Lecture 32: Glomerular Function

Question 1

Normal urine is made mostly of (6)

Answer 1

water, electrolytes (sodium, potassium), drugs/toxins, metabolites and acids

Question 2

The kidney has a variety of functions including (5)

Answer 2

• filtration
• excretion
• salt and water homeostasis
• pH regulation
• hormone synthesis

Question 3

What is meant by the drug and toxins that are present in the normal urine composition?

Answer 3

drugs like aspirin

plant toxins

Question 4

What would happen in we didn’t remove drugs in our urine?

Answer 4

Drugs like aspirin need to removed otherwise if we kept taking them, they would accumulate in the blood and have bad side effects

Question 5

What is filtration fraction?

Answer 5

how much blood that reaches the kidneys is actually filtered

Question 6

What is filtered load?

Answer 6

how much of a substance is actually filtered

Question 7

What is clearance?

Answer 7

clearing a substance from the blood

Question 8

What is the main role of kidneys?

Answer 8

filters blood

Question 9

What happens during filtration?

Answer 9

liquids are extracted to form a plasma-like filtrate

Question 10

Where does filtration occur?

Answer 10

at the glomerulus

Question 11

What three things define renal filtration?

Answer 11

• renal blood flow
• filtration barrier
• driving forces

Question 12

Define renal blood flow

Answer 12

the amount of blood that flows into a kidney

Question 13

What does the renal corpuscle consist of?

Answer 13

the glomerulus/glomerular capillaries and the glomerular capsule

Question 14

How does the nephron control its own perfusion?

Answer 14

by sensing the NaCl level in the DCT and then cells in the juxtaglomerular complex adjust the afferent and efferent arterioles to adjust the perfusion of the glomerular capillary

Question 15

What is perfusion?

Answer 15

the delivery of blood to a capillary bed

Question 16

What percentage of the cardiac output does the renal output take up?

Answer 16

20-25%

Question 17

Where does filtration take place?

Answer 17

in the glomerulus/glomerular capillary

Question 18

What three things is the filtration membrane composed of?

Answer 18

1. fenestrated endothelium
2. basement membrane
3. podocytes with foot processes and filtration slits

Question 19

What is freely filtered by the filtration barrier?

Answer 19

small substances

Question 20

What is not filtered by the filtration barrier?

Answer 20

large substances

Question 21

Define a small substance that is filtered by the filtration barrier

Answer 21

one which has a low molecular mass

Question 22

Define a large substance that is not filtered by the filtration barrier

Answer 22

one which has a high molecular mass

Question 23

One of the things that defines renal filtration is driving forces. What are the driving forces? What do these come down to?

Answer 23

pressure gradients between the glomerular capillary and the capsular space and this comes down to the permeability of the glomerular capillary and the surface area of the glomerular capillary

Question 24

What are the four forces that determine the net filtration pressure?

Answer 24

1. glomerular hydrostatic pressure (GHP)
2. blood colloid osmotic pressure (BCOP)
3. capsular hydrostatic pressure (CsHP)
4. capsular colloid osmotic pressure

Question 25

Define glomerular hydrostatic pressure

Answer 25

fluid in the glomerular capillary exerting a pushing force across the barrier that favours filtration

Question 26

Define blood colloid osmotic pressure (BCOP)

Answer 26

Proteins and other osmotically active solutes act like magnets and “pull” water towards them

Question 27

Define capsular hydrostatic pressure (CsHP)

Answer 27

the pushing force in the opposite direction to the glomerular hydrostatic pressure due to fluid in the capsule and the fact that the capsule is embedded in the in a tissue and unable to expand

Question 28

How can you calculate renal clearance? What is the unit?

Answer 28

Cs = (Us x V)/Ps in mL/min

Question 29

In the equation for renal clearance, what does Us stand for? What is the unit?

Answer 29

the concentration of substance in the urine (mg/L or mol/L)

Question 30

In the equation for renal clearance, what does V stand for?

Answer 30

volume of urine produced per unit time (mL/min or L/hr)

Question 31

In the equation for renal clearance, what does Ps stand for?

Answer 31

concentration of the substance in the plasma (mg/L or mol/L)

Question 32

What does the equation for renal clearance describe?

Answer 32

the rate at which the substance is cleared by the kidneys per unit time

Question 33

What is the glomerular filtration rate (GFR)?

Answer 33

The volume of filtrate formed by both kidneys per minute

Question 34

We can estimate GFR using

Answer 34

renal clearance

Question 35

to be used as a measure of GFR, a substance must

Answer 35

• not be reabsorbed from the tubule
• not be secreted into the tubule
• not be metabolised

Question 36

What are two main substances that we can use renal clearance to estimate GFR?

Answer 36

• inulin

- creatinine

Question 37

What is inulin?

Answer 37

• a polysaccharide not metabolised by the body

Question 38

What is creatinine?

Answer 38

a waste product produced by muscles

Question 39

Creatinine is filtered freely at the glomerulus but is not ______, _______ or ________

Answer 39

reabsorbed
secreted
metabolised

Question 40

How is plasma creatinine an indicator for kidney function?

Answer 40

if plasma creatinine is low, both kidneys are working

Question 41

What is the filtration fraction and how can it be calculated?

Answer 41

how much blood reaching the kidney is actually filtered

it can be calculated by the glomerular filtration rate/renal plasma flow

Question 42

How much is the renal plasma flow?

Answer 42

about half the volume of blood

Question 43

Define filtered load

Answer 43

the amount of a particular substance filtered per minute

Question 44

How can you calculate filtered load?

Answer 44

the glomerular filtration rate x solute plasma concentration

Question 45

Define capsular colloid osmotic pressure

Answer 45

The pressure if proteins entered the capsular space. It is therefore usually zero because normally no proteins enter the capsular space