Renal Perfusion and Glomerular Filtration Flashcards
What does the Glomerular filter do?
Produces an ultrafiltrate of plasma
molecular level filtration
modified along renal tubule until it becomes urine in collecting ducts
What are the 3 layers of glomerular filters?
Endothelium
Basement membrane
Podocytes
What does capillary endothelium do?
Fenestrated capillaries
Blocks cells and platelets
What does the Basement membrane do?
Secreted by podocyes
main filtration barrier
collagen and glycoproteins
negatively charged
What do podocytes do?
Maintain basement membrane
interdigitating foot processes pedicels
Negatively charged glycocalyx coating
act as supplementary filtration barrier via slit membranes
Phagocytic - escaping cells and macromolecules
What are filtration characteristics?
Free filtration below 7000 DA
Virtually none above 7000 da
Negative charges prevent filtration of most proteins
Glucose,AA,Salts,Urea FREELY FILTERED
What is Pbc?
Bowmans capsule hydrostatic pressure 10mmhg
What is Pcap?
Capillary hydrostatic pressure 45mmhg
What is Piecap?
Capillary protein oncotic colloid pressure 25mmhg
As protein does not get normally filtered what value is it?
Piebc = Ommhg
What is the NFP?
Pbc
Pcap
Piecap
What is the glomerular filtration rate GFR?
Proportional to NFP
Kf (Pcap - Pbc- Piecap)
What do GFR measurements need to add?
Filtration coefficient Kf = function of glomerular capillary permeability and area availble for filtration
What is normal GFR?
125ml/min
Kf = 12.5ml/min
What factors affect GFR?
Kf filtration coefficient Capillary hydrostatic pressure Capillary oncotic pressure Bowmans capsule hydrostatic pressure Bowmans capsule oncotic pressure
What is regulation of renal blood flow?
1.1L/min
Not all filtered
only 600ml of blood is filterable as rest is cells
600ml represents renal plasma flow RPF
How much RPF remains unfiltered?
80%
How is RBF and GFR autoregulated?
Constant through normal range of BPs
Occurs in isolated kidneys in the lab, must be regulated by kidney itself
What are 2 methods of autoregulation?
Myogenic feedback
Tubuloglomerular feedback
What dilates to increase RBF AND GFR?
afferent arterioles
How does tubuloglomerular feedback work?
Loop of henle passes close to renal corpuscle
Contacts afferent and efferent arterioles
so called juxtaglomerular apparatus
How does Tubuloglomerular feedback work?
High GFR = high NaCl and fluid flow in DCT
Sensed by macula densa
Decreased NO causes vasoconstriction of Aff arterio
MD inhibits NO secretion
Returns GFR to normal
Normal NACL level and fluid flow restored
What is neural regulation of RBF GFR?
Rich sympathetic innervation to kidney
Fibres to afferent arteriole walls
Tonic activity low
Denervation has little effect (transplantation)
What does increased activation of nerves lead to?
Vasoconstriction of affernt arteriole
Reduces RBF GFR
GFR low as a few mls
Conservation mechanism
