Unit 2, L12 Renal Filtration and Blood FLow

Question 1

What is the glomerular filtration barrier

Answer 1

A selective barrier, highly permeable to water and small solutes. It is impermeable to large substances in the blood (RBCs, WBCs, and proteins), and glomerular filtration is an ultrafiltrate of plasma

Question 2

What is the glomerular filtration barrier composed of?

Answer 2

Fenestrated capillary endothelium, fused basement membrane with a negative charge barrier, and podocyte foot processes - slit diaphragm

Question 3

Why can’t albumin cross through the filtration barrier?

Answer 3

It is small enough to fit through the fenestrations but the basement membrane is negatively charged so it can’t fit through

Question 4

What factors affect the glomerular filtration barrier?

Answer 4

Molecular size of the molecules and electrical charge of molecules

Question 5

How much of the RPF passes through into the Bowman’s space?

Answer 5

The filtration fraction is GFR/RPF, which is about 20%

Question 6

Does glucose go through the glomerular filtration barrier?

Answer 6

Yes, as glucose gets filtered and completely reabsorbed

Question 7

Do large proteins go through the glomerular filtration barrier?

Answer 7

No, they are too large to fit through the fenestrations

Question 8

What is the equation for the rate of filtration

Answer 8

Rate of filtration = hydraulic permeability * surface area * NFP

Question 9

What is NFP

Answer 9

Net Filtration Pressure, its the algebraic sum of the Starling forces that favor and oppose the glomerular filtration

Question 10

What is the equation for Kf

Answer 10

Permeability GC * Area GC

Question 11

What is the equationi for GFR

Answer 11

GFR = Kf * NFP

Question 12

What is Kf

Answer 12

Filtration coefficient

Question 13

Is total renal vasculature resistance high or low? Why?

Answer 13

Low, because everything is arranged in parallel

Question 14

P GC (starling forces) means what

Answer 14

Hydrostatic pressure in the GC (+P GC) will push filtrate out of the blood and into the BS

Question 15

P BS (starling forces) means what?

Answer 15

P BS is hydrostatic pressure in BS (- P BS) and will push filtrate out of BS and back into blood

Question 16

pi GC (starling forces) means what

Answer 16

Pi GC is oncotic pressure in GC (-pi GC), which will pull filtrate out of BS and back into the blood

Question 17

pi BS (starling forces) means what

Answer 17

Pi BS is oncotic pressure in the BS (+ pi BS = 0), which will pull filtrate out of blood into BS

Question 18

What is the equation for net filtration pressure?

Answer 18

Net filtration pressure = P GC - P BS - pi GC + pi BS

Question 19

What does the overall equation for GFR become after adding in starling forces?

Answer 19

GFR = Kf * (P GC - P BS - pi GC + pi BS)

Question 20

Which pressure is greater on one end of the arterioles?

Answer 20

Oncotic pressure in the glomerular capillaries, stronger near the efferent arterioles

Question 21

As arterial blood flows through glomerular capillaries, from afferent to efferent, what happens with P GC

Answer 21

It will fall slightly, from 60 to 58 mmHg

Question 22

As arterial blood flows through glomerular capillaries, from afferent to efferent, what happens with Pi GC

Answer 22

It will increase greatly, from 28 to 35 mmHg, due to the concentration of proteins that are not being filtered

Question 23

As arterial blood flows through glomerular capillaries, from afferent to efferent, what happens with pi BS

Answer 23

It will stay around 0, because no proteins filter out and the few that do get reabsorbed by pinocytosis

Question 24

As arterial blood flows through glomerular capillaries, from afferent to efferent, what happens with P BS

Answer 24

This will remain around 15 mmHg as the pressure here is needed to drive urine through the entire kidney, all the way to the bladder

Question 25

What is the starling force that favors filtration and what is the average value for it

Answer 25

Glomerular capillary blood pressure (P GC) and it is normally 60 mmHg

Question 26

What are the starling forces that oppose filtration and what are their average values

Answer 26

1) Fluid pressure in Bowman's space (P BS) and its normal value is 15 mmHg 2) Osmotic force due to protein in plasma (pi GC) and its normal value is 29 mmHg

