Urinary Session 3- GFR, Blood Flow And Pharmacology

Question 1

Starting from renal artery what path will blood entering the kidney follow?

Answer 1

Renal artery
5 segmental arteries
Interlobar arteries
Arcuate arteries
Interlobular arteries
Afferent arterioles

Question 2

What is the renal lobe?

Answer 2

Renal pyramid and cortex immediately above

Question 3

How do the diameters of afferent and efferent arterioles affect hydrostatic pressure of blood in glomerulus?

Answer 3

Diameter of afferent arteriole is slightly greater than the diameter of the efferent arteriole so hydrostatic pressure of blood in the glomerulus is increased

Question 4

What is forced out of the blood at the glomerular capillaries?

Answer 4

Most of the water
Most/all of the salts
Most/all of the glucose
Most/all of the urea

Question 5

Why are blood cells and plasma proteins not filtered out?

Answer 5

Too large

Question 6

What are water and solutes forced out of the glomerular capillaries called once in the Bowman’s capsule?

Answer 6

Ultrafiltrate

Question 7

What is the rate of production of glomerular filtrate?

Answer 7

125ml per minute

Question 8

Of the volume that reaches the glomerulus, what percentage is filtered out?

Answer 8

About 20%

Question 9

What percentage of glomerular filtrate produced leaves the body?

Answer 9

About 1%

Question 10

What are the 3 mechanisms of tubular reabsorption?

Answer 10

Osmosis, diffusion and active transport

Question 11

Where is most of the volume of the glomerular filtrate reabsorbed?

Answer 11

PCT

Question 12

What is most of the energy used by the kidneys used for?

Answer 12

Reabsorption of sodium ions

Question 13

How does sodium more from the glomerular filtrate into the cells of the PCT?

Answer 13

Symporters on apical membrane- also facilitate passage of other substances through the membrane

Question 14

What substances can be reabsorbed with Na?

Answer 14

Glucose, amino acids, water soluble vitamins, lactate, acetate, ketones and krebs cycle intermediates

Question 15

What creates the Na gradient used for symporters?

Answer 15

NaKATPase on the basolateral membrane

Question 16

How is water reabsorbed?

Answer 16

Osmosis following solutes

Question 17

What is tubular secretion?

Answer 17

Substances added to glomerular filtrate in the nephron tubule to remove excessive quantities of certain dissolved substances

Question 18

Which substances are secreted into the glomerular filtrate to be removed from the body?

Answer 18

K, H, ammonium ions, creatinine, urea, some hormones and some drugs

Question 19

Where does tubular secretion occur?

Answer 19

From the epithelial cells that line the renal tubules and collecting ducts into the glomerular filtrate

Question 20

How is continuous glomerular filtration maintained across a wide range of systemic blood pressures?

Answer 20

Selective vasoconstriction or dilation to maintain renal blood flow at a constant rate

Question 21

What mechanisms are believed to mediate renal autoregulation?

Answer 21

Faster myogenic and slower tubuloglomerular feedback system

Question 22

What is the purpose of autoregulation of renal blood flow?

Answer 22

To maintain GFR

Question 23

Define clearance

Answer 23

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

Question 24

What is the equation to calculate clearance?

Answer 24

C=UV/P

C= clearance, U= amount in urine, V= urine flow rate, P= arterial plasma conc

Question 25

What are the units for clearance?

Answer 25

L/hr or ml/min

Question 26

Why is calculating clearance important?

Answer 26

It allows you to calculate GFR which is used clinically as a measure of kidney function

Question 27

What properties must a substance have to be used to measure GFR?

Answer 27

It must be freely filtered across the glomerulus, not be reabsorbed, secreted or metabolised by cells of the nephron and pass directly into the urine

Question 28

What substance is usually measured for GFR?

Answer 28

Creatinine

Question 29

What is the equation for creatinine clearance?

Answer 29

GFR = UV/P

Same as clearance equation

Question 30

Why does progressive overestimation of GFR occur with severe disease?

Answer 30

Tubular secretion by organic cation secretory pathways in the proximal tubule accounts for 10-20% of urinary creatine and a progressively higher percentage as GFR falls

Question 31

Define fractional excretion

Answer 31

Proportion of filtered solute that remains un-reabsorbed by the nephron

Question 32

How can you calculate FE (hint: 3 step equation)

Answer 32

1. Calculate filtered load of substance
([P]z x [U]cr x V) / [P]cr = A
[P]=plasma conc
[U]=urinary conc
V=urinary volume
2. Calculate amount of substance excreted. 
[U]z x V = B
3. Calculate percentage!
Bx100/A = FE