Renal Perfusion and Glomerular Filtration

Question 1

What does the Glomerular filter do?

Answer 1

Produces an ultrafiltrate of plasma
molecular level filtration
modified along renal tubule until it becomes urine in collecting ducts

Question 2

What are the 3 layers of glomerular filters?

Answer 2

Endothelium
Basement membrane
Podocytes

Question 3

What does capillary endothelium do?

Answer 3

Fenestrated capillaries

Blocks cells and platelets

Question 4

What does the Basement membrane do?

Answer 4

Secreted by podocyes
main filtration barrier
collagen and glycoproteins
negatively charged

Question 5

What do podocytes do?

Answer 5

Maintain basement membrane
interdigitating foot processes pedicels
Negatively charged glycocalyx coating
act as supplementary filtration barrier via slit membranes
Phagocytic - escaping cells and macromolecules

Question 6

What are filtration characteristics?

Answer 6

Free filtration below 7000 DA
Virtually none above 7000 da
Negative charges prevent filtration of most proteins
Glucose,AA,Salts,Urea FREELY FILTERED

Question 7

What is Pbc?

Answer 7

Bowmans capsule hydrostatic pressure 10mmhg

Question 8

What is Pcap?

Answer 8

Capillary hydrostatic pressure 45mmhg

Question 9

What is Piecap?

Answer 9

Capillary protein oncotic colloid pressure 25mmhg

Question 10

As protein does not get normally filtered what value is it?

Answer 10

Piebc = Ommhg

Question 11

What is the NFP?

Answer 11

Pbc
Pcap
Piecap

Question 12

What is the glomerular filtration rate GFR?

Answer 12

Proportional to NFP

Kf (Pcap - Pbc- Piecap)

Question 13

What do GFR measurements need to add?

Answer 13

Filtration coefficient Kf = function of glomerular capillary permeability and area availble for filtration

Question 14

What is normal GFR?

Answer 14

125ml/min

Kf = 12.5ml/min

Question 15

What factors affect GFR?

Answer 15

Kf filtration coefficient
Capillary hydrostatic pressure
Capillary oncotic pressure
Bowmans capsule hydrostatic pressure 
Bowmans capsule oncotic pressure

Question 16

What is regulation of renal blood flow?

Answer 16

1.1L/min
Not all filtered
only 600ml of blood is filterable as rest is cells
600ml represents renal plasma flow RPF

Question 17

How much RPF remains unfiltered?

Answer 17

80%

Question 18

How is RBF and GFR autoregulated?

Answer 18

Constant through normal range of BPs

Occurs in isolated kidneys in the lab, must be regulated by kidney itself

Question 19

What are 2 methods of autoregulation?

Answer 19

Myogenic feedback

Tubuloglomerular feedback

Question 20

What dilates to increase RBF AND GFR?

Answer 20

afferent arterioles

Question 21

How does tubuloglomerular feedback work?

Answer 21

Loop of henle passes close to renal corpuscle
Contacts afferent and efferent arterioles
so called juxtaglomerular apparatus

Question 22

How does Tubuloglomerular feedback work?

Answer 22

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

Question 23

What is neural regulation of RBF GFR?

Answer 23

Rich sympathetic innervation to kidney
Fibres to afferent arteriole walls
Tonic activity low
Denervation has little effect (transplantation)

Question 24

What does increased activation of nerves lead to?

Answer 24

Vasoconstriction of affernt arteriole
Reduces RBF GFR
GFR low as a few mls
Conservation mechanism