Z. Lecture 23 Renal perfusion and glomerular for filtration Flashcards
what is a glomerulus ?
- ball of capillaries supplied by afferent arteriole and drained by efferent arteriole
- initial site of urine production
- inserted into the bowman’s capsule (site of blind end of nephron)
Describe the structure of the bowman’s capsule
- Outer parietal layer continuous with renal tubule outer layer
- Capsular space (where filtrate collects)
- Inner visceral layer composed of podocytes which envelop glomerular capillaries
what is the function of Glomerular filter ?
- Glomerular filter produces an ultrafiltrate of plasma via ultrafiltration (molecular level filtration)
- Glomerular ultrafiltrate is modified along renal tubule until it becomes urine in the collecting ducts
What are the 3 layers of the Glomerular filter?
Endothelium
Basement membrane
Podocytes
Describe the features and function of the capillary endothelium of the glomerular filter
- Fenestrated capillaries (50-100x leakier than normal capillaries)
- Blocks cells and platelets
Describe the features and function of the basement membrane of the glomerular filter
- Secreted by podocytes
- Main filtration barrier
- Collagen and glycoproteins
- Negatively charged
describe the features of the podocytes of the glomerular filter
- Complex structures
- Interdigitating foot processes (pedicels)
- Negatively charged glycocalyx coating
Describe the functions of the podocytes of the glomerular filter
-Maintain basement membrane
-May act as supplementary filtration barrier via slit membranes
Phagocytic – escaping cells and macromolecules
describe the the filtration characteristics
- Free filtration below 7000 Da
- Virtually none above 70000 Da
- Negative charges prevent filtration of most proteins
- Glucose, amino acids, salts, urea freely filtered
what is: P bc P cap pie cap pie bc
P bc= Bowman’s capsule hydrostatic pressure
P cap= capillary hydrostatic pressure
pie cap= capillary protein oncotic (colloid) pressure
pie bc= Bowman’s capsule protein oncotic (colloid) pressure
Why is P cap higher in the glomerular capillary bed when compared with the idealised/typical capillary from the previous lecture?
as it has two arterioles supplying it rather than just one.
Give typical values to of: P bc P cap pie cap pie bc
P bc=10 mmHg
P cap=45
pie cap = 25
pie bc= 0, As protein does not normally get filtered
what is the relationship between GFR and NFP
Glomerular Filtration Rate (GFR) is proportional to the NFP
what is the equation for working out NFP
NFP = forces favouring filtration – forces opposing filtration
GFR is proportional to (Pcap + pie bc) – (Pbc + pie cap)
give equation for GFR
[Kf = function of glomerular capillary permeability and area available for filtration]
Thus:
GFR = Kf (Pcap - Pbc - pie cap)
Factors affecting GFR?
Kf (filtration coefficient)
Factors affecting GFR? (capillary)
Capillary hydrostatic pressure
Capillary oncotic pressure
Factors affecting GFR? (Bowman’s capsule)
Bowman’s capsule hydrostatic pressure
Bowman’s capsule oncotic pressure
what is value of Renal blood flow (RBF)?
1.1 litres/min
Is all of RBF filtered?
NO
How much of RBF is filtered?
Only 600 ml of the 1.1 litres of blood is filterable as rest of volume is cells
Value representing renal plasma flow (RPF)?
600ml/min
What is normal GFR value?
125ml/min
What fraction of RPF is 125 ml/min?
125/600 x 100 = approx 20%
( = Filtration Fraction)
