubuloglomerular feedback
What is the aim of renal autoregulation?
Constant renal blood flow and GFR (80-180mmHg)
What would happen if we didnt have renal autoregulation?
25% increase in BP would lead to a roughly 4 fold increase in volume of urine (4.6L a day from the normal 1L)
What is the myogenic mechanism of renal autoregulation?
Vascular smooth muscle will repsond to its own stretch, predominantly in the preglomerular resistance vessels.
High BP would cause high GFR so to decrease GFR we would constrict the afferent arteriole and dilate the efferent (lower glomerulus hyrdrostatic pressure)
Which afferent vesselsare most active in the myogenic mechanism of renal autoregulation?
Arcuate, interlobular and afferent arterioles.
What is the time scale for myogenic mechanisms to kick in?
3-10 seconds
How could we use the myogenic effect to increwase GFR in instances of low CO?
Afferents mostly affected and they will dilate
Efferents will constrict
Within what blood pressure range is the myogenic effect sufficient to regulate a constant GFR?
80-180mmHg
What is Tubular glomerular feedback?
If GFR changes the concentration of Na+ and Cl- will change in the DCT. The DCT will feed back to the afferent and efferent arterioles- will also feedback to reabsortion
Where does the DCT sit?
In the cortex next to the glomerulus at a site between the afferent and efferent arteriole so it can hormonally control them according to what the macula densa detects.
What is released by the juxtaglomerular apparatus to control GFR?
Vasoactive substances-
Prostaglandins increase GFR
Adeonisine to decrease GFR
Which transporter in the apical memebrane of macula densa cells is improtant in tubular glomerular feedback?
NaKCC
Sodium Potassium cotransport channel (its concetration dependent so tells the MD cell if [NaCl] changes in the tubule
What affect does adenosine have on filtration?
Decreases by acting on A1 receptors in the afferents constrict afferent and A2 receptors in the efferernt to dilate them
How do prostaglandins increase GFR?
Vasodilate afferent arterioles
If BP increases what would happen to DCT [NaCl]
Increase
When does yje GFR and distal salt concentration become closely linked?
Acute changes
What neural system controls GFR?
Sympathetics and Parasympathtics
Outline to action of sympathtetic innervation on GFR
Systemic vasococntriction reduced blood flow to kidney and lowers GFR
(This is rare- only in fight or flight sistuations)
How does the parasymoathtic system regulate GFR?
Ach causes NO release which vasodulates to increase GFR.
What is the first line adjuster of GFR when the BP quickly changes?
Myogenic (afferent changes as a result of stretch in vessels)
What is the second line for GFR adjustments with changing BP?
Tubular-glomerular feedback
(afferents and efferents affected as result of changes in [NaCl] detected by MD cells. Hormonal feedback by juxtaglomerula apparatus (adenosine or prostaglandins)
