Filtration

Question 1

Define glomerular filtration rate? (GFR)

Answer 1

Passage of fluid from the blood into Bowman’s space

Question 2

State 6 factors that determine glomerular filtration rate?

Answer 2

1) Pressure gradients
2) Size of the molecule
3) Charge of the molecule
4) Rate of blood flow
5) Surface area; directly proportional to membrane permeability and surface area
6) Binding to plasma proteins e.g. Ca2+, hormones, fatty acids

Question 3

What is GFR value?

Answer 3

125ml/min

Question 4

What does 125ml/min represent?

Answer 4

GFR

Question 5

What percentage of plasma passes through glomerulus?

Answer 5

20%

Question 6

State GFR formula?

Answer 6

GFR = (UrineM x urine flow rate) / PlasmaM
M= conc x volume

Question 7

How to calculate M in fluid? (creatine)

Answer 7

Concentration x Volume

Question 8

Why is measuring GFR used in clinical settings?

Answer 8

Disease cause loss nephrons
GFR fall

Question 9

What is used calculate GFR?
Why?

Answer 9

Creatine
Freely filtered by glomerulus but not secreted or absorbed in tubules and not metabolised

Question 10

What is function of creatine in diagnostic tests?
Why?

Answer 10

Used estimate GFR
Freely filtered by glomerulus
Not secreted/absorbed in tubules
Not metabolised

Question 11

Define myogenic autoregulation?

Answer 11

Smooth muscle contraction in response to external stretching force, occurs in capillary walls, passive mechanism

Question 12

If increased NaCl conc what will occur to afferent arteriole?

Answer 12

Constrict

Question 13

If decreased conc NaCl what will occur afferent arteriole?

Answer 13

Dilation

Question 14

What causes fast response in arterioles?

Answer 14

GFR

Question 15

What causes slow response in arterioles?

Answer 15

RAAS

Question 16

State value normal GFR?
in 24 hrs?

Answer 16

125ml/min
180L in 24 hrs

Question 17

How much of GFR is reabsorbed?

Answer 17

99%

Question 18

What is total plasma volume?
IF? Transcellular?

Answer 18

3L
IF- 2 Transcellular- 1

Question 19

How many times in 24hrs is plasma volume filtered?

Answer 19

60 times/day

Question 20

What is value hydorstatic pressure?

Answer 20

35mmHg

Question 21

What is value osmotic pressure?

Answer 21

26-28mmHg

Question 22

Define oncotic pressure?

Answer 22

Pressure due to colloids that can’t escape vessel eg proteins

Question 23

Does hydrostatic pressure increase/decrease/stay constant across length glomerular capillary?

Answer 23

Constant

Question 24

Does oncotic pressure increase/decrease/stay constant across length glomerular capillary?
Why

Answer 24

Increases across length
Proteins more concentrated (not filtered)
20% higher

Question 25

What is equation GFR?

Answer 25

GFR= Hydrostatic pressure-oncotic pressure

Question 26

At end of glomerular capillaries what is balance hydrostatic and oncotic pressure?

Answer 26

Eqbm

Question 27

Explain water movement in and out capillaries

Question 28

Does oncotic pressure bring water in or out?

Answer 28

In Plasma proteins create gradient water diffuses across

Question 29

Is pressure higher on arterial end of capillary bed or venule? Figures?

Answer 29

Arterial- 30mmHg Venule- 20mmHg

Question 30

Where does exchange occur? What is exchanged? Where does move?

Answer 30

Capillary bed Oxygen, glucose, ions, hormones From capillary bed into interstitial space

Question 31

Explain how water and ions leave and BP is maintained?

Answer 31

1) Arterial pressure pushes out water and ions etc in IF 2) Plasma proteins too big leave capillary bed 3) Plasma protein increased @venule end 4) Plasma proteins create low water conc (high solutes) Colloid osmotic pressure 5) Draw water back capillary bed 6) Maintain BP

Question 32

Is pressure higher at arterial or venule end?

Answer 32

Arterial

Question 33

Are proteins in glomerular filtrate?

Answer 33

No

Question 34

Define ultrafiltrate?

Answer 34

Contain virtually all substances found in plasma in similar concentrations No large prteins?

Question 35

What is present in filtrate? (4 examples) What size can pass?

Answer 35

Small molecules and ions- 10 kDa or smaller 1) Glucose 2) Uric acid 3) K+ 4) Creatinine

Question 36

Why is albumin not filtered?

Answer 36

Negatively charged glomerular bm repels negative ions

Question 37

Is glucose filtered?

Answer 37

Yes

Question 38

What is only protein found urine (filtered)?

Answer 38

Tamm– Horsfall protein (uromodulin)

Question 39

Why is lack of protein in urine of clinical relevance?

Answer 39

Protein not normally found urine If protein in urine indicate damage to filtration barrier- protein link Diabetes

Question 40

State the equation for filtration fraction?

Answer 40

Filtration Fraction = GFR / Renal Plasma Flow Proportion filtered

Question 41

What is rate of renal blood flow? What is renal plasma flow? Filtration fraction?

Answer 41

1mL/min 40% cells 60% plasma 600ml/min Filtration Fraction = 125/600 = ~0.2%

Question 42

What is value filtration fraction?

Answer 42

0.2%

Question 43

What is urine output value?

Answer 43

Urine output = 0.5ml/kg/h

Question 44

Define renal clearance? Equation

Answer 44

Volume of plasma from which a substance is completely removed from the kidney per unit time Clearance = (urine concentration x urine volume) / plasma concentration

Question 45

What is renal clearance of creatine?

Answer 45

125ml/min Equal GFR

Question 46

Is creatine filtered at glomerulus?

Answer 46

Yes

Question 47

Is creatine absorbed or secreted in tubule? Where end up?

Answer 47

No Urine

Question 48

What is used measure GFR? Why?

Answer 48

Creatine Not absorbed or secreted tubule