Lesson 29: Topic 25 - Glomerular Filtration

Question 1

calculating glomerular filtration is determined by?

Answer 1

hydrostatic and osmotic pressures across the glomerular capillary and Bowman’s space

Question 2

what pressure dictates filtration?

Answer 2

glomerular capillary blood pressure (Pgc) (55mmHg)
- driving pressure of the blood in the glomerular capillary to drive plasma into the Bowman space and across the glomerular capillaries

Question 3

what pressures oppose filtration?

Answer 3

1. bowman’s space fluid pressure (Pbs) (15mmHg)
2. plasma protein osmotic pressure (Pi gc) (30mmHg)

Question 4

why is there no osmotic pressure from the plasma proteins in bowman’s space?

Answer 4

because they cannot pass the barrier from the capillary into the bowman’s space

Question 5

what is the NET glomerular filtration pressure?

Answer 5

= Pgc - Pbs - Pigc = 10mmHg
- positive number then indicated that there is filtration occurring across the glomerulus

Question 6

is there reabsorption happening at the glomerulus capillary?

Answer 6

no, there is not a long capillary like there is in blood vessels. it is a very blunt filtration space

Question 7

what is the glomerular filtration rate (GFR) equation?

Answer 7

GFR = net filtration pressure x Kf

Question 8

what is net glomerular filtration pressures biggest determinant?

Answer 8

glomerular capillary blood pressure

Question 9

what is glomerular filtration rate determined by?

Answer 9

1. net filtration pressure (largely controlled by Pgc - glomerular capillary blood pressure)
2. filtration co-efficient (Kf)

Question 10

what is filtration co-efficient determined by?

Answer 10

• dependent on:
• surface area of capillaries
  and
• glomerular permeability (capillary pores)

Question 11

true or false: glomerular permeability is a determinant of net glomerular filtration rate

Answer 11

true

Question 12

what is plasma protein fluid pressure?

Answer 12

nothing. it is called plasma protein osmotic pressure. not fluid pressure

Question 13

how does blood pressure affect GFR? (glomerular filtration rate)

Answer 13

• increased arterial blood pressure (increases blood flow into the glomerulus) –> increases glomerular capillary blood pressure –> increases net filtration pressure –> increases GFR

Question 14

what is the indirect way of affecting GFR?

Answer 14

• we are going to alter the afferent arteriole (we can also use the efferent arteriole) by vasoconstricting or vasodilation but also by keeping MAP the same

ex1. vasoconstrict afferent arteriole (producing less blood being delivered to glomerulus) –> lowers glomerular capillary blood pressure –> lower net filtration pressure –> lower GFR

ex2. vasodilation = the oppose of ex1

Question 15

if we vasoconstrict the efferent arteriole, does the afferent need to vasoconstrict?

Answer 15

no. there is typically no correlation. they are independent of each other

Question 16

how is GFR affected if we vasoconstrict the efferent arteriole?

Answer 16

• increased glomerular capillary pressure (Pgc) (more blood accumulation in the glomerulus)–> increase glomerular filtration rate

Question 17

how is GFR affected if we vasodilate the efferent arteriole?

Answer 17

• decreased glomerular capillary pressure (Pgc) –> decrease glomerular filtration rate

Question 18

which of the indirect GFR affects will cause the greatest decrease in glomerular filtration rate?

Answer 18

afferent vasoconstriction (restricting the amount of blood flow entering glomerulus) and efferent vasodilation (opening the leak of blood)

Question 19

does glomerular filtration rate (GFR) ALWAYS vary with changes in MAP?

Answer 19

yes
- if MAP increases –> glomerular capillary pressure (Pgc) Increases –> GFR increases

Question 20

an increase in MAP is dangerous. what are the implications?

Answer 20

dangerous imbalance of fluids, electrolytes, and wastes (excess excretion)
- we need a regulatory mechanism to maintain a steady GFR

Question 21

what is the regulatory mechanism to maintain a steady GFR?

Answer 21

1. flow autoregulation
2. juxtaglomerular (tubuloglomerular) feedback

Question 22

how does the flow autoregulation in the kidneys work?

Answer 22

if we increase MAP, that is going to cause a myogenic response in the afferent arteriole. which will then immediately increase glomerular capillary pressure and increase GFR
- but then we have the reflex response. the myogenic response where the afferent arteriole is going to constrict and then it is going to help maintain glomerular capillary pressure (decrease it) and bring GFR to normal

Question 23

juxtaglomerular feedback alter glomerular filtration rate based on?

Answer 23

the amount of sodium chloride concentration that is in the tubule

Question 24

where does the juxtaglomerular feedback happen?

Answer 24

in the juxtaglomerular apparatus

Question 25

where is the juxtaglomerular appartus?

Answer 25

at the intersection between where the afferent arteriole and the efferent arteriole meet

Question 26

in the kidney, there is a sensor of NaCl. where is it?

Answer 26

in the macula densa cells that are inside the distal tubule

Question 27

what are the macula densa cells?

Answer 27

they are specialized epithelial cells that sense distal tubule NaCl FLOW --> secrete paracrine factors that affect afferent arteriole diameter

Question 28

what are granular cells?

Answer 28

specialized endothelium within afferent arteriole --> produce factors in response to macula dense factors and SNS

Question 29

too much NaCl excreted in urine means that?

Answer 29

we have less ability to hold water

Question 30

assuming the distal tubule detects a high NaCl concentration inside the distal tubule, it will be sensed by the Macula densa which will then secrete?

Answer 30

adenosine

Question 31

what does adenosine do?

Answer 31

cause vasoconstriction of the afferent arteriole which will decrease glomerular pressure which will decrease GFR and then decrease the NaCl - which will then help retain NaCl and water in the body - negative feedback loop

Question 32

assuming the distal tubule detects a low NaCl concentration inside the distal tubule, it will be sense by the Macula densa which will then secrete?

Answer 32

prostaglandin

Question 33

low NaCl indicates?

Answer 33

low blood volume or low blood pressure

Question 34

what does prostaglandin do?

Answer 34

induce afferent arteriole vasodilation --> increase blood flow to the capillary --> increase glomerular capillary pressure --> increase glomerular filtration rate

Question 35

what does high GFR do?

Answer 35

high GFR helps retain NaCl and water in the body by increasing tubular reabsorption

Question 36

if the GFR is too low then our kidneys are or are not function properly?

Answer 36

are not functioning properly

Question 37

what happens to our Macula dense if we do not have sufficient sodium?

Answer 37

the sensor of macula densa (which regulates glomerular filtration rate) does not have sufficient sodium to work as a sensor to cause afferent arterial vasodilation or constriction to regulate GFR

Question 38

how do we ensure that there is always enough NaCl for the macula densa to sense it?

Answer 38

because the negative feedback loop of the juxtaglomerular apparatus, the increase GFR helps retain NaCl and water in the body

Question 39

why does someone urinate more when they drink coffee?

Answer 39

it blocks the rate of adenosine - which then prevents afferent arteriole vasoconstriction from occurring which then increases glomerular capillary pressure and increases GFR