Glomerular filtration and regulation of renal blood flow Flashcards
What does the renal corpuscle consist of
the renal corpuscle consists of a clump of capillaries and bowman’s capsule
Describe the mechanism of glomerular filtrate formation
The key features of glomerular filtrate are therefore –
* For small solutes, such as NaCl, glucose and urea:
* Concentration in glomerular fluid = concentration in plasma.
* For plasma proteins:
* Concentration in glomerular fluid = almost zero.
* Hence, urine is routinely tested on wards for protein (proteinuria).
* Proteinuria is a sign of renal/urinary tract disease.
* A net pressure drop across the glomerular membrane drives the ultrafiltration process.
An imbalance of which force drives glomerular fluid formation and what is the equation for net filtration force
An imbalance of starling’s forces drives glomerular fluid formation (filtration)
Net filtration force= capillary blood pressure - ( plasma colloid osmotic pressure + pressure in bowmann’s space)
Explain the definition of filtration slits and characteristics
filtration slits- are gaps between the processes in the glomerular membrane
*Central spine with lateral
rungs
*Subdivides filtration slit
into pores 4 nm wide.
*Made of proteins
nephrin & podocin
*Deficiency of these
proteins causes nephrotic
syndrome.
An albumin mol
Explain what happens with myeloperoxidase
-myeloperoxidase injected into plasma
-black material is enzyme reaction product
-penetrates through basal lamina but piles up at filtration sites
-none penetrates into urinary space
What are two methods of control for the pressure within glomerular capillaries
1) autoregulation mechanisms (within kidney)
2) extrinsic mechanisms (involving PNS)
explain a bayliss myogenic response in brief
Increase in perfusion
pressure → immediate
increase in vessel radius
(few seconds only) →
blood flow goes up
briefly
Bayliss observed that
resulting stretch of
smooth muscle in afferent
arteriole quickly results in
contraction → reduction
in diameter & increase in
resistance flow returns
to control value in 30s
What is the equation for blood flow (F) in this bayliss myogenic response
Blood flow (F) = change in pressure (AP)/ Resistance (R)
What is one cause of autoregulation
myogenic response of afferent arterioles to pressure is one cause of autoregulation
How is autoregulation maintain ed
-changes in diameter of afferent arterioles alter resistance maintaining autoregulation
Describe JG cells and macula densa
JG cells: modified
smooth muscle cells
in walls of afferent
arteriole proximal
to glomerulus –
store inactive pro-
renin
Macula densa:
specialised epithelial
cells
Explain the stages of tubuloglomerular feedback
1) GFR increases
2) flow through tubule increases
3) flow past macula densa increases
4) paracrine diffuses from macula densa to afferent arterioles
5)afferent arteriole constricts
6) resistance in afferent arterioles increases
7) hydrostatic pressure in glomerulus decreases
8) GFR decreases
How do macula densa cells detect increased flow
- Mechanically
via cell surface cilia - Chemically
via increased [NaCl] *
Explain the role of macula densa cells when causing contraction of afferent arterioles
macula densa cells release ATP—-> triggering contraction of afferent arterioles.
More tubular flow = More ATP released
More NaCl = More ATP released
Note: mesangial cells = lacis cells
explain extrinsic control of glomerular filtration rate
Renal sympathetic nerves (vasoconstriction, noradrenergic) can reduce GFR by re-setting
autoregulation to a lower level
The role is to conserve body fluid volume during physical stress
This happens in 3 conditions:
* standing upright (orthostasis)
* heavy exercise
* haemorrhage & other forms of clinical shock
What are two major clinical disorders of the GFR
1) Glomeruli too leaky to plasma protein:
-nephrotic syndrome
-proteinuria
-hypoproteinaemia
-oedema
2) GFR is too low:
-chronic glomerulonephritis
-when GFR is below 30ml/min—-> chronic renal failure