Question 27

What is the overall net glomerular filtration pressure

Answer 27

16 mmHg, favoring filtration

Question 28

Prerenal diseases that affect the GFR

Answer 28

Heart failure or hemorrhage, both of which would decrease effective circulating volume, which would decrease GFR

Question 29

Intrarenal diseases that affect the GFR

Answer 29

The immune complex deposition in glomerulus, leads to a decreased GFR. Examples being glomerulonephritis, proteinuria

Question 30

How would leaky glomerular capillaries affect GFR

Answer 30

Increase GFR by increasing Kf

Question 31

Postrenal diseases that may affect the GFR

Answer 31

Kidney stones would increase P BS, which would decrease GFR

Question 32

What is glomerulonephritis

Answer 32

When an immune complex, like from strep, binds to the basement membrane and causes inflammation of capillaries. Loss of glomerular integrity results in RBCs and casts in urine

Question 33

What are urinary casts

Answer 33

Cylindrical shaped aggregations from distal nephron, seen with low urine flow, acidic conditions, and proteinuria

Question 34

Renal cortex gets what percentage of renal blood flow

Answer 34

90%

Question 35

Outer medulla gets what percentage of renal blood flow

Answer 35

8%

Question 36

Inner medulla gets what percentage of renal blood flow

Answer 36

2%

Question 37

Average value for renal blood flow

Answer 37

1200 mL blood/min

Question 38

Hydrostatic pressure decreases from __________ to _________

Answer 38

From renal artery to renal vein

Question 39

Hydrostatic pressure has the largest decreases where

Answer 39

In the afferent and efferent arterioles, as they have high resistance

Question 40

Oncotic pressure increases along _________

Answer 40

The glomerular capillaries, as plasma proteins are concentrated during filtration

Question 41

Oncotic pressure decreases ___________

Answer 41

Decreases along peritubular capillaries, as plasma proteins are diluted during reabsorption

Question 42

What happens if you constrict the afferent arteriole

Answer 42

Decrease in renal blood flow, decrease in P GC, decrease in GFR

Question 43

What happens if you constrict the efferent arteriole

Answer 43

Decrease in renal blood flow, leads to an increase in P GC, leading to an increase in GFR

Question 44

What happens if you dilate the efferent arteriole

Answer 44

Increase in renal blood flow, leads to a decrease in P GC, leading to a decrease in GFR

Question 45

What happens if you dilate the afferent arteriole?

Answer 45

Increase in renal blood flow, increase in P GC, leads to an increase in GFR

Question 46

What is autoregulation of GFR and RBF

Answer 46

Maintaining GFR and RBF relatively constant in the face of changing arteriole blood pressure

Question 47

GFR and RBF will be (increased or decreased) when arterial blood pressure is > 180 mmHg

Answer 47

Increased

Question 48

GFR and RBF will be (increased or decreased) when arterial blood pressure is < 100 mmHg

Answer 48

Decrease

Question 49

At what point does renal shutdown occur?

Answer 49

< 70 mmHg

Question 50

At what point does renal death occur?

Answer 50

0 mmHg

Question 51

What is the intrinsic regulation for the GFR and RBF?

Answer 51

1) Intrinsic (vasoconstrictor and vasodilator) factors 2) Myogenic hypothesis 3) Tubuloglomerular feedback

Question 52

What is the extrinsic regulation of GFR and RBF

Answer 52

1) Sympathetic nervous system 2) Blood borne or endogenous substances (ang II) 3) Stress factors (hemorrhage)

Question 53

What are some of the vasoconstrictors for autoregulation

Answer 53

Sympathetic nervous system, catecholamines, ang II (extrinsic), and endothelin (intrinsic)

Question 54

What are some vasodilators for RBF and GFR

Answer 54

Prostaglandins (intrinsic), NO (intrinsic), bradykinin, and dopamine

Question 55

Explain the extrinsic regulation flow chart

Answer 55

Hemorrhage leads to a drop in arterial blood pressure. This leads to two things. 1) increased renin secretion, which will increase plasma and renal renin. This will then increase plasma and renal ang II. 2) an increase in activity of renal sympathetic nerves. Together, these will both cause constriction of renal arterioles. This will decrease RBF and GFR, and decrease renal excretion of sodium and water. Additionally, Ang II will increase tubular sodium and water reabsorption and facilitate the decreased excretion. Taken together, all of these will increase arterial blood pressure