The Renal system lecture 2

Question 1

what is the ultrafiltration barrier composed of ?

Answer 1

1. Fenestrated endothelium
2. Basement membrane
3. Podocytes

Question 2

what does the fenestration pore of the glomerular endothelial cell prevent ?

Answer 2

prevents filtration of blood cells but allows all components of blood plasma to pass through

Question 3

what does the Basal lamina of the glomerulus prevent ?

Answer 3

prevents filtration of larger proteins

Question 4

what does the slit membrane between pedicels prevent ?

Answer 4

prevents filtration of medium-sized proteins

Question 5

who described ultrafiltration ?

Answer 5

using micropuncture, wearn and richards described ultrafiltration

Question 6

what is the definition of glomerular filtrate ?

Answer 6

the fluid formed by ultrafiltration

Question 7

what does the term glomerular filtration rate or GFR refer to ?

Answer 7

The rate at which the 2 kidney’s form ultra filtrate is GFR.

Question 8

what does the term single nephron GFR refer to ?

Answer 8

the rate at which a single nephron forms ultra filtrate

Question 9

what substances are freely filtered?

Answer 9

substances of low molecular weight are freely filtered. water urea glucose inulin myoglobin

Question 10

what molecules are retrcietd ?

Answer 10

large molecules

Question 11

give me 3 examples of molecules that are restricted

Answer 11

haemoglobin, serum, albumin

Question 12

what molecules are more restricted ? negatively or positively

Answer 12

negatively charged molecules like albumin

Question 13

what governs GFR ?

Answer 13

a balance of hydrodynamic forces

Question 14

what are the two forces that oppose each other that constitute the hydrodynamic forces ?

Answer 14

Hydrostatic pressure (plasma leaves capillaries because of pressure )
oncotic pressure beacause of the protein that remained  in the plasma  because of size and charge

Question 15

why does oncotic pressure oppose hydrostatic force ?

Answer 15

because of capillary pressure

Question 16

what does the term net filtration pressure refer to ?

Answer 16

small oncotic pressure from bowman’s space opposing hydrostatic pressure

Question 17

what is Pc?

Answer 17

Capillary hydrostatic pressure Pc - the pressure that will force fluid out from the capillary

Question 18

What is Pi?

Answer 18

Interstitial hydrostatic pressure Pi - the pressure that will force fluid out from the interstitial space

Question 19

What is πc?

Answer 19

Capillary oncotic pressure πc - the osmotic pressure that will force the fluids to enter the capillary from the interstitial space

Question 20

What is πi?

Answer 20

Interstitial oncotic pressure πi- the osmotic pressure that will force the fluids to enter the interstitial space from the capillary

Question 21

what is fluid filtration determined by ?

Answer 21

Fluid filtration is determined by the difference of hydrostatic pressures across the capillary
Pc - Pi

Question 22

what is fluid reabsorption determined by ?

Answer 22

Fluid reabsorption is determined by the difference of osmotic pressures across the capillary
Πc - Πi

Question 23

in systemic capillaries is there a net flow out of capillaries ?

Answer 23

no

Question 24

what is the value of Pc in the renal corpuscle ?

Answer 24

55 mmHg

Question 25

what is the value of Pi in the renal corpuscle ?

Answer 25

15 mmHg

Question 26

what is the value of Πc in the renal corpuscle ?

Answer 26

30 mm Hg

Question 27

what is the value of Πi in the renal corpuscle ?

Answer 27

0.3 mmHg

Question 28

what is the formula of GFR ?

Answer 28

GFR=[(PC –PBC)–(Πc–ΠBC)].K

Question 29

whats the net glomerular filtration pressure ?

Answer 29

10 mmHg

Question 30

what would an increase in Pc lead to ?

Answer 30

An increase in PC increases GFR

Question 31

what would a decrease in Pc decreases GFR ?

Answer 31

A decrease in PC decreases GFR

Question 32

what would an increase Pbc do ?

Answer 32

An increase in PBC decreases GFR,

such as stones in the urinary tract, or retention of urine

Question 33

what would a decrease in ΠC lead to ?

Answer 33

A decrease in ΠC increases GFR, i.e. liver failure

Question 34

what would an increase in ΠBC lead to ?

Answer 34

An increase in ΠBC decreases GFR, i.e. renal failure

Question 35

how can GFR be measured ?

Answer 35

It can’t be measured, but it can be estimated.
• By measuring the rate of excretion of substances that are:
1. Freely filtered.
2. Not reabsorbed or secreted by tubules.
3. Have no influence on renal function (e.g. blood flow)
Inulin meets these criteria.

Question 36

what is the definition of renal clearance ?

Answer 36

the volume of plasma completely cleared of a given substance in 1 min

Question 37

what is the GFR for inulin clearance ?

Answer 37

120-130 ml/min for adult humans. in a day that is 180 litres of plasma filtered

Question 38

why is inulin not convenient for clinical measurement of GFR?

Answer 38

it’s concentration in the plasma is not steady - not accurate

Question 39

what substance fits the criteria already found in plasma ?

Answer 39

creatinine - however small amounts of creatinine are secreted into the proximal tubule

Question 40

Homeostasis requires kidneys to maintain a relatively constant GFR ?

Answer 40

Too high – substances pass too quickly and are not reabsorbed
• Too low – nearly all reabsorbed and some waste products not adequately excreted

Question 41

give me three reasons for renal failure ?

Answer 41

pre-renal (e.g poor blood supply)
renal ( loss of nephrons or nephron function )
post-renal ( e.g blockage of ureter and lower tract)