Glomerular Filtration

Question 0

What can pass through the glomerular filter?

Answer 0

Water
Salts
Small proteins
Glucose
Urea

Question 1

What percentage of the blood which passes through the renal artery is filtered?

Answer 1

20%

Question 2

What cannot pass through the filter?

Answer 2

Large proteins

Cells

Question 3

What causes the pressure to be increased inside the glomerulus?

Answer 3

Afferent arteriole has a slightly larger diameter than the efferent

Question 4

What repels proteins from being filtered?

Answer 4

The podocyte glycocalyx and the basement membrane have negatively charged glycoproteins

Question 5

What is the ultrafiltrate?

Answer 5

The water and solutes forced through the filter

Question 6

What are the physical forces involved in filtering of plasma and where are they? Do they favour or oppose filtration?

Answer 6

Hydrostatic pressure in the capillary - favours filtration
Hydrostatic pressure in Bowman’s capsule - opposes filtration
Osmotic pressure difference between capillary and tubular lumen - opposes filtration

Question 7

Structure of the basement membrane of the filter?

Answer 7

Acellular
Gelatinous
Layer of collagen and glycoproteins

Question 8

What are the three layers of the filtration barrier?

Answer 8

Capillary endothelium
Basement membrane
Podocytes

Question 9

If you get loss of the negative charge on the glycoproteins, what can this lead to?

Answer 9

Proteinuria

Question 10

What is clearance?

Answer 10

The volume of plasma from which a substance can be completely cleared to the urine per unit of time

Question 11

What is renal blood flow? Value?

Answer 11

Volume of blood delivered to kidneys per unit of time

1.1L/min

Question 12

Define renal plasma flow. Value?

Answer 12

Volume of blood plasma delivered to kidneys per unit time

605ml

Question 13

What is measured to calculate renal plasma flow?

Answer 13

Haematocrit (volume percentage of red blood cells in blood)
This = 0.55
1.1 x 0.55 = 605ml/min

Question 14

Value of the glomerular filtration rate?

Answer 14

125ml

20% of renal plasma flow

Question 15

What is the filtration fraction?

Answer 15

Proportion of a substance that is actually filtered

Question 16

How is the filtration fraction calculated?

Answer 16

GFR / RPF

Question 17

What do you use to calculate a patient’s GFR?

Answer 17

Clearance of something eg urea

Question 18

How is clearance rate worked out? (Equation)

Answer 18

Clearance rate =
{urine conc of P x urine flow (ml/min)} /
plasma conc of p

(so if a compound is completely cleared from the plasma that is filtered, then the rate it appears in the urine is the GFR)

Question 19

Define glomerular filtration rate

Answer 19

Volume of plasma from which any substance is completely removed by the kidney in a given amount of time

Question 20

Normal GFR for males and females?

Answer 20

Males = 115-125 ml/min
Females = 90-100 ml/min

Question 21

What conditions must there be when choosing a substance to use to measure the GFR?

Answer 21

Must be freely filtered across the glomerulus

Must not be reabsorbed, secreted or metabolised by cells of the nephron

Must pass directly into the urine

Question 22

What are substances that can be used to measure GFR?

Answer 22

Creatinine and inulin

Question 23

What is autoregulation used for?

Answer 23

To keep the GFR within normal limits when arterial BP is within the physiological limit

Question 24

What is the myogenic response in autoregulation?

Answer 24

If arterial blood pressure rises, get afferent arteriole constriction. If it falls, get afferent arteriole dilation

Question 25

How does tubular glomerular feedback occur

Answer 25

Changes in GFR causes changes in tubular flow rate | This causes a change in the amount of NaCl reaching the distal tubule

Question 26

If there is an increase in arterial pressure, what happens in tubular glomerular feedback?

Answer 26

Increase in arterial pressure - increase in GFR - increase in [Na] and [Cl] in distal tubule Macula densa cells respond - cause release in adenosine which causes vasoconstriction of afferent arteriole

Question 27

What happens if NaCl concentration decreases in distal tubule (for tubular glomerular feedback)

Answer 27

Macula densa cells cause release of prostaglandins which cause vasodilation of afferent arteriole

Question 28

What is general overflow aminoacidura?

Answer 28

All amino acids are present in the urine.

Question 29

What can general overflow aminoacidura be caused by?

Answer 29

- Inadequate deamination in the liver - Increased GFR - Often seen in early pregnancy

Question 30

What is specific overflow aminoacidura?

Answer 30

Only a specific amino acid is in the urine

Question 31

What can cause specific overflow aminoacidura?

Answer 31

Genetic inability to break down an amino acid | Eg phenylalanine in PKU due to lack of phenylalanine hydroxylase

Question 32

Which amino acid is usually associated with renal stone formation? Why?

Answer 32

Cysteine (cystinuria) | It is an insoluble amino acid, especially in acidic urine