lecture 32 - renal / urinary physiology

Question 1

what is freely filtered through the filtration barrier

Answer 1

small substances (mostly everything), not large substances (like haemoglobin and albumin)

Question 2

what is renal blood flow equal to

Answer 2

20% of cardiac output

Question 3

why is renal blood flow high

Answer 3

for filtration

Question 4

what are the two types of driving forces and their directions

Answer 4

• hydrostatic pressures = due to volume of fluid, pushes fluid away
• colloid osmotic pressures = due to protein, pulls fluid towards

Question 5

what does positive pressure favour

Answer 5

filtration

Question 6

what does negative pressure oppose

Answer 6

filtration

Question 7

what is glomeruluar hydrostatic pressure

Answer 7

blood pressure = favouring filtration, 50+mmHg

Question 8

what is blood colloid osmotic pressure

Answer 8

albumin = trying to pull fluid from capsule back into blood, -25mmHg

Question 9

what is capsular hydrostatic pressure

Answer 9

pressure of filtrate already present = trying to push fluid from capsule into the blood, -15 mmHg

Question 10

what is the capsular colloid osmotic pressure

Answer 10

no protein in capsular space = 0 mmHg

Question 11

what is net filtration pressure usually equal to

Answer 11

10 mmHg

Question 12

what is filtration fraction

Answer 12

how much of the kidneys plasma flow is filtered

Question 13

what is the filtration fraction equation

Answer 13

glomerular filtration / renal plasma flow

Question 14

how much of renal plasma is filtered

Answer 14

20%

Question 15

what is the glomerular filtration rate

Answer 15

the amount of plasma filtered per unit time by the kidneys

Question 16

what is the glomerular filtration rate normally per day and per minute

Answer 16

180L/day and 125ml/minute

Question 17

what is the renal filtered load

Answer 17

the amount of a particular substance filtered per unit time

Question 18

what is the equation of the filtered load

Answer 18

glomerular filtration rate x solute plasma concentration

Question 19

what is renal clearance

Answer 19

the volume (ml) of plasma that is cleared of a substance by the kidneys per unit time

Question 20

what can clearance be used for

Answer 20

• quantify how a substance is handled by the kidneys
• estimate glomerular filtration rate

Question 21

is creatinine and inulin filtered, secreted, reabsorbed, excreted ?

Answer 21

• freely filtered
• not secreted
• not reabsorbed
• all filtered is excreted in urine

Question 22

what is the clearance of creatinine equal to

Answer 22

volume of plasma filtered per minute (GFR)

Question 23

is medications and toxins (e.g PAH) filtered, secreted, reabsorbed, excreted ?

Answer 23

• freely filtered
• entirely secreted
• not reabsorbed
• all in blood is excreted in urine

Question 24

what is the clearance of PAH

Answer 24

volume of plasma flowing through the kidneys per minute

Question 25

is glucose filtered, secreted, reabsorbed, excreted ?

Answer 25

- freely filtered - not secreted - FULLY reabsorbed in proximal tubule - NONE excreted in urine

Question 26

what is the clearance of glucose

Answer 26

no plasma is cleared of glucose

Question 27

is sodium filtered, secreted, reabsorbed, excreted ?

Answer 27

- freely filtered - not secreted - almost fully reabsorbed in most parts of the nephron - small amount excreted in urine

Question 28

what is the clearance of sodium

Answer 28

very small volume of plasma per minute

Question 29

what is the clearance equation

Answer 29

concentration of X in urine x volume of urine produced per unit time / concentration of X in plasma

Question 30

to estimate GFR a substance must be ......

Answer 30

- freely filtered - not reabsorbed from the tubule - not be secreted into the tubule

Question 31

what substances can be used to estimate GFR and what is the more common one

Answer 31

inulin and creatinine - creatinine most common because already found in the body

Question 32

if both kidneys are working what will the creatinine levels be like

Answer 32

low in the plasma

Question 33

if kidneys ability to clear products reduces then what will the creatinine levels in the plasma be like

Answer 33

increase