Z. Lecture 23 Renal perfusion and glomerular for filtration

Question 1

what is a glomerulus ?

Answer 1

• 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)

Question 2

Describe the structure of the bowman’s capsule

Answer 2

• Outer parietal layer continuous with renal tubule outer layer
• Capsular space (where filtrate collects)
• Inner visceral layer composed of podocytes which envelop glomerular capillaries

Question 3

what is the function of Glomerular filter ?

Answer 3

• 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

Question 4

What are the 3 layers of the Glomerular filter?

Answer 4

Endothelium
Basement membrane
Podocytes

Question 5

Describe the features and function of the capillary endothelium of the glomerular filter

Answer 5

• Fenestrated capillaries (50-100x leakier than normal capillaries)
• Blocks cells and platelets

Question 6

Describe the features and function of the basement membrane of the glomerular filter

Answer 6

• Secreted by podocytes
• Main filtration barrier
• Collagen and glycoproteins
• Negatively charged

Question 7

describe the features of the podocytes of the glomerular filter

Answer 7

• Complex structures
• Interdigitating foot processes (pedicels)
• Negatively charged glycocalyx coating

Question 8

Describe the functions of the podocytes of the glomerular filter

Answer 8

-Maintain basement membrane
-May act as supplementary filtration barrier via slit membranes
Phagocytic – escaping cells and macromolecules

Question 9

describe the the filtration characteristics

Answer 9

• Free filtration below 7000 Da
• Virtually none above 70000 Da
• Negative charges prevent filtration of most proteins
• Glucose, amino acids, salts, urea freely filtered

Question 10

what is:
P bc
P cap
pie cap 
pie bc

Answer 10

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

Question 11

Why is P cap higher in the glomerular capillary bed when compared with the idealised/typical capillary from the previous lecture?

Answer 11

as it has two arterioles supplying it rather than just one.

Question 12

Give typical values to of:
P bc
P cap
pie cap 
pie bc

Answer 12

P bc=10 mmHg
P cap=45
pie cap = 25
pie bc= 0, As protein does not normally get filtered

Question 13

what is the relationship between GFR and NFP

Answer 13

Glomerular Filtration Rate (GFR) is proportional to the NFP

Question 14

what is the equation for working out NFP

Answer 14

NFP = forces favouring filtration – forces opposing filtration

GFR is proportional to (Pcap + pie bc) – (Pbc + pie cap)

Question 15

give equation for GFR

Answer 15

[Kf = function of glomerular capillary permeability and area available for filtration]

Thus:

GFR = Kf (Pcap - Pbc - pie cap)

Question 16

Factors affecting GFR?

Answer 16

Kf (filtration coefficient)

Question 17

Factors affecting GFR? (capillary)

Answer 17

Capillary hydrostatic pressure

Capillary oncotic pressure

Question 18

Factors affecting GFR? (Bowman’s capsule)

Answer 18

Bowman’s capsule hydrostatic pressure

Bowman’s capsule oncotic pressure

Question 19

what is value of Renal blood flow (RBF)?

Answer 19

1.1 litres/min

Question 20

Is all of RBF filtered?

Answer 20

NO

Question 21

How much of RBF is filtered?

Answer 21

Only 600 ml of the 1.1 litres of blood is filterable as rest of volume is cells

Question 22

Value representing renal plasma flow (RPF)?

Answer 22

600ml/min

Question 23

What is normal GFR value?

Answer 23

125ml/min

Question 24

What fraction of RPF is 125 ml/min?

Answer 24

125/600 x 100 = approx 20%

( = Filtration Fraction)

Question 25

how much of PRF remains unfiltered?

Answer 25

80%

Question 26

T/F

RBF and GFR constant throughout normal range of BPs

Answer 26

True

Question 27

Autoregulation of RBF and GFR occurs wherE?

Answer 27

occurs in isolated kidneys in the lab

Question 28

Autoregulation

Answer 28

regulated by the kidney itself

Question 29

Mechanisms involved in Autoregulation of RBF and GFR?

Answer 29

Myogenic feedback

Tubuloglomerular feedback

Question 30

Loop of Henle/distal tubule region passes close to what?

Answer 30

renal corpuscle

Question 31

Tubuloglomerular Feedback involves contact what arterioles?

Answer 31

Contacts afferent and efferent arterioles

Question 32

juxtaglomerular apparatus?

Answer 32

region of contact ( afferent and efferent arteriole) is called the juxtaglomerular apparatus

Question 33

High GFR?

Answer 33

high NaCl and fluid flow in distal tubule

Question 34

high GFR sensed ny?

Answer 34

macula densa

Question 35

MD inhibits?

Answer 35

No secretion

Question 36

decreased NO CASUSES?

Answer 36

vasoconstriction of afferent arteriole

returning GFR to normal

Question 37

GFR return to normal ?

Answer 37

Normal NaCl levels and fluid flow in distal tubule restored

Question 38

Neural regulation of RBF and GFR?

Answer 38

Rich sympathetic innervation to kidney

Question 39

where are fibres sent to during neural regulation?

Answer 39

to afferent arteriole wall

Question 40

what happens to tonic activity?

Answer 40

low

Question 41

What effect does denervation have ?

Answer 41

little effect

Question 42

What does increased activation of nerves leads to?

Answer 42

Vasoconstriction of afferent arteriole

Reduces RBF and GFR

Question 43

how low can GFR go?

Answer 43

as low as a few mls/min